Field ManualNo. 5-277

*FM 5-277HEADQUARTERS

DEPARTMENT OF THE ARMYWashington, DC, 9 May 1986

B A I L E Y B R I D G E

*This publication supersedesTM 5-277, 3 August 1972.

i

Distribution Restriction: Approved for public release. Distribution is unlimited

FM 5-277C1

Change 1 HeadquartersDepartment of the Army

Washington, DC, 15 August 1991

FM 5-277

ii

9 May 1986

FM 5-277

iii

FM 5-277

LIST OF FIGURES - BAILEY BRIDGE (FM 5-277)

iv

FM 5-277

v

FM 5-277

vi

FM 5-277

v i i

FM 5-277

viii

FM 5-277

i x

FM 5-277

x

FM 5-277

xi

FM 5-277

x i i

LIST OF TABLES – BAILEY BRIDGE (FM 5-277)

xiii

FM 5-277

x i v

FM 5-277

x v

FM 5-277

PREFACE

This manual is intended for use by engineercommanders, staff officers, combat engi-neers, and bridge specialists who are requiredto build the Bailey bridge.

The purpose of this manual is to provide theuser instructions needed to build the standardBailey bridge and its several variants. Itdescribes bridge components, loading andtransport, methods of assembly, and main-tenance. It also describes special applica-tions, such as two-lane, extra-wide, deck,railway, pier- and barge-supported bridges,and towers built from Bailey bridge compo-nents.

The Bailey bridge has several distinctivefeatures. It is built by manpower alone. It ismade entirely from prefabricated parts, themost notable of which are its light-steelpanels linked by pinned joints. It is a‘through-type bridge. And it can be movedfrom one site to another.

The Bailey bridge was invented by DonaldColeman Bailey, an English civil engineer.In 1941, Bailey gave his first sketch of the

bridge to the British War Office which paidhim the equivalent of $48,000 in 1985American currency.

The Bailey bridge used in World War II wasdesigned to be moved, rebuilt, or replaced inseveral hours, even under enemy fire. It wasused widely and well by Allied armies in Italyand northwest Europe, 1943-45. British FieldMarshal Lord Bernard Law Montgomerysaid: “Without the Bailey bridge, we shouldnot have won the war. It was the best thing inthat line we ever had.” Donald Bailey wasknighted in 1946 for this contribution to theAllied victory in World War II.

The proponent agency of this publication isthe US Army Engineer School. Submitchanges for improving this publication onDA Form 2028 (Recommended Changes toPublications and Blank Forms) and forwardto Commandant, US Army Engineer School,ATTN: ATZA-TD-P, Fort Belvoir, Virginia22060-5291.

xvii

FM 5-277

1

FM 5-277

CHAPTER 1

H I S T O R Y A N D U S E O F T H E B R I D G E

This change supersedes page 2.

At the outset of World War II, the UnitedStates (US) Army sought a versatile bridgethat could span a variety of gaps and bequickly assembled by manpower alone. Forthis reason, we adopted the design for theBritish prefabricated Bailey bridge, USnomenclature Ml. We revised the design toprovide a greater roadway width of 12% feetand designated it the Panel Bridge, BaileyM2 (Figure l-l). The British then modifiedthe US version by widening the bridge again,thus producing the extra-wide Bailey M3bridge. The US Army does not stock the M3bridge in its arsenal. The Bailey bridge is athrough-type truss bridge, the roadway beingcarried between two main girders. The trussesin each girder are formed by 10-foot panelspinned end to end. In this respect, the Baileybridge is often referred to as the “panel” or“truss” bridge.

ADVANTAGESSome of the characteristics that make theBailey bridge valuable to field commandersare—

It is easy to install. Each part of theBailey bridge is a standard machine-made piece and is interchangeable amongspans. Inmost cases, no heavy equipmentis required to assemble or launch a Baileybridge; only basic pioneer skills and equip-ment are needed.

It is highly mobile. All parts of the bridgecan be transported to and from the bridgesite by 5-ton dump trucks and trailers.

It is versatile. Standard parts can be usedto assemble seven standard truss designsfor efficient single spans up to 210 feetlong and to build panel crib piers sup-porting longer bridges. With minor non-standard modifications, the expedientuses of bridge parts are limited only bythe user’s imagination.

CONSTRUCTIONTransverse floor beams, called transoms, areclamped to the bottom chords of the trussesand support stringers and decking. Swaybraces between the girders provide horizontalbracing; rakers between the trusses andtransoms keep the trusses upright; andbracing frames and tie plates between thetrusses provide lateral bracing within eachgirder.

Main girdersThe main girders on each side of the center-line of the bridge can be assembled from asingle truss or from two or three trusses sideby side. For greater strength, a second storyof panels can be added to the trusses. Theupper stories are bolted to the top chord of thelower story. For greatest strength, a thirdstory is added. These three basic types are

shown in Figure 1-2 (page 4). The types ofpossible truss assemblies are given in Table1-1 (page 4). A single-truss, double-or triple-story bridge is never assembled because itwould be unstable. All triple-story bridgeswith the deck in the bottom story are bracedat the top by transoms and sway braceswhich are fastened to overhead-bracing sup-ports bolted to the top chords.

MaterialsThe decking, called chess, is wood. Panels,end posts, transoms, and ramps are a low-alloy, high-tensile steel. All other parts arecarbon structural steel. All joints in the partsare welded.

DeckThe clear roadway between curbs, called rib-bands, is 12 feet 6 inches wide. The transomssupporting the roadway are normally set onthe bottom chords of the bottom story. Foot-walks can be carried on the transoms outsideof the main trusses on each side of the bridge.

BearingsEnd posts pinned to the end of each truss siton cylindrical bearings which rest on a steelbase plate. On soft soil, timber grillage isused under the base” plates to distribute theload. The bridge can be assembled betweenbanks of different elevations, but the slopeshould not exceed 30 to 1.

2

This change supersedes page 3. FM 5-277

TYPES OF STRUCTURESPanel bridge equipment can be used toassemble fixed bridges and panel crib piersand towers. Other special structures such asfloating bridges, suspension bridges, retract-able bridges, and mobile bridges, can beassembled using special parts. Panel bridgeequipment is normally used to assemble fixedsimple-span, through-type bridges from 30 to210 feet long. The bridge can be assembled tomeet varying conditions of span and load.Bridge weight per bay is given in Table 1-2(page 5). The following special assemblies arealso possible:

Two-lane, through-type bridges; deck-typebridges; railway bridges; bridges on piers;and floating bridges can be built withpanel bridge equipment.

Panel crib piers and towers up to 70 feethigh supporting continuous spans, andup to 110 feet high supporting brokenspans, can be assembled with panel bridgeequipment and special crib-pier parts.

Many expedient structures can also bebuilt with panel bridge equipment. Theseinclude causeways, box anchors, towersfor floating bridge cables, and loadinghoppers and gantries.

3

FM 5-277

4

This change supersedes page 5.FM 5-277

5

FM 5-277

CHAPTER 2

B A S I C E Q U I P M E N T

BRIDGE PARTS 6

ERECTION EQUIPMENT 15BRIDGING TRUCK LOADS 19

The Bailey M2 bridge set contains 29 differentitems of bridge parts and 30 items of erectionequipment. Table A-1 in Appendix A showsthe number of parts needed to build a specificBailey bridge.

BRIDGE PARTSWARNING: Due to the size and weight ofcomponents, personnel are advised to use

extreme care when handling them. Failure

to do so may result in serious.

PANELThe panel (Figure 2-1) is the basic member ofthe bridge. It is a welded, high-tensile steeltruss section 10 feet (3.0 meters) long, 5 feet 1inch (1.5 meters) high, and 6 1/2 inches (16.5centimeters) wide. It weighs 577 pounds (262kilograms) and can be carried by six soldiersusing carrying bars.

The horizontal members of the panel arecalled chords. Both chords have male lugs atone end and female lugs at the other. Panelsare joined end to end by engaging these lugsand placing panel pins through the holes inthe lugs. On the top of the bottom chord arefour seatings or dowels. The beams that

PANEL PINsupport the bridge roadway will be clamped The panel pin (Figure 2-2) is 8 5/16 inches (21.1to these dowels. Table 2-1 lists the holes in the centimeters) long, 1 7/8 inches (4.8 centimeters)panel. in diameter, and weighs 6 pounds (2.7 kilo-

grams). It has a tapered end with a small hole

6

FM 5-277

for a retainer clip. A groove is cut across thehead of the panel pin parallel to the bridgepin retainer hole. Panel pins should beinserted with the groove horizontal; other-wise, the flanges of the panel chord channelsmake it difficult to insert the retainer clip.

WARNING: Never jack against transomsthat are held in place by transom clamps, asthe clamps will fail. This failure may resultin severe injury or death and/or extremedamage to bridge components.

SHORT PANEL PINThe short panel pin (Figure 2-3) is 3/4 inch (1.9centimeters) shorter than the normal panelpin and weighs 5.8 pounds (2.6 kilograms). Itis used to pin the end posts of the outer andmiddle trusses in a triple-truss bridge.

TRANSOMThe transom (Figure 2-4, page 8) is a steelbeam that supports the floor system of thebridge. It is 10 inches (25.4 centimeters) by 19feet 11 inches (6.1 meters) long. It has a 4 1/2-inch (11.4 centimeters) flange and a 5/16-inch

7

FM 5-277WARNING: Sway brace is a multi-hingedcomponent; use care when handling toprevent injury.

(0.8 centimeter) cover plate on each flange.The transom weighs 618 pounds (280 kilo-grams). It can be carried by eight soldiersusing carrying tongs clamped to the upperflange or carrying bars inserted throughholes in the web.

SWAY BRACEThe sway brace (Figure 2-6) is a 1 1/8-inch (2.9centimeters) steel rod, hinged at the center,

The underside of the transom has six holesinto which the panel dowels fit. The transomrests on the lower chord of the panel and isheld in place with a transom clamp. Theupper side of the transom has six lugs with anadditional lug near each end. The stringersand rakers (explained later in this chapter)attach to these lugs.

Transoms are normally spaced 5 feet (1.5meters) apart, one at the middle and one atthe end of each panel, to support vehicles ofclass 70 or less. Four transoms per bay—twoin the middle and one at each end of thepanel—are required to support vehicles overclass 70.

WARNING: Transom clamp is a hingedcomponent; use care when handling toprevent injury.

TRANSOM CLAMPThe transom clamp (Figure 2-5) is a hingedscrew-in type clamp, 13 1/2 inches (34.3 centi-meters) high and 8 inches (20.3 centimeters)across the top. It weighs 7 pounds (3.2 kilo-grams). It clamps the transom to the verticaland bottom chord of the panel. It is tightenedby a vise-handled screw.

and adjusted by a turnbuckle. It weighs 68pounds (30.8 kilograms). At each end is aneye, and a chain with a pin attached. This pinis inserted through the eye to the sway braceto the panel. The sway brace is given theproper tension by inserting the tail of anerection wrench in the turnbuckle andscrewing it tight. The locknut is then screwedup against the turnbuckle. Two sway bracesare required in the lower chord of each bay ofthe bridge, except the first bay of thelaunching nose, and in each bay of overheadbracing.

RAKERThe raker (Figure 2-7) is a 3-inch (7.6 centi-meters) steel beam with a 2 3/8-inch (6.0 centi-meters) flange. It is 3 feet 8 5/16 inches (1.11meters) long and weighs 22 pounds (10.0kilograms). A raker connects the ends of the

8

FM 5-277

transom to the top of one end of each panel ofthe inner truss. This prevents the panels fromoverturning. An additional raker is used ateach end of the bridge. Both ends of the rakerhave hollow dowels for the bracing bolts. Thedowels fit through a hole in the panel and ahole in the transom.

BRACING FRAMEThe bracing frame (Figure 2-8) is a rec-tangular frame, 4 feet 3 inches (1.3 meters) by1 foot 8 inches (50.8 centimeters) with ahollow conical dowel in each comer. It weighs44 pounds (20.0 kilograms). The bracingframe is used to brace the inner two trusseson each side of the double- and triple-trussbridge. Bracing bolts attach the bracingframes horizontally to the top chords of the

bridge, and vertically on one end of eachpanel in the second and third stories.

TIE PLATEA tie plate (Figure 2-9, page 10) is a piece offlat steel 2 1/2 by 3/8 by 12 inches (6.4 by 1.0 by30.5 centimeters) weighing 3 1/2 pounds (1.6kilograms). It has a hollow conical dowel ateach end. The tie plate is used only in triple-truss bridges. It secures the second truss tothe third truss using the unoccupied rakerholes in the panels at each joint and at theends of the bridge.

9

FM 5-277

BRACING BOLTA bracing bolt (Figure 2-10) is 3/4 inch(1.9 centimeters) in diameter, 3 1/2 inches(8.9 centimeters) long, and weighs about1 pound (0.5 kilograms). A special lug on itshead prevents rotation when the bolt istightened. A l 1/8inch (2.9 centimeters) wrenchis used to tighten it. The bracing bolt is usedto attach rakers, bracing frames, and tieplates to panels. It is inserted into the hollowdowels of the braces to draw parts into properalignment.

CHORD BOLTA chord bolt (Figure 2-11) is 1 3/4 inches (4.4centimeters) in diameter, 10 1/2 inches (26.7centimeters) long, and weighs 7 1/2 pounds (3.4kilograms). It is tapered through half itslength to assist in drawing the panels intoalignment. A 1 7/8-inch (4.8 centimeters)wrench is used to tighten the bolt. Chordbolts join the panels, one above the other, toform double and triple-story bridges. Twobolts per panel pass upward through holes inthe panel chords and are tightened with nutson the lower chord of the upper story. Theyare also used to fasten overhead bracingsupports to the top panel chord.

STRINGERSStringers (Figure 2-12) carry the bridge’sroadway. Each stringer consists of three 4-inch (10.2 centimeters) steel beams, 10 feet(3.0 meters) long, joined by welded braces.There are two types of stringers: plainstringers weighing 260 pounds (118 kilo-grams) and button stringers weighing 267pounds (122 kilograms). They are identicalexcept that the latter has 12 buttons which

hold the ends of the chess (roadway) in place.Each bay of the bridge has six stringers: fourplain stringers in the middle, and a buttonstringer on each side. The stringers are posi-tioned by the lugs on the top of the transoms.

CHESSChess (Figure 2-13), often referred to as deckor decking, form the road surface. A pieceof chess is 2 inches (5.1 centimeters) by8 3/4 inches (22.2 centimeters) by 13 feet10 inches (4.2 meters). It is made of wood andweighs 65 pounds (29.5 kilograms). It isnotched at the ends to fit between the buttonsof the bottom stringer. Each bay of the bridgecontains 13 chess, which lie across thestringers and are held in place by the buttons.Chess are held down by ribbands.

STEEL RIBBAND (CURBS)A ribband (Figure 2-14) is a metal curb8 inches (20.3 centimeters) high and 10 feet(3.0 meters) long. It weighs 162 pounds (73.5kilograms). It is fastened to the buttonstringers by four J-type ribband bolts.

RIBBAND BOLTA ribband bolt (Figure 2-15) is a J-type bolt, 1inch (2.5 centimeters) in diameter and 8 5/8inches (21.9 centimeters) long. It weighs 4 1/2pounds (2.0 kilograms). A 1 1/2-inch (3.8 centi-meters) wrench is used to tighten it. Theribband bolt fastens the ribband to the buttonstringers and ramps. The hook end of the boltgrips the lower flange of the outer beam of thebutton stringer or ramp.

1 0

FM 5-277

11

END POSTSEnd posts (Figure 2-16, page 12) are used onboth ends of each truss of the bridge to takethe vertical shear. They are placed only onthe story carrying the decking. They are 5-foot 8-inch (1.7 meters) columns made of two4-inch (10.1 centimeters) channels and plateswelded together. There are two types; maleand female, having male and female lugs,respectively. These lugs are secured to theend panels of the bridge by panel pins placedthrough holes in the lugs. The male andfemale end posts weigh 121 and 130 pounds(54.9 and 59.0 kilograms), respectively. Endposts have a step to support a transom outside

FM 5-277

12

the panel at one end of the bridge. In jackingthe bridge, the jack is placed under the step.The lower end of the end post has a bearingblock with a semicircular groove which fitsover the bearing.

BEARINGThe bearing (Figure 2-17) spreads the load ofthe bridge to the base plate. A bearing is awelded steel assembly containing a roundbar which, when the bridge is completed,supports the bearing blocks of the end posts.During assembly of the bridge, it supportsthe bearing block of the rocking roller (ex-plained later in this chapter). The bar isdivided into three parts by two intermediatesections that act as stiffeners. The bearing is4 5/16 inches (11.9 centimeters) high andweighs 68 pounds (30.8 kilograms). Onebearing is used at each corner of a single-truss bridge and two bearings per corner for adouble- or triple-truss bridge.

BASE PLATEThe base plate (Figure 2-18) is a welded steelassembly with built-up sides and lifting-hookeyes on the top at each corner. It is used underthe bearings to spread the load from thebearings over the ground or grillage. Thebottom surface of the baseplate is 13 1/2 squarefeet (1.25 meters 2). The base plate weighs 381pounds (173 kilograms) and is large enoughfor the bearings at one corner of a single-,double-, or triple-truss bridge. Bearings canslide 9 inches (22.9 centimeters) longitudi-nally on the baseplate. The numbers 1,2, and3 are embossed on the edges of the base plateto indicate the position of the plate under theinner truss of single-, double-, and triple-trussbridges respectively.

RAMPSRamps (Figure 2-19) are similar to stringersbut consist of three 5-inch (12.7 centimeters),instead of 4-inch (10.2 centimeters), steelbeams. They are 10 feet (3.0 meters) long andare joined by welded braces. The lower surfaceof the ramp tapers upward near the ends.There are two types of ramps: plain rampsweighing 338 pounds (153 kilograms), andbutton ramps weighing 349 pounds (158 kilo-grams). They are identical except that. thelatter have 12 buttons which hold the ends ofthe chess in place. The ends of the ramps fitinto lugs on the transoms at the ends of thebridge.

RAMP PEDESTALRamp pedestals (Figure 2-20) are built-upwelded steel assemblies weighing 93 pounds(42.2 kilograms). They prevent the transomssupporting multiple-length ramps from over-

FM 5-277

turning and spread the transom load over theground. They are held in place by spikes orpickets driven through holes in their baseplates.

FOOTWALKThe footwalk (Figure 2-21, page 14) may be ofwood or aluminum. The wood footwalks are 2feet 6 inches (0.8 meter) wide and 10 feet (3.0meters) long. The aluminum footwalks are25 3/4 inches (65.4 centimeters) wide and 9 feet11 1/2 inches (3.0 meters) long. Supported onfootwalk bearers, footwalks are laid alongthe outer sides of the bridge for use by foottroops.

FOOTWALK BEARERA footwalk bearer (Figure 2-22) is a built-up

beam of pressed steel 4 feet (1.2 meters) long,

13

FM 5-277

weighing 23 pounds (10.4 kilo grams). Bearersare attached to all transoms and hold thefootwalk post.

FOOTWALK POSTA footwalk post (Figure 2-23) is 4 feet (1.2meters) high, weighs 10 pounds (4.5 kilo-grams), and is fitted into every footwalkbearer. Hand ropes are threaded through twoeyes on each post and secured either toholdfasts on the banks or end footwalk posts.

OVERHEAD-BRACING SUPPORTThe overhead-bracing support (Figure 2-24)is used to clamp overhead transoms and

sway braces to trusses for overhead bracingof triple-story bridges. The support is a weldedmetal assembly that weighs 150 pounds (68.0kilograms). It is fastened to the tops of third-story panels by chord bolts. A transom isseated over the pintles on top of the supportand secured by cleats over the lower flangeheld by four nuts and bolts. One support pergirder is placed on each bay of bridge.

14

FM 5-277

ROCKING ROLLERThe rocking roller (Figure 2-25), weighing 206pounds (93.4 kilograms), consists of threerollers housed in a balanced arm which fitsover the bearing, and is free to rock on it. Twoside rollers on the flange on each side of therocking roller frame act as guides for thetrusses. The side rollers can be removed fromthe flanges by removing split pins fromspindles underneath the flange; they thenremain loosely attached to the frame by achain. The rollers distribute the bridge loadalong the bottom chord during launching.The maximum allowable load on one rockingroller is 30 tons (27.2 metric tons).

ERECTION EQUIPMENTPLAIN ROLLER

The plain roller (Figure 2-26) is 2 feet 1 1/2inches (64.8 centimeters) wide and weighs116 pounds (52.6 kilograms). It consists of awelded housing containing a single rollersplit in two. The maximum allowable load onone roller is 10 tons (9.1 metric tons). Trussesof single-truss bridges can be carried oneither half of the roller. Second and thirdtrusses of triple-truss bridges are carried onboth halves.

TRANSOM ROLLERThe transom roller (Figure 2-27) is a rollerhaving an outside diameter of about 1 7/8inches (4.8 centimeters) (or 1 1/2-inches [3.8centimeters] extra-heavy steel pipe) and a

15

FM 5-277

length of 6 5/8 inches (16.8 centimeters). Theroller is fitted with bronze bushings at eachend and revolves on a l-inch (2.5 centimeters)diameter steel pin mounted in a steel framewhich is built up from standard steel barsand angles. The roller assembly is 8 inches(20.3 centimeters) long, 7 5/8 inches (19.4 centi-meters) wide, and 5 3/4 inches (14.6 centimeters)high overall. It weighs about 12 pounds (5.4kilograms). The roller is used to make theplacement and removal of transoms easierduring the assembly and disassembly of thebridge.

WARNING: Two personnel are requiredon each jack handle to operate jack. Thesetwo persons must work together to preventeither from taking all of the load.

JACKThe jack (Figure 2-28) is used to lift the bridgeon and off the rocking rollers. It is a mechan-ical lifting jack (the type normally used inrigging, railroad, and construction work). Ithas a lifting range of 15 inches (38.1 centi-meters) and a capacity on the top of 15 tons(13.6 metric tons). When the weight is carriedon its toe, its capacity is only 7 1/2 tons (6.8metric tons). Jacks from different manufac-turers have different spacing (pitch) betweenthe teeth, as listed in Table 2-2. Where jacksare lifting at the same point, all jacks usedmust have the same tooth pitch so they can beoperated in unison. The jack weighs 128pounds (58.1 kilograms).

JACK SHOEThe jack shoe (Figure 2-28)assembly which fits over the

is a weldedbearing and

supports the jack. In jacking under the step ofthe end posts, the bearing can be placedreadily without removing the jack shoe. Theshoe is 4 3/16 inches (10.6 centimeters) highand weighs 36 pounds (16.3 kilograms). It fitsover the bearing on the base plate.

WRENCHESThe wrenches provided in the bridge set areshown and listed in Figure 2-29.

PANEL LEVERThe panel lever (Figure 2-30), used in assem-bling the second and third trusses after thefirst truss is in place over the gap, is a woodenbar 7 feet 9 inches (2.4 meters) long weighing48 pounds (21.8 kilograms). It has a fulcrumnear the center and a lifting link at the end.The lifting link has a swiveling crosspiecewhich can be readily attached to the top of apanel by passing it through the upper chordand turning it. The upper end of the linkslides in a slot—the inner end of the slot isused when erecting the second truss, theouter end is used when erecting the thirdtruss. The fulcrum is always placed on the topof the first truss. Two levers per panel arerequired, with two soldiers operating eachlever.

CARRYING BAR AND TONGSA wooden carrying bar (Figure 2-31) is 3 feet 6inches (1.1 meters) long and reinforced by asteel band at the middle. It is used to carrypanels and transoms. It weighs 8 pounds (3.6kilograms). Carrying tongs are steel and

1 6

FM 5-277

shaped like railroad tongs, as shown in Figure2-32. These tongs are used to carry transomsby clamping them over the top flange. One

soldier carries one of the two handles. Nor-mally, four pair of tongs and eight soldiersare used to carry a transom.

17

FM 5-277

CHORD JACKThe chord jack (Figure 2-33) consists of twowelded steel frames joined by a knuckle-threaded screw assembly. It is operated by aratchet lever. The lever has a shackle at itsend to which a rope can be attached, makingoperation easier. The chord jack is used toforce the panels apart so the chord lug holesalign and the chord bolts can be inserted.

PIN EXTRACTORThe pin extractor (Figure 2-34) assists indismantling the bridge. After the pin hasbeen driven part way out, and the recessunder the head of the pin is exposed, the pinextractor grips the pin head and forces thepin out by a levering action. It is particularly

1 8

useful for dismantling the third truss of atriple-truss bridge where the closeness of thesecond truss makes it impossible to drive thepins out with a hammer.

LAUNCHING-NOSE LINK MK IIThe launching-nose link Mk II (Figure 2-35)is about 10 inches (25.4 centimeters) long and7 inches (17.8 centimeters) wide and weighs28 pounds (12.7 kilograms). It consists of twosteel frames welded back to back. The lugs oftwo panels fit into the link. The sides of thelink have holes into which panel pins can beinserted. The links lie flush with the undersideof the bottom chords and have a false flangewelded on the bottom edge so the bridge canbe rolled out on launching rollers. It also hasa pintle on the top to seat a transom.Launching-nose links overcome the sagoccurring when the launching nose is canti-levered over the gap. They are also usedbetween the upper jaws of span junctionposts during the launching of broken-spanbridges.

TEMPLATESTwo types of templates are provided, one tolocate the bearings for the rocking rollers andthe other for the plain rollers. The rocking-roller template (Figure 2-36) weighs 78 pounds(35.4 kilograms) and consists of a timber basewith timber strips on top forming two spaceslarge enough for rocking-roller bearings. Atone end of the template are two angle cleatswhich are used as measuring points. Theplain-roller template (Figure 2-37) weighs 22pounds (10.0 kilograms). It consists of atimber base with timber strips on three sides

and a steel strip on the fourth. The stripssurround a space large enough for the base-ofa single plain roller. The template also hastwo angle cleats at one end for measuringpoints.

FM 5-277

BASIC BRIDGE SETParts for standard truck loads are drawnfrom these basic sets. Tables A-2 and A-3 inAppendix A list components of the M2 panelbridge basic set. The set contains enoughparts. and equipment to install two 80-foot(24.4 meters) double-single M2 bridges withlaunching nose or one 130-foot (39.0 meters)double-double bridge with launching nose.

Conversion Set No. 3, Panel Crib Pier, M2 isused with equipment from the basic set tobuild panel crib piers. Table A-4 in AppendixA lists component parts of conversion set No.3. Enough parts are issued with each of thesesets to provide the assembly of a triple-trusspier supporting two triple-truss broken spansand containing both horizontal and verticalstories.

BRIDGING TRUCK LOADS

RECOMMENDED BRIDGING LOADSThe engineer company (panel bridge) nor-mally transports one set of the Bailey bridgeon 5-ton dump trucks and 4-ton bolstertrailers. The company has two platoons, eachcapable of transporting one 80-foot (24.4meters) bridge (the most common bridgeinstalled). The loads shown in Figures 2-38through 2-47 and Tables 2-3 through 2-13(pages 20 through 30) have the followingfeatures:

All loads are within the rated capacity ofthe assigned vehicles.

The loading lends itself to stockpiling orassembly on a restricted site. A launchingnose can be started with only three loadson the site.

The number of trailers is 40 percent of thenumber of trucks. This makes it possibleto use trucks to tow trailers if necessary.

Erection equipment is spread over fourtrucks and one trailer, thereby minimizingthe effect of loss or breakdown.

Trucks are loaded with all the female orall the male panel ends toward the rear ofthe vehicles.

Steel cables are used for tiedowns on alltruckloads.

19

FM 5-277

20

FM 5-277

21

FM 5-277

22

FM 5-277

23

FM 5-277

24

FM 5-277

25

FM 5-277

26

FM 5-277

27

FM 5-277

28

FM 5-277

Conversion set No. 3 is carried in 2 crib-pierloads. Information on the capabilities of dif-ferent standard truck loads is given in Table2-13, and Tables A-5 and A-6 in Appendix A.

BAY LOADSThe recommended bridge load for combatoperations is the bay load (Figure 2-47, page30). Each bay load truck contains all theparts, except transoms, required for one bay(10 feet) (3.0 meters) of double-single Baileybridge. This loading lends itself well to mostcombat engineer Bailey bridge missions.Table 2-14 (page 30) lists the parts found inthe bay load. Four-ton bolster trailers carrythe transoms with the bridge load mentionedearlier. The bay load is designed to be easilyunloaded by crane. However, the load mayalso be unloaded by hand or dumped if acrane is not available. If the load is dumped,take care not to damage the chess. For acomplete bridge, parts and grillage,launching nose, ramp, footwalk, spares, andoverhead-bracing loads must alsobe included.

29

FM 5-277

30

FM 5-277

CHAPTER 3

P L A N N I N G A N D O R G A N I Z A T I O N

Each bridge site must be reconnoitered toselect the site most economical in use ofavailable personnel, equipment, and time.The reconnaissance officer must be told thefollowing before making the reconnaissance

Where bridge is needed. The generallocation of the bridge is determined bytactical requirements.

Class of bridge needed. The class of thebridge is determined by the type ofvehicles it must carry.

When bridge is needed. The time set forthe bridge to become operational affectsseriously planning for the mission.

Who is to construct the bridge.

SITE RECONNAISSANCEA thorough evaluation of information frompreliminary studies may aid the reconnais-sance by limiting it to a few suitable sites.Sources of preliminary information are intel-ligence studies and reports, interviews withlocal civilians, maps, aerial photographs(including stereo-pairs), and aerial recon-naissance.

SITE SELECTIONWhenever possible, make aground reconnais-sance. The following site selection factors aredesirable for a panel bridge:

There should be access routes at each endof the bridge tying into the main road net.These routes should not require excessivemaintenance or preparation.

Approaches should require little prepara-tion. These approaches should be twolane and straight for 150 feet (45.7 meters)at each end of the bridge. Their slopeshould not exceed 10 percent (1 in 10).Special consideration must be given tothe amount of work required to preparethe approaches and piers, since this workfrequently takes as much time as thebridge installation itself.

Banks should be firm and stable and ofabout equal height.

The site should be large enough forassembly of the bridge and wide enoughfor unloading and stacking the parts anderection tools. The approach road oftenprovides such space.

There should be a turnaround area largeenough to allow trucks and bolster trailersto completely turn around so they canback into the site. This area is normallylocated about 50 feet (15.2 meters) fromthe bridge site.

There should be space for an engineerequipment park—a covered and concealedarea ½ to 5 kilometers behind the bridge

site, in which to store vehicles andequipment when not in use at the bridgesite.

A bivouac site for construction and main-tenance crews and crossing noncommis-sioned officer in charge should beavailable.

Following the reconnaissance, make out areport. The reconnaissance report describesevery usable site reconnoitered, and recom-mends a site. The report includes

Location of site.

Width at gap.

Length, truss type, and type of grillage ofbridge that would be assembled at site.

Slope of bridge.

Condition of banks and capacity ofabutments.

Proposed location of site layout.

Site preparation required.

Recommended method of transportingtroops and equipment to far bank.

Sketch showing profile of centerline ofthe bridge, extending 100 feet (30.5 meters)

31

FM 6-277

on the near shore and 50 feet (15.2 meters)on the far shore.

Sketch showing layout of assembly site,and location of turnaround and engineerequipment park.

Truck route to bridge site from engineerequipment park.

SITE LAYOUTWhen the bridging is being unloaded directlyfrom the trucks, the site must be cleared for atleast as long as the width of the gap, but thewidth of the site need only be the width of theapproach. If the bridging is to be unloadedand stacked at the site, the site must be about150 feet (45.7 meters) wide. The stacks arearranged as shown in Figure 3-1. In restrictedareas, 30 feet (9.1 meters) should be availableat least on one side of the bridge to permitinsertion of transoms. Otherwise, transomsmust be threaded from within two bridgetruss girders.

ORGANIZATIONThe work force is normally organized intounloading parties and an assembly party.Each unloading party consists of one non-commissioned officer and eight soldiers. Thenumber of unloading parties depends on thelength and type of the bridge (Table 3-l).Unless an unusually large cleared area existsat the site, no more than three or four un-loading parties will be able to work efficientlyat one time.

32

FM 5-277

WARNING: The left rear soldier calls thelift commands after ensuring that all crewmembers are prepared to lift to preventinjury.

The various details in the assembly party areshown in Table 3-2. In most cases, this in-cludes the panel, transom, bracing, anddecking details. The duties of the panel detailare as follows:

5.1

2

It carries, places, and pins together panelsin the launching nose and bridge.

As soon as all panels are in place, itdivides into two crews. One crew crossesto far bank and begins dismantling thelaunching nose. The other carries neces-sary parts to the far bank for completion

3

4

of the end of bridge and installation of theramp.

6It reforms as a single detail and completesdismantling of the launching nose.

It installs far-bank end posts.

It jacks down far end of bridge.

It installs far-bank ramp, placing chess andribbands.

33

FM 5-277

Duties of the transom detail areas follows:

1 It carries, places, and clamps down tran-soms.

2 It removes plain rollers on near bank.

3 It installs end posts on near bank.

4 It helps decking detail in jacking downnear end of bridge.

5 It installs near-bank ramp and helpsdecking detail in placing chess and rib-bands on it.

Duties of the bracing detail are to obtain,install, and adjust the following parts:

Sway braces.

Rakers.

Bracing frames, on all but single-singlebridges.

Chord bolts, on double- and triple-storybridges only.

Tie plates, on triple-truss bridges only.

Overhead-bracing supports, on triple-story bridges only.

Duties of the decking detail areas follows:

1 It assists panel detail in starting assemblyof the launching nose.

34

2 It lays stringers, chess, and ribbands onbridge.

3 It jacks down near end of bridge.

4 It lays chess and ribbands on near-bankramp.

ASSEMBLY TIMETime for assembly and installation of anormal bridge is given in Table 3-3. Table 3-3shows estimated times for daylight assemblyand launching of various lengths of differenttypes of bridges when built by manpoweralone and when using one crane. Times donot include preparation of site and layout ofrollers. These times assume there is a favor-able assembly site, trained personnel are

available, equipment is stacked at the site,and footwalks are omitted. Use of untrainedtroops, poor weather, various terrain condi-tions, and enemy activity will lengthenassembly time by 30 percent. Added timemust also be allowed for placing wear treads.Add ½ to 4 or more hours for preparation ofsite and layout and placing of rollers (de-pending upon the amount of work required tolevel site, install grillages, and crib up rollers).Add ½ hour for unloading from trucks ifseparate unloading parties are available. Ifnot available, add 1 to 2½ hours according totype of bridge. For blackout conditions,increase daylight times by 50 percent. Formission-oriented protection posture (MOPP)conditions, increase final construction (allother conditions considered) by 50 percent.

FM 5-277

INSTALLATION PROCEDUREInstallation procedure begins with site prep-aration (clearing mines, removing obstacles,constructing a turnaround for trucks). Instal-lation then includes the following steps: rollerlayout (including baseplates), unloading ofbridge equipment, bridge assembly andlaunching, bridge jackdown and ramp assem-bly, and installation of wear treads andfootwalks.

MOVEMENT CONTROLProper planning for the movement of bridgetrucks is important in providing, withoutconfusion, the bridge equipment when it isneeded. If the equipment is to be stacked atthe site, time the transportation to arrive assoon as the stacking site is ready.

35

FM 5-277

CHAPTER 4

F I E L D D E S I G N A N D C L A S S I F I C A T I O N

LENGTH, TRUSS TYPE, AND GRILLAGE TYPE 36

LAUNCHING NOSE 49

ROLLERS AND JACKS 51RAMP REQUIREMENTS 52

EXAMPLE FIELD DESIGN PROBLEM 54

BRIDGE CLASSIFICATION 56

The Bailey bridge may be adapted to fit mined. Finally, the required grillage isalmost any gap. The field design procedure determined. However, the grillage type mayfirst determines the initial length of bridge cause a change to the initially determinedrequired, and then the truss type needed to bridge length. If so, the truss type will have tocarry the required class of traffic is deter- be rechecked, as well as the grillage type, for

LENGTH, TRUSS TYPE, AND GRILLAGEDETERMINING INITIAL

BRIDGE LENGTHThe initial bridge length is determined byadding the width of the gap, the safetysetbacks, and the roller clearances.

GapThe measurement of the gap depends on thecondition of the abutments (Figure 4-1). Theseare usually classified as prepared, unpre-pared, or a combination of the two.

Prepared abutments are abutments whichcan hold the bridge load close to the facewithout failing. Examples of prepared abut-ments are mass concrete, headwall with piles,

36

and headwall with footers and deadman.Technical Manual (TM) 5-312 gives moredetailed information on prepared abutments.The gap is measured between the faces of twoprepared abutments.

An unprepared abutment is one which wouldprobably fail if the bridge load were appliedclose to its edge. Examples of unpreparedabutments are natural slopes, demolishedabutments, or abutments with headwalls thatare not strong enough to hold the load. Thegap is measured from the toe of the slope ofone unprepared abutment to the toe of theslope of the other.

the new bridge length. To complete the fielddesign, the number of rollers and jacks neededmust also be determined.

TYPEIf both prepared and unprepared abutmentsexist on one bridge site, the gap is measuredfrom the face of the prepared abutment to thetoe of the slope of the unprepared abutment.

Caution: Care must be taken whencompleting the design process or thebridge will fail. Abutment types andlocation of the toe of the slope forunprepared abutments should be donecarefully. Incorrectly classifyingabutment types or locating the toe ofthe slope is the most common anddangerous design mistake. When indoubt, always classify the abutmentas unprepared. If an abutment is par-

FM 5-277

tially prepared, determine the toe ofthe slope at the base of the preparedface. If the face is in poor condition,determine the "real" toe of slope. Besure to remember to measure bankheight at the toe of the slope.

Safety setbackSafety setback is the minimum distance thateach rocking roller must be behind the bankof the gap. This distance depends on thecondition of the abutments on each bank(Figure 4-2). If the bridge site has preparedabutments, the rocking rollers are set back aminimum of 3 feet 6 inches (1.1 meters) fromthe edge of the abutment.

When unprepared abutments exist, the safetysetback must be calculated. If the rollers are

placed too close to the edge of the gap, the soilmay fail during launching. Therefore, placethe rocking rollers at a location behind thetoe of slope of the soil. For field design, the toeof slope is where the bank’s surface is 45degrees (an average value) from the hori-zontal direction. This would mean that therocking roller should be set back a distanceequal to the height of the bank. However, anadditional safety factor of 50 percent is added.Therefore, the safety setback is 1.5 times thebank height. The bank height is measuredfrom the toe of the slope to the ground level atthe abutment. The safety setback is measuredback from the toe of the slope.

EXAMPLE:Given:

Unprepared abutmentBank height 8 feet (2.44 meters)

Required:Determine the safety setback (SS)

Solution:Safety setback = 1.5x bank heightor 1.5 x 8 feet = 12 feet (3.66 meters)

Roller clearanceRoller clearance is the distance from thecenter of the rocking roller to the center of thebearing on which the bridge end posts willrest (Figure 4-3, page 38). The normal rollerclearance, about 2 feet 6 inches (0.76 meters),is always used when determining the initialbridge length. The actual roller clearance willbe determined by the type of grillage used.

3 7

FM 5-277

An example of computing bridge length withboth abutments prepared (Figure 4-4) is asfollows:

Given:Gap is 56 feet (17.07 meters)(abutment to abutment)

Required:Determine initial bridge length

Solution:Initial bridge length (bLi) = gap +safety setbacks + roller clearances

3 8

bLi = 56 feet+ (3.5 feet+ 3.5 feet) +(2.5 feet + 2.5 feet)

bLi = 68 feet (20.73 meters)

Round up to the next 10-foot (3.05 meters)length to equal 70 feet (21.37 meters)

An example of computing bridge length withboth abutments unprepared (Figure 4-4) is asfollows:

Given:Gap measurement (toe to toe)—57 feet (17.37 meters)

Bank height—Near shore: 9 feet(2.74 meters)Far shore: 12 feet(3.66 meters)

Required:Determine initial bridge length

Solution:bLi = gap + safety setbacks + roller

clearances

bLi = 57 feet + [1.5(9 feet) +1.5 (12 feet)] + (2.5 feet+ 2.5 feet)

= 93.5 feet (28.5 meters)bLi = 95.5 (29.11 meters)

Round up to the next 10 feet (3.05 meters)to equal 100 feet (30.48 meters)

An example of computing bridge length withone prepared and one unprepared abutment(Figure 4-4) is as follows:

Given:Gap measurement (toe to toe)—53 feet (16.15 meters)

Bank height unprepared shore—10 feet (3.05 meters)

Required:Determine initial bridge length

FM 5-277

Solution:bLi = gap + safety setbacks +

roller clearances

bLi = 53 feet+ [3.5 feet+1.5(10 feet)] + (2.5 feet + 2.5 feet)

bLi = 76.5 feet (23.32 meters)

Round up to 80 feet (24.38 meters)

TRUSS TYPEThe required truss type for a given length ofBailey bridge to carry a specified class oftraffic is found in Table A-7 in Appendix A.The actual class of the bridge maybe greaterthan required, but not less.

Note: The truss type required for a normalcrossing is always used unless otherwisedirected by the field commander.

EXAMPLE:Given:

Bridge length — 80 feet(25.97 meters)

Required class — 60 wheel/60 track

Required:Determine the truss type required

Solution:From Table A-6 in Appendix A TYPE OF GRILLAGE NEEDEDTruss type: triple-single The end posts at each end of the bridge areDesign class — 85 wheel/80 track supported by bearings set on base plates.

During launching, the entire weight of thebridge is carried by the near-bank rockingrollers, which rest on rocking-roller tem-

plates. Grillages are used to spread the loadover a larger area (Figures 4-5 through 4-11,pages 40 through 44) when the soil-bearingcapacity is exceeded. Grillages also serve ascribbing to raise base plates or rollers to thedesired level.

DescriptionGrillages are made of squared timbers laidunder the base plate or roller template. Thesemust be carefully leveled transversely; grill-ages on each side of the bridge must be levelwith each other so that all trusses will rest onbearing plates. If bearing plates are not leveltransversely, only one truss will carry theload at first, until deflection under load bringsthe other trusses to bear. The first truss tobear will then be overstressed before the lasttruss can be fully utilized. This can result infailure under less than the rated load of thebridge.

Timbers for use as standard grillages aresupplied in panel bridge sets. The panelbridge set supplies 144 each 6-by 6-inch (15.2by 15.2 centimeters) timbers 4½ feet (1.4 meters)long, and 48 each 3- by 6-inch (7.6 by 15.2centimeters) timbers 4½ feet (1.4 meters) longfor grillage. Standard grillages using thesetimbers and panel bridge parts are illustratedin Figures 4-5 through 4-8.

On soft soils, some of the heavier bridges willrequire larger grillages than can be builtfrom the timbers supplied in the set. For thesebridges, grillages built from 8- by 8-inch (20.3by 20.3 centimeters) timbers are shown inFigures 4-9 through 4-11.

39

FM 5-277

4 0

FM 5-277

4 1

This change supersedes page 42.

4 2

FM 5-277

4 3

FM 5-277

4 4

This change supersedes page 45. FM 5-277

Nonstandard grillages, made of other sizetimbers, can be used if each layer is at least asthick and wide as the corresponding standardgrillage. Squared timbers should be used,since rough cut timbers often result in uneven,wobbly cribs.

Selection of grillageThe selection of grillage is determined by thebridge length, the truss type, and the soil-bearing capacity. Table 4-1 give the safebearing pressure in tons per square foot (t/sf)on various soils. A careful evaluation of thesoil character is essential to prevent grillagefailures. Note that in sandy or gravelly soils,the bearing power of the soil is increasedwhen the grillage is dug in so that it bears onthe soil 1½ feet (.46 meter) or more below thesurrounding surface.

Note: If soil-bearing capacity value fromTable 4-1 is not listed on Table 4-4, thenumber must be rounded down to obtainthe proper grillage type.

Table 4-2 (page 46) gives the load on grillageat one comer of the bridge. Note that in somebridges the rocking-roller reaction is greaterthan the base-plate reaction. Table 4-3 (page47) gives the load capacities for the grillage invarying soils. The type of grillage requiredmay be found by determining the bridgereaction from Table 4-2 and then selecting agrillage type from Table 4-3 which has therequired capacity for the proper soil type. The

grillage types for various soils and bridgetypes are also given in Table 4-4 (page 48).

EXAMPLE:Given:

Bridge length—80 feet(25.97 meters)

Truss type—triple-single

Soil type—loose fine sand

Required:Determine the grillage typerequired

Field solution:From Table 4-1, soil-bearing capacity is2 t/sf

From Table 4-4, grillage type required istype 4

Detailed analysis:From Table 4-2, corner reactions are 59tons (54 metric tons)—base plate, 19.0 tons(17.2 metric tons)—rocking rollers

From Table 4-3, type 4 grillage provides thenecessary capacities. Type 4 provides 71tons (64 metric tons)—base plate, 57 tons(52 metric tons)—rocking roller.

It is unlikely that the near and far bankswould have different soil-bearing capacitiesbut, if so, grillage is determined separatelyfor each bank. The maximum allowable slopefor a Bailey bridge is 1 to 30. If bank heightsdiffer enough to cause a greater slope, the lowend may be cribbed up to decrease the slope.The cribbing must have at least the samebearing area as the required grillage. Ifcribbing is impractical, the high end may beexcavated to reduce the slope. Figures 4-5through 4-11 show the dimensions and neces-sary materials for the grillage types.

Note: Types 5, 6, and 7 are made frommaterials not issued with the bridge set.

DETERMINING FINALBRIDGE LENGTH

The grillage type required may increase theroller clearance. This may affect the requiredbridge length. If so, the truss and grillagetype must be rechecked for the new bridgelength. The required roller clearances for

4 5

FM 5-277

each type of grillage are shown in Figures 4-5through 4-11. The roller clearance and totalgrillage height are given in Table 4-5 (page49).

EXAMPLE:Given:

Initial bridge length—76.5 or 80 feet (23.9or 24.4 meters)

Required class—50 wheel/55 track

Initial truss type—double-single

Soil-bearing capacity—2 t/sf

Required:Determine the final bridge length, truss,and grillage type

Solution:Use the following steps:

1

2

3

Grillage from Table 4-4—type 1 required

Roller clearance from Table 4-5 orFigure 4-5—4 feet 6 inches (1.4 meters)

Initial roller clearance was 2 feet 6 inches(.76 meter); therefore, 2 more feet (.6meter) must be added to each end ofbridge:

New bridge length= 76.5 feet + 2 feet + 2 feet= 82.5 or 90 feet (27.43 meters)

4 6

FM 5-277

4 Recheck truss type, Table A-6 inAppendix A—90 feet—triple-single required

5 Recheck grillage, Table 4-4—type 3 required

6 Recheck roller clearance, Table 4-5,Figure 4-7—3 feet 6 inches (1.07 meters)

7 Final design—90 feet (27.43 meters)triple-single,type 3 grillage

This will not increase the bridge length

4 7

FM 5-277

4 8

FM 5-277

COMPOSITIONThe launching nose (Figure 4-12, page 50) is askeleton framework consisting of panels,transoms, rakers, sway braces, and, whennecessary, launching-nose links. It does nothave stringers or decking. One transom withtransom clamps and rakers is used behindthe leading upright of each panel. Swaybracing is used in all but the first bay at thefront of the launching nose. Footwalks arenot assembled on the nose.

USE OF LAUNCHING NOSEThe panel bridge is normally launched bycantilevering the launching nose over thegap. The weight of the bridge acts as thecounterweight. When the launching nosereaches the far shore, it rests on the rockingrollers and supports the bridge as it is pushedacross the gap. The composition of the nosedepends on the length of the bridge and thetype of assembly. The composition of thelaunching nose for the various combinationsof span and bridge assembly is shown inFigure 4-12 and given in Chapter 6, Tables 6-1through 6-3; Chapter 7, Tables 7-1, 7-2; and

LAUNCHING NOSEChapter 8, Tables 8-1, 8-2. These tables mustbe followed exactly.

USE OF LAUNCHING-NOSE LINKSThe launching nose tends to sag as it iscantilevered over the gap. The approximatesag at the end of the nose just before itreaches the far bank is shown in the abovementioned tables. To overcome this sag,launching-nose links are used. Using onelaunching-nose link in each truss increasesthe length of the bottom chords of the nose by7½ inches (19.0 centimeters); thus, the end ofthe launching nose is raised by 13½ inches(34.3 centimeters) for each bay ahead of thelinks. Because links must not be insertedwith more than four bays of the launchingnose ahead of them, the maximum amount oflift that can be obtained from one pair of linksis about 54 inches (137 centimeters). If agreater amount of lift is required, an addedpair of links can be used in one of the jointsbetween the original pair and the end of thenose. Its position depends on how much lift isrequired. Figure 4-12 shows the vertical liftsthat can be obtained using one or more pairs

of links. The maximum lift obtainable usinglaunching-nose links is 94½ inches (239.8centimeters). When calculating the positionof the links, add 6 inches (15.2 centimeters) tosag values shown for safety.

When the far-bank seat is higher than or levelwith the near-bank seat, launching-nose linksmust be used to compensate for sag, and thetops of all rollers must be in the same plane. Ifnecessary, block and tackle should be used toprevent the bridge from sliding backwards.

Launching-nose links are necessary if thefar-bank seat is low enough to require the useof block and tackle on the near bank toprevent the bridge from running away whenthe balance point passes the rocking rollers.

Use the following steps to determine theposition of launching-nose links:

1 Determine sag from Tables 6-1 through6-3, 7-1 and 7-2, or 8-1 and 8-2

2 Safety sag of 6 inches (15.27 centimeters)

4 9

FM 5-277

3

4

Lift required (LR):LR = steps 1 + 2

Position of launching-nose link (Figure4-12)

EXAMPLE:Given a 160-foot (48.8 meters) triple-singlebridge with grillage type 1 on both the nearshore (NS) and far shore (FS). The far-bankseat is level with the near-bank seat.

Problem:Are launching-nose links required? Iflinks are required, at what distance arethey placed from tip of launching nose?

Solution:Launching-nose links are required. There-fore the following steps are used:

1

2

Determine sag for 160-foot triple-single(Table 6-3)

77 inches (195.58 centimeters)

Safety factor of6 inches (15.24 centimeters)

5 0

FM 5-277

3

4

Lift required (LR):

LR = (steps 1 + 2)LR = 77 inches + 6 inchesLR = 83 inches (210.82 centimeters)

Position of launching-nose link (Figure4-12):

Two pairs of launching-nose links placedat 30 feet (9.144 meters) and 40 feet(12.192 meters) from the tip of the nose

ROCKING ROLLERSUse rocking rollers on both banks duringlaunching. Normally, use two rocking rollerson the near bank for single-single and double-single truss bridges of 100 feet (30.5 meters)and shorter. Use four for all other assemblies.Two rocking rollers are normally required onthe far bank; however, use four if the skeletonlaunching nose is double-truss in any part.Table 4-6 shows the required number ofrocking rollers on near and far banks forvarious bridge lengths and assemblies.

PLAIN ROLLERSPlace rows of plain rollers behind the rockingrollers at intervals of 25 feet (7.6 centimeters)to support the bridge during construction.The number of rollers in each row depends onthe type of bridge. Single-single and double-single bridges need two plain rollers per row.All other types of construction need fourplain rollers per row (Chapter 5). The numberof rows required depends on the construction

Table A-1 in Appendix A gives the numberand position of launching-nose links requiredfor normal bridges. This table assumes thatboth near-and far-shore rocking rollers are atthe same elevation.

ROLLERS AND JACKS

backspace needed. Place plain rollers onlyevery 25 feet (7.6 meters). More rollers are notrequired to support an overhang under 25 feet(7.6 meters). In addition, two constructionrollers are used to aid in inserting the launching-nose links. These are plain rollers placed 12½feet (3.8 meters) behind the rocking rollersand 2 to 4 inches (5.0 to 10.1 centimeters)below the plane of the other rollers. They maybe removed once the construction extendsback to the first row of plain rollers. Thenumber of plain rollers needed for variousbridges is shown in Table 4-7 (page 52).

JACKSThe number of jacks required to jack down abridge depends on the span length and thetype of the bridge. The number of jacksneeded to jack down the end of the bridge isshown in Table 4-8 (page 52). Details onjacking procedures are given in Chapters 6, 7,and 8.

Note: Jacks must be positioned so thatthey carry no more than 7½ tons (6.8metric tons) on the toe or 15 tons (13.6metric tons) on the top.

5 1

FM 5-277

RAMP REQUIREMENTSRamps are used at each end of the bridge. Theslope of the ramp must not exceed 10 to 1 forloads up to and including 50 tons, and 20 to 1for loads over 50 tons.

SUPPORT FOR END OF RAMPThe end of the ramp will carry about onequarter of the weight of the heaviest trackedvehicle to pass over it when the ramp issupported at midspan. If there is no midspansupport, the end of the ramp will carry about40 percent of the weight of the tracked vehicle.One or two stacks of chess, side by side, arelaid in two layers under the tapered end of theramp to provide the necessary bearing areaon the soil. If greater area is needed for heavyloads on very soft soil, footings are usedunder the chess. On soil capable of supporting2 tons per square foot, two chess under the

5 2

tapered end of the ramp are enough forbridges up to class 67. For higher capacitybridges, four chess are used (Figure 4-13). Onechess on edge at the end of the ramp serves asan end dam, so the approach can be madelevel with the ramp floor. An alternatemethod for supporting the ramps on theground is to use a transom as a sill under theramp.

MIDSPAN RAMP SUPPORTSFor loads of 45 tons (40.8 metric tons) or over,each ramp section must be supported at itsmidpoint by cribbing and wedges. This sup-port will carry one half of the class of thevehicle passing over, and the base of thecribbing should be large enough to spread theload over the soil without exceeding theallowable bearing pressure of the soil. On soil

This change supersedes page 52.

capable of supporting 2 tons per square foot,two chess side by side under the cribbingprovide enough bearing area for all bridges.An alternative method for loads of 45 tons ormore is to make the ramp level with at least3½ feet (1.07 meters) of the ramp supported onthe abutment (Figure 4-14).

FM 5-277

PEDESTAL SUPPORTSBecause the slope of the ramp should notexceed 1 to 10, it may be necessary to use twoor more ramp bays. The junction of the rampbays rests on a transom supported by fourramp pedestals spaced as shown in Figure4-15. These pedestals (Figure 4-16, page 54)take two thirds of the class of the vehiclespassing over and must be set on enoughgrillage to spread the load over the soil. Three6-by 6-inch (15.2 by 15.2 centimeters) timbers4 feet 6 inches (1.4 meters) long under eachpair of pedestals provide enough area for 40-ton loads on soil that will carry 2 tons persquare foot. For heavier loads, three chess areplaced side by side under the 6- by 6-inch (15.2centimeters by 15.2 centimeters) timbers.

5 3

FM 5-277This change supersedes page 54.

SUPPORTS FOR END TRANSOMFor loads of 40 tons (36.3 metric tons) or more, usecribbing and wedges under the midpoint of the endtransom. This support will carry 40 percent of theweight of the heaviest tracked vehicle to pass over,and the area of the base of the cribbing should belarge enough to spread the load over the groundwithout exceeding the allowable bearing pressureon the soil. Seven 6- by 6-inch (15.2 centimeters by15.2 centimeters) timbers 4-feet 6-inches (1.4meters) long laid side by side provide enough areafor all the bridge loads on soil that will carry 2 tonsper square foot.

EXAMPLE FIELDDESIGN PROBLEM

MISSION GIVEN: Design a Bailey to span thegap shown in Figure 4-17. Bridge must haveMilitary Load Class (MLC) 60 wheeled/60 tracked.All data required is given in Figure 4-17.

I. INITIAL BRIDGE DESIGN(Steps 1 through 6)

1. Gap measured during reconnaissance (p 36)1. 112'

2. Safety setback. (p 37)a. Prepared abutment = constant of 3.5’.b. Unprepared abutment = 1.5x bank height.

2. NS 1.5 x 18' = 27'FS 3.5'

3. Initial roller clearance. Always use a constant of2.5’.

3. NS 2.5’FS 2.5’

4. Initial bridge length.a. Add steps 1+2+3.

4a. 147.5'b. If value in step 4a is NOT a multiple of 10,

round UP to the next highest 10.

5. Initial truss/story type. (Table A-7, p 303)5. DT

6. Initial bridge class. (Table A-7, p 303)a. Class must meet or exceed the MLC given in

the mission.b. The truss/story type selected is always based

on a NORMAL CROSSING unless otherwisedirected by the TACTICAL COMMANDER.

6. 60/60II. ADJUSTED/FINAL BRIDGE DESIGN7. Selection of grillage.

a. Safe soil bearing. (Table 4-1, p 45)NS 2 tons/ft²FS 6tons/ft²

7a.

b. Safe soil pressure. (Table 4-4, p 48). If thesoil bearing capacity values from step 7a are NOTlisted in Table 4-4, round DOWN to the closestvalue listed. Use these values for step 7c.

7b. NS 2 tons/ft²FS 3.5 tons/ft²

54

This change supersedes page 55. FM 5-277

c. Grillage required.7c. NS Type(s) 4,6,& 7

FS Type(s) 28. Determine adjusted bridge length.

a. Distance required for new roller clearance.(Table 4-5, p 49)

8a. NS 4.5'FS 4.5'

b. Add steps 1+2+8a.8b. 151.5'

c. If value in step 8b is NOT a multiple of 10,round UP to the next highest 10.

NOTE: Compare the value in step 8C to the valuein step 4b. If different, you must redesign thebridge as outlined in steps 9 through 12, usinglength from step 8C to find truss type in step 9. Ifnot, use this as your final bridge length and go tostep 13.

9. Final truss/story type. (Table A-7, p 303)

10. Final bridge class. (Table A-7, p 303)a. Class must meet/exceed the MLC given in the

mission.b. The Truss/Story Type selected is always

based on a NORMAL CROSSING unless other-wise directed by the TACTICAL COMMANDER.

11. Final grillage selection.a. Safe soil bearing. (Table 4-1, p 45)

b. Safe soil pressure. (Table 4-4, p 48). If thesoil bearing capacity values from step 11a are NOTlisted in Table 4-4, round DOWN to the closestlisted. Use these values for step 11c.

c. Grillage required.

12. Determine final bridge length.a. Distance required for new roller clearance.

(Table 4-5, p 49)

b. Add steps 1+2+12a.

c. If value in step 12b is NOT a multiple of 10,round UP to the next highest 10.

NOTE: (1) FOR TRY 1: Compare the value instep 12c to the value in step 8c.

a. If the same, go to step 13.b. If different, compare this value (step 12c) to

the value in step 4b:1. If these are the same, the designer is placed

in a judgmental situation. Repeating the design se-quence under the "TRY 2" column using the bridgelength from step 12c of "TRY 1" column will placeyou in an endless circle unless the final bridgelength can be reduced. In these cases, one willhave to use common sense and either overdesign alonger final bridge as shown in the "TRY 1" columnor choose a higher number grillage than thatoriginally selected in step 7c. The latter procedurecould reduce the roller clearance on one or bothbanks so that the required bridge length/final truss-story may be at the minimum to do the job. Youmay choose a higher number grillage than allowedwithin step 11c; however, you must be careful not to

exceed the BP and RRT capacities listed in Table4-2, p 46 and Table 4-3, p 47, FM 5-277. Makeyour decision and go to step 13. In this exampleproblem, the designer chose to select Type 3 gril-lage for the FS. Since this was not an option withinstep 11c he had to look at Tables 4-2 and 4-3 undera 150' DT bridge with a safe soil pressure of 3.5tons/ft2 to see if the BP and RRT capacities wereexceeded:Table 4-2 Table 4-3BP Reaction BP Allowable= 55 tons = 61 tons OKRR Reaction RRT Allowable= 54.8 tons = 60 tons OK

Had the designer not accomplished this, hewould have been forced to build the 160’ TT bridgeshown under the "TRY 1" column and wasted a lotof assets.

2. If these are different, you must redesign thebridge by entering the "TRY 2" column with thebridge length from step 12c "TRY 1" to determinethe truss/story type in step 9.NOTE: (2) FOR TRY 2 and HIGHER: Comparethis value in step 12c to the value in step 12c of theprevious "TRY" column. If the same, go to step 13.If different, use the same methodology and repeatthe design sequence until the value obtained in aparticular step 12c matches the value in step 12c ofthe previous design. Go to step 13.

55

FM 5-277 This change supersedes page 56.

13. Slope check. (p 45)a.- The maximum allowable bank height dif-

ference is 1 in 30. Therefore, maximum allowablebank height difference = final bridge length + 30.

13a. 150+30 = 5 2b. If:

(1) The step 13a value > actual bank heightdifference the slope is all right.

(2) The step 13a value < bank height dif-ference

(a) Choose another site,OR

(b) Crib up/excavate the FS or NS until thebridge slope is within limits.

13b. (GO)/NO GO(circle one)REMARKS:14. Final bridge requirements:

Length 150'Truss/Story Type DT

Class 60/60Grillage: NS Type 6

FS Type 315. Launching nose composition. (Tables 6-1through 6-3, p 64/65, Tables 7-17-2, p 95, or Tables8-1/8-2, p 104, dependent upon truss type)

15. 9 Bays (5 Sgl Truss/4 Dbl Truss)

16. Placement of launching nose links.a. Sag. (See tables as in step 15)

16a. 34"b. Safety sag. (Constant of 6")

16b. + 6"c. Lift required. (Add steps 16a + 16b)

16c. = 40"d. Position of launching nose links (Figure 4-12,

pg 50)16d. 30' from tip of nose

17. Rocking rollers needed. (Table 4-6, pg 51)17. NS 4

FS 4 18. Plain rollers needed.

a. SS and DS bridges ONLY have two rollers perrow. All others have four rollers per row. UseTable 4-7 to determine the number of rows thenmultiply.

18a. 4x4= 16 rollersb. Add two more plain rollers to allow for your

construction rollers.18b. + 2

c. Add steps 18a to 18b.18c. = 18 rollers

19. Jacks required. (Table 4-8)19. 8 jacks

NOTE: Only one end of the bridge will be jackeddown at any onetime.

b. Support for end ramp (check one)(1) Final bridge class < 67 = 2 Chess (x).(2) Final bridge class > 67 = 4 Chess ( )

c. Midspan ramp supports (check one)(1) Final bridge class < 44 = Not needed ( ).(2) Final bridge class > 44 = Needed (x)

d. Pedestal supports (check one)(1) Not needed ( )(2) Needed (x)

NOTE: See Page 53 for criteria and drawings.Ramp length must be estimated from the site sketch.

e. Support for end transoms (check one)(1) Final bridge class < Class 39 = Not

needed ( ).(2) Final bridge class > Class 39 = Needed

(x)21. Personnel required. (Table 3-2, p 33)21. 7/122 w/o Crane 7/97 with Crane

NOTE: Check the difference between manpoweronly and crane construction.22. Assembly time. (Table 3-3, p 34)

22. 13 1/4 hrs w/o Crane/ 11 3/4 w/Crane

20. Ramp requirements.a. Slope requirements (check one)

(1) Final bridge class < 50= 1 to 10 ( ).(2) Final bridge class > 50 = 1 to 20 (x)

56

This change is inserted. FM 5-277

CLASSIFICATION OFEXISTING BRIDGES

Bailey bridge classifications may be deter-mined by entering Table A-6 in Appendix Awith the span length and truss type. This willgive the classification of the bridge for nor-mal, caution, and risk crossings. Table 4-9gives restrictions for the types of crossing.

Notes: The caution class number is foundby test and is normally 25 percent greaterthan the normal class. Risk loads willprobably cause permanent deformation ofbridge parts and may result in failure ifrepeated. Therefore, the engineer officermust thoroughly check the condition of thebridge before and after such a crossing.The grillage, cribbing, and number of tran-soms per bay must also be checked and thebridge class reduced or upgraded to obtainthe required classification. The conditionof the bridge and its supports must also beconsidered in its classification. If thebridge is deformed or damaged, the grillagehas rotted, or the abutment has failed, thebridge classification must be drasticallylowered.

EXAMPLE:Given:

Bridge length—80 feet(24.4 meters)

BRIDGE CLASSIFICATION

Cribbing—none 3

Condition—excellent

Required:Determine the normal trackclassification of the bridgewithout upgrading

Solution:Take the following steps: 4

1

2

Class—55 track(from Table A-6 in Appendix A) 5

Grillage—install type 1 as aminimum (Table 4-4)

Cribbing

Midspan ramp supportsNone—limits class to 44 tons

(39.9 metric tons)

End transomsNone—limits class to 39 tons

(35.4 metric tons)

Condition—excellent,no reduction

Final classification—39 track. The over-all classification is determined by thelowest classification of steps 1 and 3.

Truss type—double-single

Grillage—none

Soil-bearing capacity—10 t/sf

56-1

FM 5-277 This page is inserted.

56-2

FM 5-277

CHAPTER 5

R O L L E R L A Y O U T

This chapter describes the longitudinal andlateral spacing of rocking rollers and plainrollers. The elevation of rollers and baseplates, as well as a simple method of levelingand placing rollers, is discussed.

LAYOUT OF ROCKING ROLLERSEstablish the longitudinal location of therocking rollers by the safety setback deter-mined in the field design of the bridge. Todetermine the lateral spacing, place a rockingroller (Figure 5-1, page 58) on each side of thebridge 7 feet 5 inches (2.26 meters) from thecenterline (Figure 5-2, page 58). This gives aconstant value of 14 feet 10 inches (4.52meters) between the centers of the rockingrollers. Most bridges are double- or triple-truss and need another set of rocking rollers(Figure 5-3, page 59) placed 1 foot 6 inches (.46meter) out from each of the first set of rockingrollers (Figure 5-4, page 59).

Rocking-roller templates have been madewhich help the proper 1-foot 6-inch (.46 meter)center-to-center spacing of the rocking rollers.On the interior side of these templates, small-angle iron lugs are attached to aid rollerspacing. The edge-to-edge spacing of therocking-roller templates (lug to lug) is 11 feet6½ inches (3.51 meters) (Figure 5-4). The lugsare, however, frequently lost through use andthe most accurate method of spacing therollers is to use the 14-foot 10-inch (4.52meters) constant. The Bailey bridge transomis manufactured with a small hole in its

center web and two dowel holes toward eachend. These holes can be used to properlyspace the rocking rollers, as shown in Figure5-5 (page 60).

LAYOUT OF PLAIN ROLLERSTo determine longitudinal spacing, place twoor more plain rollers every 25 feet (7.6 meters)behind the rocking rollers to support thebridge during assembly and launching. Placetemporarily an extra set of plain rollers(called construction rollers) 12½ feet (3.8meters) behind the rocking rollers. The con-struction rollers aid in inserting thelaunching-nose links and provide clearancebetween the links and the ground. Removethese construction rollers after the links havepassed over the rocking rollers.

To determine lateral spacing, for single-story,single- and double-truss bridges, place twoplain rollers one on each side of the centerlineevery 25 feet (7.6 meters). The center-to-centerroller spacing is 14 feet 10 inches (4.52 meters)or 7 feet 5 inches (2.26 meters) each side of thecenterline. Plain rollers are normally placedon plain-roller templates which increase thebearing area over the ground. These tem-plates also aid in the lateral spacing of therollers. The templates are equipped with angleiron lugs, like the rocking-roller templates.Place the template so the lugs face the center-line. The distance between lugs, then, is 11feet 6½ inches (3.51 meters) (Figure 5-6, page60).

For all other assembly types use four plainrollers every 25 feet (7.6 meters), two on eachside of the centerline. Each plain roller con-sists of two small independent rollers. Fortriple-truss or multistory bridges, place theinside plain rollers so that the inside trusswill rest upon the second small roller (Figure5-7, page 60). The spacing between the centersof these small rollers, then, is 14 feet 10 inches(4.52 meters). Place the other set of plainrollers so that the second truss will rest on thefirst small rollers of this set (Figure 5-7). Thedistance between these trusses is 1 foot 6inches (.46 meter). The third truss will rest onthe outermost small roller. Plain-roller tem-plates also aid in lateral spacing of the plainrollers for the triple-truss or multistorybridges. Use one template under each roller.Place two templates end to end on each side ofthe centerline, with the angle iron lugs of theinside templates facing center and the outsidelugs facing away from center. When thespacing between the inside lugs is 10 feet 10%inches (3.31 meters), the plain rollers will beat the proper spacing (Figure 5-7).

BASE PLATESEstablish, by the type of grillage required,longitudinal spacing between the center ofthe rocking rollers and the center of the baseplate. The grillage type is determined asdescribed in Chapter 4. To establish lateralspacing, place the base plates under thetrusses as shown in Figure 5-9 (page 61).

5 7

FM 5-277

Space the bearings on the base plates (underthe trusses), as shown in Figures 5-8 (page 61)and 5-9.

GRILLAGESFigures 4-5 through 4-11 show the size of theareas to be leveled off to accommodate thegrillages. Take care that the rocking rollersand base plates are properly positioned whenplaced on the grillage. The grillage can becribbed up or dug in as needed for leveling.

ELEVATION OF ROLLERS AND BASEPLATES

Set the base plates at an elevation to keep theslope of the ramp bays less than 10 to 1. Also,allow for the depth of wear tread. Set allrollers (both plain and rocking), except theconstruction rollers, so their tops are in thesame horizontal plane. Normally this planeis level, but a slight inclination, not to exceed30 to 1 slope along the line of the bridge, ispermissible. Set the construction rollers 2 to 4inches (5.1 to 10.1 centimeters) below the levelof the other rollers. Placing the far-bankrocking rollers a few inches lower than theplane formed by near-bank rollers allows fornear-bank settlement caused by bridgeweight.

PLACEMENT CONTROL LINESA simple method of leveling and placingrollers is the use of placement control lines.The bridge centerline is first placed andextended 25 feet (7.6 meters) on the far shoreand the length of the bridge and launchingnose on the near shore. Then position twoplacement control lines parallel to and 7 feet

5 8

FM 5-277

5 inches (2.26 meters) to either side of thecenterline. Position the placement controllines level with the proposed plane of therollers. Use line levels at several spots on theplacement control lines to ensure that theyare level. It is also important to ensure thatthe placement control lines are parallel to thecenterline. The rollers can then be cribbed upor dug in as needed to bring their tops to thelevel of the placement control lines (Figure5-10, page 62).

59

FM 5-277

60

FM 5-277

61

FM 5-277 This change supersedes page 62.

62

FM 5-277

CHAPTER 6

A S S E M B L Y O F S I N G L E - S I N G L E B R I D G E S

LAUNCHING NOSE 64ASSEMBLY OF DOUBLE-SINGLE BRIDGE 71

ASSEMBLY OF TRIPLE-SINGLE BRIDGE 83LAUNCHING, JACKING DOWN, AND RAMPING 85

REINFORCING BRIDGE AND CONVERTING BRIDGE 91

This chapter describes the assembly andcomposition of double-truss single-story andtriple-truss single-story bridges and theirrespective launching noses. The assembly ofsingle-truss single-story bridges, which havelittle carrying capacity, is the same as thatfor the launching nose (Figure 6-l). Thischapter also covers the launching, jackingdown, and ramping of these bridges. The

procedure for adding extra trusses to increasethe class of single- and double-truss bridges isalso covered.

Single-story bridges are normally assembledand launched by manpower. They can beassembled on the rollers and launched or thebridge and nose can be pushed out over thegap after every two bays are assembled.

63

FM 5-277

LAUNCHING NOSECOMPOSITION

The number and types of bays used in the 6-3. These tables must be followed exactlynose depend on the length and truss type of with respect to the composition of thethe bridge. The composition of the launching launching nose. Assembly of the launchingnose for the various lengths of the single- nose is the same for all three types of single-story bridge is given in Tables 6-1 through story Bailey bridges.

64

FM 5-277

ASSEMBLY AND LAUNCHINGAfter roller layout is complete, proceed withassembling and launching of nose as follows:

1 Place two panels (female ends forwardand male ends resting on constructionroller) on the ground directly behind therocking rollers. Clamp the transom to the

panel behind the forward uprights. Securerakers to transom and panel with bracingbolts (Figure 6-2, page 66).

2 Connect second bay (Figure 6-3, page 67).Insert panel pins (points outward) withgrooves in the heads of pins horizontal.Clamp transom to panels behind forwarduprights.

3

4

5

6

Place pair of sway braces in second bay.

Lift front end of assembled bays ontorocking rollers (Figure 6-4, page 68) andsecure with steel pickets through bottomchord of panels and rocking rollers (Figure6-5, page 69) to prevent rolling.

An alternative method (for rocking rollerson low cribbing) is as follows:

a

b

c

d

Assemble first bay on ground.

Lift front end of bay onto rocking rollers(Figure 6-6, page 70) and secure withsteel pickets.

Raise rear end and slide constructionrollers under it 2 inches (5.1 centi-meters) below plane of tops of rollers.This places construction rollers approxi-mately 9 feet (2.7 meters) from rockingrollers.

Add second bay.

If required, place launching-nose links inposition between panels as determined byassembly conditions. See Chapter 4 todetermine the number of links and theirposition in the nose.

Continue adding panels with a transomevery 10 feet (3.0 meters). Add sway bracesin every bay and rakers on every transomuntil the required amount of skeleton isbuilt.

65

FM 5-277

66

FM 5-277

67

FM 5-277

68

FM 5-277

69

FM 5-277

70

FM 5-277

ASSEMBLY OF DOUBLE-SINGLE BRIDGE

FIRST BAY OF BRIDGEWhen assembly of the nose is completed,assemble the first bay of the bridge as follows:

1

2

3

Connect first two panels of inner trusswith last bay of nose (Figure 6-7). Insertpanel pins with points outward andgrooves in heads of pins horizontal. Placetransom roller on top of the lower panelchord at the transom location. Hook thebottom angle lug of the roller over thenear side of the top flange on the chord tohold the roller assembly in position. Liftthe head of the transom onto the rollerand shove it halfway across bridge width,at which point two soldiers should guideit to its seat on the panel chord. Then raisethe near end of the transom enough topermit removal of the roller. Place thefirst transom in front of the middle ver-tical and clamp loosely with transomclamps. Then move the transom roller toeach succeeding transom point.

Add panels of outer truss in first bay andhold in place with transom clamps (Figure6-8, page 72).

Insert second transom in front of rearvertical and third transom behind frontvertical. Clamp loosely. Fix rakers tosecond transom and panel (Figure 6-9,page 73). Then position sway braces withshort ends pinned to same side of bridgeso both turnbuckles are under one string-er. All sway braces, transom clamps,bracing frames, rakers, and tie plates inone bay should be left loose until all parts

71

FM 5-277

4

5

6

7

8

except stringers and decking are fitted forthe next bay being assembled.

Add second bay of panels (Figure 6-10,page 74). Place outer truss with panel pinspointing inward and inner truss withpanel pins pointing outward.

Place a chess on top of transom behindfront vertical in first bay and positionstringers for first bay. Leave stringer oversway-brace turnbuckles on edge untilsway braces have been tightened (Figure6-11, page 75). After bridge has beenlaunched and end-post transom is in-serted, the chess holding up the stringersand decking in the first bay can be pushedclear with crowbars, and decking willdrop into position.

Position panels of third bay. As panels ofthe third bay are being placed, inserttransoms in second bay, one in front ofmiddle vertical and one in front of rearvertical (Figure 6-12, page 76).

After transoms are in position in secondbay, fix sway braces, rakers, and bracingframes loosely (Figure 6-13, page 77).Rakers are installed only on the transomsat the end verticals.

Tighten bracing in first bay, and deckfirst bay (Figure 6-14, page 78).

72

FM 5-277

REMAINDER OF BRIDGEAssemble the remainder of the bridge asfollows:

1

2

3

Position stringers in second bay and leavestringer over sway-brace turnbuckles onedge until sway braces have beentightened (Figure 6-15, page 79).

Add fourth bay of panels and at sametime insert transoms in third bay (Figure6-16, page 80).

Add bracing in third bay. Tighten bracingin second bay, and deck second bay(Figure 6-17, page 81).

The sequence is complete. Use the samesequence for the rest of the bridge. Do all jobsat the same time; the sequence is used toprevent crowding of assembly and carryingparties.

Normally, footwalks are not used. However,when time, troops, and materials are avail-able, footwalks can be assembled. Footwalksshould be assembled before launching be-cause it is awkward to place bearers andfootwalks after bridge is in place. Attachbearers to all transoms. They fit over andunder special lugs welded to the transom.Position footwalks by lugs on bearers. Insertfootwalk posts in sockets at the ends ofbearers and thread hand ropes through theeyes of the posts. Figure 6-18 (page 82) showsthe completed footwalk.

73

FM 5-277

74

FM 5-277

75

FM 5-277

76

FM 5-277

77

FM 5-277

78

FM 5-277

79

FM 5-277

80

FM 5-277

81

FM 5-277

8 2

FM 5-277

ASSEMBLY OF TRIPLE-SINGLE BRIDGE

METHOD OF ASSEMBLYThe method of assembly for the triple-singlebridge is similar to that for the double-singlebridge. The assembly of the outer truss in onebay must be delayed, however, so panel pinsin the second truss can be inserted. In addi-tion, use short pins in the middle and outertruss end posts because normal length pinswill not fit.

FIRST BAY OF BRIDGEAssemble the first bay of the bridge as follows(Figure 6-19, page 84):

1

2

3

4

Connect first two panels of inner trusswith last bay of nose. Insert first transomin front of middle vertical and clamploosely with transom clamp.

Add panels of middle truss in first bayand hold in place with transom clamps.

Insert second transom in front of rearvertical. Attach rakers and positionbracing frames and sway braces. Theconstruction transom behind front ver-tical is omitted until the outer truss in thefirst bay has been positioned.

Add middle truss panels in second bay.This panel must be positioned before theouter truss panel in the first bay so panelpins can be inserted.

5

6

7

8

Add outer truss panels to first bay. Posi-tion construction transom behind forwardverticals in first bay. Add inner trusspanels to second bay.

Place chess on the construction transomand position stringers in the first bay.

Position middle truss panels in third bay.As panels are being placed in the thirdbay, insert transoms in second bay, one infront of the middle vertical and one infront of the end vertical.

Add bracing in second bay. Tightenbracing in first bay, and deck first bay.

REMAINDER OF BRIDGEAssemble the remainder of the bridge asfollows:

1 Position outer truss of second bay. Con-nect to middle truss with tie plates boltedto top raker holes in forward verticals ofpanels (Figure 6-21, page 85). Add innertruss of third bay (Figure 6-19). Figures6-20 (page 85) and 6-21 show the positionof panel pins in triple-single bridge.

2

3

Place stringers in second bay. Positionmiddle truss panels in fourth bay, and atsame time insert transoms in third bay(Figure 6-19).

Add bracing in third bay. Tighten bracingin second ‘bay, and deck second bay(Figure 6-19).

The sequence is complete, and the samesequence is used for the rest of the bridge.

When loads greater than class 70 are to becarried, such as an 80-foot (24.4 meters) triple-single bridge, four transoms per bay arerequired. The procedure for assembling thetransoms in the first bridge bay is the same.In addition. a fourth transom is added behindthe center vertical. In order to clamp bothtransoms at the center vertical, the transomheld behind the vertical should be clamped tothe inside trusses and the other to the outsidetrusses. In all subsequent bays, the fourtransoms are placed in regular order, the firstbehind the front vertical, one in front of thecenter vertical, one behind it, and one in frontof the rear vertical.

83

FM 5-277

84

FM 5-277

LAUNCHING, JACKING DOWN, AND RAMPING

USE OF COUNTERWEIGHTDuring launching, the entire bridge (in-cluding the nose) must be counterbalanced sothe structure does not tip into the gap. Thecounterbalance is normally obtained byadding enough bays of bridge behind thenear-shore rocking rollers to act as a counter-weight, keeping the balance point betweenthe plain rollers and the rocking rollers. Thiscondition must prevail until the launchingnose reaches the rollers on the far bank. Thepoint is illustrated in Tables 6-1 through 6-3which show the bridge and launching nosejust spanning the gap. In this position, thebridge is completely assembled and thebalance point is slightly behind the near-shore rocking rollers. As the bridge is pushedacross the gap from this position, the balancepoint passes the rocking rollers. The part ofthe bridge acting as a counterweight is no

longer needed to maintain balance sincethere is now no danger of it tipping into thegap.

Note: Counterbalance is still needed, how-ever, to avoid excess stress in the launchingnose until launching is complete. Dis-mantling any part of the bridge behind therocking rollers will throw additional stresson the launching nose and on the part ofthe bridge which is across the gap. Thismay result in failure of the nose.

Caution: The near-bank rockingrollers and the far-bank rockingroIlers must carry the entire load afterthe launching nose reaches the far-bank rocking rollers (Figure 6-22,page 86). The launching nose may failif the near-bank plain rollers are per-

mitted to carry any load after the nosereaches the far-bank rocking rollers.The rear of the bridge must hang freeto act as a counterweight. This is doneby cribbing up the near-bank rockingrollers, or removing plain rollers sothe rear end of the bridge does notrest on them after the launching nosereaches the far-bank rocking rollers.

If removal of plain rollers does notprovide the required clearance, exca-vate until the overhang is free of theground. If the far-bank rocking rollersare placed several inches below thelevel of the other rollers, the entireweight of the bridge on the near-bankrocking rollers will be offset so thatthe resulting launching plane will belevel or err on the safe side. In addi-

85

FM 5-277

tion, the extra 6-inch (15.2 centi-meters) safety allowance in the posi-tioning of the launching-nose linkswill help prevent an unsupportedlength of bridge from the far-bankreeking rollers to the first near-bankplain rollers from being clear of therocking rollers. Once the links havepassed over the far-bank rollers,check the launching plane. If too muchsettlement has occurred on the nearbank, remove the plain rollers.

LAUNCHINGAfter the nose and first bay of the bridge havebeen completed, proceed with launching asfollows:

2

1

86

One pair of plain rollers has been placed25 feet (7.6 meters) behind the near-bankrocking rollers. Additional plain rollers

are not required when launching bridgesup to 80 feet (24.4 meters) long. Bridgesover 80 feet (24.4 meters) long requireadditional sets of plain rollers spaced at25-foot (7.6 meters) intervals. Bridges areassembled on the rollers. When necessary,

jacks are used to aid insertion of the lowerpanel pins of panels resting on rollers.

Continue assembly of bridge and pushingit out on the rollers (Figure 6-23). Whenthe forward end of the launching nose

FM 5-277

3

reaches the rollers on the far bank (Figure6-24), a detail guides it onto the rollers(Figure 6-25, page 88) and dismantles itbay by bay.

When the end of the bridge proper clearsthe rollers on the far bank, attach thenear-bank end posts. At the same time,attach the far-bank end posts and lay atransom across their steps. The middleand outer truss end posts on the triple-truss bridge are pinned with short panelpins and tied together with tie plates inthe raker holes. Pins in middle truss endposts are inserted with points outwardand in outer truss with points inward(Figures 6-20 and 6-21). Normal pins andmethods of pinning are used on the inner-

truss end posts. Remove constructionchess behind the front vertical in the firstbay so decking drops into place.

Take the following precautions whenpleting the assembly and launching

Do not use bent or distorted parts.

com-

Do not attempt to convert the launchingnose into the bridge by adding parts to it.

In launching the bridge over rollers, keepthe center of gravity behind the rockingrollers until the launching nose reachesthe far bank. Thereafter, do not dismantlethe bridge behind the near-bank rockingrollers or remove the counterweight until

all of the launching nose has cleared thefar-bank rocking rollers.

After the launching nose passes over thefar-bank rocking rollers, always makecertain the weight of the bridge is carriedonly by the near-and the far-bank rockingrollers.

JACKING DOWNAfter the end posts and end transom havebeen installed, proceed with jacking down asfollows:

1 Place jack shoe in baseplate and jacks onshoes with toes of jacks under steps of endposts (Figure 6-26, page 88). Only enoughroom is present to work four jacks at oneend of the bridge. More jacks may beplaced under a transom only when heldby end posts. To prevent failure of jacks,use them in unison so the load is distri-buted evenly between them.

Note: Pitch of teeth may vary in jacks ofdifferent manufacture. Jacks used togethermust always have the same pitch. Checkjacks to ensure that they have the samemanufacturer’s name.

2

3

Jack up the ends of the bridge successivelyand remove the rocking rollers. Placebearings on baseplate as shown in Figure5-9.

Lower bridge in stages (Figure 6-27, page89). Place cribbing under the bottom chordof the trusses to catch the bridge if it slips

87

FM 5-277

off the jacks. It does not matter which end RAMPINGof the bridge is lowered first, but the jacks Refer to already determined design in Chaptermust be operated in unison. 4 for installing cribbing and supports (Figure

6-28). Position ramps and add decking (FigureNote: Jacks must be operated on only one 6-29, page 90). Brace approach to ramps, andend of the bridge at a time. bridge is complete.

88

FM 5-277

89

90

FM 5-277

REINFORCING BRIDGE AND CONVERTING BRIDGE

PROCEDUREThe class of existing single- and double-trussbridges can be increased by adding extratrusses. Construction starts from the centerof the bridge, and panels are added towardeach end. Panel levers are used to aid inpositioning the extra panels (Figure 6-30).

For all assemblies over class 70, the decksystem must be reinforced by increasing thenumber of transoms per bay from two to fourand by adding a 3-inch (7.6 centimeters)longitudinal wear tread. These transoms canbe threaded a bay at a time from inside thebridge.

CONVERTING SINGLE-SINGLETO DOUBLE-SINGLE

TO convert a single-single bridge to a double-single bridge, proceed as follows:

5

1

2

3

4

Remove footwalk (if any).

Position first panel at center of bridge.

Lower panel over side with chain or ropeslings at ends of panel and position withlevers (Figure 6-30).

Insert transom clamps and tighten.

6

7

Tightening transom clamps helps reduceeffect of sag.

Position second panel, insert transomclamps, and tighten. Insert panel pins(point inward) first in bottom and then intop of panel.

Connect outer truss to inner truss withbracing frames bolted to top chord. Con-tinue adding panels toward each end ofbridge.

Jack bridge off bearings (ramps need notbe removed) and install end posts.

Caution: At the end of bridge wherethe transom is in the end post, paneland post must be added as one unit.

8

9

Position bearings for double-trussassembly, jack bridge down on bearings,and replace footwalks (if any).

Check to ensure that the existing grillageis strong enough to carry the reinforcedclass.

Figure 6-31 (page 92) shows a completedouble-single bridge with footwalk.

91

FM 5-277

CONVERTING DOUBLE-SINGLETO TRIPLE-SINGLE

To convert double-single bridge to a triple-single bridge, proceed as follows:

4

1

2

3

Use same procedure as for convertingsingle-single to double-single bridge,through insertion of panel pins in top andbottom of panel.

Connect outer truss to middle truss withtie plates bolted to top raker holes in thesame upright of successive panels(Figure 6-20). Continue adding panelstoward each end of bridge.

Jack bridge off bearing (ramps need notbe removed) and crib under first andsecond truss (Figure 6-32).

Note: Cribbing must not extend out be-yond second truss.

Install end panel and end post by raisinginto position with levers (Figure 6-33).

Caution: At the end of the bridgewhere the transom is in the end post,the panel and post must be added asone unit.

5

6

7

8

Insert panel pins, point inward, slothorizontal. Add tie plates.

Shift bearings for double-truss assemblyto bearings for triple-truss assembly. Jackdown bridge on bearings (Figure 6-34).

Replace footwalk if needed.

Check to ensure that the existing grillageis strong enough to carry the reinforcedclass.

92

FM 5-277

93

FM 5-277

CHAPTER 7

A S S E M B L Y O F D O U B L E - S T O R Y B R I D G E S

Methods of assembly for double-story bridgesare similar to those used for single-storybridges. The second-story panels, however,can be hand carried from trucks or otherplatforms. Truck-mounted cranes, 5-tonwreckers, or gin poles can also be used. It is

FIRST BAY OF BRIDGEWhen the nose is completed, proceed with thefirst bay of the bridge as follows:

1

2

THE DOUBLE-DOUBLE BRIDGE 94

THE TRIPLE-DOUBLE BRIDGE 97

LAUNCHING AND JACKING DOWN 98

REINFORCING BRIDGE AND CONVERTING BRIDGE 99

possible to assemble the second story duringbridge assembly or after the bridge has beenentirely launched. It is preferable, however,to assemble the entire bridge before pushingit across the gap. The same methods oflaunching are used as for single-story

THE DOUBLE-DOUBLE BRIDGE

Panels must be loaded on trucks to allowstanding room in the truck for the workingparties. The second story is assembled asfollows:

Assemble three bays of double-singlebridge as shown in Figure 7-1 (page 96) aand as described in Chapter 6.

Begin double-story assembly in the firstbay of bridge with a separate working bparty (Figure 7-1). Continue bottom-storyassembly at the same time, using theprocedure for the single-story bridge. Thesecond story always lags by two bays.Use an erection platform when placing csecond-story panels. Footwalks can beused as a working platform or panels canbe hand carried from trucks maneuvered dalongside the bridge (Figure 7-2, page 96).

Lift panel from truck at side of bridge.Place flat on top chord of bridge. Slidepanel in toward center of bridge.

Lift panel upright. Pivot so it is parallelto existing truss. Position and pinpanel. Insert chord bolts, but do nottighten them.

Repeat process with panels on outertruss.

Position bracing frames on front andrear verticals and on top chord.

assembly. For long heavy bridges, it maybenecessary to use trucks or a bulldozer. Thecomposition of the launching nose for thevarious combinations of spans and trusstypes is given in Tables 7-1 and 7-2. Thetables must be followed exactly.

e

f

Tighten chord bolts and bracing framebolts.

When footwalks are not used and truckscannot be maneuvered alongside thebridge, second-story panels can beplaced from a temporary deck insidethe bridge or by the use of gin poles.

REMAINDER OF BRIDGEThe remainder of the bridge is built the sameas the first bay except that bracing framesare positioned only on the rear verticals andtop chord of the second story (Figure 7-1).When enough bays of bridge have been builtto counterbalance the nose, move the bridgeforward so the first bay is over the rockingrollers. Movement will not be necessary againduring assembly unless the overhang at the

94

This change supersedes page 95. FM 5-277

tail causes excessive sag. When adding panelsfrom outside the bridge, place inner panelsfirst with panel pins inserted from the outside.Then place outer truss panels with pins in-serted from the outside. When adding panelsfrom inside the bridge, place the outer panelsfirst and insert all pins from the inside.

9 5

FM 5-277

96

FM 5-277

THE TRIPLE-DOUBLE BRIDGE

METHOD OF ASSEMBLYThe triple-truss, double-story assembly(Figure 7-3) is essentially the same as doubletruss, double-story assembly. With triple-trussassembly, however, the outer truss in boththe lower and second story must lag by onebay to allow insertion of the panel pins in themiddle truss when panels are added fromoutside the bridge. When second-story panelsare added from inside the bridge, the innerand middle trusses must lag by one bay toallow insertion of the panel pins in the outertruss.

LAUNCHING NOSEThe composition of the launching nose is thesame as that for the double-double bridge.For the length and assembly of nose requiredfor various spans, see Table 7-2.

FIRST BAY OF BRIDGEWhen assembly of the nose is completed,proceed with the first bay of the bridge asfollows:

1 Assemble four bays of single-story bridgeas shown in Figure 7-4 (page 98) anddescribed in Chapter 6.

2 Add double-story assembly using the same

3

assembly method as for the double-doublebridge (Figure 7-1).

Position bracing frames on the front andrear verticals and on the top chord of thefirst bay of bridge before the chord boltsare tightened.

97

FM 5-277 This change supersedes page 98.

REMAINDER OF BRIDGEAssemble the remainder of the bridge thesame as the first bay, but position bracingframes only on the rear verticals and topchords of the second story. Connect outertruss to middle truss with tie plates bolted tothe top raker holes in the forward paneluprights of both stories. See Chapter 4 forramp construction and Chapter 9 for trafficcontrol.

LAUNCHINGLaunching of double-story bridges normallybegins after the assembly of the entire bridge.Use the same launching methods and pre-cautions as for launching single-storybridges. When launching with bulldozers ortrucks, take the following precautions:

Do not apply power directly to the end of apanel except at the junction of the di-

LAUNCHING AND JACKING DOWN

agonals. Apply it against the end posts,or a transom at the junction of the diag-onals (Figure 7-5). When applying poweragainst a transom, make sure it is distri-buted across the length of the transom.

Roller heights must be fixed so that thetail of the bridge is at least 6 inches (15.2 centimeters) off the ground during theentire launching.

Rig a line to control lateral movement ofthe bridge.

If the bridge requires two trucks or bull-dozers to move it, use one against the endpost of each girder.

When using a bulldozer, bolt ribbands atthe tail of the bridge so they extendbeyond the end of the bridge. Place a

98

FM 5-277

transom on its side on the ribbands so thetransom rests against the end vertical atthe junction of the diagonals. Face tran-som lugs toward the nose of the bridge.Control lateral movement of the bridge byfastening winch lines from two trucks tomale panel holes for positive control.Launch the bridge with the bulldozerblade pushing against the transom(Figure 7-5).

JACKING DOWNUse the same jacking methods and precau-tions used for single-story bridges (Chapter6).

REINFORCING BRIDGE AND CONVERTING BRIDGEMETHOD

The class of existing single-story bridges canbe increased by adding extra stories. For allassemblies over class 70, the decking systemmust be reinforced by increasing the numberof transoms per bay from two to four, and byadding a 3-inch (7.6 centimeters) longitudinalwear tread.

CONVERTING DOUBLE-SINGLETO DOUBLE-DOUBLE

To convert an existing double-single bridgeto a double-double bridge, proceed as follows:

1

2

Remove bracing frames.

Carry first panel to midpoint of bridgeand place on top chord of existing bridge.

3

Erect outer truss first (Figure 7-6, page a100). Before raising panels, insertwrenches in the top chord of the existingbridge to prevent the panel from skiddingout. The inner truss assembly should bfollow closely behind the outer truss inorder to speed construction.

Insert chord bolts and panel pins. Where cnecessary, use chord jacks (Figure 7-7,page 100) to overcome sag when insertingpanel pins. Tightening chord bolts alsohelps reduce difficulty caused by sag. dChord jacks are not required when addinga second story to double-truss spans 120feet (36.6 meters) or less in length if thefollowing method is used simultaneouslyon both sides of the bridge:

Place first panel of second story atcenter of bridge and insert chord bolts.Do not tighten bolts.

Place a panel at each end of the centerpanel of the second story. Insert chordbolts and upper panel pins.

Tighten all chord bolts to reduce sag.Drive lower panel pins with a sledgehammer.

After the first three panels are in place,add other panels, one at a time, workingtoward both ends of the bridge.

99

FM 5-277

e As each panel is placed, insert chordbolts. Do not tighten until the upperpanel pin has been inserted.

f It maybe necessary to drive upper andlower panel pins simultaneously,starting at the ends of the bridge.Tighten chord bolts to reduce sag.

g Place bracing frames vertically on thesame end of successive panels andhorizontally along the top chord of thesecond story.

See Figure 7-8 for partially completed bridge.

100

FM 5-277

101

FM 5-277

CHAPTER 8

A S S E M B L Y O F T R I P L E - S T O R Y B R I D G E SLAUNCHING NOSE AND OVERHEAD BRACING 103

THE DOUBLE-TRIPLE BRIDGE 107

THE TRIPLE-TRIPLE BRIDGE 107

ASSEMBLY OF BRIDGES WITH UNDERSLUNG STORY 109

This chapter describes the assembly andcomposition of triple-story bridges and theirlaunching noses. The normal cantilevermethod used for launching single- anddouble-story bridges is used for launchingtriple-story bridges. However, some triple-story bridges must be launched incomplete toreduce launching weight.

Triple-story bridges are normally assembledby truck-mounted cranes. If cranes are notavailable, parts can be placed with gin poles,5-ton wreckers, or carried by hand. Triple-story bridges can be assembled with all threestories above the decking system (Figure 8-1)or with one story underslung (Figure 8-2).When all three stories are above the deckingsystem, the top chord of the upper story mustbe braced laterally with transoms and swaybraces. When one story is below the deckingsystem, lateral bracing in the bottom chord ofthe underslung story is required only whenthe wind velocity is more than 50 miles (80.6kilometer) per hour. The class of triple-storybridges is not affected by the location of thedeck or by the omission of one story of panelsin each end bay.

102

FM 5-277

LAUNCHING NOSE AND OVERHEAD BRACING

LAUNCHING NOSE ASSEMBLYAND COMPOSITION

Assembly of the launching nose for triple-story bridges is the same as for single- anddouble-story bridges. However, the launchingweight of the nose and bridge is limited by the120-ton (108.8 metric tons) capacity of thenear-bank rocking rollers and the lower-bridge chords which they support. The com-position of the launching nose for the variouscombinations of span and bridge assembly isgiven in Tables 8-1 and 8-2 (page 104). Thesetables must be followed exactly.

OVERHEAD BRACINGThe upper story of triple-story bridges, withall three stories above the floor system, isbraced by using overhead-bracing supports

with transoms and sway braces on the topchord of the upper story (Figure 8-l). Anothermethod is to invert the third-story panels andplace transoms and sway braces in theirnormal seating on the inverted panels.

With overhead-bracing supportsWhen overhead-bracing supports are used,place one support per girder on each bay ofthe bridge. Position the supports on panels ofthe inner and second truss over the chord-boltholes nearest to the female lugs. This providesclearance for the bracing frames on the topchord. Fasten transoms to the tops of thesupports and pin sway braces to the pro-jecting ears on the supports (Figure 8-3, page105).

Without overhead-bracing supportsWhen overhead-bracing supports are notused, the panels of the third story must beinverted so that transoms and sway bracescan be inserted (Figure 8-4, page 106). Tran-soms are fitted on the transom seats beneaththe upper chord of the top story and are heldin place by transom clamps. Sway braces areplaced in the sway-brace holes in the sides ofthe upper chord of the third-story panels. Onetransom and two sway braces are used perbay.

103

FM 5-277

104

FM 5-277

105

FM 5-277

106

FM 5-277

THE DOUBLE-TRIPLE BRIDGE

DESCRIPTIONDouble-triple bridges are normally assembledbay by bay on rollers and launched complete.Some of the longer, spans, however, must belaunched incomplete to reduce the launchingweight.

METHOD OF ASSEMBLYWhen assembly of the nose is completed,assemble the first bay of the bridge as follows:

1 Connect inner and outer truss panels tolast bay of nose. Assemble parts intoplace.

2 Add transoms, bracing, and decking inthe same way as for single-story bridges.

3 Add panels to second and third story withcranes. Stockpiles are located near cranes

DESCRIPTIONTriple-triple assembly is uncommon. Itsheavy launching weight could cause failureof the rollers or lower chord of the bridge. Forthis reason, special methods must be used forassembling triple-triple bridges.

ASSEMBLY AND LAUNCHINGTriple-triple bridges can be launched incom-plete or by using a temporary launching pier.Triple-triple bridges are launched incomplete,using the assembly given in Table 8-2, toreduce launching weight and prevent over-load of the rollers. The bridge is assembledand launched as follows:

4

5

6

to aid handling. Place bracing frames onfront and rear panel verticals in secondand third stories and on top chord of thirdstory.

Lift overhead-bracing supports withcranes and position over chord-bolt holesnearest female lugs of panels. Bolt togirder on one side of bridge only. Bolts onother side are left out because bolt holesmay not line up when transom is placedon supports, since the girders tend to leanslightly toward center.

Position overhead transom and fasten bythe two clamps on each support.

Insert jack between support that is notbolted and outer truss of bridge. Force

THE TRIPLE-TRIPLE BRIDGE

1

2

3

Assemble nose and partial bridge exactlyas shown in Table 8-2 according to spanlength, and launch to far-bank rollersusing normal methods of assembly andlaunching.

Continue launching bridge over gap untilnear-bank rocking rollers are under lasttriple-triple bay of bridge. Dismantle nosebeyond far-bank rocking rollers (Figure8-5, page 108).

Make near-bank end double-triple baytriple-triple, and add enough triple-triplebays to obtain required bridge length (six

7

8

9

4

girders out and insert two chord bolts inthe support.

Position overhead sway braces but do nottighten until overhead transom in nextbay has been fixed.

Place the rest of the panels with cranes.Assemble on the ground a single-trusssection of two panels connected by chordbolts. When the two-panel section iscompleted, attach a sling and lift thesection into place by a crane. Insert toppanel pins first and bottom ones next.

Add the transoms and deck whileassembling the rest of the stories.

more triple-triple bays at most). This givesthe required bridge length for all but the210-foot (64 meters) span. Because ofstaggered assembly, the end bay of thelatter bridge must be left double-triple atthis point. Decking in 180-foot (54.9meters) and shorter spans can be con-tinued to the end of the bridge (Figure 8-5).

Continue launching bridge until the near-bank rocking rollers are again under thelast triple-triple bay of bays added (Figure8-5).

107

FM 5-277

5

6

7

Add five bays of double-single nose to thenear-bank end of all bridges (Figure 8-5).Add two more bays to the 210-foot (64meters) bridge to get the required bridgelength before adding this tail assembly.

Launch bridge forward until the threedouble-triple bays at front of bridge arebeyond far-bank rollers. Complete double-triple bays by converting to triple-tripleand adding transoms (Figure 8-5).

Pull bridge back to final position, removedouble-single tail, and complete assemblyin usual manner (Figure 8-5).

Triple-double bridges can be launched usinga temporary launching pier. Assemble andlaunch a normal triple-double bridge. At thesame time, assemble a temporary launchingpier from panel-bridge parts. The pier can beoffset from the center of the gap so the shortspan is not less than 60 percent of the longspan. After the pier is completed, place aplatform on top of it to carry jacks. When thetriple-double bridge has been jacked downonto the bearings, insert jacks under thebridge at the pier, and jack up the bridge toabout horizontal. Then use a truck crane toplace the third-story panels and the overheadbracing. Jacking most of the sag out of thebridge makes it possible to place the third-story panels. When a fixed pier cannot beused, use a floating pier. The pontons arepartly filled with water to float the pier under

108

FM 5-277

the bridge, and the water is pumped out toraise the bridge. Information on pier reactionsis given in Chapter 16, and on panel crib piersin Chapter 17.

VERTICAL CLEARANCEThe vertical clearance in triple-story bridgesis of prime importance when loaded tanktransporters are to pass over them. This isespecially true when expedient overheadbracing is used. If greater vertical clearanceis needed, underslung stories or deck-type

construction may be used to provide therequired bridge class.

USE OF MECHANICAL MEANSIt is normally necessary to launch triplestory bridges by mechanical means. Takespecial care to see that the assembly of thebridge and nose is correct and that the rollersare properly leveled. The launching weight ofthese bridges is high and slight errors cancause failure.

JACKING DOWNNormal jacking down methods cannot beused for triple-story bridges. There is notenough room at the end posts to use therequired number of jacks. Use either jacks ofhigher capacity or the methods of jackingdown bridges on intermediate piers. Usingintermediate pier methods requires roomahead of the bearings for placing the jacksand the timber grillage under the bottomchord to catch the bridge if the jacks slip orfail.

ASSEMBLY OF BRIDGES WITH UNDERSLUNG STORY

METHODSTriple-story bridges with underslung storyare normally assembled and launched by oneof the following methods:

Launched with underslung story, using atemporary launching pier at center ofgap. This method is normally used whenthe launching pier can be positioned.

Launched as double-story bridge, withunderslung story added after bridge is inplace. This method is normally used whenthe launching pier cannot be positioned.

Launched as double-story bridge, jackeddown approximately 6 feet (1.8 meters),with third story added on top chord. Thismethod requires jacking the bridge anexcessive distance and generally is notused.

USING TEMPORARYLAUNCHING PIER

This method requires a temporary inter-mediate launching pier at the center of thegap. It also requires enough room under thenear-bank abutment to add one story ofunderslung panels. The bridge is assembledand launched as follows:

1 Assemble a panel crib pier at the center ofthe gap strong enough to carry the com-pleted triple-story bridge (Chapter 17).The pier must have at least two bays ofpanels horizontal (Figure 8-6, page 110).On the pier bay toward the far bank, placerocking rollers at same elevation as near-bank rollers. On the near-bank side of thepier, assemble a bay one panel heightbelow the bay toward the far bank, andplace rocking rollers.

2 Assemble double- or triple-truss single-story bridge using normal launching nose

and assembly methods for abridge lengthequal to one half the width of the gap(distance from near bank to forwardrocking rollers on pier).

3 As soon as the launching nose has landedon the pier rocking rollers on the far-bankside of the pier, add underslung panels,starting with the second bay of bridge.

4 Continue launching the double-or triple-truss single-story bridge and adding theunderslung story until the underslungstory reaches the pier (Figure 8-6).

5 When the underslung panels land on thepier rocking rollers on the near-bank sideof the pier (Figure 8-6), remove the pierrocking rollers under the launching nose.Also remove the top bay of panels on thefar-bank side of the pier under thelaunching nose.

109

FM 5-277

6

7

8

9

Continue launching until bridge lands onfar-bank rocking rollers. Removelaunching nose and position end posts.Before jacking bridge down onto bearings,remove one complete story from pier andplace a working platform on the pier.

Jack up center of bridge at intermediatepier until bridge is approximately level.This reduces sag and eliminates difficultyin placing third-story panels.

Add third-story panels by using truckcrane or truck, or by hand.

Remove construction pier. Bridge is nowcomplete.

ASSEMBLY IN PLACEAn underslung story can be added to adouble-story bridge in place by using a truckcrane. This is the easiest and fastest way.Lower single panels over the side with a truckcrane and attach them with chord bolts.Place inner panels first. Use blocks andtackle to position the inner truss panels.Other truss panels can be positioned directlywith the crane.

When a truck crane is not available or when itcauses too much sag in the bridge, the under-slung story can be added as follows:

1 After the double-story has been assembledand launched, position plain rollers out-side of and about 10 inches (25.4 centi-meters) from the existing outside truss.Place the front roller 3 feet 6 inches (1.07

110

FM 5-277

2

3

4

meters) from the base plate position andanother roller 25 feet (7.62 meters) fromthe first. Additional rollers 25 feet (7.62meters) apart can be placed if necessary.

Assemble a single-truss girder one half ofthe total length of the bridge minus onebay (not to exceed 12 bays).

Attach one raker per bay to the bottombracing-frame hole on the inner trusspanel chord. Lay rakers flat across thebottom chords of the panels so they projectbeyond the side of the bridge and over thegap.

Place 3-by 6-inch (7.6 by 15.2 centimeters)packing timbers on top chord of bridge inevery fourth bay. Hold in place withchord bolts through chord-bolt holesnearest female lugs. Place l-inch (2.54centimeters) timber packing between gril-lage and chord. Suspend double-or triple-block and tackle from each timber, one at

5

6

7

8

outside end and one between first andsecond truss.

Launch single girder over plain rollers onbank and rakers on bridge until it is inposition to be lowered. Attach outer tackleto girder, remove rakers, and then lowergirder until top chord is below bottomchord of the bridge. Attach inside tacklebelow the bottom chord of the bridge tothe girder with a sling which passesaround the bottom chord of the innertruss of the bridge (Figure 8-7).

Remove outer tackle and lift girder intoposition under lower chord of bridge withinner tackle.

Insert chord bolts and tighten to fix girderinto position.

Remove inner tackle and repeat procedurefor the rest of the trusses.

111

FM 5-277

CHAPTER 9

T R A F F I C C O N T R O L

To ensure that vehicle drivers recognize andfollow class and clearance restrictions, andthat vehicles come upon the bridge properly,use traffic control measures.

BRIDGE SIGNSMark bridges and access roads with standardNorth Atlantic Treaty Organization (NATO)bridge and vehicle classification signs. Thesesigns state the class, the roadway width, andthe overhead clearance of the bridge. Detailson the proper posting of NATO bridge signsare found in Field Manual 5-34.

BRIDGE GUIDESPost traffic guides at each end of long bridgesor at one end of short bridges. The guides’duties are to—

Enforce traffic restrictions and bar unsafevehicles. The guide determines the propercrossings of critical vehicles and bars allvehicles having vehicle class numbersexceeding the posted bridge class. Theguide permits caution and risk crossingsonly when so authorized and in thepresence of higher authority. (This higherauthority must have theater or areaapproval of caution and risk crossings.)

Keep traffic moving to avoid congestion.

Arrange for alternative flow of trafficwhen needed to keep the bridge exit clear.

112

To avoid congestion, waiting vehicles aredirected to park off the road.

Stop traffic when bridge is damaged.

Keep vehicles spaced properly and withinspeed limits specified for the type ofcrossing authorized.

Help drivers of wide vehicles by givinginstructions and signal guidance acrossthe bridge.

Maintain markers in a clean and easilyrecognizable condition. This is parti-cularly necessary for the luminouspainted panel verticals and roadway center-line when these are used.

Approach guides are stationed on approachroads or at the intersection of an approachroad with the main traffic net. They controlthe traffic on the approach roads. Normally,units other than the bridge crew provide theapproach guides.

The two guides on long bridges shouldcommunicate by telephone. The guides at thebridge and the guides on the approach roadsshould also be able to communicate directly.

BRIDGE MARKINGLuminous tape for distinguishing the bridgeduring blackout conditions is provided with

the bridge set. The tape is attached to theapproach posts and is not visible from the air.These markers help guide drivers to andthrough the bridge and help to keep trafficmoving steadily. They may be arranged onthe bridge and at the approaches in differentways, according to the type of approach,length of the bridge, and amount of skylight.Figure 9-1 shows a suggested arrangement ofblackout markers on the approach and on thebridge. On the bridge, place tape level withthe top of the bottom story.

As a further aid in night driving andparticularly as a guide for very wide vehicles,a 4-inch (10.1 centimeters) wide centerline inthe roadway should be painted with luminousor white paint. Ribbands, end posts, panelverticals, panel chords, and gusset platesmay also be painted with luminous or whitepaint. These painted markings aid in guidingwide vehicles in the daytime as well as allnight traffic (Figure 9-2). Since luminouspaint might be seen from the air, use it onlywhen and where the tactical situation permitsits use.

ROAD SURFACETo avoid shocks and possible displacement ofthe bridge from the impact of vehicles strikingits end, build up the road surface to about aninch (2.5 centimeters) above the decking ofthe ramp.

FM 5-277

113

FM 5-277

CHAPTER 10

T W O - L A N E T H R O U G H - T Y P E B R I D G E

The two-lane through-type panel bridge isused to provide two-way traffic where bridgesupports at a demolished bridge are toonarrow for two separate bridges (Figure 10-1).This type of bridge is also useful where anarrow launching site necessitates lateralmovement of separately launched bridges toposition them on their bearings. In this case,it would be easier to build a two-lane bridge.

The maximum span that can be launched NUMBER OF PARTS AND SPARESby standard launching methods is 160 Formulas for computing the number of partsfeet. and spares required to assemble the bridge

and nose are given in Table A-8, Appendix A.Launching and jacking down are more The percentage of spares used for single-lanedifficult than for a single-lane bridge. bridges is also used for two-lane bridges.

DESCRIPTIONThe bridge consists of two independent outergirders and a common middle girder, as-sembled from standard panel-bridge parts.The middle girder carries about half the totalload and must be about twice as strong as theouter girders. Transoms overlap and occupyalternate transom seatings on the middlegirder. Only the types of construction shownin Figures 10-2 to 10-7 (pages 116 and 117)and listed in Table 10-1 are used. Table 10-2gives maximum spans that can be assembledand launched with standard equipment.Longer spans can be launched by usinggreased timbers or other expedients.

CLASSThe class and maximum spans of two-lanebridges are the same as those of single-lanebridges, with the same truss assembly as theouter girders (Table 10-3, page 118).

LIMITATIONSTwo-lane through-type bridges have the fol-lowing limitations:

114

ASSEMBLY DETAILSThe assembly of two-lane bridges differsfrom single-lane assembly in several ways.The first of these concerns transom seatingin triple-single/triple-double bridges. Thespacing of trusses in the girders of this bridgeis normal with respect to one lane. Withrespect to the other lane, however, the twomiddle-girder trusses nearest that lane arespaced at 8 1/2 inches (20.8 centimeters) insteadof 1 foot 6 inches (44.1 centimeters). Accord-ingly, transoms from that lane do not fit onseating pintles of the center truss; thesepintles must be removed or transoms drilled(Figure 10-8, page 119).

Ramp clearance also differs. To provide clear-ance between transoms and ramps at theends of single-single/double-single and double-single/double-double bridges, cut a 3 1/2- by4 1/2-inch (86 by 11 centimeters) notch in tran-

soms seated on the end posts and offset theramp transoms 2 1/4 inches (5.5 centimeters)from the bridge centerline (Figure 10-9, page120).

The number of bays and assembly oflaunching noses is determined as follows:

For single -single/double-single anddouble-single/ double-double bridges,noses consist of three single-singletrusses. Assemble one completely bracednose of the required length for one lane.For the second lane, add a single trussand connect it to the middle truss bytransoms overlapping the transoms ofthe first lane. Add rakers to the secondlane, but omit sway bracing (Figure 10-10,page 121).

For triple- single/triple-double, triple-

FM 5-277

single/quadruple-double, and double-double/quadruple-double bridges, nosesnormally consist of single-single outergirders and two single-single middle gir-ders (Figure 10-11, page 121). However, allgirders in the last two nose bays of the140-foot (43 meters) double-double/quadruple-double and the last three nosebays of the 150- (46.2 meters) and 160-foot(49.2 meters) double-double/quadruple-double bridges are double-truss assembly.In all cases, place transoms in alternateseatings and brace the nose the same asfor normal assembly. Transoms connectthe nose girders of the triple-single/triple-double bridge. However, the nose girdersof the triple-single/quadruple-double anddouble-double/quadruple-double bridgescannot be connected because transomsare not long enough except in double-single/quadruple-single nose bays.

115

FM 5-277

116

FM 5-277

117

FM 5-277

118

FM 5-277

119

FM 5-277

120

FM 5-277

121

FM 5-277

WORKING PARTIESAND ASSEMBLY TIME

With the same party organization as for asingle-lane bridge, assembly time for a two-lane bridge is slightly more than twice aslong. With a specially organized crew (Table10-4), assembly time for a two-lane bridge isslightly less than twice the assembly time fora single-lane bridge. Unloading and securitydetails are the same as for a single-lanebridge.

ROLLER LAYOUTFigures 10-2 to 10-7 show lateral spacing ofrocking rollers for various types of bridgeassembly. Roller loads for outer girders arethe same as for single-lane bridges. However,since roller loads for the middle girder areabout double, use enough plain rollers under

this girder to prevent overloading them.These plain rollers must be staggered toprovide clearance between them (Figure 10-12). Chapter 5 describes the method of using atransom to position bearings for rockingrollers. Rocking rollers are used on the farbank for all bridges except single-single/double-single, where plain rollers may beused.

ASSEMBLY AND LAUNCHINGMethods of assembling and launching thetwo-lane bridge are the same for both thesingle-lane assembly party and the organi-zation given in Table 10-4.

AssemblingAssemble a single-single/double-single, anddouble-single/double-double bridge asfollows:

1

2

3

4

Assemble one lane of launching nosewith sway bracing in every bay, usinglaunching links if necessary. Place onetransom behind forward upright of panelin first bay and one transom on front ofrear upright of panel at each joint. Fixrakers at each joint.

Add third truss for other lane, usinglaunching links if necessary.

Place one transom of panel in first bayand one transom behind upright of panelat each joint. Fix rakers at each joint.

Assemble bridge the same as for single-lane bridge assembly, keeping panels inone lane one bay ahead of panels in theother lane. Attach all bracing frames asfor a single-lane bridge.

Assemble a triple-single/triple-double, a triple-single/quadruple-double, and a double-double/quadruple-double bridge the same asfor single-lane assembly, keeping panels inone lane one bay ahead of panels in otherlane. For double- and triple-truss middlegirders, attach bracing frames, tie plates,and rakers as in single-lane bridge assembly.When middle girder is quadruple-truss as-sembly, do not use tie plates between centertrusses; use full number of bracing framesand rakers (Figures 10-2 to 10-7).

122

FM 5-277

Assemble a double-triple/quadruple-triplebridge the same as a double-double/quad-ruple-double bridge. However, when usingoverhead bracing supports in both lanes,make sure female panel lugs in one lane facein opposite direction to female lugs in otherlane. This prevents interference between over-lapping transoms.

LaunchingTable 10-3 gives the launching weight foreach type of assembly. The lighter bridgeslisted in the table can be launched by single-lane launching methods. For heavier bridges,use vehicles with winches to aid in launching.To keep the balance point of bridge and nosebehind the near-shore rocking rollers, becareful not to overload rollers. Spans longerthan those listed in Table 10-2 can belaunched by—

Skidding the bridge over greased timbersto give more bearing along the lowerchord of the girders. The bridge load,however, must not exceed the crushingstrength of the timber.

Launching the bridge in skeleton form sothe allowable load on the rollers is notexceeded.

Using a special rocking distributing beamfor mounting two rocking rollers in lineunder each truss.

JackingJacking of a single-span two-lane bridge isdone the same as for a single-lane bridge. Forjacking bridges on piers, see Chapter 16.Table 10-5 (page 124) gives maximum lengthsof adjacent spans of continuous-span two-lane bridges that can be jacked over inter-mediate piers with jacks arranged as shownin Figures 16-18 and 16-19.

REINFORCED TWO-LANE BRIDGESTwo-lane bridges are reinforced by addingtrusses or stones using the same methods asfor single-lane bridges. Normally, reinforce-ment for only one lane is necessary. Forcapacity greater than class 70, the decksystem must be reinforced by using fourtransoms per bay instead of two and byadding longitudinal wear treads. Table 10-6(page 125) gives the truss asssembly ofreinforced two-lane bridges. Stories can beadded to the top of the existing girders or theycan be underslung. However, when the middlegirder is reinforced to triple-story, the panelsmust be underslung unless the reinforcedouter girder is also triple-story; otherwise,overhead bracing cannot be installed.

Reinforcing one outer girderOne lane of a two-lane bridge can be rein-forced by reinforcing one outer girder. How-ever, the reinforced lane has the capacity of asingle-lane bridge of the same assembly asthe reinforced outer girder only when thenormal lane is closed to traffic.

Reinforcing one outer girderand middle girder

When both the outer and middle girders arereinforced, the reinforced lane has the samecapacity as a single-lane bridge of the sameassembly, without closing the normal lane totraffic.

123

FM 5-277

CONVERSION OF SINGLE-LANEBRIDGES TO TWO-LANE BRIDGES

A single-lane bridge can be converted to atwo-lane bridge without closing the bridge totraffic for along period. If a two-lane bridge isto be centered on an old bridge centerline,proceed as follows

1 Remove approach ramps on each bankand jack bridge up. Lay transom on threeplain rollers on each bank perpendicularto bridge centerline, so raker lugs comedirectly under space between girders ofend bays. Add extra bays to the bridgewhere insufficient working space on bankis available, before placing transoms.

2 Prepare new bank seats and positiongrillage. The center grillage must be twicethe width of the outer grillage.

3 Jack bridge down on the transoms restingon the rollers, and move bridge sidewaysto new position.

Note: Launching nose for triple-single/triple-double, triple-single/quad-ruple-double, and the remainder of double-double/quadruple-double bridges is sim-ilar, with extra transom and two bays ofdouble-single/quadruple-single assemblyomitted.

4 Position bearings for bridge in its newlocation. Bearings are placed under orig-inal end span or extra span, depending onbank conditions. Jack bridge ontobearings.

5 Place ramps and open single lane ofbridge to traffic (Figure 10-13).

6 Position rollers for third girder and launchby single-girder method (Figure 10-13).See Chapter 19 for launching by singlegirders. The third girder can also belaunched by using a truck crane on deckof existing bridge.

124

FM 5-277

7 Connect third girder to rest of bridge withtransoms. If available, use a truck craneto place transoms. If a truck crane is notavailable or if sag is great, add secondstory to middle girder before connectingthird girder with transoms.

8 Add second story to middle girder.

9 Deck second lane.

If the existing bridge is to remain in position,proceed as follows:

1 Jack bridge up and double grillage areaunder center girder. Jack bridge down. Ifbridge is to be lengthened, add extra baysand locate bearings and grillage in newposition.

2 Proceed as for two-lane bridge.

Note: Single lane is open to traffic duringconstruction.

125

FM 5-277

127

FM 5-277

CHAPTER 11

E X T R A - W I D E N E D B A I L E Y B R I D G E M 3

COMPONENT PARTS 130ASSEMBLY AND LAUNCHING OF SINGLE-STORY BRIDGES 132

ASSEMBLY AND LAUNCHING OF DOUBLE-STORY BRIDGES 135

ASSEMBLY AND LAUNCHING OF TRIPLE-STORY BRIDGES 136

GRILLAGES AND RAMP SUPPORTS 136

The introduction of wider vehicles promptedthe development of the extra-widened Baileybridge M3. The US Army does not stock theM3 Bailey bridge. It is a standard bridge inthe United Kingdom. This bridge has a 13-foot 11¾-inch (4.3 meters) clear roadway anda clear distance between trusses of 15 feet 81/2inches (4.8 meters), as shown in Figure 11-1.This added width requires certain new partsthat are not contained in the M2 bridge set.The most important of these are a longtransom, more stringers, long chess, swaybraces, and bracing frames. The bridge nor-mally is assembled for either class 30 or class80 loads. The maximum spans for each typeof assembly at these classes are given inTable 11-1. The weight, in short tons, pertypical bay for each type of assembly, class,and span is given in Table 11-2.

128

FM 5-277

129

FM 5-277

COMPONENT PARTSTRANSOM

The transom is a 12-inch (29.4 centimeters)I-beam, 19 feet 11 inches (6.1 meters) long,tapered at the ends to 10 inches (24.5 centi-meters) as shown in Figure 11-2. Two tran-soms per bay are used for class 30 bridges andfour transoms per bay are used for class 80.

CHESSThe chess are 15 feet (4.6 meters) long, 8¾inches (21.4 centimeters) wide, and 3 5/8 inches(8.9 centimeters) deep. Thirteen chess arerequired for each bay of the bridge except thehead bay, which requires 14. The latter is forclass 80 only.

STRINGERSThe plain and button stringers are the sameas those used in the M2 bridge, except thatthe length of the head bay for class 80 bridgesrequires two long button stringers, M3, andtwo plain stringers, M3. These stringers are10 feet 11½ inches (3.2 meters) long. They areused in the class 80 bridge only and not in theclass 30 bridge.

TRANSOM CLAMPThe transom clamp is the same as that usedin the M2 bridge except that the width acrossthe top has been reduced slightly to preventthe arm from interfering with the verticalbracing frame used in the bottom story oftriple-truss bridges.

RIBBANDSThe ribbands are the same as those in the M2bridge, except that two long ribbands, M3,are required in the head bay of the class 80

bridge. These are 10 feet 11¼ inches (3.4meters) long.

END POSTSThe male and female end posts are the sameas those used in the M2 bridge except that intripe-truss bridges the male end posts for themiddle truss of both class 30 and class 80bridges above the transom bracket removed.This permits rakers to be connected betweenthe end posts on the inner trusses and thetransom. Use female end posts, M3, only onthe middle truss of the end bay of class 80bridges.

HEADLESS PANEL PINHeadless panel pins are used on triple-trussassembly to connect the end posts, M3, to themiddle trusses. They enable the end posts tobe fitted after the launching nose has beenremoved and allow damaged end posts to bereplaced. These panel pins, M3, are similar tothose in the M2 bridge except the head isremoved (Figure 11-3).

RAKERA new type of raker, M3, has been developedfor use with the extra-widened Bailey bridge,

M3. It is a 3-inch (7.4 centimeters) channel, 3feet 8 5/16 inches (1.1 meters) long, as shown inFigure 11-4.

RIBBLT BOLTA ribband bolt, M3, is used as shown inFigure 11-5.

130

FM 5-277

BRACING FRAMEThe bracing frame, M3, has an additionalpair of dowels, as shown in Figure 11-6, toaccommodate the bracing bolts connecting itto the middle truss of a triple-truss bridge.

SWAY BRACEThe sway brace, M3, is similar to that in theM2 bridge, but is 18 feet 1/8 inches (5.3 meters)between centers of eyes with the turnbucklescrewed tight.

OVERHEAD SWAY-BRACE EXTENSION

The overhead sway-brace extension has aneye at one end and a jaw at the other. It isconnected to the sway brace, M3, for use inthe overhead bracing of intermediate bays oftriple-story bridges.

RAMP PEDESTALThe ramp pedestal, M3, is used to support thedeeper (12-inch) (29.4 centimeters) portion ofthe M3 transom. It is similar to the pedestalused in the M2 bridge, but is deeper and has awider space for the transom (Figure 11-7).

131

FM 5-277

ASSEMBLY AND LAUNCHING OF SINGLE-STORY BRIDGES

METHODThe method of assembling and launchingsingle-story M3 bridges is the same as thatfor the M2 bridge except for roller layout,launching nose, triple-truss assembly, andclass 80 decking. The number of parts re-quired per bay is given in Tables A-9 andA-10, Appendix A, for class 30 and class 80bridges.

ROLLER LAYOUTThe lateral spacing of rollers is shown inFigure 11-8. The rollers must be staggered fortriple-truss assembly. There is no suitablebridge part to use as a distance gage, and theroller templates must be positioned by meansof steel tape or improvised gage.

For 30- and 40-foot (9.2 and 12.3 meters)bridges, place a plain roller 15 feet (4.6 meters)from the rocking roller. On longer spans,space plain rollers at 27 feet (8.3 meters) andup, in increments of 25 feet (7.7 meters);consequently, the longitudinal spacing ofplain rollers is normally at 27 feet (8.3 meters),52 feet (23.3 meters), 77 feet (23.7 meters), andso forth.

LAUNCHING NOSEInformation on launching weights andlaunching nose assemblies for various typesof class 30 and class 80 bridges is given inTables 11-3 and 11-4 (page 134).

Note the following:

The bridge is launched complete withdecking and footwalks, except whereshown.

132

FM 5-277

For the class 80 double- or triple-trussbridge, two rocking rollers are neededunder each side, including the far bankfor the launching nose.

Use launching links not more than 40 feetbehind the end of the single-single portionof the nose, and not more than 20 feetbehind the end of the double-single portionof the nose.

Due to the greater width of the bridge, setone transom with two rakers in each bayof the nose, and also set sway braces ineach bay.

TRIPLE-SINGLE ASSEMBLYAfter assembly of the skeleton launchingnose, assemble the bridge trusses in echelon,with each outer truss always having onepanel more than the adjacent truss. It is notpossible to add a third truss to a double-trussbridge.

Assemble the first bay of the bridge asfollows:

1 Connect the first two inner-truss panelsto the inner trusses of the launching nose,driving the panel pins outward.

2

3

4

5

6

7

8

Place a transom through these panels infront of the center vertical, and connectthe long arms of the sway braces to thefront ends of the panels.

Assemble two panels for the middletrusses, and connect them to the transomclamps.

Assemble two panels for the outer trusses,and connect them to the transom clamps.

Pass a second transom through all threetrusses of the first bay behind the frontvertical, and a third transom in front ofthe rear vertical. Connect the panels tothe transom with transom clamps.

Connect the short arms of the sway bracesto the rear position, and fit bracing framesin the first bay on the top chords.

Fit bracing frames in front of the frontverticals and behind the rear verticals.The front bracing frames are removedbefore the end posts are fitted.

Tighten transom clamps and sway braces.Place stringers and decking.

Assemble the second bay of the bridge asfollows:

1 Place two panels for the outer trusses andconnect them with pins driven inward.Drive outward all further pins on alltrusses.

133

FM 5-277

2 Place two panels for the outer trusses ofthe third bay, and connect them with pinsdriven outward.

3 Place two panels for the middle trusses inthe second bay, using headless panelpins.

4 Connect two additional panels in baysfour, three, and two, driving the panelpins outward.

5 Fit front end of sway brace in the secondbay.

6 Pass a transom through all trusses in thesecond bay in front of the rear vertical,and another in front of the center vertical.Connect them with transom clamps.

7 Connect the sway braces to the rearpositions.

8 Fit the bracing frames on the top chords,and behind the rear verticals of the secondbay.

9 Tighten transom clamps and sway braces.

For subsequent bays, the sequence of as-sembly is similar to that described above.Make sure that each truss in each outer bayhas one more panel than the truss in the nextinner bay.

For decking, the placing of stringers andchess follows the same sequence as in the M2bridge, except for the number of stringers in

134

all bays, and the number of chess in the head truss, and the rear transom to the panelsbay.

CLASS 80 DECKINGThe triple-single assembly procedure justgiven is based on class 30 decking. For class80 decking, the procedure is as follows:

1 Four transoms are required per bay. Inboth double- and triple-truss bridges, addthe extra two transoms behind the centerand front verticals.

2 Fit transom clamps alternately on thecenter vertical. For example, clamp thefront transom to the panel in the second

in the first and third trusses.

3 Continue the stringers to the transoms onthe end posts at each end. This makes thehead bay of decking an n-foot bay. To dothis, lay the first bay of stringers with twobutton stringers, M3, on the outside, thentwo plain stringers, M2, inside these, andtwo plain stringers, M3, inside again, andone plain stringer, M2, in the center. Inthe last bay use three plain stringers, M3.In all other bays use plain and buttonstringers, M2.

FM 5-277

4 In the first bay use 14 chess and ribbands,M3. Use M2 ribbands and 13 chess inother bays.

END OF BRIDGEPlace the end posts, bearings, and base platesin the same way as the M2 bridge for single-and double-truss bridges. Make the followingchanges on triple-truss bridges:

Place base plates as for double-trussbridges. The outer bearing carries the endposts of the second and third trusses onthe two seatings each side of the center

seating. The inner bearing carries the endpost of the inner truss on its outer seating,as shown in Figure 11-9.

Fit end posts, M3, to each end of thesecond truss, using headless panel pins.

Fit rakers on inner end posts, and tieplates between end posts on second truss.It is not possible in the class 30 bridge tofit rakers at the tail end of the bridgebecause there is no transom on the endposts.

ASSEMBLY AND LAUNCHING OF DOUBLE-STORY BRIDGESMETHOD

The method of assembling and launching adouble-story M3 bridge is the same as that forthe M2 bridge, except for a few differencesand the need to assemble the lower story.

ROLLERSIn addition to the pair of plain rollers requiredon each side of the bridge 50 feet (15.4 meters)behind the launching rollers, a pair is re-quired 75 feet (23.1 meters) behind them. Forbridges over 140 feet (43.1 meters), doublerollers are required at 125 feet (38.5 meters)behind the launching rollers.

SECOND-STORY,TRIPLE-TRUSS BRIDGE

For a second-story, triple-truss bridge, theassembly is the same as that for the M2bridge, but the sequence of adding panelsmust be the same as in triple-single assembly.It is not necessary to use headless pins,provided the order of assembly is as follows:

Bay No. l—Outer panelBay No. 2—Outer panelBay No. l—Second panelBay No. 3—Outer panel

Bay No. 2—Second panelBay No. l—Inner panelBay No. 4—Outer panelBay No. 3—Second panel

Headless pins must be used on the end posts,M3, where they are connected to the lowerchords of the second truss of the second story.Tie plates are not required.

135

FM 5-277

ASSEMBLY AND LAUNCHING OF TRIPLE-STORYMETHOD

BRIDGESOVERHEAD BRACING

The method of assembling and launching atriple-story bridge is the same as that for anM2 bridge, except for several factors. For atriple-triple bridge, the sequence of addingpanels in the top story must follow the ordergiven for a second-story, triple-truss bridgeexcept that assembly begins in the secondbay. There are no panels in the top story ofthe first and last bays. Similarly, the sequence

for the lower story of a bridge with underslung The only difference from the assembly of thebottom story must be the same. M2 bridge is that the overhead sway-brace

extensions are fitted to the sway braces beforeLAUNCHING they are connected to the overhead-bracing

For all class 30 bridges, launch the bridge supports, which are reversed so that thewith the top story in place. For the class 80 sway-brace pinholes are on the outside of thebridge with a span of 120 feet (36.9 meters), it girders.is possible to launch the bridge as doublestory and add the third story afterwards.

GRILLAGES AND RAMP SUPPORTS

GRILLAGESThe same grillages as those for the M2 bridgecan be used. The maximum base plate re-actions are given in Table 11-5 and themaximum launching roller weights in Tables11-3 and 11-4.

RAMP SUPPORTSThe end transoms of both class 30 and class80 bridges must be supported at their mid-point. For class 80 bridges, the ramps must besupported as shown in Figure 11-10.

136

FM 5-277

137

FM 5-277

CHAPTER 12

D E C K - T Y P E B R I D G E S

Deck-type panel bridges are normally two-lane, class 50 or higher bridges assembled toreplace single-lane bridges. A deck-type panelbridge has the following advantages over athrough-type bridge

Roadway can be wider for passage ofextra-wide vehicles.

Deck-type assembly allows greater sideoverhang of vehicles.

A lighter decking system can be usedwhen the roadway is supported by trusses.

With some sloping banks, the span be-tween abutments is shorter than in athrough-type bridge, because bearings areset 5 feet (1.5 meters) below road level.

Demolished piers need not be built Up tothe level of the roadway.

There are no overhead restrictions.

A deck-type panel bridge has the followingdisadvantages:

Excavation at abutments may be neces-sary because bearings are 5 feet (1.5meters) below the roadway.

It is more difficult to launch.

It must be lowered 5 feet (1.5 meters) ontothe bearings.

Waterway clearance is decreased.

RECOMMENDED BRIDGE DESIGNSUse the following guidance in designingdeck-type bridges:

Group the trusses into three-truss girders,and space girders evenly under the road-way. The trusses may be single-or double-story assembly, as shown in Figure 12-1.

Use bracing frames staggered at oppositeends of each bay (see Figure 12-1) to tie thetrusses of each girder together. Every twobays are cross braced by angles weldeddiagonally across the bottom chords of alltrusses. The decking system serves as toplateral bracing.

Make the decking system from standardpanel-bridge parts (transom, stringers,and chess) or timber.

End posts attached to top-story panelsmay be rested on standard panel-bridgebearings. In multistory assembly, omitthe end panels of the lower stories to allowroom for the abutment. If end posts arenot used, rest the trusses on timberblocking or a rocker bearing under the

joint between the first and second bayfrom each end. If the spans are broken atthe pier, fit the two ends with end posts. Ifthe spans are continuous, use a distri-buting beam and rocker bearing (seeChapter 16).

CLASSThe capacity of the standard two-lane deck-type panel bridge varies with the span andthe number of traffic lanes loaded. Thebridges are given two class ratings, one forone-way traffic and the other for two-waytraffic. Each of these ratings may be either asingle or a dual classification. For maximumspans and classes of standard design two-lane deck-type bridges, see Table 12-1 (page140).

STANDARD DESIGNSStandard design deck-type panel bridges areillustrated in Figure 12-1. Material require-ments of the standard-design deck-typepanel bridge can be found in Table A-11,Appendix A.

ASSEMBLYThe most practical load distribution is ob-tained by spacing the trusses uniformly undera relatively stiff deck. Use five three-trussgirders (15 trusses) under the bridge deck.Space trusses in each girder 1 foot 6 inches(44.1 centimeters) apart and tie together withbracing frames.

138

FM 5-277

BracingUse bracing frames as much as possible atpanel junctions to space the trusses and toprovide lateral stability in each three-trussgirder. To brace and tie the five three-trussgirders together, weld 3-by 3-inch (7.4 by 7.4centimeters) angles diagonally across thebottom chords of each two bays. Weldingmust be done carefully so the properties of thehigh tensile steel in the panel-bridge partsare not changed. Use mild steel bracing members,and weld them in place before any loads areapplied to the bridge.

DeckingBefore the timber decking is laid, weld 3-inch(7.4 centimeters) angles transversely to thetop chords of the trusses at 5-foot (1.5 meters)centers. These angles tie the trusses togetherand provide a brace for clamping the ribbandbolts.

Laminate the timber decking or lay it in twolayers. Laminated decking (Figure 12-2, page141) is better than layered decking becausethe nails cannot work out under trafficvibration. This reduces maintenance. Laytimbers on edge perpendicular to the longaxis of the bridge and nail together horizon-tally. For ease of assembly, 2½-foot (73.5centimeters) sections of laminated deck canbe prefabricated before-hand and then twosections laid between each pair of angles.Notch the end timber of each section to fitover the horizontal legs of the angles. Thennail timber wear treads to the deck.

139

FM 5-277

For layered decking (Figure 12-3, page 142),lay 3- by 12-inch (7.4 by 29.4 centimeters)planks across the trusses between the angles.Notch every fifth timber to fit over thehorizontal legs of the angles. Then nail timberwear treads to the deck.

BearingsWhen end posts are used (Figure 12-4, page143), place them at both ends of each trussand seat them on standard bearings. Cutoffthe top lugs of the end posts flush with thetrusses so they do not interfere with thedecking.

When end posts are not used (Figure 12-4),support the span on timber blocking at thefirst panel junction from each end. The timberblocking must extend at least 1 foot (29.4centimeters) on each side of the joint. Analternative method is to use a distributingbeam on a rocker bearing similar to thesupport over immediate piers. With this typeof bearing, the effective bridge length is 20feet (15.2 meters) greater than the gap be-tween bearings. Also add timber blockingunder the cantilevered end of the panel toeliminate a reversal of stress in panels nearthe end of the bridge as a vehicle moves ontothe bridge. Over intermediate piers, thetrusses can be continuous or broken. If theyare continuous, provide a rocker bearing(Chapter 16). If they are broken, attach endposts to the ends of the trusses and seat twoends on separate bearings. If timber deckingis used, the gap between the ends of thespans may require an intermediate trestle tosupport the decking (Figure 12-5, page 143).

With panel-bridge decking, the gap betweenthe ends of spans can be bridged by expedienttimber or steel stringers and chess (Chapter16).

EXPEDIENT ASSEMBLYFor ease in launching, group trusses into two-or three-truss girders tied together by bracing

frames. (Space these girders uniformly underthe deck.) If other spacings of the trusses areused, expedient braces must be welded to theend verticals of the panels in place of bracingframes. Cross bracing must also be weldedacross the bottom chords. Examples of ex-pedient assembly are given in Table A-12,Appendix A.

140

FM 5-277

LAUNCHINGUse the following guidelines when launchinga deck-type panel bridge:

Each three-truss girder may be launchedseparately, or the entire bridge may belaunched as a unit by welding addedbracing to tie the girders together.

Launch individual girders of a single-story bridge by pushing or pulling thegirder and launching nose out over thegap, by launching from a high line, bylaunching with derrick and preventertackle, or by lifting directly into placewith one or two cranes. Over a water gap,girders may be placed on rafts and floatedout into the gap and then lifted into placeby a crane on a raft. See Chapter 19 fordetails of these launching methods.

A single-story bridge may also belaunched as a unit by pushing or pullingit on rollers out over the gap.

Use the following guidelines when launchinga double-story bridge as a unit

Tie the girders together by transversechannels welded across the tops of thebottom and intermediate chords.

The entire unit may be launched with alaunching nose and then jacked downonto the bearings.

If a temporary pier can be built in themiddle of the gap to support the canti-levered end, the bridge can be launched as

141

FM 5-277

a single-story platform just below thenear-bank seat. This method reduces thejacking height. It is similar to the methodfor launching triple-story bridges withthe underslung bottom story described inChapter 8.

LOWERING TO BEARINGSA crane at each end of the bridge can be usedto lower the girders to the bearings. Jacks canbe used as an expedient, although the 5-foot(1.5 meters) drop requires several lifts. Duringjacking, blocking must be used under thetrusses to take the load in case the jacks fail.

EXPEDIENT DESIGN BRIDGESTable A-12, Appendix A lists several typicalWorld War II deck-type panel bridges built inthe European theater of operations (ETO).

142

FM 5-277

1 4 3

FM 5-277

CHAPTER 13

R A I L W A Y B R I D G E S

Panel-bridge equipment can be used as anexpedient for the assembly of railway bridges.However, use it only in special conditionsbecause there is much deflection. Spanslonger than 70 feet (21.5 meters) are normallyimpractical because a quadruple-double trussbridge is required (Table 13-1). Usually,panel-bridge railway bridges are assembledas single-track bridges.

Panel-bridge equipment has the followingadvantages for use as railway bridging

Equipment can be transported in trucksto the bridge site. This permits bridgeassembly at the same time repairs arebeing made on the approach tracks.

Either through- or deck-type bridges canbe assembled.

—

Panel-bridge equipment has the followingdisadvantages for use as railway bridging:

Through-type bridges provide restrictedclearance.

Traffic over bridge must be controlled toeliminate excessive vibration and sidesway.

Pin clearance allows more sag than isfound in a normal bridge.

Bridge requires more maintenance than astandard bridge.

RAILWAY BRIDGE ASSEMBLYRailway panel bridges are either through-type or deck-type. Assemble the through-typerailway bridge the same as the normal panelbridge, but use ties and rails in place of chess.Girders can be single-, double-, triple-, orquadruple-truss and single- or double-story.

The trusses of double-story bridges infringeUS main line and Berne international clear-ance gages but allow passage at slow speeds(Figure 13-1). If decking of double-storytrusses is placed in the top story, the trussesdo not infringe standard clearance gages.

In the deck-type railway bridge, space thetrusses under the ties. The trusses are usuallysingle story. Tie them together laterally by

144

FM 5-277

bracing frames, tie plates, expedient anglecross bracing, and the ties.

CLASSThe standard designs described will carrystandard or modified Cooper’s E-72 loading.See Figure 13-2 (page 146) for diagrams ofloadings. Table 13-2 gives the shears andmoments caused by these loadings. Table 13-1 gives the assembly required for 10-to 100-foot (3.1 to 30.1 meters) spans using twostandard designs.

ASSEMBLY OFTHROUGH-TYPE BRIDGE

Single-, double-, and triple-truss assemblycan be used as in normal panel-bridge as-sembly. A quadruple truss can be assembledby inserting a fourth truss between the innerand second truss of a triple-truss assembly.Use bracing frames and tie plates to tie thefour trusses together (Figure 13-3, page 147).Use transom clamps on all panel verticalsexcept the three verticals in each bay coveredby bracing frames. Modify transoms by

cutting a hole in the flange and web at eachend to seat the pintle of the fourth truss. Sincethe fourth truss interferes with the use ofrakers, double-story quadruple-truss bridgesare usually assembled with the decking in thetop story.

Decking systemFor railway loads, always use double tran-soms. Place stringers as in a normal panelbridge. If 8- by 10-inch (19.6 by 24.5 centi-meters) by 14-foot (4.3 meters) ties are used,place them directly on the stringers at 2-inch(4.9 centimeters) spacings and hook-bolted tothe button stringers (Figure 13-4 page 147).To use standard ties (6 by 8 inches by 8 feet 6inches) (14.7 by 19.6 centimeters by 2.6meters), lay chess and ribbands in the normal

145

FM 5-277

manner and spike the ties to the chess (Figure End bearings13-5). By building up timber treads on each Use end posts and bearings as in a normalside and between the rails, the bridge can be panel bridge. Grillage must be enough toused for rail or highway traffic (Figure 13-6). carry the loads given in Table 13-3. RampTo reduce impact, rail joints on the bridge sections must be level with the bridge deck.should be tight, with no allowance forexpansion.

146

FM 5-277

147

FM 5-277

ASSEMBLY OF DECK-TYPE BRIDGETwo deck-type assembly designs are de-scribed here. Type I is used for spans up to 90feet (27.7 meters), type II is used for spans upto 100 feet (30.8 meters). Use the followingsteps to assemble type I designs:

1 Arrange trusses side by side and connectthem by bracing frames and tie plates, asshown in Figure 13-7. Bracing is suppliedby the ties, welded sway bracing, andmodified transoms. Seat the modified tran-soms adjacent to the center vertical in thetop and bottom chord of every second andthird bay. To seat the upper transom,invert every other truss. Cut the modifiedtransoms to the desired length and holethem to seat the pintles on the panels.Weld three-inch (7.4 centimeters) anglesway bracing diagonally under the bot-tom chords of every two bays.

2 Use four 6- by 12-inch (14.7 by 29.4centimeters) ties in each bay for the decksystem. Chord bolt every other tie to thetrusses. Drill holes for the chord bolts asshown in Figure 13-8 (page 150). Spike a6-by 6-inch (14.7 by 17.4 centimeters) curbto the ties.

3 Use end posts at each end of each trussand seat them on standard bearings.Grillage under the bearings at each abut-ment must be sufficient to support loadsgiven in Table 13-3. Rocker bearings overintermediate piers can be made similar tothose described in Chapter 16.

148

FM 5-277

Use the following steps to assemble type IIdesigns:

1 Brace trusses by bracing frames and tieplates into two-, three-, or four-trussgirders suitable for launching separately.Group the girders together to form six-,seven-, eight-, nine-, ten-, twelve-, andsixteen-truss bridges as shown in Figure13-9 (page 150). The two-truss girder ismade from two trusses braced at the endverticals by bracing frames. A 3-foot (92.3centimeters) wide three-truss girder is

made from three trusses braced by bracingframes. A 1½-foot (44.1 centimeters) three-truss girder is made by adding a thirdtruss between the trusses of the two-trussgirder and bracing it with tie plates to oneof the outer trusses. A four-truss girder ismade by adding another truss 8½ inches(21.6 centimeters) outside a 1½-foot (45.7centimeters) three-truss girder andbracing it with tie plates. Tie the girderstogether in the bridge by the ties and twomodified transoms on the bottom chord ofeach bay. Modify transoms by cutting

149

FM 5-277

holes in the flange to seat the pintles onthe panels. Weld raker lugs to the transomso rakers can be used betweeen thetransom and the outside trusses.

2 Use the same deck system as that used inthe type I bridge.

3 Use bearings of the same type as thoseused in the type I bridge.

150

FM 5-277

LAUNCHINGLaunch a through-type bridge on rollers inthe same manner as that for a normal panelbridge.

Use the following guidance when launchinga deck-type bridge:

Type I bridges are designed to be launchedcomplete on rollers. They can be pushedor pulled across by a winch line.Launching noses can be used as shown inFigure 13-10 (page 152). During launching,use extra bracing frames and tie plates onthe top chords.

Type II bridges are launched, girder bygirder, by cantilevering out on rollers.Add decking and bracing between girdersafter girders are in place. For othermethods of launching single girders, seeChapter 19.

EXPEDIENTSTable A-13, Appendix A lists panel railwaybridges built in World War II in the Europeantheater of operations (ETO). Figures 13-11through 13-17 (pages 153 and 154) illustrateexpedient bridges. The following expedientsare available:

Welded vertical cross bracing at eachpanel junction can be used instead ofbracing frames and tie plates. Four-inch(10.2 centimeters) channels welded acrossthe panel chords can be used in place oftransoms.

If end posts are not used, the abutmentbearings can be made from a rigid distri-buting beam on timber grillage. The beammust support at least two panel-supportpoints (Figure 13-11).

151

FM 5-277

Each truss or two-truss girder can belaunched from a highline or lifted directlyinto place by a crane.

152

FM 5-277

153

FM 5-277

154

FM 5-277

CHAPTER 14

R E I N F O R C E D B R I D G E S

The critical design factor in most fixed-panelbridges is bending moment. This factor variesfrom a maximum at the center of the span tozero at the supports. Unit assembly of thepanel bridge, however, produces girders ofuniform section and strength throughouttheir entire length. Therefore, only centerbays of most spans are fully stressed. Thegreater part of the capacity of end bays is notused. By reinforcing only the center bayswhere bending moment load is greatest, amore uniform distribution of stress is ob-tained. Reinforced bridges carry more loadfor bridge parts used in their assembly thando standard bridges. Short spans of single-single, double-single, double-triple, and triple-triple are limited in capacity by shear in endbays. They cannot be strengthened by localreinforcement of center bays and are notincluded in capacity Tables 14-1 and 14-2(pages 156 and 157).

REINFORCEMENT WITHPARTIAL STORY

Double-single, triple-single, double-double,and triple-double bridges, not limited by endshear, can be strengthened by converting thecenter portion to spans double-double, triple-double, double-triple, and triple-triple, re-spectively. The number of bays converteddepends on the increase in load class. Addedpanels must be complete with bracing framesand tie plates; in triple-story assembly, over-head bracing is also necessary.

Assembly and launchingPartial stories can be added before or afterlaunching. When added before launching,use standard launching nose for completebridges of the heavier assembly if the lengthof reinforcement is more than half the “span.If the length of reinforcement is half the spanor less, use launching nose for standardbridge of the lighter assembly.

ClassTable 14-1 gives safe classes of bridges rein-forced with partial stories. Length of reinforce-ment and the class of each is also shown.

Note the following

Caution classes are all 25 percent greaterthan the safe values.

Check grillage to ensure it will carryincreased load.

Build bridges with a normal rating overclass 70 with double transoms.

REINFORCEMENT WITHSUPPLEMENTARY CHORDS

All types of bridges except spans limited byend shear can be reinforced with supple-mentary chords cut from damaged panels.Pin the supplementary chords together andbolt to existing top and bottom chords withchord bolts. Bracing frames, modified to clear

the chord bolts, must be used (Figure 14-1).Overhead bracing supports cannot be usedwith supplementary chords unless bolts 4inches (10.2 centimeters) longer than stand-ard chord bolts are used. If overhead bracingsupports are not used, overhead transomscan be clamped under the top chord or weldedon top of the supplementary chords.

SPECIAL PARTSSpecial parts for reinforced bridges are—

Supplementary chords (Figure 14-1, page158) cut from salvaged panels. Thesechords must be straight and undamaged.The web channels must be burned off andground smooth without damaging thechord channels. Both upper and lowerchords must always be reinforced. To uselower panel chords as top-chord reinforce-ment on all types of bridge, transom seatsmust also be carefully removed andground smooth. A supplementary chordweighs about 200 pounds (90.9 kilos).

Horizontal bracing frames on double-andtriple-truss bridges reinforced with supple-mentary chords. These frames must bemodified to clear the projecting chordbolts (Figure 14-1). Weld a tube, 1½ inch(3.8 centimeters) long and between2¾ inches (7 centimeters) and 3¼ inches(9.5 centimeters) in internal diameter,into each longitudinal angle 8 7/16 inches

155

FM 5-277

(21.5 centimeters) from the bolt holes atone end of the frame. Use an improvisedjig to hold the bracing frame duringcutting and welding to maintain align-ment of the bolt holes. This modificationdoes not prevent normal use of the bracingframe.

Assembly and launchingSupplementary chords cannot be added tothe lower chord before launching becauseprojecting chord bolts interfere with rollers.They can be added to upper chords, however,with no change in standard launching noses.Bracing bolts for fastening horizontalbracing frames must be inserted in supple-mentary chords before the chords are boltedto the truss. When chord bolts are tight,remove nuts from the bracing bolts, and addbracing frames (Figure 14-1).

ClassTable 14-2 gives the maximum safe class ofbridges reinforced with supplementarychords and the corresponding length of rein-forcement required.

Note the following:

Caution classes are 25 percent greaterthan the safe values.

Check grillage to ensure it will carryincreased load.

Build bridges with a normal rating overclass 70 with double transoms.

156

This change supersedes page 157. FM 5-277

157

FM 5-277

1 5 8

FM 5-277

CHAPTER 15

C A B L E R E I N F O R C E M E N T S E T

The cable reinforcement set for panel bridgeM2 (Bailey type) increases to class 60 wheeland track the classification of triple-singleBailey bridge for span lengths from 100 feet

PRINCIPLE OF OPERATIONThe cable reinforcement set consists of asystem of cables attached to each end of thebridge and offset from under the bridge byposts. The cables are tensioned, causing thebridge to deflect upward. When a vehiclecrosses the bridge, the bridge deflects down-ward, transferring most of the load into thecables.

USETo install the cable reinforcement set with apanel bridge use the following procedure:

1 Sling from two to six cables under thebridge (Table 15-1). Connect them to endsof the bridge by cable-connection beams.

DESCRIPTION AND USE

COMPONENTSINSTALLATION AND DISMANTLING

OPERATION UNDER UNUSUAL CONDITIONS

OPERATOR’S AND ORGANIZATIONAL MAINTENANCESHIPMENT AND LIMITED STORAGE

159

167

177

187

187

189

to 170 feet (30.8 to 52.3 meters). For a span of180 feet (55.4 meters) the class is 50 wheel and60 track. This system significantly reduces

DESCRIPTION AND USEThe standard Bailey end posts on eachtruss must be replaced by standard spanjunction posts in order to install the cable-connection beams (Figure 15-1, page 161).Hold cables away from bottom of bridgeby two or four, approximately 8-foot (2.5meters) vertical posts (Figure 15-2, page161). The number and placement of theseposts depend on bridge span length (Table15-1).

2 Pretension cables to cable tension givenin Table 15-1. The cables are tensioned bythe cable-tensioning assembly, consistingof double-action hydraulic cylinders anda hydraulic power unit. Two types ofhydraulic power units are used: electric

the assembly time and equipment necessaryto cross class 60 traffic over spans of between100 and 180 feet (30.8 and 55.4 meters).

and hand. The electric unit (Figure 15-3,page 162) is normally used for installationof the system. Two are needed and requireone 10-kilowatt or two 5-kilowatt electricgenerators.

3 Check cable tension, using a hand-drivenhydraulic pump (Figure 15-4, page 163).Read cable tensions directly from a cable-tension gage mounted on either hydraulicpower unit. Tension cables from nearbank only. The near-bank end of thebridge is called the tensioning end. Thefar end is called the dead end.

Six cables are provided with the set. Eachcable is 179 feet 6 inches (55.2 meters) long.

159

FM 5-277

On the tensioning end of the cable is athreaded stud. On the dead end of the cableare nine buttons spaced about 10 feet (3.1meters) apart starting 100 (30.8 meters) feetfrom the stud end. This provides a connectionof the cable at the dead end, according to thebridge span length.

TRANSPORTATIONThe cable reinforcement set is transported inthree 5-ton dump trucks. One truck carriesthe set assemblies and components (Figure15-5), the second carries the cables (Figure15-6), and the third carries the span junctionposts (Figure 15-7).

CLASSIFICATIONThe classifications in Table 15-2 are obtainedwith the cable reinforcement set.

160

FM 5-277

161

FM 5-277

162

F M 5 - 2 7 7

163

FM 5-277

164

FM 5-277

165

FM 5-277

166

FM 5-277

COMPONENTS

DESCRIPTIONThe following assemblies and componentscomprise the cable reinforcement set. Descrip-tion of these parts includes function andlocation.

POST ASSEMBLYThe vertical-post assembly is a fabricatedstructural steel member suspended directlybelow a vertical member of the bridge panel.A saddle welded on the lower end of thevertical post provides a seat for the cables,and a cable retainer is bolted to the base tosupport the cables before they are tensioned.The post assembly is secured to the lowerpanel chord of the M2 Bailey bridge by thepost-connection fixture (Figure 15-8). The postassembly weighs 269 pounds (122.3 kilos).

167

FM 6-277

POST-CONNECTION FIXTUREThe post-connection fixture (Figure 15-9) con-nects the post assembly with the bridge panellower chord (Figure 15-8). Secure this fixtureto panel lower chord by four bolts and hexnuts. Use two chord plates on one side ofconnection fixture to adapt bridge panel forsecuring fixture. The fixture weighs 178pounds (80.9 kilos).

BRACE-CONNECTION FIXTURELeft-hand and right-hand brace-connectionfixtures (Figure 15-10) secure braces, whichsupport the post assembly, to lower chord ofbridge panel. Secure one brace-connectionfixture to panel lower chord by three boltsand hex nuts. Secure the opposite braceconnection by the same hardware plus add-ition of chord for securing this brace-connection fixture. The fixture weighs 32pounds (14.5 kilos).

BRACESThere are two types of post braces, longitu-dinal and transverse (Figure 15-11). The longi-tudinal braces are flat steel bars bolted to thebrace-connection fixtures and the lower endof the post assembly (Figure 15-8). They are 8feet ¼ inch (2.5 meters) long, 3 inches (7.6centimeters) wide, 3/8 inch (1 centimeter) thick,and weigh 32 pounds (14.5 kilos) each. Trans-verse braces are steel angles which are placedbetween posts on each side of the bridge(Figure 15-12). These braces are bolted towelded plates on each end of the vertical post.For convenience of storage and transpor-tation, each transverse brace consists of twoparts: a 7-foot 4-inch (2.3 meters) brace anglewith a welded splice plate on one end, and a

securing the brace-connection fixture andpost-connection fixture to the panel lowerchord.

10-foot (3.1 meters) brace angle bolted to thesplice plate of the shorter bracing. A high-strength bolt and hex nut secure the twotransverse braces together where they crossbetween post assemblies (Figure 15-12). Thetotal weight of one transverse brace is 88pounds (40 kilos).

CHORD PLATEThe chord plate (Figure 15-13) is used toadapt the bridge panel lower chord for

CABLE ASSEMBLYThe cables are 1¼-inch (3.2 centimeters)diameter high-strength wire ropes withthreaded stud on one end and nine buttons atspecific intervals along the cable length. Thefirst button is about 100 feet (30.8 meters)from the stud end of the cable and the re-maining eight buttons are spaced at approx-imately 10-foot (3. 1 meters) intervals towardthe opposite end. Each button is marked withthe applicable length of the M2 panel bridge.Screw stud end of cable into a rod-to-cablecoupling (Figure 15-14, page 170) and secureby a bolt-type setscrew. The rod-to-cablecoupling also has internal threads to retainthe pull rod. The cables are 179 feet 6 inches(55.2 meters) long and weigh 595 pounds(270.5 kilos). They are wound on wooden

168

FM 5-277

cable reels for convenience of storage and CABLE REEL SUPPORTSshipping. The reels weigh 180 pounds (81.8 The cable reel supports (Figure 15-15, pagekilos) each. Six cables come with the reinforce- 171) are steel frames that support a cable reelment set. shaft on which three cable reels are retained.

Secure cable reel shaft to each cable reelsupport by a bolt inserted through each endof the pipe shaft and secure bolt by a nut. Thecable reel support and cable reel shaft to-gether weigh 287 pounds (130.5 kilos). Theshaft is 10 feet (3.1 meters) long.

CABLE-CONNECTION BEAMLeft-hand and right-hand cable-connectionbeams (Figure 15-16, page 171) are steelframes secured to each corner of the M2 panelbridge for connection and tensioning ofcables. Pin these components to bottom ofspan junction posts which replace end postsof M2 panel bridge. Each cable-connectionbeam is a frame, with provisions for threecables with buttons or pull rods to passthrough it. The cable-connection beam weighs315 pounds (143.2 kilos). These beams servetwo purposes:

They serve as a dead-end cable-connectionbeam. After inserting the cables, withbuttons, through the holes provided in the

169

FM 5-277

cable-connection beam, place half-cableretainers (Figure 15-17) between thebearing surface and the button to anchorthe cable (Figure 15-18).

They serve as a tensioning-end cable-connection beam. After connection to therod-to-cable couplings, feed pull rodsthrough the cable-connection beam andretain them by serrated nuts (Figure 15-19, page 172).

A double-acting hydraulic cylinder, wheninstalled on each pull rod, bears against thefront surface of the cable-connection beamthrough the use of an adapter (Figure 15-20).Use the double-acting hydraulic cylinders totension cables (Figure 15-21).

170

FM 5-277

171

FM 5-277

1 7 2

F M 5 - 2 7 7

BRIDGE SEAT ROCKERSBridge seat rockers (Figure 15-22) are placedbetween the bridge bearing and the cable-connection beam at the tensioning end only(Figure 15-23, page 174). These rockers pro-vide for longitudinal displacement that oc-curs while heavy traffic is crossing the bridge.Each rocker weighs 15 pounds (6.8 kilos).

PULL-ROD ASSEMBLYThe pull-rod assembly (Figure 15-24, page174) consists of a 2¼-inch (5.7 centimeters)high-strength threaded rod, a rod-to-cablecoupling, and two serrated nuts. The as-sembly provides for the connection of thecable to the cable-connection beam on thetensioning end and serves as a means to

tension the cables. Thread one end of pull rodinto one end of rod-to-cable coupling. Securepull rod and rod-to-cable coupling by bolt andnut (Figure 15-14). When the cable is ten-sioned, a serrated nut bears against thebearing surface of the cable-connection beamto take cable-tensioning loads. The secondserrated nut retains the double-acting hy-draulic cylinder when it is installed on thepull rod. The two serrated nuts are identical.The nut used to retain the cable is called thecable nut and the nut used to retain thedouble-acting hydraulic cylinder is called thecylinder nut. The pull-rod assembly is 5 feet10 inches (1.8 meters) long and weighs 60pounds (27.3 kilos).

173

FM 5-277

PULL-ROD CHAINThe pull-rod chain (Figure 15-20) is 12 feet (3.7meters) long and is screwed into the end ofthe pull-rod assembly after installation ofpull rods in the cable-connection beam. Thispull-rod chain helps to advance the cable nutbefore installation of hydraulic cylinders.

CABLE-TENSIONING ASSEMBLYThe cable-tensioning assembly is used totension the cables. It has two basic com-ponents: a hydraulic power unit asembly,and double-acting hydraulic cylinders.

ADAPTERAn adapter (Figure 15-25) is used during thecable-tensioning procedure to take the cable-tensioning load from the hydraulic cylinderuntil the cable nut is tightened. Use oneadapter for each cable. The adapter weighs20 pounds (9.1 kilos).

174

The hydraulic power unit assembly consistsof a hydraulic power unit gage, hose assem-blies, quick-disconnect couplings, and a flowregulator. The hydraulic power unit has afiller/vent plug for adding or removinghydraulic oil, an electric switch for con-trolling the amount of fluid flow, and a valvefor controlling the direction of fluid flow. Twohydraulic power units are required for a

FM 5-277

bridge. Each weighs 65 pounds (29.5 kilos).They are powered by either one 10-kilowattgenerator or two 5-kilowatt generators.

One double-acting hydraulic cylinder (Figure15-21) is required for each cable. A holethrough the center of the cylinder allowsinstallation of the cylinder on the pull rod.The power unit is used to expand and retractthe cylinders. When the cylinder is pres-surized to expand, it advances the pull rodthrough the cable-connection beam, in-creasing cable tension. Each cylinder weighs65 pounds (29.5 kilos).

HYDRAULIC RAM PUMPThe hand-driven hydraulic ram pump (Figure15-4) is included in the kit to provide a meansfor periodic checking and adjusting of cabletension. It has an end dipstick/plug forchecking and adjusting fluid level, a gageadapter, gage, hose assemblies with quick-disconnect couplings, flow regulator, and acontrol valve to direct fluid flow to and fromthe cylinders.

BOLTSThree types of bolts (Figure 15-26) are used tosecure major parts of the cable reinforcementset together and to the M2 panel bridge:machine, chord, and high-strength bolts.Machine bolts secure parts in assembliessuch as the cable reel shaft. Chord boltssecure fixtures to the panel lower chord.High-strength bolts secure bracings to thepost assemblies. High-strength bolts areidentified by radial lines embossed on thehead.

JACKING LUGJacking lugs (Figure 15-27), when pinned toend holes of the span junction posts, providea lifting surface for jacking up bridge.

SPAN JUNCTION POSTSMale and female span junction posts (Figure15-28, page 176) from bridge conversion setNo. 3, Bailey type, panel crib pier, fixed M2are used in place of the standard end post.The male post weighs 194 pounds (88.2 kilos)and the female post weighs 202 pounds (91.8kilos).

BOX WRENCHA special 2 5/8-inch (14.3 centimeters) boxwrench (Figure 15-29, page 176) with offsethead is used to tighten the chord bolts insertedthrough chord plates. After the nut is tight-ened as much as possible by normal means,use this wrench to tighten it another one-fourth turn by striking the end of the wrenchwith a sledgehammer.

175

FM 5-277

176

FM 5-277

INSTALLATION AND DISMANTLING

SERVICE UPON RECEIPTWhen new, used, or reconditioned material isfirst received by the using organization, makesure this material has been properly servicedby the supplying organization, and that it isin proper working condition. Keep records onany missing assemblies or component partsand equipment. Perform the following inspec-tions and services for the cable reinforcementset before any installation procedures:

Remove any cushioning material or pro-tective covers from packaged cable-tensioning assemblies and pull-rodassemblies.

Perform preventive maintenance checksand services as required, in accordancewith Table B-3, Appendix B.

Inspect cable-tensioning assembly for anyleakage or damage which would limiteffective operation.

USE WITH NEW BRIDGEThe cable reinforcement set can be used withboth new and existing panel bridges. Whenused with a new bridge, it should be installedconcurrently with assembly of the new bridge.

Placement of materialInstall material before assembly of the bridgeas follows:

1 Unload contents of trucks which carry allassemblies and component parts (exceptthe cables and cable reels) and stack themin the vicinity of the end posts in the M2panel bridge standard layout.

2 Place three cable reels with cables, whichare retained on the cable reel supports, oneach side of the roadway at rear of bridgeerection site. Remove cable reels from bedof truck by using crane or gin poles.

To erect cable reel supports, place three un-loaded cable reels side by side; insert cablereel shaft through center hole of cable reels;lift one end of cable reel shaft, close to cablereel; and slide cable reel support on cable reelshaft. Repeat for other end of cable reel shaft.

Post assemblyAttach post assemblies to the lower panelchords of the bridge according to Table 15-1.To install each vertical post, proceed asfollows:Caution: In order to install a postassembly correctly, the post-connec-tion fixture must be installed directlybeneath the vertical member betweentwo panels (from now on referred toas the panel point).

1

2

When panel point has sufficiently clearedrocking roller, position post-connectionfixture directly beneath panel point.

Secure post-connection fixture to bridge-panel lower chord using four l¾-inch (4.5centimeters) diameter chord bolts andhex nuts. Tighten bolts firmly. Place boltson one end of the post-connection fixturein holes normally used for adding second-or third-story tiers to Bailey bridge. Securethe other end by placing two chord plates

on top of lower chords, using two 1¾-inch(4.5 centimeters) bolts and hex nuts.

3 When a point approximately 4 feet (1.2meters) behind the panel point has clearedthe rocking rollers, install brace-connec-tion fixtures. Position large holes inbrace-connection fixtures about 3 feet 9inches (1.2 meters) ahead of and behindpanel point. On one side, holes will lineupwith holes in lower chord used for multi-story construction. Secure brace-connec-tion fixture by placing chord bolts throughthese holes and tightening hex nuts. Onthe other side, use two chord plates andbolt through the panel lower chords. Placebolt with nut on top of chord plate. Tightennut enough to secure brace-connectionfixture but to allow for adjustment later.

4 When at least 8 feet (2.5 meters) ofclearance is available below panel point,install vertical post. Remove cable re-tainer from vertical post and lower postover side of bridge using ¾-inch (1.9 centi-meters) hemp rope. Secure vertical post topost-connection fixture, using four ¾-inch(1.9 centimeters) diameter high-strengthbolts and hex nuts.

WARNING: All personnel who are loweredover the side of the bridge in a boatwain'schair must also wear a safety belt connectedto a lashing which, in turn, is secured to theside of the bridge.

177

FM 5-277

5 Secure one longitudinal brace to plateweldment of brace-connection fixture withtwo ¾-inch (1.9 centimeters) diameterhigh-strength bolts and hex nuts. Boltopposite end of longitudinal brace to plateweldment on bottom end of vertical post,using two high-strength bolts and hexnuts (Figure 15-8).

6 Secure second longitudinal brace to plateon brace-connection fixture which issecured with chord plates, with two ¾-inch (1.9 centimeters) diameter high-strength bolts and hex nuts. Attachopposite end of brace to plate weldmenton lower end of vertical post using thesame hardware. A small adjustment inposition of this longitudinal brace-connection fixture may be necessary tocomplete installation of the second longi-tudinal brace. Once brace-connectionfixture is positioned, tighten chord boltsthrough chord plates using 2 5/8-inch (6.7centimeters) box wrench having offsethead. Turn nut on bolt threads one-fourthturn, from point where a person can nolonger tighten bolt by applying handpressure to wrench, by striking wrenchwith sledgehammer (Figure 15-30) tocomplete installation of longitudinalbraces.

7 Connect long transverse brace to shorttransverse brace, which has a weldedsplice plate, with four ¾-inch (1.9 centi-meters) diameter high-strength bolts andhex nuts to form full-length transversebrace. Repeat this procedure to form all

. .

full-length transverse braces. Connect two through the hole provided in the bracestransverse braces to plates on each end of (Figure 15-12).vertical posts to form X-type bracing.Secure each end of transverse braces to Caution: This bolt provides a stabi-vertical post weldment plates by two lizing function for the transverse¾-inch (1.9 centimeters) high-strengthbolts and hex nuts. Bolt the two transverse braces. Do not forget to install it.braces together where they cross by Omission of this bolt could result in

damage to the equipment.installing a ¾-inch (1.9 centimeters)diameter high-strength bolt and hex nut

178

FM 5-277

tate carrying and lashing of cable (Figure15-31). Using these ropes to support cable,carry cable onto bridge.

3 When cable button number 180 is at the

Position of cables 1 Unwind one cable at a time from cableThe total number of cables used depends on reels, button end first.

panel which will be the end panel on farshore, lash cable to panels.

4 Repeat the three steps above for eachcable on each side of bridge. If threecables are installed on each side of bridge,lash cable to be installed in inner slot ofvertical-post saddle to lower part of bridgepanels. Lash cable for center saddle slotto middle of panels and lash outside cableto top part of panels.

Span junction postsJust before final positioning of the bridge,install female span junction posts on one sideof the bridge. Then do as follows:

1 Insert a transom through holes in femalespan junction posts and push throughhole until flange of transom hits side offemale span junction posts.

2 Install female span junction posts on theother side.

3 Position the transom properly on studs ofthe six female span junction posts.

the bridge span; Table 15-1 gives the numberneeded for various spans. Place the required 2 Loop 16-foot (4.9 meters) length of ¾-inchcables in a preliminary position on the bridge (1.9 centimeters) diameter hemp rope tostructure before launching the bridge, using cable at 2-foot (61.1 centimeters) intervals.the following procedure: Make a loop at each end of rope to facili-

1 7 9

FM 6-277

Bridge bearing plateTo position the bridge bearing plate, do asfollows:

1 Position bridge so that centerline of firstpanel pin, through bottom of span junc-tion post, measures 4 inches (10.2 centi-meters) to centerline of outer rockingroller.

2 Place the back inside edge of the baseplate about 18 inches (45.8 centimeters)behind centerline of first panel pin.

3 On tensioning end of bridge, place specialbridge seat rocker (Figure 15-22) overeach bearing to allow longitudinal dis-placement of bridge under load.

Note: When bridge is jacked down, bearingshoe on bottom of installed cable-connec-tion beam will mate bearings on baseplateor rockers on bearings.

Jacking up of bridgeJack up the bridge as follows:

1 Install two jacking lugs (Figure 15-27) ateach bridge corner, one on end hole ofoutside span junction post and one on theend hole of inside span junction post,using panel pins (Figure 15-32).

2 Install railroad jacks and jack up end ofbridge to ease installation of cable-connection beams.

180

FM 5-277

3 Use normal bridge installation procedurefor removal of rocking rollers and tem-plates, and we cribbing under the lowerchord for safety in case bridge slips offjacks.

Cable-connection beamTo install cable-connection beam, do asfollows:

1 Position cable-connection beams onbridge seat rockers (tensioning end only)or bearings (dead end) under raised spanjunction posts.

2 Using normal jacking procedure, lowerbridge onto cable-connection beams untilholes in beam lugs align with lower centerholes in span junction posts (Figure 15-33).

3 Secure the cable-connection beams tospan junction posts using a set of standardpanel pins, and secure panel pins withretainer clips.

4 Complete jacking bridge down onto thebearings (Figure 15-34, page 182) andcontinue with normal procedure for stand-ard installation of the bridge.

1 8 1

FM 5-277

Caution: It is essential that both near-and far-shore abutment cribbings belevel transversely with each other inorder to eliminate eccentric loadingcausing bridge elements to be stressedbeyond their capacity. It should alsobe noted that the bridge seat rockerswill cause the tensioning end to behigher by the installed height of therockers.

Installation of cableAfter the bridge has been decked, install allcables. Use the following procedure for eachcable

1 Remove lashing ropes from side panels ofbridge but not from cable.

2 Using the ropes to support the cable,thread button number 180 and the fol-lowing cable through dead-end cable-connection beam. If only two cables areused, one on each side, thread each cablethrough center hole of cable-connectionbeam. If four cables are used, two on eachside, no cable is threaded through centerhole. Continue threading operation untilcable button stamped with number cor-responding to span length in feet haspassed through cable-connection beam.

3 Place two half-cable retainers betweenbutton and cable-connection beambearing surface (Figure 15-18) to preventbutton from being pulled through cable-connection beam during cable tensioning.

4 At tensioning end of the bridge, removecable and cylinder nuts from pull rod andthread pull rod into rod-to-cable coupling.

182

FM 5-277

Continue turning pull rod until it bottomsin rod-to-cable coupling. Turn pull rodback one-half turn or more to align holethrough pull rod and rod-to-cablecoupling. Insert a 1/2-inch (1.3 centimeters)diameter bolt (inset, Figure 15-14) throughthe rod-to-cable coupling and pull rod.Install hex nut on end of bolt. Threadcoupling onto stud end of cable until it

bottoms. Insert a 1/2-inch (1.3 centimeters)diameter setscrew.

5 Feed pull rod through proper hole incable-connection beam and retain withcable nut (Figure 15-35). Then advancecable nut so that pull rod extends beyondcable-connection beam at least 21 inches(53.4 centimeters). This may be done bythreading the eyebolt on the 12-foot (3.7meters) pull-rod chain into pull rod andpulling, advancing the cable nut as pullrod advances; by advancing pull rod usinghemp rope tied to cable at or near rod-to-cable coupling; or by advancing cable nutusing chord-bolt wrench.

6 Position cable below vertical posts andremove all rope lashings from cable.

Caution: The cable must be guidedinto the correct slot of the vertical-post saddle by bridge personnel whilethe cables are being tensioned.

7 Repeat the six steps above to install allcables on bridge. After cables are installedon both sides of bridge, secure each cableretainer to vertical-post saddle with four1/2-inch (1.3 centimeters) diameter boltsand hex nuts.

USE WITH EXISTING BRIDGEThe procedures for installing the cable rein-forcement set on an existing panel bridge,M2, are similar to those for a new bridge.Place the contents of the trucks carrying all

assemblies and component parts on each sideof the bridge as close to the area of installationas possible. Next, remove the cable reels fromthe trucks on the near shore and install oncable reel supports on each side of theroadway, close to the bridge.

Cable-supporting structuresInstall the post-connection fixture, post cableassembly, brace-connection fixtures, and lon-gitudinal and transverse braces like theinstallation for a new bridge and as follows:

1 Using rope, lower post-connection fixturesover side. Pull up into position usingropes placed through the two openingsbetween the three panels. Note thatbearing plate on top of post-connectionfixture must be placed under center panel.

2 Remove cable retainer from vertical postby removing four 1/2-inch (1.3 centimeters)diameter bolts and hex nuts. Install ver-tical post using a rope over outside ofbridge. Attach two ropes to the top ofvertical post and pull it into position withropes through the two openings betweenthe three panels. Note that fixtures onvertical post for transverse braces mustbe on inside.

3 Attach brace-connection fixtures in asimilar manner. Note that bolts on thebrace-connection fixture not using theslotted holes in the bridge panel shouldnot be tightened yet, to allow for lateralmovement when fitting longitudinalbrace.

183

FM 5-277

4 Attach longitudinal and transversebraces, using a boatswain's chair.

WARNING: All personnel who are loweredover the side of the bridge in a boatswain'schair must also wear a safety belt connectedto lashings, which, in turn, are secured tothe side of the bridge.

Span junction postsTo install span junction posts and cable-connection beams, jack up end of bridgeenough to place cribbing under lower panelchords near end posts to temporarily supportbridge. Remove jacks from end of bridge.

Note: Ignore any reference to rockingrollers, since these items have been pre-viously removed from under bridge.

Remove standard end posts from bridge andinstall span junction posts. Install cable-connection beams.

Cable assembliesTo install cable assemblies, do the prelimi-nary procedure to prepare cables for instal-lation on the bridge. Carry the cable acrossthe bridge and install button end of cablethrough cable-connection beam on far shore.Then complete installation of cables asdescribed earlier.

CABLE TENSIONINGBefore tensioning the cables, set up a levelreference so the deflection of a point on thebridge at midspan, relative to a point at the

support, can be measured. The purpose ofmeasuring deflections is to provide a checkduring cable tensioning. Tension all cablessimultaneously.

Note: One 10-kilowatt or two 5-kilowatt,60-cycle alternating current (ac) generatorsare required for operation of the hydraulicpower unit.

To tension each cable, install an adapter anda double-acting hydraulic cylinder on eachpull-rod assembly; connect the hydraulic hoseto the cylinders and the hydraulic power unit;and install and tighten cylinder nut on eachpull rod to retain adapter and cylinder ofcable-tensioning assembly (Figure 15-20).

The hydraulic power unit is operated asfollows:

1 Loosen filler plug to vent reservoir.

2 Place control-valve lever in advance posi-tion (inset, Figure 15-36).

3 Turn switch to RUN position.

4 Turn switch to OFF position when anycylinder has reached full stroke. The JOGposition on switch may be used to runpower unit in short bursts.

5 Pressure may be slowly released bymoving control-valve lever toward centerposition.

The cable-tension gage (Figure 15-36) islocated on the hydraulic power unit of thecable-tensioning assembly and the hand-driven hydraulic ram pump. The gage is 31/2inches (8.9 centimeters) in diameter and hasl-ton (.9 metric ton) graduations on the dialthroughout a 60-ton (54.6 metric tons) scale.Cable tensions for the various bridge spansare given in Table 15-1.

Note: Loads should be read while ten-sioning cables. Readings during deten-sioning are inaccurate due to gage lag.

The retract position is used to return cylindersto normal operating position, after cable nutshave been tightened during tensioningprocedures.

Operate the hydraulic power unit of the cable-tensioning assembly to cause one completestroke of the cylinder at a time to tension thecables. Cable tensioning is accomplished inincrements of cylinder strokes, as follows:

1 As cylinder advances, tighten cable nutby hand against bearing surface of thecable-connection beam. At the end of eachcylinder stroke, release pressure, retractcylinder, and hand tighten cylinder nutback to retracted cylinder.

Note: If cable nut cannot be hand tightenedbecause thread on pull rod is damaged orburred, use a Bailey structural wrench, asshown in Figure 15-37 (page 186) to pry

184

FM 5-277

cable nut free of damaged area. Handtightening of cable nut can then be con-tinued. Cylinder nut can also be turnedthrough damaged or burred threads, usinga chord-bolt wrench.

2 Repeat the last two steps until load, asindicated on gage of cable-tensioningassembly (Figure 15-38, page 186), is equalto 2 tons (1.82 metric tons) more thanvalue listed in Table 15-1. Then slowlyrelease pressure in hydraulic cylinder byslightly opening valve on hydraulic powerunit until gage indicates a tension value 4tons (3.64 metric tons) less than that

listed in Table 15-1. Repressurize to appro- 4 Measure deflection of bridge at midspan,priate value in Table 15-1. This must be relative to end of bridge. Compare thedone with the cylinders near midstroke. measured value obtained to values shown

in Table 15-1. If the deflection measure-Note: This procedure eliminates friction ment is less than the values listed inbetween the cable and vertical post. Table 15-1, refer to maintenance pro-

cedures later in this chapter for trouble-3 Tighten cable nut against bearing surface shooting tips to correct conditions. As

of cable-connection beam. Release all pres- part of regular maintenance, check cablesure in cable-tensioning assembly by tension using manual hydraulic-pumpopening valve on power unit. Then hand assembly by pressurizing cylinders justtighten cylinder nut against cylinder. enough to free cable nuts, and comparing

gage reading with cable-tension value inNote: Cylinders must be fully retracted Table 15-1.before disconnecting hydraulic power unit.

185

FM 5-277

DISMANTLING OF SETThe sequence for dismantling the cablereinforcement set must be closely followed inorder to prevent damage to equipment orpossible injury to personnel.

Cable tensionTo relieve cable tension, unload tension on allcables simultaneously, as follows:

1 Move cylinder nuts away from cylindersto 1/4 inch (.6 centimeter) lees than fullcylinder stroke. By pumping, increaseload on each cable until cable nut turnsfreely.

opening valve on the power unit, per-mitting cylinder to slowly collapse.

3 Tighten cable nut against bearing surfacewhen cylinder is almost completely col-lapsed. Cylinder should not be completelycollapsed because tension in cable pre-vents hand loosening of cylinder nut.

4 Repeat the three steps above until tensionin cables is relieved and cables are free ofvertical-post saddles.

5 With cable nut against bearing surface ofcable-connection beam, remove cylindernut, cylinder, and adapter from pull rod.

Cable removalTo retrieve the cable, the following procedurefor cable removal must be used for all cablesinstalled on the M2 panel bridge

1 Reinstall lashing ropes 20 feet (6.2 meters)apart, along entire length of the cables.Make certain that cables are fully sup-ported by lashings before continuing withremoval operations.

2 Remove cable retainer from each vertical-post saddle by removing bolts and hexnuts.

3 On near-shore tensioning end of thebridge, continue retrieval as follows:unscrew cable nut from pull rod; pull pullrod out of cable-connection rod; removebolt and hex nut which retain pull rod onrod-to-cable coupling, unthread pull rodfrom rod-to-cable coupling; and reinstallcable and cylinder nuts on threads of pullrod.

4 On the far shore, pull cable from dead-endcable-connection beam far enough toremove half-cable retainers. Then pullcable back through dead-end cable-connection beam.

2 Keep cable nut free of cable-connectionbeam bearing surface while carefully

186

FM 5-277

5 Lift cable up and over panels of bridge.Carry cable to cable reel. Wind cable oncable reel, removing lashing ropes ascable wraps on reel.

Caution: During winding of cable oncable reel, be careful to prevent cablebuttons from snagging on structure,and cable from wearing against any-thing which could fray or break thewire.

Cable-connection beams andspan junction posts

To remove cable-connection beams and spanjunction posts correctly, do as follows:

1 Remove retainer clips from ends of panelpins (Figure 15-33).

2 Place safety cribbing under lower panelchords.

3 Install jacking lugs and railroad jacks,and jack up end of bridge enough tounload panel pins connecting span junc-tion posts to connection beams.

4 Continue jacking up end of bridge untilcable-connection beam is clear of spanjunction posts.

5 Install rocking rollers as when dis-mantling normal Bailey bridge (Chapter21).

6 Jack bridge down onto rocking rollers.

7 Remove jacks, jack shoes, jacking lugs,span junction posts, and cable-connectionbeams.

Posts and bracingTo remove braces, post assemblies, andconnection fixtures do the reverse of instal-lation procedures outlined earlier in thischapter. After removing post assemblies frombridge, reinstall cable retainer on vertical-post saddle with four 1/2-inch (1.3 centimeters)diameter bolts and hex nuts. To completedismantling, continue removal of the bridgeas outlined in Chapter 21.

OPERATION UNDER UNUSUAL CONDITIONS

TEMPERATURE EXTREMES SPECIAL ENVIRONMENTS Paint surfaces of parts which are subjectThe cable-reinforcement set can be installed When operating in dusty, sandy, tropical, or to rust and corrosion, in accordance withand used in all extremes of temperature salty areas, do as follows: TM 43-0139, if surfaces indicate absencewithout a change of existing components. of paint or excessive weathering. Do notCable tensions in Table 15-1 are higher than Lubricate cable, bridge set rockers, paint cable.required under normal conditions, to com- threaded surfaces, and slots in vertical-pensate for extremes of temperature. post saddles.

OPERATOR’S AND ORGANIZATIONAL MAINTENANCEBASIC TOOLS performed by the using organization. Basic Appendix B. There are no special tools

Tools and equipment normally issued to the issue tools and supplies issued with or au- required to perform operator’s and organi-panel bridge company and those issued with thorized for the cable reinforcement set are zational maintenance on the cable reinforcethe cable reinforcement set are adequate for listed in Table B-1, and shown in Figure B-1, ment set.maintaining this set. All maintenance will be

187

FM 5-277

LUBRICATIONLubrication of parts and equipment is anessential part of maintenance. Lubricationprocedures are as follows:

WARNING: Do not permit open flames inimmediate area because hydraulic fluid isflammable.

Keep all lubricants in closed containersand store in a clean dry place away fromexternal heat. Allow no dust, dirt, water,or other foreign material of any kind tomix with lubricants. Keep all lubricationequipment clean and ready to use.

Service lubrication points at properintervals.

Keep all external parts not requiring lubri-cation clean of lubricants.

Before lubricating equipment, wipe alllubrication points free of dirt and grease.

Clean all lubrication points after lubri-cating to prevent accumulation of foreignmatter.

PREVENTIVE MAINTENANCETo ensure that the cable reinforcement set isready for operation at all times, inspect itsystematically to discover and correct defectsbefore they cause serious damage or failure.Note defects found during operation of theunit and correct them immediately. Stopoperation at once if a defect is noted whichwould damage the equipment were operationcontinued. Every organization equipped withthe cable reinforcement set must train itspersonnel to effectively maintain it.

Preventive maintenance checks and servicesare listed and described in Table B-3, Appen-dix B. The item list indicates the sequence ofminimum inspection requirements.

MAINTENANCE PROCEDURESPerform maintenance procedures as follows:

Service the cable-tensioning and manualhydraulic-pump assemblies by checkingthe level of the hydraulic oil in thereservoir of the pumping unit and fillingor draining this component. This includesreplacing the gage, quick-disconnectcouplings, or hose assemblies when inspec-tion reveals a need for this.

Note: Always use the following standardprocedures when disassembling ahydraulic component

1 Make certain all pressure has been relievedbefore opening any part of a hydrauliccomponent.

2 Provide a container to catch anydraining fluid.

3 Cover any exposed openings to preventforeign matter from entering the hy-draulic system.

4 Apply a small amount of pipe dope toall threaded connections to assure atight connection.

Service the pumping reservoirs as shownin Figures B-2 and B-3, Appendix B.

When inspection reveals the need, replacethe following parts of the cable-tensioningassembly and manual hydraulic-pumpassembly, as illustrated and described inFigures B-4 and B-5, Appendix B, respec-tively: cable-tension gage; hose assem-blies and quick-disconnect couplings;gage adapter (hand pump only); and cyl-inders (cable-tensioning assembly only).

TROUBLESHOOTINGMalfunctions which may occur in the cablereinforcement set and its components arelisted in Table B-4, Appendix B. Each mal-function is followed by a list of probablecauses of the trouble and the corrective actionrecommended to remedy it. Malfunction mayoccur while the cable reinforcement set isbeing used in the field where supplies andrepair parts are not available and normalcorrective action cannot be done. When thisoccurs, follow the expedient remedies alsolisted in Table B-4, Appendix B.

REPAIR PARTSRepair parts needed to maintain the cablereinforcement set are listed in Table B-5,Appendix B. A number of these parts areillustrated in Figures B-6 through B-12,Appendix B.

188

FM 5-277

SHIPMENT AND LIMITED STORAGEPREPARING FOR SHIPMENT

Prepare the cable reinforcement set for do-mestic shipment as follows

1 Inspect entire unit for unusual conditionssuch as damage, rusting, and theft. Dopreventive maintenance services outlinedearlier in this chapter.

2 Remove all contamination from unit byan approved method. Approved methodsof cleaning and drying, types of pre-servatives, and methods of applicationare described in TM 38-230-1.

3 Repaint all surfaces where paint has beenremoved or damaged. DO NOT paint thecables.

4 Complete properly annotated DA Form2258 (Depreservation Guide for Vehiclesand Equipment), concurrently with pre-servation for each item of mechanicalequipment, and outline unusual needs in

blank space on form. Put completed guidein waterproof envelope marked "Depreservation Guide," and fasten it in a con-spicuous place. Before using equipment,and before inspection, do depreservationof the item as outlined in the guide.

5 Coat exposed machined surfaces withpreservative (P-6), conforming to speci-fication MIL-C-11796, class 3. If pre-servatives is not available, GGP-GREASE,General Purpose, may be used.

LOADING EQUIPMENTTo load the equipment for shipping, use alifting device of suitable capacity to lift heavycomponents. The cable reinforcement set maybe transported in three M51 trucks. One trucktransports cables, reels, and supports,another transports the span junction post,and the third truck transports the remainingparts of the cable reinforcement set (Figures15-5, 15-6, and 15-7).

Caution: Attach a guide rope whenlifting the equipment to avoidswinging and damaging the cable rein-forcemnent set.

Securely block and lash the cable rein-forcement set in M51 trucks. The cable-tensioning assembly is contained in its ownbox with protective wrapping. Also, the pullrods can be stored in cardboard tubes toprotect the threads from dirt or other foreignmatter. This set may also be stored in ashelter or motor pool. If stored in the open,make sure components are placed on cribbingto reduce rust and corrosion.

189

FM 5-277

CHAPTER 16

B R I D G E S O N P I E R S

Long simple spans become increasingly un-economical because of excessive dead weightand reduced class. Generally, intermediatepiers should be used to avoid assembly ofclass 50 continuous spans longer than 150

DESCRIPTIONBroken-span bridges are multispan structureswith the top chord broken and the bottomchord either broken or pinned at the piers.The two adjacent spans act independentlyunder load. One advantage of broken-spanover continuous-span assembly is that thereaction on intermediate piers is less. Also,pier settlement will not result in reducedbridge capacity, adjacent spans may be ofany length, and seating operations are simpli-fied. Existing piers of demolished structures(Figure 16-1), panel crib piers, framed bentsor cribs (Figure 16-2), pile piers, or combi-nations of these (Figure 16-3, page 192) areused for intermediate supports.

ASSEMBLYIndependent spans can be single-, double-, ortriple-truss and single- or double-story as-sembly. If truss assembly is changed over thepier when using conversion set No. 3 (Chapter

BROKEN-SPAN BRIDGES 190

CONTINUOUS-SPAN BRIDGES 198

CANTILEVER-SPAN BRIDGES 206

feet (46.2 meters) or class 75 continuous spanslonger than 120 feet (36.9 meters). Bridgessupported by piers may be either broken (ateach pier) into separate spans or continuousfor their entire length. For efficient assembly,

BROKEN-SPAN BRIDGES

17), the heavier assembly should be continuedfor two bays into the lighter assembly tostabilize the junction link. For example, if adouble-single bridge is joined to a triple-single or double-double bridge, the triple-single or double-double should be continuedfor two bays past the junction into the lightertruss types. Keep transom clamps in these

the time required to assemble one span andprepare it for launching should be as nearlyequal as possible to the time required toassemble and place one pier.

bays tight. If a triple-truss panel crib piersupports a double-truss bridge, distribute theload to all trusses in the pier by triple-trussassembly, and use three transoms over thepier and in three adjacent bays of each span.

PiersAny type of supporting crib or pier capable of

190

FM 5-277

taking the end reactions of the spans can beused. Bailey-type panel crib piers for sup-porting broken-span bridges are described inChapter 17. It is desirable to make the top ofall piers in the same plane as the abutments,but a change in slope between spans may beused if needed. Guy tall, narrow piers toprevent lateral movement.

Bridge seatingsWith panel crib pier parts (conversion set No.3), take special care that piers are exactlyaligned and spaced so that the ends of twoadjacent spans are on a common junction-link bearing. Attach span junction posts tothe end of each span, and pin the posts to thejunction links fitting in junction-linkbearings. Bridge gap between two spans with

junction chess. The use of standard con-version set No. 3 severely limits the bridgepier reaction.

If the panel crib pier parts are unavailable,attach the end posts to the ends of adjacentspans and seat on separate bearings (Figure16-4, page 192). Use any of the following threemethods to bridge the gap between spans:

If junction chess are used, seat an extratransom in the end posts of one span andspace the bearings 21¾ inches (55.4centimeters) apart center to center (Figure16-4).

If junction chess are unavailable, useseventeen 4- by 4-inch (10.2 by 10.2

centimeters) timber stringers decked withtwo chess. If bearings are butted againsteach other (Figure 16-5, page 192), thestringers must be 2 feet (61.1 centimeters)long.

Standard stringers cut to desired lengthcan be used to bridge the gap betweenspans.

If bearings are spaced 4 feet 6 7/8 inches(1.4 meters) center to center, bridge thegap by setting standard panel-bridgestringers back 5 feet (1.5 meters) alongbridge (Figure 16-6, page 192). Use extrapanels to support overhanging stringersat one end of bridge.

If end posts are not used, fasten steel plates topier cap for truss bearings. Pin only the lowerchords of spans. Omit top pin at junction sotwo spans can act independently.

If timber trestle or pile bents are used asintermediate piers, build the top of the bent asshown in Figures 16-7 through 16-11 (page193). If end posts are not used, reinforce thecapsill with a steel bearing plate under eachline of trusses. On single bents, use corbelswith knee braces to provide a jacking plat-form for light bridges (Figure 16-8). If doublebents are used with end posts and standardbearings, lay timbers across caps to provide aplatform for seating bearings (Figures 16-10and 16-11). Group timbers together undereach line of trusses.

191

FM 5-277

192

FM 5-277

CLASS class when fitted with end posts or span classes of Bailey bridges without endNormal spans, spans without end posts, and junction posts as a simple-span bridge of posts, see Table 22-3.piers each have their own class designation, the same span length and type ofas follows: assembly. In a series of broken spans, the class of

the weakest span is the class of the bridge.Since spans of a broken-span bridge act If end posts or span junction posts are not For classes of panel crib piers, see Chapterindependently, each span has the same used, the class of spans is limited. For 17.

193

FM 5-277

The load on a pier from two adjacent in-dependently supported spans can be com-puted. The formula is based on a vehiclespacing of 100 feet (30.8 meters). Allowing 15percent of the live load for impact, and acoefficient of 1.13 for eccentricity, the totalfactor is 1.3. The formula is—

R = 1.3P + 1/2 Wd

R = load in tons on pier.

P = maximum live-load shear intons.

Wd = total dead weight in tons ofthe two spans.

The following example illustrates how to findthe pier reaction of a broken-span bridge:

Given:Spans of 130 and 80 feet (40 and 24.6meters) on each side of an intermediatepier.

Broken-span panel bridge to span these gapsmust carry class 50 load in normal crossing.

Required:Determine bridge assembly needed.

Determine load on pier.

Solution:From Table A-7, Appendix A, the 130-foot(40 meters) span will require triple-doubletruss assembly and the 80-foot (24.6 meters)

span double-single truss assembly. Thetriple-double construction must be con-tinued for two bays of the double-singleconstruction to stabilize the junction link.

Using the formula given, P is determinedfrom Figure 16-12 by entering the bottomof the graph at 210 feet (64.6 meters) (totalof the two spans), reading up to the class 50curve and then to the left margin. In thisinstance P is determined to be 74 tons. Todetermine Wd, refer to Table 1-2 whichshows that one bay of triple-double bridgeweighs 5.88 tons and one bay of double-single weighs 3.41 tons. The heavier con-struction must be continued two bays intothe lighter construction. This results in 15bays of triple-double and 6 bays of double-single construction. By multiplication wefind Wd is 108.66 tons. Load on pier isthen—

R = 1.3P + 1/2 Wd

= 1.3(74) = 1/2(108.66)= 96.2 + 54.33= 150.53 tons

METHODS OF LAUNCHINGBroken-span bridges are launched by canti-levering the entire bridge with launchingnose over the gap as a continuous bridge andbreaking it, by launching each span by singlegirders, or by floating each span into position.

LAUNCHING AS ACONTINUOUS BRIDGE

Normally, an entire single- or double-storybridge with nose is launched over interme-

diate piers and then broken at the piers.Long, heavy single- or double-story bridgescan be launched incomplete to make thelaunching easier. Connect the spans directlyor by span junction posts and launchinglinks. Push the bridge across the gap or pull itacross by winch line. In general, launch acontinuous bridge as follows:

1 Place rocking rollers on each pier and onabutments in the same horizontal plane.Spike or lash rocking-roller bearings, baseplates, or templates to piers to preventshifting during launching. When spanjunction posts are not used and the bridgeis to be cut over the pier, the pier top mustbe wide enough to allow placing of tworocking rollers end to end under eachtruss.

Note: The number of rocking rollers on apier must be equal to the number requiredon the near shore.

2 Use a launching nose in the same manneras for a normal bridge. The length of thelaunching nose should be the same asrequired for a single span bridge of thesame length as the longest span in thebroken-span bridge. Use launching-noselinks in bottom chords of nose to com-pensate for sag. When estimating sag innose to determine position of links, allowan extra 6 inches (15.3 centimeters) of sagfor safety.

3 During launching, guy piers to offsetlongitudinal thrust of the bridge. When

1 9 4

FM 5-277

completely launched, pull bridge backslightly to relieve stress in guy lines.

4 Jacking down over intermediate piersrequires jacking beams similar to thosedescribed later in this chapter.

SPANS WITH SPAN JUNCTION POSTSON JUNCTION-LINK BEARINGS

Launch spans with span junction posts onjunction-link bearings as follows:

1 Fit span junction posts to ends of spansand pin bottom jaws of adjacent poststogether. Three methods of making junc-tions are-

If spans are all the same length, beginwith first junction and fit alternatejunctions with launching links betweentops of span junction posts. This makesbridge continuous at these points.These junctions are called locked junc-tions. Do not connect top chords atother junctions.

If spans are not all the same length,make first length of continuous bridgeplus launching nose twice the length oflongest span. This counterweights thenose over the gap.

In double-story assembly, place spanjunction posts in each story. Pin thebottom jaws of posts in lower storytogether and use Mk II launching-noselinks to connect top of posts in topstory. Do not make a pin connection

195

FM 5-277

between posts at top of lower story andbottom of top story.

2 Remove launching-nose links from topchords at locked junctions by the fol-lowing two methods:

For bridges with several long heavyspans, remove launching-nose links atpoint of contraflexure. In a continuousgirder, there is a point near each sup-port where the girder changes from adownward sag in the gap to an upwardbend over the pier. At this point (pointof contraflexure), there is no bendingmoment in girder, no stress in links intop chord, and panel pins are easy toremove. If the pins are heavily greased,they can be pulled by hand. To findpoint of contraflexure in span, stationpersonnel at each link to test pins forslackness as soon as links are one-thirdspan length from far pier. Push bridgeahead slowly and continue to test pins.When pins are loose, remove links.After removing links, continuelaunching until bridge is in final posi-tion over piers. Then jack down bridgesimultaneously at alternate supports.

For short light bridges of two or threespans, remove launching-nose linksover piers. Launch bridge completelybefore attempting to remove links. Afterlaunching, jack up ends of bridge andsubstitute cribbing at same height asrocking rollers at abutments. Then

remove rollers and cribbing at eachcenter pier and jack bridge down slowly.As jacks at center pier are lowered,tension in top chord decreases. Whentension is zero, remove pins in Mk IIlinks. Then jack bridge down on centerpier. Repeat this procedure at adjacentpiers, working toward abutments. SeeTable 16-1 for maximum lengths ofbridge and jacking arrangements,based on dead weight of two spans overthe intermediate pier. When using thistable, note the following:

For heavier bridges, use jacks at thepier also.

With jacks arranged as in Figure 16-18 (page 205), and two jacks undertrusses at each side of bridge, jackstrength (15 tons) limits this arrange-ment to a capacity of 56 tons. Withfour jacks used instead of two undertrusses, jack strength limits thisarrangement to a capacity of 111tons.

With jacks arranged as in Figure 16-19 (page 205), and 6 jacks undertrusses at each side of bridge, jackstrength limits this arrangement toa capacity of 85 tons (jack strengthon toe is 7.5 tons). With 12 jacks usedinstead of 6 under trusses, jackstrength limits this arrangement toa capacity of 168 tons, and two rampson each side of bridge are needed.

Whether 2, 4, 6, or 12 jacks are used,truss spacing causes eccentric loadon jacking beam.

SPANS WITH END JUNCTION POSTSON STANDARD BEARINGS

Launch spans with end posts on standardbearings as follows:

1 Launch as a continuous bridge until farspan is in position.

2 Disconnect far span from rest of bridge,and pull bridge back until next span is inposition. To remove pins, bridge may bejacked up slightly either at junction or atend.

3 Repeat procedure until all spans are dis-connected over their piers.

4 Pin end posts to ends of spans, and jackspans down on bearings.

LAUNCHING WITHOUT END POSTSLaunch spans without end posts as follows:

If bottom chords of all spans are to bepinned together and only top chordsbroken at piers, make junctions, launchbridge, and remove pins in same manneras for spans with span junction posts.

If both top and bottom chords are to bebroken at piers, launch bridge in samemanner as for bridge with end posts.

196

FM 5-277

LAUNCHING BY SINGLE GIRDERSTo launch by single girders, assemble bridgeby launching girders of each span from deckof previously completed spans. Add transomsand decking after girders are in place. Fordetailed procedure, see Chapter 19.

LAUNCHING BY FLOTATIONTo launch by flotation, assemble span onrollers on shore, launch onto pontons orcrafts, and float into position between piers.For detailed procedure, see Chapter 18.

JACKING ON PIERSWhere it is necessary to jack on intermediatepiers, the distance through which the bridgeis raised or lowered should be kept to theminimum by adjusting the levels of theintermediate rollers. In the case of flat cribs,the jacking problem is considerably eased,since the jacks can be readily positionedunder the inner trusses of the bridge. Asatisfactory method of jacking the bridge offthe intermediate rollers and positioning thedistributing beams is as follows:

1

2

Place jacks beneath panel verticals ordiagonals of inner trusses on each side ofbridge with handles toward the center,and remove sway braces. Lift bridge clearof rocking rollers, and remove rollers andcribbing. Place temporary cribbing underinner trusses, and position base platewith bridge bearing placed centrally.

Place distributing beams on bridgebearings under middle and outer trusses.Jack down to within 3 inches (7.6 centi-meters) of final position. Place cribbing

197

FM 5-277

3

between bottom chords of bridge and topof distributing beams and lower bridge onthe cribbing. Remove jacks from underinner truss.

Put distributing beams centrally underinner truss so that crib bearing is overbridge bearing.

ADVANTAGESA continuous-span bridge is one in whichboth upper and lower chords are continuousover intermediate piers between abutments.Advantages of continuous-span bridges arethat siting of piers is not limited to 10-footincrements or to exact longitudinal alignmentby panel junction, as in broken-span bridges.Assembly is faster and class is increased formost types of assembly. Classes for contin-uous spans over piers are found in Table 16-2.

ASSEMBLYThe number of spans is limited by the effectof harmonious vibration setup by loads andby the difficulty of keeping long bridges inalignment during launching. Normally, con-tinuous-span bridges are limited to four spansor 500 feet (153.8 meters).

The maximum span of a continuous-spanbridge to carry a specified load is given inTables 16-2 and 16-3. The short span must beat least 60 percent of the length of the longeradjacent span. If the short span is less than60 percent, a heavy load on the long span

4

5

Place jacks beneath distributing beam 6 Secure bridge bearing in position in baseunder inner truss of bridge, jack up, plate with timber.remove packing from middle and outertrusses, and lower onto bearings. MAINTENANCE

Check periodically to record any sinking ofWeld guide plates to end stiffeners of piers. Prevent lateral shifting of the bridge bydistributing beams, with lug on top of timber blocking on each side of bearings andplate between middle and inner trusses. lateral guy lines on high piers.

CONTINUOUS-SPAN BRIDGES

198

FM 5-277

raises the end of the short span off its bearing. If two or more piers are used in the assemblyIf spans less than 60 percent are essential,break the bridge at the pier to make the shortspan independent.

Change of assembly over a pierAvoid changes in truss assembly wheneverpossible. If changes must be made, changenumber of stories rather than number oftrusses to give better redistribution of stressesbetween adjacent spans. If one pier is used,the construction of both sides of the piershould be the same. Use Table 16-2 for equal-length spans and Table 16-3 for unequal-length spans. For both types of span, bridgeswith a normal rating over class 70 must bebuilt with double transoms.

of continuous spans (for example, 120 feet[36.9 meters], 120 feet, and 70 feet [21.5meters]), the assembly may change over thelast bay of the bridge. To determine whethera change is permissible, check Tables 16-2and 16-3 to see if the lighter construction willgive a sufficient class. Extend heavierassembly of longer span beyond intermediatepier a distance equal to 25 percent of shorterspan. Make only the following changes ofassembly between spans: single-single todouble-single, double-single to double-double,triple-single to triple-double, and double-double to double-triple. Whenever double-double or double-triple truss types are used,they must be reinforced to triple-double and

triple-triple respectively over a pier fortwo bays on each side of the pier-bridgeconnection.

Construction of piersUse any type of supporting crib or piercapable of taking the reactions of the spans.Piers are normally built before the bridge islaunched over them. Where piers are inaccess-ible from the ground because of extremeheight or a rapid stream, a high line can beused in construction or the soldiers andmaterials can be lowered from the end of thecantilevered launching nose of the bridge.Figure 16-13 (page 200) illustrates how thishas been done. On two-span bridges, thebridge may be launched across the gap andpier parts lowered from the bridge. Be sure tocheck the capacity of the bridge over thecombined gap to ensure that it will carry thepier construction crew and materials. Guytall, narrow piers to prevent lateralmovement.

Construction of bridge seatingSome form of rocker bearing must be used atthe intermediate pier to allow for deflection ofgirders under load. Normally, a rockerbearing for the bridge is placed at the top ofthe pier. If a rocker is placed at the base of thepier, the bridge can be fastened rigidly to thepier (Chapter 17). Various types of rockers attop of pier are described below. The distri-buting beam on the rocker bearing must bestrong enough to prevent excessive localbending in the bottom panel chord. Table16-4 (page 200) gives the number of panel-support points (points under panel verticals

199

FM 5-277

and junctions of panel diagonals) that mustbe effectively supported by the distributingbeam to prevent excessive bending stress inthe bottom chord. The procedures for pro-viding rocker support to panel-support pointsare as follows:

When rocker must support two panel-support points, use a crib capsill, cribbearing, and standard bearing from thepanel crib pier set as shown in Figure16-14. Because of the flexibility of the crib

capsill, this rocker gives full support toonly two panel-support points. Pier reac-tion with this arrangement is limited to17 tons (15.5 metric tons) per truss.

When rocker must support three panel-support points, use a crib capsill, aninverted junction-link bearing, and ajunction link from the panel crib pier setas shown in Figure 16-15. Pier reactionwith this arrangement is limited to 25tons (22.3 metric tons) per truss.

200

FM 5-277

When rocker must support five panel-support points, reinforce the crib capsillin Figure 16-14 with an 8-foot 4-inch (2.6meters) section of transom as shown inFigure 16-16 (page 202). Weld capsill,transom, and crib bearing together andpin by chord clamps to panel chord. Weldsmall channels across bottom of transomsections at each side of bridge to givelateral stability to each rocker. Weld morediaphrams and an end plate to the rockerbearing. The crib capsill may be omittedif a 10-foot (3.1 meters) section of transomis used, but end plates must be recessed toprevent lateral movement of the trussesbeing supported.

Anchoring of bridgeAllowance must be made for slight long-itudinal movement of the bridge due todeflection under loads, and for expansionand contraction due to temperature changes.With temperature changes of 60 degreesFahrenheit (15.6 degrees Centigrade), a move-ment of 1/2 inch (1.3 centimeters) per 100 feet(30.8 meters) of bridge can be expected. Toallow for this movement, grease base platesso bearings can move longitudinally on them.Restrain the bearings laterally with timberguides. If sloping bridges are erected, alter-nate expansion and contraction makes thebridge creep downhill. To offset this, keepslopes under 1 in 30 and fix the uphill end ofbridge to prevent creeping. At the end of abridge with a short end span, lash or clampend posts to bearings so posts cannot jumptheir seatings if end of bridge lifts when aheavy load is on the second span.

Leveling supportsThe bottom chord of the bridge must be in thesame plane over all the intermediate supports.Normally, this plane is level, but a slightinclination is permissible. If any pier settlesmore than 6 inches (15.3 centimeters) belowthe bridge plane, then the rockers must becribbed up. Without the cribbing, the super-structure will fail.

PIER REACTIONThe class of continuous-span bridges varieswith span lengths. For shorter spans, it maybe less than that of broken-span bridgesbecause shear at the piers is greater. Tables16-2 and 16-3 give the capacities of continuous-span bridges. Note that in most cases, theclass is greater than it is for correspondingsimple spans. Table 16-4 gives pier reactionsand the number of panel points (points underpanel verticals and junctions of panel diag-onals) that must be supported by the rocker-bearing distributing beam to distributestresses in bridge panels over the pier. Therocker bearing shown in Figure 16-16 has adistributing beam long and stiff enough tosupport five panel-support points and suitablefor any of the spans in the tables.

The following example illustrates how to usethis table:

Given:Spans of 130 and 80 feet (40 and 24.6meters) respectively on each side of anintermediate pier.

201

FM 5-277

Continuous-span bridge to span these gapsmust carry class 50 loads in normalcrossing.

Required:Determine bridge assembly needed.

Determine type of rocker bearing to use.

Determine load on pier.

Solution:Table 16-3 shows that double-double trussconstruction will provide desired classloading.

Table 16-4 shows three panel-supportpoints are required for two equal spans of130 feet (40 meters) using double-doubleconstruction. Since the 80-foot (24.6 meters)double-double span is not given, the 100-foot (30.8 meters) double-double span isused because this is the maximum reactionthat can be generated on a double-doubletruss. The panel-support points requiredare again three; therefore, truss of thegirder must be supported under threepanel-support points (use bearing shownin Figure 16-15).

Table 16-4 shows the pier reaction is 194tons (176.5 metric tons) for two equal spansof 130 feet (40 meters) using double-doubleconstruction. Again, since the 80-foot (24.6meters) double-double span is not shown,the length is taken as the worst condition,in this case 100-foot (30.8 meters) double-double construction. The reaction under

202

FM 5-277

two such spans is given as 226 tons (205.7metric tons). The average of these twospans is used to determine the pier loading,which in this instance is 210 tons (191.1metric tons).

Note: One advantage of continuous-spanbridges over broken-span bridges is shownby the example problem for finding pierreaction of a broken-span bridge givenearlier in this chapter. Span lengths andclass requirements are identical; however,in broken-span construction a total of 15bays of triple-double and 6 bays of double-single construction are required to obtainclass 50/55. In continuous-span construc-tion, a total of 21 bays of double-doubleconstruction will suffice and provide class60/65. Assuming panels are a critical item,the continuous-span bridge is more eco-nomical since it requires only 168 panels,whereas the broken-span bridge requires204 panels.

Another example of the use of Table 16-4 is asfollows:

Given:Spans of 80 and 120 feet (24.6 and 36.9meters) respectively on each side of anintermediate pier with triple-single trussassembly and class 30 overall.

Required:Determine type of rocker bearing.

Determine load on pier.

Solution:Three panel-support points must be used(Table 16-4). Use bearing shown in Figure16-16 to support pier load.

Load on pier from two 80-foot (24.6 meters)triple-single bridges is 167 tons (152 metrictons) and load on pier from two 120-foot(36.9 meters) triple-single bridges is 127tons (115.6 metric tons). The average of thetwo is 147 tons (133.8 metric tons).

METHODS OF LAUNCHINGContinuous-span bridges are launched bycantilevering the entire bridge withlaunching nose over the gap or by floatingintermediate spans into position and thenpinning.

When launching with launching nose (Figure16-17), the length of launching nose requiredis the same as for a simple-span bridge of thesame length as the longest span in thecontinuous-span bridge. Use launching linksto compensate for sag. When estimating sagin nose to determine position of links, allowan extra 6 inches (15.3 centimeters) of sag forsafety. The launching procedures are asfollows:

Use plain rollers as in a single-spanbridge. Place rocking rollers at eachabutment and on top of each intermediatepier.

Note: The quantity of rocking rollers ontop of each intermediate pier is equal to thenear-shore requirement.

Place rollers on intermediate piers in thesame plane as near- and far-shore rollers,and spike or lash them to piers. Checklevel and alignment of rollers beforestarting bridge assembly.

For long bridges, mechanical power maybe needed to launch the bridge. Usemethods described in Chapter 7. In addi-tion, or as an alternative, use winch on farshore to pull bridge across gap. Carefulalignment of bridge during early stagesof launching is important.

203

FM 5-277

Long, heavy bridges can be launchedincompletely to make the launchingeasier. Add extra trusses and deckingneeded to complete bridge after it islaunched.

During launching, use guy lines tocounteract forward thrust of launching.When bridge is completely launched, pullback slightly to relieve stress in guy linesif necessary.

When launching by flotation, float interme-diate spans into position, as described inChapter 18. Lower and then pin to adjacentspans.

METHODS OF JACKINGJack down shore ends of bridges with jacksunder end posts, as described in Chapter 6. Atintermediate piers, use expedient jackingmethods. Jacking load on toe of each jackmust not exceed 71/2 tons (6.8 metric tons);jacking load on top, 15 tons (13.6 metric tons).Also, jacks operated in unison must be of thesame manufacture. Figures 16-18 and 16-19show two methods of jacking at intermediatepiers. Table 16-1 gives lengths of adjacentspans of continuous-span bridges that can bejacked with these arrangements. The twomethods are as follows:

Use two jacks, one on each side of trusses,under a section of transom under topchords of lower story (Figure 16-18). A softmetal plate between jack head and tran-som eliminates danger of jack headslipping. Place transom section close toverticals of panels. Block under jacks toraise transom sections to level of topchord.

Arrange six jacks under ramp sectionplaced across underside of bottom chords(Figure 16-19).

SAMPLE PROBLEMGiven:

Spans of 80 and 120 feet (24.6 and 36.9meters) over an intermediate pier withtriple-single truss assembly.

Required:Determine number of jacks required tojack down bridge.

Solution:First select method to be used over pier.The method used in Figure 16-18 is the bestone because it makes maximum use ofmechanical advantage of jack.

Table 16-1 indicates four jacks are requiredunder trusses at each side of bridge.

Total number of jacks required for the pieris 4 + 4 = 8 jacks.

MAINTENANCEPier sinking causes increased stress in thebridge and must be checked immediately byblocking or wedging under bridge bearings.Check ends of short spans for any tendencyto lift off bearings. If end posts do lift offbearings, lash posts to bearings or breakshort end span at pier. Check anchorage tokeep bridge from creeping under traffic.Maintain blocking to prevent lateral move-ment on piers.

204

FM 5-277

205

FM 5-277

CANTILEVER-SPAN BRIDGES

USESIt is possible to use cantilever construction toproduce clear span lengths greater than thoseobtained with conventional through-typeconstruction. A clear span of 400 feet (123.1meters) can be obtained using cantileverconstruction, but this span requires the use of20 trusses, which is excessive and whichwould become too cumbersome. The designdata and information contained in this sec-tion are based on cantilever construction, asshown in Figure 16-20.

DESIGNThe following design features are assumed:

Tables 16-5, 16-6, and 16-7 (page 208) arebased on a class 60 live load on a singlelane, with a 14-foot (4.3 meters) roadway.The dead load is based on a panel weightwith bracing of 600 pounds (272.7 kilos)and an 8-inch (20.4 centimeters) woodenflooring weighing 400 pounds (181.8 kilos)per foot. A single-story truss was assumedcapable of resisting 380 foot-tons, a double-story truss 700 foot-tons, and a triple-story truss 1,310 foot-tons.

An impact equal to 15 percent of the liveload was used.

The minimum number of trusses in boththe simple span and the cantilever spanwas set at four. If less than four trussesare used, the allowable capacities must bedecreased due to excessive concentrationof wheel loads on a truss, and the type offloor must be changed.

The maximum number of trusses wastaken at 10.

The single-axle load equivalents (SALE)charts for moment and shear have beenused for those spans on which wheeledvehicles governed. Appendix C describesin detail the use of SALE charts in deter-mining moment and shear. For spans of120 feet (36.9 meters) and above, thecritical vehicle is the 60-ton (54.6 metrictons) tracked vehicle. A spacing of 100feet (30.8 meters) from front to rear of aconvoy of tanks moving across the spansgives a center of gravity of the loads at

206

FM 5-277

114 feet (35.1 meters) center to center, and Table 16-6 gives the various spans whichthis was the maximum load used.

A minimum safety factor of 1.15 was usedagainst overturning of the cantilever span(c).

The following tables should be used

Table 16-5 gives the required number oftriple-, double-, and single-story trusseswhich were used for the simple suspendedspan (S).

can be built-using cantilever-type construc-tion. The combination shown is the mosteconomical based on the number of panelsrequired for the center-to-center pier spans(L) using the minimum length of anchorarm. It is important to note that there isboth a maximum and a minimum lengthof anchor arm. The minimum length ofanchor span (A) provides the necessarycounterweight for the cantilever arm, andthe bridge is stable if built in this way.However, the positive resisting moment

of the counterweight span is not beingused to its full capacity. The maximumspan length shown provides for this usebut, if this length is exceeded, even withproper loading, the section may fail.

Table 16-7 gives combinations with thesame number of trusses in both thecantilever and the suspended spans.These combinations are not as economicalas those in Table 16-6.

The following is a design example:

Step 1: Design of suspended span(S) (Figure16-20).

Assume S = 190 ftSALE = 66.7 tonsMLL = PL/4

= 66.7 x 190/4= 3,170 ft-tons

MLL + MI = 3,170 x 1.15= 3,650 ft-tons

Estimated triple-story trusses = 5MDL = [5(.09) + .2] 1902/8

= 2,930 ft-tonsMTOT = 6,580 ft-tons

Actual number of trusses required=6,580/1,310 = 5

Therefore, 5 triple-story trusses will beused.

207

FM 5-277

Maximum end shear:LL+ I = 84 + .15 (84)

= 96.6 tonsDL shear = 61.7 tonsShearTOT = 96.6+ 61.7

= 158.3 tons

Step 2: Design of cantilever span (C) (Figure16-20).

Assume single-story construction with 6trussesTry 10-ft span:

Resisting moment = 6 x 380= 2,280 ft-tons

MDL= [6(.03) + .2] 102/2= 19 ft-tons

End shear (on hinge) possible:P(10) = 2,280-19

= 2,261 ft-tonsP = 2,261/10

= 226.1 tons.Therefore, this construction and spanlength is suitable to carry end shear ofsuspended span of 118 tons.

Step 3: Design of minimum anchor span (A)(Figure 16-20).

W = 6(.03) + .2= .38 ton/ft

(R1 assumed= 0)

A = 2,280 X 2/.38= 12,000

A = 109.5 ft (try 100 ft)

Overturning moment about R2

Resisting moment about R2

= 1,900 ft-tons

Safety factor = 1,900/1,602= 1.18

(within 1.15 assumed allowable)Therefore, minimum A = 100 ft (30.48m)

= 19 + 158.3(10)= 1,602 ft-tons

208

FM 5-277

Step 4: Design of maximum anchor span (A)(Figure 16-21).

Maximum resisting positive moment= 2,280 ft-tons

Assume span = 110 ft

SALE + SALE1

=58 X 1.15= 66.7 tons

R1 = 66.7(55) - (61.7 X 10)+

= 48.4 tons

Moment at center

= 2,087 ft-tonsTherefore, maximum A = 110 ft (33.53m)

Therefore, the total maximum length ofbridge for this combination is:

S+2(C)+ 2(A) = 190+20+220= 430 ft (131.06m)

The pier-to-pier span length:

L = S+2(C)= 190+20= 210 ft

(64.0lm) (Table 16-7)

Note: Although six single-story trusseswould be able to carry more than themaximum end shear of 158.3 tons (144.1metric tons) on a cantilevered 10-foot span,an examination of steps 3 and 4 showsthey are needed for even the minimumlength of anchor span required.

209

FM 5-277

CHAPTER 17

PANEL CRIB PIERS AND TOWERS

Panel crib piers are made of trusses withpanels set horizontally or vertically and arenormally braced with transoms, swaybracing, rakers, bracing frames, and tie platesin a panel bridge.

Panel crib piers assembled from parts of theBailey bridge set can be used as—

Intermediate supports for through- anddeck-type fixed bridges. The piers can beset on timber grillage, piles (Figure 17-1),masonry footings (Figure 17-2), or par-tially demolished piers.

Piers in barge bridges.

Intermediate landing-bay piers in floatingpanel bridges with double landing bays.

Expedient towers for suspension bridges,lift bridges, gantries, and floating-bridgeanchor-cable systems.

Expedient marine piers.

CHARACTERISTICS OF CRIBSTypes of panel crib piers have their owndistinguishing characteristics. Panel cribpiers are described by the number of trusses(single, double, triple, and so on, as in a panelbridge); the number of stories (number ofpanels along the vertical axis in one bay, asin the panel bridge); the number of bays(number of panels along the horizontal axis

210

in a given story); and the position of panels ineach story (horizontal or vertical). Table 17-1(page 212) lists the abbreviations used todescribe typical panel crib piers. Panel cribshave from one to four trusses on each side,depending on the desired capacity. Theremust always be at least as many trusses inthe crib as in the bridge it supports.

Panels in a panel crib pier are horizontal(Figure 17-3, page 212) or vertical (Figure 17-4, page 213). Horizontal panels provide a 5-

foot 1-inch (.16 meter) increment in pierheight. They are, however, weak laterallyand are used one above the other whenexpedient bracing is added. When ultimatecapacity piers are used, any horizontal storiesare weaker than vertical ones. Vertical panelsprovide 10-foot (3.1 meters) increments in pierheight. They can be used one above the otherin piers up to 70 feet (21.5 meters) highsupporting continuous spans and up to 110feet (33.8 meters) supporting broken spans.In high piers, exceeding three vertical stories,

FM 5-277

the pier base must be doubled for at least half Deflection of a span under load tends toits height or the lower story must be imbedded change the slope of the bridge at the piers.in concrete for ¾ of its height. To prevent large stresses in the bridge

and pier, allow some rocking movementTo assemble 15-, 25-, 35-, 45-, 55-, and 65-foot at intermediate supports of continuous(4.6, 9.1, 10.8, 13.8, 16.9, and 20 meters) piers, bridges.vertical stories are used with only one 5-foot(1.5 meters) horizontal story placed at the top A rocker at top of the crib can be built ofof the crib. crib bearings on standard bearings, in-

verted junction-link bearings on junctionTYPES OF BRIDGE SEATING links, or one or two I-beams at right

Seating for a continuous bridge is different angles to the bridge axis. With this type ofthan that for a broken-span bridge. Con- bridge seating, bottom chords of thetinuous-bridge seating includes the following bridge over the seating are normallyfeatures: reinforced by a steel beam to distribute

the load and prevent failure of the panelchords due to local bending. These rockers

are described and illustrated in Chapter16.

If the crib is fastened rigidly to the bridge,it must rock with the bridge as the girdersdeflect under load. A rocker at the base ofthe crib can be built of crib bearings onstandard bearings or inverted junction-link bearings on junction links. This typeof pier construction may prove useful onpiers less than 10 feet (3.1 meters) widealong the axis of the bridge. It must bebuilt from the bridge downward and thebridge must be capable of holding itself,the pier, and the work crews while restingon rollers for both span lengths until thepier is in position. Heavy bearing platesare needed beneath the crib-bearing sothat the entire bridge-pier reaction maybe distributed to the pier base.

As an expedient when rocker bearingscannot be improvised, seat bridge ontimber on top of the piers.

Broken-span bridge seating includes thefollowing features:

In broken-span assembly, the adjacentends of the two spans are seated on thejunction-link bearings by use of spanjunction posts and junction links (Figure17-5, page 214).

As an expedient, the adjacent ends of thetwo spans can be pinned to the verticalpanels in the pier, or the two ends can reston separate bearings.

211

FM 5-277

2 1 2

FM 5-277

213

FM 5-277

214

FM 5-277

SPECIAL PARTS FORPANEL CRIB PIERS

The bridge conversion set No. 3, Bailey type,panel crib pier, contains parts that are usedwith equipment from the basic bridge set tobuild panel crib piers. The major items in theconversion set are listed in Table 17-2.

SPAN JUNCTION POSTSSpan junction posts are special end posts forconnecting adjacent ends of two spans andsupporting them on the same bearing.

There are two types of span junction posts,male and female, which have lugs that arepinned to female and male ends, respectively,of standard panels. At the junction, each posthas two other connecting lugs, a male andfemale lug at the top according to type, and auniversal jaw at the base. Irrespective oftype, two posts can be connected at the baseby a normal panel pin. Always use a bridgepin retainer on the panel pin at this joint. Anintermediate pin hole and recess in the baseof each post is for the junction link.

During launching, connect the top lugs of theposts by a launching-nose link Mk II. Thelink will fit only between one female spanjunction post and one male span junctionpost, so take care when constructing the twospans to keep all the male lugs on the panelsfaced the same way. After the bridge is jackeddown and posts are pinned to the junctionlink, remove the link; leave in the pin joiningthe two posts at their base. Then the gapbetween the two lugs of the posts allows anupward slope of 1 to 6.7 or a downward slopeof 1 to 5 in one span when the other is level.

The female span junction post weighs 202pounds (91.8 kilos) and the male span junctionpost weighs 194 pounds (88.2 kilos).

M2 JUNCTION CHESSJunction chess (Figure 17-6) span the gap inthe bridge deck between the ends of the twospans connected by span junction posts. Fourjunction chess are used at each span junction.

The junction chess consists of two 6-foot 10 ½-inch (2.1 meters) timbers fastened to ninesteel I-beams 11½ inches (29.3 centimeters)long. The junction chess weighs 149 pounds(67.7 kilos).

JUNCTION LINKThe junction link (Figure 17-7 page 216)transfers the end reaction from two-spanjunction posts to a junction-link bearing. Itsuse limits truss reaction to 25 tons (22.8

215

FM 5-277

The junction link is a triangular-shaped steelassembly with two projecting male lugs on itstop side spaced to pin with panel pins to thetwo-span junction posts. Both holes areelongated to permit some play in the joint. Abridge pin retainer must always be used onthe panel pins at this joint. The bottom of thejunction link tapers down to a nose with atubular bearing which seats in the curvedbearing plate of the junction-link bearing.The junction link weighs 36 pounds (16.4kilos).

JUNCTION-LINK BEARINGThe junction-link bearing (Figure 17-8) isused under the junction link which supportsthe ends of the bridge. It can be used in thefollowing ways:

When supported by a vertical panel, ifmale lugs of panel are uppermost, pinjaws of the junction-link bearings to thepanel lugs. If female lugs are uppermost,rest jaws of junction-link bearing on topof lugs and fasten them by chord clamps.

When supported by a crib capsill (Figure17-5), secure it to the capsill with chordclamps.

When supported by a crib bearing, pinbearing to two center holes of junction-link bearing with panel pins.

When used under female end of verticalpanel, rest female lugs of panel on jaws ofjunction-link bearing and secure them bychord clamps.

When supported by timber, lay junction-link bearing directly on a timber support.

The junction-link bearing is made of two 8-inch (20.4 centimeters) channels welded backto back with the same spacing as betweenchannels in the chords of the panel. It is 5 feet1 inch (1.6 meters) long and has female jawsat each end. The distance between panel-pinholes in the female jaws is 4 feet 9 inches (1.5meters), the same as vertical distance betweenpin holes in the pane). Between the webs ofthe channels in the center of the junction-linkbearing is a curved bearing plate on whichthe junction link bears. There is a holethrough the webs of the channels just abovethe curved bearing plate for a captive pinwhich locks the junction link in place. Thereare two panel-pin holes in the webs of thechannels beneath the curved bearing plate.They are used to pin the crib bearing whichfits in the recess between the channels. Ajunction-link bearing weighs 217 pounds (99.3kilos). Its maximum capacity is 25 tons (22.8metric tons) (Table A-14, Appendix A).

CHORD CLAMPThe chord clamp (Figure 17-9) is used to pin—

Crib capsill to panel chord (Figure 17-10).Chord clamps are pinned to any of theholes in the capsill.

Crib capsill to female jaw of panel.

Crib capsill to junction-link bearing(Figure 17-5).

Junction-link bearing to female jaw ofpanel.

The chord clamp is in effect a double-lengthmale lug with two panel-pin holes and a T-head. Slip the clamp between chord channelsof a panel until the head bears on the channelflanges; then pin the clamp to a crib capsill orother female joint with a panel pin. If the

216

FM 5-277

chord clamp is slipped through two adjacentfemale jaws, pin it to each by panel pinsthrough both holes in the chord clamp. Thechord clamp weighs 11 pounds (5 kilos).

2 1 7

FM 5-277

CRIB CAPSILLThe crib capsill (Figure 17-11) distributes theload from the bridge to the main chords ofvertical panels or to the three verticals ofhorizontal panels in a crib. It has unrein-forced holes used to take the vertical load.Before panel pins can be inserted in reinforcedholes, the holes must be reamed or filedslightly. The reinforced holes are used to pinthe capsill to the following:

Male lugs of single vertical panels.

Male lugs of two adjacent vertical panels.

Crib bearing (Figure 17-12).

The crib capsill is made of two 4-inch (10.2centimeters) channels welded back to back tospacer lugs with the same spacing betweenchannels as in the chord of the standardpanel. It is 10 feet 2 inches (3.1 meters) long,and has female jaws at each end. Holes arespaced along the webs of the channels. Sixpairs of panel-pin holes are reinforced withsteel blocks and spaced so male lugs of twoadjacent panels or of a single panel can beconnected to the crib capsill with panel pins.Additional unreinforced holes for chordclamps are spaced generally at 6-inch (15.3centimeters) centers between reinforced holes.Before panel pins can be inserted through theholes they must be reamed or filed slightly.The crib capsill weighs 251 pounds (114.1kilos).

CRIB BEARINGThe crib bearing (Figure 17-13) is used as abase of panel cribs and can be pinned withpanel pins to the following:

One female jaw of vertical panel (Figure17-14).

Two female jaws of adjacent verticalpanels (Figure 17-14).

Two central holes of a crib capsill (Figure17-12).

Two central holes of a junction-linkbearing.

218

FM 5-277

The crib bearing can be spiked to a timber sill(Figure 17-14) to provide a rigid base or set ona standard bearing (Figure 17-15) to provide arocker bearing. The bearing area of the pin is1.875 inches by 3 inches, or 5.625 squareinches (36.4 square centimeters).

The crib bearing is in effect a double-lengthmale lug welded horizontally to a base block.One of the pin holes is elongated to makepinning easier when both holes are used. Ifonly one hole is needed, the circular one isused. Holes are provided in the base block ofthe crib bearing for spiking to a timber sill.The underside of the base block has a semi-circular bearing to seat on a standardbearing. The crib bearing weighs 37 pounds(16.8 kilos).

CRIB LOAD AND CAPACITYThe amount of load on and the capacity of acrib must be determined. Chapter 16 describesa method for determining the approximate

load transmitted to the crib by the ends of twoindependent spans. Continuous-spanassembly over the pier transmits greater loadto the pier. These reactions are listed in Table16-4.

Figures 17-16 and 17-21 (pages 220 and 222)show standard assembly of piers built withspecial panel-crib parts. Capacities are givenin all cases. Single-truss cribs can take 50percent of the loads given for double-trusscribs with only the inner truss loaded. Usesingle-truss cribs only for light loads on lowcribs. The capacity of panel crib piers isusually limited by the strength of the junctionlink, junction-link bearing, and crib capsill(Table A-14, Appendix A).

If special panel-crib parts are not used, theload is carried by the top members of verticalpanels in the crib. Lay timber on top membersof each panel to concentrate load at threepoints: at the center, and near each endadjacent to the panel chords. With the loadapplied in this manner, the top member ofone vertical panel will carry about 14 tons(12.7 metric tons), and piers with this type ofbearing will have the same capacity as piersof corresponding assembly built with specialparts (Table 17-3, page 222).

Table A-14, Appendix A gives the strength ofthe individual panel-crib parts for use inestimating the capacity of expedient panelcribs.

219

FM 5-277

220

FM 5-277

2 2 1

FM 5-277

BILLS OF MATERIALTable A-15, Appendix A lists the number ofparts required to build the standard crib piersillustrated in Figures 17-16 through 17-21,and the number of unit truck loads requiredto supply these parts. Panel-bridge conver-sion set No. 3, panel crib pier, supplies thespecial panel-crib parts to build a 31-foot 7-inch triple-triple pier with the addition ofstandard panel-bridge parts. The parts inconversion set No. 3 are listed in Table A-4,Appendix A. The conversion set No. 3 makestwo crib-pier loads, each carried by a 5-tondump truck. These truck loads are describedin Chapter 2. The number of crib-pier loadsand standard unit truck loads required tobuild each pier are given in Table A-15,Appendix A.

When using this table, note the following

Plain bearings and base plates are notsupplied in loads needed to build a pier.(Use extras from bridge construction.)

Launching links Mk II are used forlaunching only. Remove them after bridgeis in place.

Panel pins listed do not include pins forlaunching links Mk II.

STANDARD ASSEMBLY OFTRUSSES AND BRACES

The trusses in standard panel crib piers areparallel to trusses in the bridge. The cribmust have at least the same number oftrusses as the bridge it is to carry. More

222

FM 5-277

trusses can be added for increased strength(Figures 17-16 through 17-21). Single-trussassembly can be used only for low cribscarrying light loads. The number of bays inthe pier will normally be enough to make thelength of the base one third or more as muchas the height of the pier (Figure 17-21). Allpossible bracing frames and tie plates tietrusses together at each side of the crib. In aquadruple-truss pier, bracing frames and tieplates overlap. Brace the entire crib by tran-soms and sway bracing (Figure 17-22).

In cribs with vertical panels, space transomsat 10-feet (3.1 meters) intervals in piers up to30 feet (9.2 meters). In cribs only one baylong, invert panels of inner trusses withrespect to panels in outer trusses so transomscan be attached to both chords. Sway bracingis on the same side of the crib throughout itsheight. In cribs with two bays of verticalpanels, place panels so transoms and swaybracing are either at the center of the crib orat its sides. In cribs with four bays of verticalpanels, add extra sway bracing in the outerbays (Figure 17-21).

In cribs with horizontal panels, half thepanels may be right side up, and the otherhalf inverted so transoms are at both top andbottom. Vertical-plane cross bracing may beprovided by sway braces pinned to the sway-brace slot of the inverted second truss andfastened to the transom at the other end, orthe sway bracing may be used as describedlater in this chapter.

In cribs under two-lane panel bridges, staggertransoms at the center panels (Figure 17-23).When panels are vertical, transoms in onehalf under one lane are all on top of panelverticals; in the other half, under panelverticals. At the top and bottom of the crib,transoms can be placed only on the side ofpanel verticals. Therefore, angles must bewelded to the panel chords to take the place ofalternate transoms (Figure 17-23, page 224).When the panels are horizontal, angles arealso used to replace alternate transoms. Guyhigh piers to provide greater lateral stability.

BRIDGE SEATINGIf the bridge is broken over the pier so the twospans act independently, use span junctionposts, junction links, and junction-linkbearings to seat it (Figure 17-5). If the crib ispivoted at its base so the bridge is fasteneddirectly to the crib, slip chord clamps betweenthe channels of the bridge chord and pinthem to the crib capsill (Figure 17-16).

Figure 17-15 illustrates rocker bearings usingpanel-crib parts. This type of rocker bearingrests on abase plate on top of the pier. A wideplatform on the top of the pier, to allow someleeway in positioning the baseplates, may bebuilt from transoms and ramps welded inplace (as described in the following para-graphs). An expedient rocker bearing may bemade from one or two tranverse beams set onthe top of the pier. The bearing must be undera panel vertical or the junction of paneldiagonals. Figure 16-15 illustrates anotherexpedient bearing.

CRIB BASEThere are several ways of setting panels ontoa crib. With a fixed base, if panels in the firststory of the pier are horizontal they may beset directly on a timber or masonry pierfoundation (Figure 17-17). If panels in thefirst story are vertical, pin the female jaws ofthe panels to crib bearings which are set ontimber or steel footings (Figure 17-20).

223

FM 5-277

With a rocker base, the rocker may consist ofa crib bearing seated on a standard bearing(Figures 17-15 and 17-16) or an invertedjunction-link bearing set on an invertedjunction link (Figure 17-16). The procedure isas follows:

If panels in lower story of pier are hori-zontal, fasten crib capsill by chord clampsto bottom chord. Then pin this crib capsilldirectly to crib bearing (Figure 17-16), orby chord clamps to inverted junction-linkbearing (Figure 17-16).

If there is one bay of vertical panels withfemale ends down in the pier, connectfemale jaws by chord clamps to top of ajunction-link bearing pinned to a cribbearing.

If there are two bays of vertical panels,pin the two adjacent center female jaws toa crib bearing which is on a standardbearing (Figure 17-19).

224

FM 5-277

EXPEDIENT ASSEMBLY(STANDARD TRUSSES)

If no special panel-crib parts are available,the following expedient parts can be impro-vised for standard truss arrangement:

Panel chords or any pair of 4-inch (10.2centimeters) or larger channels with holesdrilled at the desired spacing can be usedfor improvised crib capsills.

Angles or lugs with pin holes in theirupright parts can be fastened to the cribfoundation and panels pinned to them.Another expedient is to have panel pinsin female jaws of vertical panel bear ontop of an I-beam or rail (Figure 17-24). Aload of 7½ tons (6.8 metric tons) per panelpin is allowed on unstiffened beamshaving a web thickness of ¼ to 5/16 inch (.6to .8 centimeters). Greater loads are per-mitted if web is stiffened or if web thick-ness exceeds 3/8 inch (.1 centimeter).

Other special panel-crib parts are notreadily improvised.

225

FM 5-277

Bridge seatingBridge seating assembly without panel-cribparts can be done as follows:

Figure 17-25 shows the use of transomsand ramp sections to provide a flat top onthe crib for the base plates under therocker bearing. With this type of pier cap,the bridge may be as much as 6½ inches(16.5 centimeters) off the center of thepier. This is made up from a 4½-inch (11.5

centimeters) movement of the bearingson the base plate and a 2-inch (5.1 centi-meters) movement of the baseplate on thepier top. Figure 17-26 (page 227) illustratesthe vertical dimensions and capacities ofpiers with flat top and rocker ridgebearing.

The bridge seating may consist of timberlaid laterally on the end-panel member,

but it is allowed a slight longitudinalmovement.

The pier can also be pinned to the bridgeby pinning male lugs of the two insideposts of the pier to the lower bridge chordand inserting the outer posts in the spacebetween channels of the lower chord.These outer posts just miss the centervertical in the bridge panels. If the outer

226

FM 5-277

post shoulders are cut down enough topermit deflection in the span, this con-nection can be used with a rigid pier base.The top chord of the bridge is left un-pinned so the two spans act independ-ently.

Another method of bridge seating is toinsert the male lugs of the pier posts intorecesses in the lower bridge chords.Clamps made from two tie plates andribband bolts anchor the bridge to thepier. This and the last two methods arelimited because there is only one pierposition in which the lugs fit withoutinterfering with the bridge chord spacers.

Crib baseTo make a crib base without special panel-crib parts, set the crib on timber and have thecribbing bear on the bottom panel member.

Panel connectionsTo connect horizontal and vertical panels,cut away the reinforcing plate at the bracing-bolt hole and slip the male lugs of the verticalpanel between the channels of the horizontalchord. Tie panels together by an expedientclamp made from tie plates and ribband bolts(Figure 17-27, page 228).

227

FM 5-277

EXPEDIENT ASSEMBLY(NONSTANDARD TRUSSES)

Expedient assembly of trusses and bracingcan also be built for nonstandard trussarrangements.

TrussesExpedient panel cribs can be built with panelstransverse to the bridge axis, as in Figure17-28. This type of construction is usefulwhen the pier is skewed or when the pierfoundations are restricted. Two panels pinnedend to end give a 20-foot (6.2 centimeters) pierwidth. In Figure 17--28 trusses are bracedtogether by bracing frames in every possibleposition, Bracing frames are overlapped ateach end and 5-inch- (12.7 centimeters) longbolts replace standard bracing bolts. Inlighter one-story piers, the two panels areconnected by tie plates.

The crib may be built in the form of twocellular columns, one under each side of thebridge, as in Figure 17-29 (page 230). Eachcolumn is made of four vertical panelsarranged in a square offset 45 degrees fromthe axis of the bridge. Weld chords of adjacentpanels to angles. Cap panels with improvisedcapsills, and lay timber cribbing acrosscapsills. The crib base is similarly con-structed. Tie the two columns together by tiereds welded between them.

BracingMore than one story of horizontal panels canbe used if more expedient vertical crossbracing is added. Figure 17-30 (page 231)shows sway braces in the vertical planebracing a double-story pier to carry lightloads. Bolt tie plates to one end of the sway

braces on an extension. Bolt lengthened sway to the underside of the top chord in thebraces diagonally between the lower bracing. opposite inner truss (Figure 17-31, page 231).frame hole in the end vertical of one truss andthe upper bracing frame hole of the end For heavier loads, channel sections weldedvertical on the opposite truss. As an alter- across each end of the crib give a more rigidnative, vertical sway braces can be used in cross brace (Figure 17-31).each story.

Pin the braces to the bottom chord of thesecond panel, bend them up, and weld them

228

FM 5-277

ASSEMBLY OF CRIB PIERUse the following sequence of procedureswhen building crib piers by manpower alone:

1 Lay out and accurately level pier foun-dation. Mark panel positions accurately.Position crib bearings where these areused.

2 Carry up panels for trusses on each side ofcrib and lay flat on base with female jawspointing to bearings. Lift up panels andpin to bearings.

3 Fasten transoms, rakers, bracing frames,and sway braces in the first story. Checkthat panels are vertical and square to thecenterline.

4 Construct a working platform of transomsand chess in the first story. Haul panelsup singly and lay them flat on the plat-form with the female jaws opposite thetop lugs of the first story. Lift each panelin turn and pin it into position.

5 Fasten transoms and bracing in thesecond story and again check that thecrib is vertical and square to thecenterline.

6 Repeat for the number of stories required.An improvised gin pole or davit may beused to lift panels and transoms to upperstones.

229

FM 5-277

230

FM 5-277

Use the following procedures when buildingpiers with mechanical equipment:

If site conditions permit, a truck-mountedcrane can be used to erect 20-foot- (6.2meters) high crib piers and the two lowerstories of high piers. Assemble bays onthe ground nearby, and lift the assemblyinto place by crane. For erecting higherpiers, use a long-boomed crane.

If pier construction is between existinghigh banks or piers, use cranes and high

lines with winches on banks or existingpiers to lift panels into place.

If the bridge without the pier will carrythe erection equipment, the pier can beconstructed from the bridge. Use a truckcrane or rope tackle to lower the panelover the side of the bridge into place onthe pier. When all panels in the pier are inplace, jack up the bridge over the pier toeliminate sag and allow placing of bridgeseating. This last step can be eliminatedby leaving the bridge on rollers at each

abutment until after the pier is completed.Rollers must be blocked up enough to keepthe bottom chord above the level of the topof the finished pier.

For a continuous-span bridge, the piercan be built by working from the end of acantilever span.

231

FM 5-277

LAUNCHING OF BRIDGEPlace rocking rollers on cribbing on top of thepiers before launching the bridge (Figure 17-32). Push the bridge out over these rollersuntil the entire bridge is over all the spans.Jack up the bridge, remove rollers andcribbing, and then jack down the bridge ontoits seatings on piers (Figure 17-33). A tem-porary working platform may have to bebuilt for operating the jacks (Figure 17-34,page 234). If the bridge is to have independentspans, disconnect the girders at each pier.

JACKING DOWN OFCONTINUOUS SPANS

Where the distance through which the bridgehas to be raised or lowered is more than a fewinches, jacking has to take place on morethan one pier at the same time. Since in thistype of construction the whole girder is con-tinuous, lifting through any distance pro-gressively increases the length of bridge liftedand, thereby, increases the weight to beraised. This soon exceeds the capabilities ofthe jacks that can be brought into use on onepier. Where these conditions apply, a se-quence of jacking on three piers at the sametime, as described below, is the easiestmethod. This consists of raising the bridgethrough a smaller distance on each of thepiers adjacent to the one on which the dis-tributing beams are being fitted.

232

FM 5-277

The ends of the bridge are first jacked up andlowered onto suitable cribbing slightly abovefinal level. Three complete jacking partiesare then required for the intermediate piers,working from the near bank and in thefollowing steps:

1 The first party, working on the first pier,lifts the bridge clear, removes the rollersand lowers the bridge onto the cribbing,the height of cribbing being the same asthat used at the end of the bridge.

2 The second party does the same on thesecond pier while the first party jacks upon the first pier, fits distributing beams,and lowers the bridge to the original level(level of top of cribbing).

3 The third party completes step 1 on thethird pier and the second party then fitsdistributing beams on the second pier.The first party then lowers the bridgeonto the bearings of the first pier.

4 The first party completes step 1 on thefourth pier, the third party then fits dis-tributing beams on the third pier, afterwhich the second party lowers the bridgeonto the bearings on the second pier.

233

FM 5-277

This sequence of steps is continued through-out the length of the bridge. By this means,the bridge is raised by a slightly smalleramount on the two piers adjacent to the oneon which the distributing beams are beingfitted. Strict control of the jacking parties isessential, however, to enable the distributingbeams to be fitted on the center pier.

In the case of long bridges, it may be expe-dient to begin jacking on the center pier andwork outwards toward the ends of the bridge.For this method, it is best to employ sixjacking parties, three working toward eachbank in the sequence of steps described above.

Where the distance through which the bridgehas to be lowered is such that it cannot beachieved in three stages, increase the numberof jacking parties.

234

FM 5-277

CHAPTER 18

S P E C I A L L A U N C H I N G M E T H O D S

Special launching methods are needed whena restricted site prevents normal roller layoutand launching by the standard skeleton launching-nose method. Space on either bank may berestricted in length or width by obstructionssuch as buildings, existing bridge girders,trees, and earthwork or by sloping banks andcanal dikes. Limited backspace or length ofassembly area on the near bank is the mostcommon restriction. Backspace is measuredfrom the near-bank rocking rollers to thelimiting obstruction. Far-bank conditions area less common restriction because standardlaunching tables allow progressive dis-mantling of all launching noses and thisrequires a minimum clear distance of only 12feet (3.7 meters) beyond the far-bank rollers.Several methods included in this chapter,however, reduce far-bank requirements evenmore by landing directly on bearings and byinverting the nose assembly to clear lowobstructions such as existing girders.

USE OF COUNTERWEIGHTSRestricted sites require the launching ofBailey bridges using fixed and movablecounterweights. These can be used withstandard launching-nose assembly for a sitewith limited backspace on the near bank.Several bridge bays are omitted duringlaunching. Counterbalance of the span ismaintained by placing a counterweight inthe last bridge bay equivalent to the missingbays.

These counterweights can also be used withlaunching-tail assembly for sites with far-bank limitations preventing use of launchingnose or far-bank rollers. Use counterweighttail instead of standard skeleton nose to keepbalance point behind near-bank rockingrollers during launching. Launch bridge withend posts mounted on leading end and land itdirectly on far-bank bearings.

Types of counterweightsAny available material of known weight,such as spare bridge parts, sandbags, orvehicles can be used as a fixed counterweight.Add this counterweight to the end bay of thebridge or tail just before final launching tothe far bank. When launching with a movablecounterweight, add it earlier in the bridgeassembly and roll it back onto successive endbays to counterbalance progressivelaunching stages. The two types of rollingcounterweights are vehicles and rolling plat-forms. Trucks, trailers, tanks, tractors, andbulldozers mounted on the bridge deck arepushed, or moved back under their own power,as assembly progresses. Vehicles can beloaded to weights shown in launching tablesor shifted slightly in position on the deck ofthe end bay to provide correct counterbalance.Backspace is often increased by requirementsfor ramps and space to maneuver and mountthe vehicle on the deck.

Figure 18-1 (page 236) shows two movableplatforms rolling on inverted plain rollers.

Add more counterweight in the form of sparebridge parts, sandbags, or any availablematerial of known weight. Platforms can beused singly or together with either a skeletonlaunching nose or launching tail. Specialdetails in assembly and launching are asfollows:

Four plain rollers are required for alllower platforms and for all upper plat-forms on single-single bridges. Upperplatforms on double-and triple-trussbridges require eight rollers. In triple-truss assembly, upper-platform rollersmust not bear on the outer trusses. Rollersneed not be fastened to the stringerframework.

Platforms are moved by block and tackleon both trusses.

Horizontal bracing frames on the topbridge chord are added after the bayshave passed under upper platform rollers.

Backspace and limitationsTable 18-1 (page 236) shows the backspacerequired to launch fixed-panel bridges by thestandard launching-nose method without theuse of counterweights. The center of gravityor balance point of the bridge is always keptat least 2 feet (61.1 centimeters) behind thenear-bank rocking rollers. Distances in thetable include 12 feet (3.73 meters) to add thelast bay of bridge or tail. All backspaces

235

FM 5-277

include 2 feet between the center of gravity ofthe bridge and near-bank rocking rollers and12 feet to build the last bay of the bridge ortail.

All counterweight methods increaselaunching weights. Maximum spanslaunched by these methods are thereforeshorter than those launched by the standardlaunching-nose method because of the re-sulting increase in combined stress in thelower chord over the launching rollers.

LAUNCHING NOSE ANDCOUNTERWEIGHT (ROLLING)

The length of launching nose, composition ofnose and bridge bays, and organization of

236

working parties are the same as in standard-launching method (Chapter 6). However, useof a counterweight instead of end bays ascounterbalance for cantilever launch to farbank requires several changes. On double-single assembly, use plain rollers in pairs(one under each truss) instead of singly as inthe standard method. All launching nosescan be moved forward from 12 to 17 feet, afterthe assembly of the first bridge bay, to allowmounting of rolling counterweight on deck. Ifmore space is needed, add temporary fixedcounterweight to the bridge or adjacent nosebay and launch nose further over gap.Assemble all bridge bays complete for finallaunch to far-bank rollers except for triple-single and double-double bridges, which are

double-single assembly in end bay. To speedassembly after landing on far bank, addremaining bridge bays, complete launch, andremove nose. Install far-bank end posts, jackdown, and install ramps. Move rolling counter-weight to far-bank end of bridge, install near-bank end posts, and jack down. Positionnear-bank ramps and remove counterweights.

FM 5-277

Table 18-2 gives assembly for all bridges thatcan be launched with an appreciable re-duction in backspace over the standardmethod using either fixed or rolling counter-weights of the amount shown. Data are basedon the following assumptions:

All counterweight is centered in end bayof bridge.

Minimum backspace for any bridge isthat required to assemble the launchingnose and first bay of bridge withoutcounterweight.

Length of bridge for launching withrolling counterweight of amount shownin Table 18-2 requires about the samebackspace as required to assemble noseand first bay.

All bridge bays are decked and completeat critical launching stage except thatend bays of triple-single and double-double bridges are double-single con-struction. Bridges are launched withoutfootwalks.

Fixed counterweight is added to end bayfor final launching only.

Rolling counterweight is added on firstbridge bays and rolled back onto suc-cessive end bays.

237

FM 5-277

LAUNCHING TAIL ANDCOUNTERWEIGHT (FIXED)

The launching-tail method differs from thestandard nose and counterweight method inseveral ways. The tail is of exactly the sameassembly as bridge bays (Figure 18-2). Allbridges are launched without deck andstringers, except the end bay of the tail whenusing fixed counterweight. End postsmounted on leading end of the bridge andlanding directly on bearings eliminate rollersand jacking down on far bank. The length ofbridge required is 2 feet 6 inches (76.4centimeters) longer than launching span orgap, instead of 5 feet (1.5 meters) as for thelaunching-nose method (Figure 18-2). Sincethere is no nose into which launching linkscan be inserted, allow for sag made bydifference in elevation between near-bankrocking rollers and far-bank bearings, unlesssite conditions allow cantilever end of amanually launched bridge to be raised bybearing down on tail at end posts nearbearings.

Table 18-3 gives necessary data for launchingwith tail and counterweight. Tails shown areof minimum allowable length to maintainchord stresses over rocking rollers withinallowable limits. Where the site permits theuse of longer tails, corresponding lightercounterweights can be calculated by takingmoments about the near-bank rocking rollers.When using rolling counterweight (upperplatform, Figure 18-1), values shown in thetable must be increased 1.5 tons (1.4 metrictons) in place of end-bay deck and stringers.

Data in Table 18-3 are based on the following Counterweight is 5 feet from end of bridge.assumptions:

Sags are approximate (add 6 inches forThe bridge is launched without footwalks, end-post projection).deck, and stringers, but with far-bank endposts. Two bays of the second story are omitted

at leading end of bridge.Tail construction is same as bridge.

238

FM 5-277

Five bays of the second story are omitted INVERTED LAUNCHING NOSEat leading end of bridge. Far-bank sites with low obstructions and

limited clearance widths, such as low side-walls or existing girders on narrow piers,which interfere with launching-nose tran-soms, can often be cleared with invertedlaunching noses. Assembly is the same as instandard launching tables except that nosepanels are inverted and transoms, rakers,and sway braces are in the upper instead ofthe lower chord. Vertical clearance beneath

transoms is increased 3 feet 6 inches (1.1meters). Launching links are placed in thelower chord as in the standard nose.

LAUNCHING PLATFORMSWhen a launching site is sharply sloped,launching platforms may be built as follows:

In launching from sloping banks or overcanal dikes (Figure 18-3, page 240), rollerscan be supported on panel crib piers(Chapter 17) to provide a level launchingsite.

Panel bridges can be assembled in placeor launched without nose or tail overcontinuous timber or panel falsework orcribs 25 feet (7.6 meters) on centers acrossthe gap. With rollers spaced 25 feet (7.6meters) apart, sag requires jacking ofleading end as it reaches roller position.For a double-single bridge, the sag of theleading end will be 2 to 3 inches (5.1 to 7.6centimeters) with a 25-foot (7.6 meters)overhang.

END-ON ASSEMBLYEnd-on assembly of a panel bridge is thesuccessive addition of bays on the cantileverend over the gap. Use no rollers. Support thebridge during assembly on a packing oftimber and transoms under the bottom chord.Provide counterbalance either by the simul-taneous addition of tail of the same lengthand assembly as the bridge or by a shortertail and heavy counterweight. Position panelswith improvised davits and rope tackle orcranes.

239

FM 5-277

240

FM 5-277

This method can be used on all types ofrestricted sites, being particularly adapted tobuilding from the top of canal dikes. Usingthe short tail and counterweight, it requiresthe least backspace of any launching method.

Forward packing at the edge of the gap mustdistribute the weight of the bridge over atleast 3 feet (91.4 centimeters) of the bottomchord to prevent buckling. Rear packingsupporting the tail must be low enough togive sufficient initial slope to counteract sagand bring the end posts over the far-bankbearings.

A timber 8 inches by 8 inches by 20 feet (20.4centimeters by 20.4 centimeters by 6.1 meters)and a four-way block and tackle with ¾-inch(1.9 centimeters) diameter rope can be used asan improvised davit. Braced at a 45-degreeangle (in double-story and triple-story as-sembly, against a transom at the lower end)so the upper end of the timber extends about 5feet (1.5 meters) above and beyond the end ofthe trusses, each new panel can be accuratelyplaced with the block and tackle suspendedfrom the upper end of the timber.

Tail and counterweight are kept to a mini-mum by installing only such decking on thecantilever over the gap as required to operatethe davits.

SWINGING ACROSS CANALSPanel bridges can be swung across dikedcanals by assembling complete withlaunching nose or tail on top and parallel to

the near-shore dike, and pivoting the bridgeabout its balance point on improvised piperollers.

LAUNCHING WITHOUT ROLLERSSingle-single bridges up to 40 feet (12.2meters) long can be launched by soldierswithout rollers by skidding on greased beams.Place greased timbers or greased stringers atthe edge of the gap and 20 feet (6.1 meters)back under each line of trusses. Assemble thebridge on the skids with one transom per bayand no stringers or chess. Add three bays oftail with two transoms per bay and stringersin the last bay as a counterweight. Then pushthe bridge out over the gap with the aid ofpinchbars and levers. Soldiers on the farbank lift the front end onto blocking. Removethe tail, add end posts, and jack down thebridge onto bearings. Complete the bridge byadding a second transom in each bay andlaying decking and ramps. If end posts andbearings are not available, support the endsof the bridge as described in Chapter 22.

LAUNCHING BY FLOTATIONThere are several advantages of launchingby flotation. With this method a large as-sembly site is not needed and it can be awayfrom the centerline of the bridge. Also, alaunching nose or cantilever tail is notneeded.

The disadvantages of launching by flotationare that the gap must be water-filled withsufficient unobstructed depth to float a loadedponton. In a stream current over 3 feet (91.4centimeters) per second, it is hard to maneu-

ver the rafts. This method also takes longerthan normal launching procedures.

Multiple spansFor launching intermediate spans by flo-tation, use pontons of suitable capacity undereach end of the span to float it into position.Place cribbing on pontons to raise the bridgeso the lower chord clears the top of the piers.Make sure the bridge overhangs pontons ateach end; this provides clearance for ma-neuvering between piers when floating thespan into position. Normally, launch thespan on ponton rafts just downstream fromthe bridge site. The launching sequence for atypical 90-foot triple-single span on pontons(Figure 18-4, page 242) is as follows:

1 Assemble far-shore raft with two pontonsand enough cribbing to keep end of bridgeabove pier. Assemble bridge on rollers onshore. Place launching rollers slightlyhigher than cribbing on raft.

2 Push bridge on rollers until it rests onfar-shore raft with enough overhang toensure clearance between raft and pierwhen span is in position over pier. Con-tinue to push bridge and far-shore raftuntil end of bridge is near rocking rollers.

3 Assemble near-shore raft with four pon-tons and cribbing. Pump water into near-shore raft until it can be floated undershore end of bridge. If near-shore raftcannot be brought close inshore, placerocking rollers on cribbing on near-shoreraft.

241

FM 5-277

4 When raft is in position under bridge,pump water out until lower chord of spanis supported by cribbing or rocking rollers(whichever is used) on raft. Continuepumping until span is raised clear oflaunching rollers on shore. If rockingrollers are used on raft cribbing, roll spaninto position and insert picket throughlower chord of span and rocking roller tohold span in position.

5 Maneuver raft into position between piers.

6 Pump water into pontons until span issupported on piers. Remove rafts.

Note: Instead of pumping water into andout of the pontons to raise and lower thebridge, use jacks on top of each raft. Toraise the bridge, jack it up and insert morecribbing. To lower the bridge, jack it up,remove cribbing, and jack the bridge down.

For a shore span with assembly on and offcenterline, the launching sequences are asfollows:

For assembly on centerline, launch theshore span from rollers on the abutmentalong the bridge centerline. Place thefront of the bridge on a raft and float outto seating on bent. Then jack up tail end,remove rollers, and jack bridge down onbearings. If end posts are not used andend panels of adjacent spans are con-nected by panel pins over the bent,cribbing may raise shore end of span toohigh and only top panel pins can be

242

FM 5-277

inserted. Then remove top pins and jackdown shore span to bearings on abutment.

For assembly off centerline, assembleand launch the shore span in the samemanner as the intermediate span, floatingit into position between the abutment andfirst pier.

Single spansFor single spans launched by flotation withthe assembly either on or off centerline, thelaunching sequences are as follows:

For assembly on centerline, float frontend of bridge on raft across gap as bays ofbridge are added at tail which is on rollerson near shore. Use enough cribbing onraft to keep front end of bridge above far-bank abutment. Launching links and ashort upturned nose ahead of raft can beused to raise the end high enough to clearthe far-bank abutment.

For assembly off centerline, assemblespan off centerline of bridge and launchon rafts. Float span into position betweenabutments and lower into place. Cribbingon rafts must keep bridge above abut-ments and overhang must be enough toprevent grounding of rafts.

243

FM 5-277

CHAPTER 19

L A U N C H I N G B Y S I N G L E G I R D E R S

It may be advisable to launch a panel bridgeone girder at a time. This method is advan-tageous when launching from an existingbridge where piers are wide enough to takethe ends of a new span, but the existingbridge is not wide enough to launch the newspan complete. Such launching is recom-mended when there is—

An existing through-type panel bridge(Figure 19-1).

An existing through-type civilian bridgewhere the width between side walls ortrusses is less than 20 feet 8 ½ inches (6.32meters) (Figure 19-2).

An existing deck-type bridge where widthof deck is less than 20 feet 8 ½ inches (6.32meters) (Figure 19-2).

A launching of span of panel bridge to a to intermediate landing bay of a floatingpoint much lower or of varying height, as bridge in tidal water (Figure 19-3).

244

FM 5-277

TYPES OF GIRDERSA single girder may be made up of a singletruss or of two or more trusses connected bybracing frames and tie plates. Five trussesare the maximum number that can be han-dled practicably. Figure 19-4 (page 246) showsgirders with various combinations of two tofive trusses. Single, double-, and triple-trussgirders are used for through-type panelbridges. Any of the girders may be used for adeck-type panel bridge.

To save launching time, the wider girders arepreferred to many narrow bridges. Four- andfive-truss girders usually are used for mul-tilane deck-type bridges.

Assembly sequenceThe assembly sequence for launching bysingle girders is as follows:

1 Assemble girder on deck of existingbridges and then launch over gap.

2 Lower or slide it into position and thenlaunch next girder.

3 To complete the bridge, add standardsway braces, transoms, stringers, anddecking, or expedient bracing andflooring.

Methods of launchingSingle-truss girders may be launched withgin poles or high line. Multitruss girders maybe launched by any one of the followingmethods:

Counterweight.

Launching nose.

Gin pole and snubbing tackle.

High line.

Working partiesThe size of working parties varies with size ofgirder. To assemble girders, divide soldiersinto panel parties, pin parties, and bracingparties. Combine them to launch the girders.After the girders are in place, divide thesoldiers into bracing and decking parties tocomplete the bridge.

LimitationsThere are limitations of this kind oflaunching. Launching by single girders takeslonger than the normal method of launchingpanel bridges.

A girder is always launched as a single-storygirder; other trusses or stones are added afterthe girder has been launched. Bracing framesbetween trusses prevent overturning and givethe girder rigidity. (However, when launchinglong girders in the wind with counterweightor launching nose, the end is subject toconsiderable whipping.) And plain rollersmust be placed under every truss to supportthe girder evenly and prevent twisting.

LAYOUT OF ROLLERSPlain rollers are used in sets under the girder,so each truss rests on a roller. In some cases,plain rollers must be staggered to preventinterference between rollers. Figure 19-4shows the arrangement of plain rollers insets under the girder.

Rocking rollers cannot be staggered. Whentrusses are spaced 1 foot 6 inches (5.3 centi-meters) on center, rocking rollers are placedunder every truss. The two outer trusses arespaced 8½ inches (21.6 centimeters) on centersby tie plates and a single rocking roller isplaced under the inner of the two trusses(Figure 19-5, page 247). Remove the outerguide roller. Wedge shims between tie plateand chord-channel flanges to prevent outsidetruss from slipping down. Under the four-truss (2-foot 21½-inch) (67.4 centimeter) girder,the rocking rollers are placed under the outertrusses (Figure 19-6, page 247).

245

FM 5-277

2 4 6

FM 5-277

The procedure for laying out sets is—

Use rocking rollers at the edge of the gapand place plain rollers at about 25-foot(7.6-meter) intervals back along the girder(Figure 19-7, page 248). With double-trussgirders, plain rollers can be used insteadof rocking rollers at the edge of the gap.

When using a counterweight (Figure 19-8,page 249) or launching nose (Figure 19-9,page 250), assemble and launch the girderon the side of the existing bridge nearestits final position. Assemble a secondgirder simultaneously at the other side ofthe deck of the existing bridge. Lay outrollers accordingly.

When using a gin pole and snubbingtackle, two gin poles, or a high line, layout the rollers so as to assemble andlaunch the girder along the centerline ofthe bridge.

When launching from an existing panelbridge, place all plain rollers directly overtransoms to avoid overstressing stringers(Figure 19-7). Set rocking rollers pre-ferably on cribbing directly on the pier. Ifit is necessary to place the rocking rollerson the deck of the existing panel bridge,place them directly over the end transom.If the total launching weight on rocking

rollers is more than 14 tons (12.7 metrictons), use two transoms under the rollers;if the launching weight is more than 28tons (25.5 metric tons), wedge the cribbingunder the center of the end transoms.

ASSEMBLY OF GIRDERSThe girder may have from two to five trusses(Figure 13-10).

Connect trusses of multitruss girders at everypossible place by bracing frames and tieplates across the top chords and ends ofpanels. All tie-plate bolts must be tight andshims must be used to prevent the outer trussfrom slipping down when the end of thegirder is over the gap (Figure 19-5). In girderswith outer trusses spaced 8 ½ inches (21.6centimeters), insert panel pins connectingthe nose to the main girder from the inside sothe nose can be disconnected after launching.In both the main girder and the nose, alwaysinsert the pins from the outside toward thecenterline of the girder.

Place end posts on the front end of all trussesbefore launching, except when using alaunching nose, in which case place the frontend posts after the girder has been launched.Place the rear-end posts when the girder is inposition for jacking down. Table 19-1 (page250) lists the parts required to assemble eachtype of girder.

247

FM 5-277

2 4 8

FM 5-277

249

FM 5-277

LAUNCHING OF GIRDERSThere are several methods of launching bysingle girders. These are the counterweight,launching-nose, gin-pole and snubbing-tackle, direct-lift, and high-line methods.

Counterweight methodLaunch a single girder by counterweight asfollows:

Add the counterweight to the rear end ofthe girder to balance the front end of thegirder as it is pushed on rollers out overthe gap. Long girders may be kept in lineby using side guys and a pull winch fromthe far pier. When across the gap, thefront end lands on rollers at the far bankor pier, or on landing-bay pier of a floatingbridge. Then disconnect the counter-weight, attach the rear end posts, removethe rollers at each end, and jack down thegirder onto a skidding beam.

Girders may be counterweighted eitherby adding weights to the last bay of ashort tail on the girder or by making thegirder of the same assembly and twice aslong as the span so the tail alone willcounterbalance the span. Table 19-2 listsweights needed on short tails to counter-weight various spans of multitrussgirders. (Longer spans cannot belaunched by this method because of insuf-ficient lateral stability.) If the long tail isused, it may be disconnected after thefirst girder is launched, and used for asecond girder.

The counterweight method is useful whensite conditions at the far side prevent use,removal, or disposal of a launching nose, orerection of a gin pole or high line. Whenlaunching long girders of a deck-type bridge,a counterweight permits tipping the far enddirectly onto the pier without jacking down.

Launching-nose methodLaunch a single girder by the launching-nosemethod as follows:

Attach a lightweight launching nose tothe front end of the girder, and push thegirder with nose on rollers out over thegap. To compensate for sag, launching-nose links may be used in the samemanner as when launching the normal

panel bridge. Long girders may be kept inline by using side guys and a pull winch.When across the gap, the nose lands onrollers on the far bank. Then disconnectnose, attach front end posts, removerollers at each end, and jack down thegirder onto skidding beams.

Table 19-3 (page 253) lists the types andlengths of noses needed to launch multi—truss girders. Single-truss girders cannotbe launched by this method. Bracelaunching noses the same as the girder.When launching the triple-truss girderwith an eccentric double-truss nose, thenose must be dismantled bay by bay as itpasses over the landing rollers. Otherwise,the nose beyond the landing rollers twiststhe girder, and may cause failure.

250

FM 5-277

The launching-nose method is used forlonger girders, where sag is appreciable.It can also be used for girders too heavyfor a gin pole or high line. Launching bythis method is easier than with a counter-weight, because the girder with nose islighter than the girder with counter-weight.

Gin-pole and snubbing-tackle methodLaunch a single girder by the gin-pole andsnubbing-tackle method (Figure 19-10, page252) as follows:

Erect a gin pole at the far bank or pier. Rigtackle from the gin pole to the front end ofthe girder with the fall line running to thewinch of a truck on the bridge or bank.When a truck-mounted crane or tractor isused at the tail of the girder, lead the fallline around it by a snatch block at the sideof the bridge. For long, heavy girders,attach guy lines near the center of the

girder on each side and control by wincheson trucks to each side of bridge. Thegirder rides on rollers on the near bank.Brake it by snubbing tackle attached tothe rear end of the girder to keep it uprightand to lift it onto the bearings. Powerapplied to the hauling winch pulls thegirder across the gap. Move a truck-mounted crane forward with the girder,keeping the snubbing line taut to preventtoo rapid movement. When the girder haspassed its balance point, let it dip aboutone-tenth of its length to lessen stress in

251

FM 5-277

the tackle. After the girder is across thegap, the gin pole and truck-mounted cranelift it directly onto the bearings.

When a truck-mounted crane is not avail-able, two gin poles may be used, one oneach bank. Attach both gin-pole lines tothe front end of the girder, which is pulledover the gap by taking up on the far gin-pole line and slacking off on the near gin-pole line. When the front end of the girderis over the far bank, change the line fromthe near gin pole from the front to the rearof the girder. Then lower the girder ontoits bearings.

This method is better for short spans,since long girders are heavy and difficultto handle. It also saves bridge equipment,because it eliminates the need for either alaunching nose or counterweight. Inaddition to handling girders, the gin poleand truck-mounted crane can be used totelegraph transoms and decking intoplace.

Direct-lift methodLaunch a single girder by the direct-liftmethod as follows:

Assemble the girder on ground beside thepiers. Use two cranes or gin poles to liftthe girder into place on the piers. In caseof a water gap, the girder may be floatedout to the piers and lifted into place bycranes on rafts or on the piers. Cranes are

not needed if the piers are low enough so The length of girder that can be launchedthe girder can be floated into place and by this method is limited by the capacitylowered onto the piers by pumping water of the cranes. If the girders are short andinto the raft pontons. light, a single crane can be used.

262

FM 5-277

2 5 3

5 - 2 7 7

High-line methodLaunch a single girder by the high-linemethod (Figure 19-11) as follows:

Rig a high line of suitable capacity acrossthe gap along the centerline of the bridge.Suspend the girder from the high line,pull it over the gap, and lower it ontoskidding beams. Attach the trolleys onthe high line to slings on the girder nearthe quarter points. Roll the girder on theapproach span to its balance point on thefirst roller before it is carried by the highline. Use tag lines at both ends of thegirder to control it during launching.

This method is useful for launching deck-type bridges where the girder has to belowered a considerable distance to theskidding beams. In addition to handlingthe girders, the high line can be used tocarry out the transoms and decking, andwhere trestle-approach spans are used, itcan be used to carry out bridge parts forthe approach spans. This method alsoeliminates the need for either a launchingnose or counterweight. The capacity ofhigh lines is usually limited to shortsingle or double-truss girders. Table 19-4lists the weight, in tons, of various lengthsof girders.

JACKING DOWNJack down the girders either with a jackunder each end post or with jacks under anequalizing beam supporting the underside ofthe girder (Figure 19-12). Work the jacks inunison so the girder is lowered evenly. Duringthe lowering, guy the girders to prevent

254

FM 5-277

overturning. To lower the girder in its finalstage, place equalizer beam under top chordas in Figure 16-18. Place cribbing under thebottom chords or equalizer beam to preventthe girder from dropping if it slips off thejacks. If the distance to be lowered is great,lower the girder by successive stages. Whentruck-mounted cranes or gin poles are avail-able at each end of the bridge, lower thegirders directly on the bearings.

SKIDDING AND SQUARING UP After the first girder is lined up with theAfter launching, move the girder into position existing bridge, square up the second girderby truck cranes, or skid it into position on with the first. If the trusses cannot be movedgreased skidding beams by prying with panel in a longitudinal direction without rollers,levers or pinchbars (Figure 19-13). Panel- reinsert rollers after skidding.bridge stringers are preferred for skiddingbeams, but I-beams or timber beams may beused.

255

FM 5-277

COMPLETION OF BRIDGEFor normal through-type assembly, completethe bridge bay by bay, working out from thenear shore as follows:

1 Insert sway braces of first bay withadjusting collars on the same side ofbridge. Use two lashings from centers ofbottom brace to hold center of sway bracesup until ends are pinned in place. Do nottighten.

2 Place transoms in first bay. A truck-mounted crane with gin pole on far bankmay be used to telegraph transoms intoplace, or they may be placed by hand. Inthe telegraph method, attach to the tran-som both a line from the gin pole on thefar bank and a line from the crane on thenear bank. Then pick up the transom andplace it by taking up the gin-pole line andslacking off on the crane line. Use a tagline on the transom to guide it. Whenhandling it manually, push the transomout from the bank and swing it intoposition with the aid of ropes attached tothe top chords. The transoms are difficult

to fit at first, but this becomes easier asmore bays are completed.

3 Place stringers in first bay.

4 Remove vertical bracing frames and in-sert rakers. Do not tighten.

5 Repeat above procedure to install swaybraces, transoms, stringers, and rakers insecond bay.

6 After bracing members are inserted insecond bay, tighten all bracing in firstbay and lay chess and ribbands in firstbay.

7 Add remainder of decking in the samemanner.

8 Install ramps.

Deck-type bridges take either standard panel-bridge decking or expedient timber decking.For details of deck-type bridges, see Chapters12 and 13.

256

FM 5-277

CHAPTER 20

BRIDGES ON BARGES

The panel bridge on barges consists of astandard panel bridge supported on floatingpiers made from river or coastal barges ofsuitable type and capacity. Special spans orparts are used to provide hinged jointsbetween floating bays (Figure 20-1).

PIERSPiers consist of barges or vessels suitablyprepared to support the panel-bridge super-structure. The several kinds of piers are—

Floating-bay piers, which support thefloating bays in the interior of the bridge.

Landing-bay piers, which support theshore end of the floating bay and theriverward end of either the fixed-slopelanding bay or the variable-slope landingbay.

Intermediate landing-bay piers, whichsupport the shore end of the fixed-slopelanding bay and the riverward end of thevariable-slope landing bay. The inter-mediate landing-bay pier is not usedwithout the fixed-slope landing bay.

257

FM 5-277

BAYSThe span between two articulating pointssupported by two floating piers or betweenthe shore and a floating pier is called a bay(Figure 20-2). The several-kinds of bays are-

Floating bays, which are the interior ofthe bridge from the end floating bay onthe near shore to the end floating bay onthe far shore. They are supported neareach end by floating-bay piers.

End-floating bays, which form the con-tinuation of the bridge between thefloating bays and the landing bays. Theyare supported by a landing-bay pier and afloating-bay pier.

Landing bays, which form the connectionbetween the end floating bay and thebank. There are two types of landingbays: the variable-slope landing bay,which spans the gap between the bank-seat and the landing-bay pier (or theintermediate landing-bay pier if a fixedslope landing bay is used); and the fixed-slope landing bay, which, spans the gapbetween, the intermediate landing-baypier and the landing-bay pier.

SPECIAL SPANSSpecial spans include connecting spans, liftspans; and draw spans. Connecting spansconnect two adjacent floating bays wherebarges are grounded. They each provide twoarticulating points to compensate for the

changes in slope between the floating bays.Lift spans (Figure 20-3) connect two adjacentfloating bays. They can be lifted vertically byuse of block and tackle or chain hoists toallow passage of water traffic through thebridge. Draw spans provide a wider gapbetween adjacent floating bays for passageof river traffic. They can be split in the middleand each half pivoted up.

DESIGN ANDCAPACITIES OF BARGES

Coastal and river barges differ widely inconstruction and capacity throughout theworld. In Europe and the Americas, bargesare generally flatbottomed. Barges withround or semiround keels are also found onEuropean canals and rivers (Figure 20-4).

258

FM 5-277

Asiatic barges have less capacity thanEuropean or American barges. Generally,European and American barges have acapacity of from 80 to 600 tons (73 to 546metric tons). The general condition of thebarge has a direct effect on its use in a bridge.

RibsStructural ribs of barges are designed forbending stresses induced by water pressureon the outside of the hull. They are normallybulb-angled steel sections 5½ to 7 inches (14to 17.8 centimeters) deep, closely spaced, andcurved rather than straight. Ribs should notbe loaded as struts unless they are braced andload is distributed. To distribute the load,timber cribbing can be used along the gun-wale directly over the ribs. If the rib is notcurved and the length of rib from deck to keeldoes not exceed 10 feet (3.1 meters), each rib

will support approximately 5 tons (4.6 metrictons).

DecksBarge decks are designed for distributedloads. A wide variation of deck design existsand care must be taken in estimating theircapacity. European flat-bottomed bargesnormally use transverse beams of Z section, 6to 7 inches (15.3 to 17.8 centimeters) deep,carrying light channels or I-beams fore andaft to support a timber deck. A deck of thistype can carry a bearing pressure of 0.5 ton(.45 metric ton) per square foot.

DESIGN OF SUPERSTRUCTUREThe superstructure of a bridge on barges maybe assembled either by normal or by specialmeans. Superstructures of normal bays con-sist of double-single, triple-single, double-

double, or triple-double assembly of standardpanel-bridge equipment. Normally, afloating-bay superstructure is a single-storyassembly and a landing-bay superstructureis a double-story assembly.

Decking for a superstructure of normal baysconsists of standard chess with 3-inch (7.6centimeters) wear treads laid diagonally overthe chess. Add angle irons to deck on landingbay to increase traction. When connectingposts are used to connect floating bays,transoms and junction chess cannot be usedto fill gap between bays. Place cut stringerson the two transoms at the end of each bay,and place two thicknesses of 3- by 12-inch (7.6by 30.5 centimeters) planks spiked togetheron top of the cut stringers (Figure 20-5, page260). Wire planks in place to prevent shifting.When span junction posts are used to connectbays, fill gap between bays in normal manner,using transoms and junction chess. Wheremaximum road width is desired, ribbandscan be eliminated by a 2- by 24-inch (5.1 by61.1 centimeters) hub guard installed 6 inches(15.2 centimeters) above deck to protectpanels.

Use special connecting posts to connect baysand provide articulation (Figure 20-6, page260). These special connecting posts provideample strength and allow development of fullcapacity of superstructure. Equal articulationabove and below connecting pin providesunrestricted space for movement in theconnection. Such connectors do not requirerestrictive linkages, guides, or maintenance.Combination special connecting posts can be

259

FM 5-277

used in place of normal posts and also toconnect two male or two female ends ofpanels.

Use special spans when barges are groundedor when passage of water traffic through thebridge is necessary. The capacities of thespecial spans are the same as the normalspans. However, their full capacity cannot bedeveloped unless the suspending connectionat each end is made strong enough. In addi-tion, the weight of the lift span and drawspan is limited by the lifting power andstrength of the hoists, thus affecting the typeof construction that can be used in these

260

FM 5-277

spans. The three types of special spans usedare connecting spans, lift spans, and drawspans. They are used as follows:

Use the connecting span when barges aregrounded or when special connectingposts are not used. It is a short span ofsingle-single or double-single assemblysuspended between two floating bays byspan junction posts (Figure 20-7).

Use the lift span only in short bridgeswhere current is slow and there are nolongitudinal forces in the bridge. Whencurrent is swift, pier heights can beincreased to arch the bridge enough topass water traffic under one of the centerspans without use of a lift span. The liftspan is single-single or double-single

assembly 20 or 30 feet (6.1 or 9.4 meters)long. It is raised horizontally by blockand tackle attached to span and to paneltowers in adjacent bays.

Use and restrictions of the draw span arethe same as for the lift span. The drawspan is a single-single or double-singleassembly, usually 20 feet (6.1 meters) long(Figure 20-8, page 262). Hinge and sus-pend it to adjacent bays by span junctionposts. Raise it at one end by block andtackle attached to span and a panel towerin one of the adjacent bays. If resultinggap is insufficient, use span of 40 feet(12.2 meters) and make cut at center ofspan. Then use towers with block andtackle at both ends and lift each halfseparately.

DESIGN OF BAYSThe barges and the superstructure togetherform sections called bays. These are designedas either floating or landing bays.

Floating bays are normally double-singleassembly. However, for loads of 100 tons (9.1metric tons) or more, unsupported spanlengths are limited to 60 feet (18.3 meters) andassembly must be triple-single. The class islimited by type of assembly, by the spanbetween centers of barges, and by the methodused to support the superstructure on thebarges. The class of floating bays is given inTable 20-1 (page 263). Normally, a barge neareach end of a bay supports the superstructure.The superstructure must not overhang thebarge at each end more than 15 feet (4.6

meters) from the centerline of the barge.However, a single barge can be used if it hasample width and capacity and the bay isstable under the load.

The type of assembly used in landing baysdepends on length of span and on loads to becarried. A triple-double assembly is theheaviest type used. Maximum slope of thebay is 1 to 10 with adequate traction devicesprovided; without traction devices, slope is 1to 21. Length of landing bay depends onconditions near shore. Use double landingbays where considerable change in waterlevel is expected or when high banks areencountered. Assemble landing bays thesame as normal panel bridges and use thesame type of end support.

ADVANTAGES ANDDISADVANTAGES

The panel bridge on barges has the followingadvantages:

It does not use standard floats andpontons which may be needed at othersites.

It allows long landing floating bays foruse in tidal estuaries or rivers with highbanks.

It has large capacity barges which allowgreater bridge capacity than standardmilitary floating supports.

It provides a stable bridge in swift cur-rents.

261

FM 5-277

It minimizes hazards of floating debrisand ice.

The bridge has the following disadvantages:

It uses barges which may be hard toobtain.

It can be used only in navigable streamsor waterways used by barges or vessels ofthe type and size necessary for use in thepiers.

It is not adaptable in combat areasbecause of equipment, material, labor,and time requirements.

262

FM 5-277

BARGE EQUIPMENT After determining the type of barge loading.Barges must be processed and their required prepare a material estimate and an an equip-equipment determined. Procure barges locally

. .ment requirement list for each barge. Nor-

and then examine and rate them for capacity; mally, steel beams, timber, blocking, wiredetermine the best point for use in the bridge; rope, and miscellaneous bolts and fittings areestablish the type of barge loading (described needed. See Chapter 17 for equipment re-later in this chapter) to be used; and sketch quired if panel crib piers are used as supportsthe construction needed to bring the bearings on the barges.to exactly the elevation established for super-structure bearings.

PARTS FOR SUPERSTRUCTURENormal spans use fixed-span panel-bridgeparts (Chapter 1). Connections between spansare made with special connecting posts thatmust be fabricated in the field (Figure 20-6) orby connecting spans using span junctionposts supplied in the panel crib pier set(Chapter 17).

Special fittings to guide both the lift span andthe draw span during raising and loweringmust be made in the field. Block and tacklerequired are supplied in the freed-panel bridgeset. Counterweights to aid in raising andlowering the span can be improvised. The liftspan or the draw span, and the floating bays,are connected by span junction posts fromthe panel crib pier set.

The normal erection equipment supplied inthe fixed-panel bridge set is sufficient toassemble the superstructure. Truck cranesaid the erection of the superstructure and thepreparation of the barges. Acetylene torches,arc welders, chain falls, power and handwinches, diving equipment, and sea mules orpower tugs with enough power to movefloating bays into position should be avail-able at the site.

SITE SELECTIONTactical requirements determine the generalarea within which a site must be selected. Thefollowing factors should be carefully con-sidered in choosing the site:

There should be a road net close to the siteover which equipment can be moved.

263

FM 5-277

Roads and approaches should require aslittle preparation and construction aspossible and should be straight and levelfor at least 150 feet (45.7 meters) beforereaching the stream bank.

Near-shore area should afford suitablesites along the shore for barge preparationand bay assembly.

Banks should be reasonably steep andfirm so that water gap will not changematerially with water level. Banks highenough to allow launching of superstruc-ture to barge piers are desirable.

The site should be on a straight reach ofthe stream or estuary and free from crosscurrents that would exert a longitudinalforce on the bridge. Water at bridge siteshould be deep enough to float barges atlow water if no barges are to be grounded.Water at assembly sites should be deepenough to allow preparation of bargesclose to shore and launching of super-structure directly to barges. If barges canbe grounded at low water, the streambottom should be reasonably smooth andlevel. The stream should be free ofobstruction at the assembly sites andbridge site.

SITE RECONNAISSANCEAfter the general area has been determined,make a study of aerial and terrain maps todetermine possible bridge sites along thestream within the specified area.

Direct aerial reconnaissance generally givesthe following information on these bridgesites:

Site relation to existing road net, withestimate of road construction required.

Alignment of river at site and channelobstruction in the vicinity.

Approximate height of banks to decidesuitability for approaches and landingbays.

Approximate width, shore to shore, ofriver, and length of bridge required.

Location, relative to bridge site, ofmaterial storage, equipment, and workareas, and of barge site next to near shorefor floating-bay assembly.

Location of barges large enough to beexamined later in detail by ground recon-naissance.

Nature of open water route from barges tobridge site, noting and locating obstruc-tions to navigation.

Routes over existing road nets for trans-portation of bridge materials from dumpor other sources to bridge site.

Location of adjacent quarries and aggre-gate supplies.

Ground reconnaissance gives the followingdata:

Width of river from bank to bank.

Profile of approaches and streambed.

Character of soil in approaches, banks,and streambed.

Profiles of possible routes of approachand linking roads to existing road nets.

Current velocity.

High and low water data indicated onprofile and rate of flood and ebb of tide, ifpossible.

Sketch showing location and descriptionof suitable material storage and workareas, downstream assembly area withprofiles at possible shore barge prepara-tion sites, and floating-span erection sites.

Sketch of barges located in aerial recon-naissance.

Routing on open water from assemblysites to bridge site, with description andlocation of obstacles and estimate of worknecessary to clear passage.

Information on location, quality, andquantity of nearest aggregate source.

264

FM 5-277

SITE LAYOUT AND PREPARATIONBefore actual construction, alignment andgrade of roads and approaches must bedetermined. Plan and locate storage andassembly areas so as to ensure uninterruptedprogression of work and avoid unnecessaryhandling. After determining location andlayout of site, complete road work andapproaches to expedite delivery of bridgematerial. At the same time, prepare landing-bay and floating-bay assembly areas.

WORKING PARTIESTo build bridges of 500 feet (152.4 meters) ormore, assign an engineer combat or construc-tion group of three battalions, two panelbridge companies, one light equipmentcompany, and one harbor craft company. Forshorter bridges, reductions in personnel canbe made. Table 20-2 presents a suggestedbreakdown of tasks and troops required forconstructing an 810-foot (246.9 meters) class70 bridge in a moderate current. Approachroad construction will need five companydays.

An example of how to distribute work partiesis—

Assume bridge will consist of the followingbays, proceeding from near to far bank:

One 100-foot (30.4 meters) double-doublevariable-slope landing bay.

One 100-foot (30.4 meters) double-doublefixed-slope landing bay.

One 80-foot (24.4 meters) triple-singleend floating bay.

One 40-foot (12.2 meters) double-singledraw span.

Three 100-foot (30.4 meters) triple-singlefloating bays.

One 90-foot (27.4 meters) triple-singleend floating bay.

One 100-foot (30.4 meters) double-doublelanding bay.

Assume an engineer group of:3 battalions.2 panel bridge companies.1 light equipment company.1 harbor craft company.

One possible assignment of units to con-struct this bridge is as follows:

One battalion to construct:One 100-foot (30.4 meters) double-

double variable-slope landing bay.One 100-foot (30.4 meters) double-

double fixed-slope landing bay.One 80-foot (24.4 meters) triple-single

end floating bay.One 100-foot (30.4 meters) triple-single

floating bay.

One battalion to construct:One 100-foot (30.4 meters) double-

double landing bay.One 90-foot (27.4 meters) triple-single

end floating bay.0ne 40-foot (12.2 meters) double-single

draw span.Two 100-foot (30.4 meters) triple-single

floating bays.

One battalion to:Prepare approach roads.Unload equipment.Prepare anchorages.

Two panel bridge companies to:Haul bridge equipment.

One harbor craft company to:Assist in maneuvering barges and

bays.

One light equipment company to:Supply construction equipment with

operators.

Time required for completion is approxi-mately 6 days of daylight construction.

BARGE SELECTIONBefore starting to build the bridge, bargesmust be chosen and positioned with care. Inselecting barges, structural condition, capac-ity, shape, freeboard, type, and location ofbarge must all be considered. Examine andrate barges located on the reconnaissance.Barges which meet the requirements shouldbe assigned a position in the bridge. Working

265

FM 5-277

sketches and a plan of preparation for eachbarge are necessary to adapt it for use as afloating pier. Clear nonusable, easily un-loaded material from the selected barges tohelp towing to barge preparation sites.

METHODS OF LOADINGBarges are adapted for use as piers by threemethods. The method employed depends onthe type of barge, flat-bottomed or keeled, andgrounding conditions. The three methods ofloading are gunwale loading, crib loading,and grillage loading.

Gunwale loadingAs few barges are designed for gunwaleloading, determine the strength of the bargeribs before using this method. Barges arenormally built with a narrow deck runningfull length along each side of the hold. Thisdeck space can be used for gunwale loading ifthe ribs and the deck are strong enough andthe load is applied as nearly as possible overthe ribs. Gunwale loading must not be appliedto barges that will ground at low water unlessthe barge and the bay will remain level. Ifkeel-type barges are used, the site ofgrounding should be in soft mud. Flat-bottomed barges should ground on flat sandybed free from obstructions.

Use packing between the gunwale and thesuperstructure to distribute the load. Thedeck is normally cantilevered from the ribsand considerable load is placed on the ribswhen the deck is loaded. The deck willprobably have to be supported by struts fromthe barge floor to the edge of the deck or by

266

FM 5-277

packing the gunwales. The load on the gun-wale can also be reduced by using a rein-forcing bent built up from the floor in thecenter of the barge. Barges with curved ribsmust be braced by rods between the gunwalesor by struts from the reinforcing bent (Figures20-9 and 20-10). If ribs are not curved and thelength of rib from deck to keel does not exceed10 feet, reinforcing of ribs is unnecessary.

Crib loadingCribs made of panel-crib parts (Chapter 17)can be used to support the superstructure onthe barge if the barge is unsuitable for gun-wale loading or uneven grounding occurs

Barge floors are designed to carry distributedloads, and grillage must be used under thecribs to ensure adequate distribution of theload. Crib loading requires more time forconstruction than gunwale loading but cribloading distributes the load to the floor of thebarge, which is able to carry more load thanthe gunwales. Take special care to observethe behavior of cribs when the bridge is firstloaded and during tidal changes. Mark theposition of bearings so that movements canbe determined. If careful observations aremade, adjustments can be made in time toprevent serious movements and avoid thedifficulty of repositioning barges and cor-

recting misalignment of superstructurs. Se-cure anchorage of cribs prevents most of thisdifficulty.

There are two types of cribs: fixed, androcking. Fixed cribs are used in both flat-bottomed and keeled barges that do notground during low water. Use them also inkeeled barges that ground during low waterto prevent the barge from tipping. Connectfixed cribs rigidly to both the superstructureand the barge floor and guy both laterallyand longitudinally to the gunwale. Details ofassembly and methods of attaching the cribsto the superstructure and the barge floor aresimilar to those given in Chapter 17. Rockingcribs are used in flat-bottomed barges whenuneven grounding occurs. Details of assemblyand methods of making the rocking connec-tions are given in Chapter 17. Clearancebetween the crib and the gunwale must beenough to permit the full articulation re-quired. Determine the required clearance fromthe slope of the stream bottom where thegrounding occurs. Guy rocking cribs fore andaft on the centerline of the barge as an addedsafeguard against movement. An expedientrocking crib is shown in Figures 20-11 and20-12 (page 268). The crib is made to rock byremoving one of the panel pins in the cribbearing before the barge has grounded.

Grillage loadingUse grillage loading when the barge isunsuitable for gunwale loading and the panelcrib pier parts are unavailable. Build upgrillages from the floor of the barge with steelor timber beams (Figure 20-13). When using

267

FM 5-277

grillage loading, take care in bracing andtyping of grillage and in ensuring adequatedistribution of the load on the floor of thebarge.

PREPARATION OF PIERSBoth types of landing-bay pier are preparedin a similar manner (Figures 20-14 and 20-15). Since the intermediate landing-bay pieracts as a compensator in ramping, it alwayshas a higher elevation than the landing-baypier. Build up piers to the required elevationusing I-beams, bolted down or welded toprevent sliding. When special connectingposts are not used to connect landing bays,

268

FM 5-277

weld base plates to the piers, and standardbearings to the plates, to support end posts.

Floating-bay piers are prepared similar to thelanding-bay piers. Pair barges so those usedin any pier have about the same freeboard.When the barges in the floating-bay piershave different freeboards, crib up the super-structure seats to the elevation of the super-structure seat on the barge with the greatestfreeboard.

LANDING-BAY ASSEMBLYAND LAUNCHING

Use normal assembly methods given inChapter 6 for assembling landing bays. Longspans are normally launched undecked.

Where the piers can be moved close to thebank, launch landing bays over rollers on thebank to the pier. Use the skeleton tail method(Chapter 18) where bank conditions preventmoving barges in close.

Where double landing bays are required,launch them as a continuous span, sepa-rately, or by use of construction barges, asfollows:

Assemble the two bays as a continuousspan on the centerline of the bridgeabutment. Launch this span over rollersplaced on intermediate landing-bay pieronto cribbing on the landing-bay pier.Break the top chord over the intermediatepier by removing pins, and then jack theriver end into final position. Removebottom pins and pull back the variable-slope bay to permit installation of endfittings on the intermediate pier for bothbays. Place abutment fittings in usualmanner.

When launching separately, launch thefixed-slope bay as described earlier, butplace rollers on the intermediate pier

instead of on the bank. Then launch thevariable-slope bay.

The fixed-slope bay can be assembled offsite and launched to position on theintermediate floating-bay pier and aconstruction barge. Float the bay thusformed into position and connect to theend floating bay. Remove the constructionbarge. Then launch the variable-slopebay.

FLOATING-BAY ASSEMBLYAND LAUNCHING

Use methods given in Chapter 6 for assem-bling floating bays. Several methods oflaunching floating bays are as follows:

Where barges can be placed close to thebank, launch the span over rollers on thebank to the off-bank barge. Then push outbarge, permitting in-bank barge to be

269

FM 5-277

positioned, and jack down the span intoplace on the in-bank barge. A constructionbarge can be placed adjacent to shore touse jacks on. This should have a lowerfreeboard than other barges.

Where bank conditions permit, moor bothbarges side by side and launch the spanover rollers on the in-bank barge to aposition on the off-bank barge. Then jackdown the span into position on the in-bank barge.

When barges have wide beams, assemblesections of the bridge on each barge andthen join to form bays; for long bays,partly flood surplus barges and float fromunder the superstructure.

Cranes can place bridge equipment onbarges, where it can be assembled onrollers. Spread barges to obtain properbay length as superstructure is assembled.

CONNECTING BRIDGE SECTIONSBridge sections are linked by landing andfloating bays. Landing bays have eitherspecial connecting posts or standard endposts, as follows:

Special connecting posts are desirable forconnecting all bays. The articulationprovided is normally ample under allconditions. When both a fixed-slopelanding bay and variable-slope landingbay are required, the special connectingpost on the river end of the variable-slope landing bays have bearing blocks

welded to the bottom. The posts are seatedon bearings welded to base plates whichare welded to the intermediate landing-bay pier grillage.

Fix the shore end of the variable-slopelanding bay with standard end postsmounted on bearings welded to baseplates. The base plates rest on rollers setin an expedient box plate (Figure 20-16).This provides for lengthening and con-traction of the bridge during changes inwater level. The river and shore ends ofthe fixed-slope landing bay are suspendedby treadway pins in the special connectingpost.

Where special connecting posts are notavailable for connecting landing bays,the bays can be seated on standard endposts on bearings. Rest the end posts onadjacent ends of variable-slope and fixed-slope landing bays on bearings welded tobase plates mounted on the intermediatelanding-bay pier grillage. Seat the riverend of the fixed-slope landing bay onstandard end-post bearings resting onbase plates welded to the end floating-baypier. Mount the shore end of the variable-slope landing bay as described for specialconnection posts.

Details of floating bay connection are asfollows:

Connection of floating bays is made easierby carefully constructing each bay to thesame elevation. A ballast of water can be

loaded for adjusting freeboard of the bay.A vehicle on the bay to be connected canbe moved to aid in aligning connectingpinholes.

Considerable tug power is required tomove and handle bays into connectingposition. Use both towing and pushertugs to provide adequate control of thebays and prevent damage. Floating baysover 100 feet (30.5 meters) long are hard totow and control.

In connecting bays fitted with specialconnecting posts, it may be necessary tojack truss into place to get enough pin-hole alignment for treadway pin.

Carefully estimate maximum articulationand movement of junctions between baysduring grounding. Too much articulationwill cause undesirable changes of slope inthe decking and may cause tilting orlifting of stringers or chess. If such acondition develops at grounding, mini-mize junction articulation by use of aconnecting span between bays.

CONNECTING SPANSConnecting spans are normally 20 to 30 feet(6.1 to 9.1 meters) long. Assemble each con-necting span directly on a single constructionbarge at a correct elevation for connection inthe bridge. Install proper male and femaleconnecting posts at span ends to connect andsuspend the span to girders of the adjacentbays in the bridge.

270

FM 5-277

LIFT SPANSThe lift span (Figures 20-3 and 20-17, pages258 and 272) is normally assembled on aconstruction barge at a correct elevation forconnection in the bridge. Determine lengthand lift of span by the beam and clearance ofvessels to be passed through the bridge. Tolift the span, build panel towers on the ends ofadjacent floating bays. Install suitable con-nectors, guides, and lifting and counter-balancing devices on the towers for controland lifting of the lift span; install girders ofadjacent floating bays for connection whenspan is lowered and in position to receivevehicular bridge traffic. Floating bays sup-

porting the lift span must be designed toensure a level bridge.

DRAW SPANSThe length of the span is determined by thebeam of the vessels to be passed. Build towerson adjacent floating bays similar to lift spantowers. Methods of building draw spans areas follows:

Draw spans can be assembled on aconstruction barge to the correct eleva-tion, and then moved and connected intothe bridge.

One-half the draw span can be added toeach adjacent floating bay after towererection at the bay-assembly site. The twofloating bays can then be connected intothe bridge, and the draw-span halves canthen be connected.

Draw spans can be built by assembly ofsingle girders on the deck of adjacentspans. These girders can be launched byusing tackle from towers to support freeends. Pin girders to bays and then deckthem.

271

FM 5-277

span to ensure proper pinhole alignment forreinsertion of connecting pins upon lowering(Figure 20-18).

Use the following procedure to connect aCONNECTING SPECIAL SPANS Connect a lift span to supporting adjacent draw span:

When used to connect grounded bridge bays bays by special connecting posts or spanwith special connecting posts, no special junction posts when positioned and pinned 1 Connect draw span to its adjacent floatingdevices or maintenance is required after a for vehicular bridge traffic. Provide a vertical girders with a suspension link or hingeconnecting span is connected and suspended guide system on the tower to control longi- mechanism. The link consists of spanfrom girders of adjacent bay ends. tudinal movement of span during lifting of junction posts.

272

FM 5-277

2 Arrange the decking to allow for move- The pins are readily removed when thement across junctions. Cut stringers as weight of the draw span is taken on theshown in Figure 20-8, with one end lashed tower tackles. In lifting draw span halves,down to the end transom of draw span. raise one side until jaws are clear. Then

lever panels sideways, if required, to allow3 Install a pair of span junction posts at the simultaneous raising of the span halves

center of the draw span to ease procedure. without fouling.

ANCHORS AND ANCHOR LINESThe bridge is secured by anchors and guylines (Figures 20-19 through 20-21, page 274)against the effects of wind and current.

To determine needed types of anchors, exa-mine the stream bottom and compute theexpected pull on anchor lines due to theseconditions. Barges loaded with stone or metalcan be sunk upstream of bridge to serve asanchors.

Anchor line pull equals the sum of pull due toeffect of current on submerged portion ofbarge and effect of wind on exposed portionof barge and superstructure. The followingformulas may be used to determine this pull:

Pull due to current:

Pull due to wind:

On barge:

273

FM 5-277

Winches should be placed on barges to adjusttension in anchor lines.

On superstructure:

The pull due to current and wind is computedbased on maximum expected conditions.Anchor lines should pull parallel to current.

274

FM 5-277

GUY LINESUse guy lines to anchor landing-bay piers tothe riverbank. Place these lines at about a45-degree angle to the bridge centerline.Longitudinal tie cables from stern to sternand bow to bow of each barge help to keepbridge aligned and to prevent longitudinalmovement of parts of the bridge.

Special spans need modification of the anchorand guy system, as shown in Figures 20-20and 20-21. In the lift span and draw span, thelongitudinal tie cables must be broken toallow passage of river traffic. In lift spans,extra cables can be strung over the top of thetowers to tie the bridge together over the gap.In draw spans, extra anchor barges may besunk at each side of the gap to prevent thebridge from shifting when the span is open.

ANCHORAGE OFGROUNDING BARGES

Grounding barges may slide downhill, whichcan cause the landing bay to slide and dis-lodge the base plate and its bearings. Suchslides can be avoided as follows:

A barge which tends to slide down thebank when grounded must be suitablyanchored to shore. Cables fastened to thebank can be passed under the barge to aconnection on the off-bank gunwale of thebarge. Use packings to prevent damage tothe barge chines by the cables.

When a barge slides on grounding, theresulting shift in the superstructure maycause the landing bay to slide beyond thelimits allowed for bearings in the baseplates. Rig tackle to prevent furthermovement until the bearings and baseplates are reinstalled and secured inproper position.

MAINTENANCE DETAILBridges on barges require round-the-clockmaintenance arrangements. A detail of aboutone engineer combat company is needed tomaintain an 800-foot (243.8 meters) panelbridge on a 24-hour-a-day basis. Normally,two squads each shift are enough to tightenbolts, check anchor cables, repair decking,and maintain adequate bridge signs. Thisleaves three squads to maintain approachroads, perform any major repairs, and manfireboat and standby tugs.

A duty officer should be at the bridge 24 hoursa day. The officer must ensure that thefollowing regulations are in force at all times:

Communication is maintained betweenthe ends of the bridge.

A wrecker is on call to remove disabledvehicles from the bridge.

Guides having thorough knowledge ofstandard hand signals are available toguide minimum-clearance vehicles acrossthe bridge.

Alignment of the bridge is constantlymaintained.

Tension in all anchor cables is kept uni-form.

Buffers are maintained between allanchor and guy cables that rub againstmetal.

All cable connections are inspected every12 hours.

All pins, bolts, and clamps are inspectedevery 24 hours.

All barges are inspected and bailed atleast once every 24 hours.

All base plates are inspected once every24 hours.

275

FM 5-277

A source of electrical power is availablefor operation of trouble lights and tools.

Immediate approach roads are main-tained.

All signs in the vicinity of the bridge aremaintained.

Traction strips and decking are main-tained. All nailheads must be kept flushwith surface.

Tugs are stationed upstream and down-stream at the bridge.

A fireboat is available.

USE OF RAFTSMultiple-lane rafts can be assembled frompanel-bridge equipment supported on barges.Because of their ample freeboard and sta-bility, such rafts can be used either as trail oras free ferries in swift currents and roughwater.

AssemblyNormally, the raft superstructure is double-single or triple-single assembly. Details ofassembly and launching, and of barge prepa-ration, are given elsewhere in this chapter.

A typical barge raft used successfully isshown in Figure 20-22. This raft has a three-carriageway superstructure of four double-single girders 90 feet (27.4 meters) long ontwo 100-ton (91 metric tons) capacity Thames-type barges. This raft accommodates 12vehicles having a combined weight of 120tons (109.2 metric tons).

Inset position of barges in the raft as shownin Figure 20-22 is necessary, except in caseswhere the raft will be used in smooth water;otherwise, if the barges are placed near theends of the raft in rough water, there isexcessive stress in the connections betweenthe barges and superstructure.

When the raft is towed in heavy seas, thedecks may become awash, causing completebays of decking to lift off the barges. Toprevent this, use stringer clamps.

The superstructure must be secured to thebarges to prevent fore-and-aft movement.Sway braces can be used for this purpose byfixing one end of the brace to a barge deckbollard or cleat and attaching the other endto a deck transom by means of two tie plates.The brace can then be tightened in the normalmanner.

Use quays or docks to facilitate assembly andoperation of a raft. It is preferable to operatebetween quays or docks of proper height forconvenience in loading and unloading theraft. Where such site conditions exist, theheight of the raft deck can be adjusted, withinlimits, by packing the superstructure girdersup on cribs or by building a deck-type ratherthan a through-type raft. If quays or docksare unavailable, build ramps.

OperationFor continuous use of the raft as a ferry,install an upstream cable. Run bridle lines towinches mounted on the barges, allowing theraft to be swung at suitable angles to thecurrent, and operate as a trail ferry.

When the raft is being grounded, the bargesmay assume different angles of slope. Torelieve the superstructure of stresses, removeeither all top or all bottom pins at the center-panel connections of the raft. This allows thetwo halves of the raft to articulate andconform to the lay of each barge. Closeobservation is required as the tide falls todetermine whether the top or bottom pins areto be removed, and also the proper time toremove them.

276

FM 5-277

2 7 7

FM 5-277

CHAPTER 21

BRIDGE MAINTENANCE AND REPAIR

This chapter tells how to handle and storepanel-bridge parts and equipment. It alsotells how to repair damaged Bailey bridges,as well as how to dismantle and to replacethem.

CARE OF PARTS AND EQUIPMENTWhen storing and transporting panel-bridgeparts, keep them clean and handle them asfollows:

For panels, grease jaws and inside of allholes. Panels are easily distorted byimproper storage and handling. When-ever possible, store them in upright posi-tion resting on the long side. If it isnecessary to store them horizontally forstability, do not stack more than 10 on aflat base. Stack on timber cribbing ratherthan on the ground.

For bracing frame, rakers, and tie plates,grease conical dowels.

For end posts, grease curved bearingsurfaces and pinholes.

For bearings, grease bar segments.

For panel pins, grease shanks.

For sway braces, grease threads and pins.

For bolts, grease entire bolt.

Protect pieces of erection equipment, such asrollers, jacks, panel levers, pin extractors,and wrenches, by keeping them clean andlubricated to prevent rust.

Before launching abridge, lubricate bearingsof plain and rocking rollers through greasefittings at both ends of shafts. Lubricateplain rollers as follows:

1

2

3

4

5

Clean out old grease and dirt aroundshaft at each end of both rollers.

Wedge rollers tight against outer bearingswhere grease fittings are located.

Add grease until it is forced out aroundshaft at inner bearings.

If no grease appears at inner bearing ofeither roller, disassemble and clean entireunit.

After reassembling the roller, repeat thesecond and third steps above.

BRIDGE MAINTENANCE DETAILFor important bridges subject to enemyaction, the maintenance party usually con-sists of the entire assembly crew. For routinerepair work, however, the detail consists ofonly six soldiers. In rear areas, one travelingcrew maintains all bridges in an assignedarea or route. The maintenance detail—

Checks bridge thoroughly after first 30minutes of use and periodically thereafterfor tightness of bracing bolts, chord bolts,transom clamps, and sway braces.

Examines base plates and grillagesperiodically for uneven settlement andadds grill age when necessary.

Checks tightness of cribbing under endtransoms and ramps.

Makes sure all panel-bridge pin retainersare in place.

Lubricates all exposed threads and occa-sionally pours a small quantity of oil overeach panel joint if the bridge is to remainin place for a long period or if it is to bedismantled in freezing weather.

Repairs wearing surface on deck andramps, and keeps stone and gravel offdeck.

Maintains immediate approaches andditches.

During heavy rainstorms, checks closelyfor erosion of bank seats, abutments,approaches, and drainage ditches.

Replaces damaged end-post guards.

278

FM 5-277

Tools for routine maintenance work are listedin Table 21-1.

SPARE BRIDGE PARTSBridge supplies include about 10 to 25 percentspares for all bridge and nose parts exceptbearings, ramp pedestals, pickets, baseplates, ramps, and ribbands. For replacingdamaged parts of bridges subject to enemyfire, the spare parts in the bridge supply andadditional parts covering the above excep-tions are dispersed about the bridge site aftercompletion of the bridge. Depending on thetactical situation, the spares may be in-creased up to 50 percent for forward-areabridges. Rear-area bridges require onlyenough spare deck parts and wear-treadplanking to replace those worn or damagedby normal use.

For bridges subject to enemy action, completeerection equipment must be kept available atthe site.

ASSESSMENT OF DAMAGEThe class of damaged bridge is found bycomparing the residual strength of adamaged member with the actual maximumstress it must take according to its position inthe bridge. Unit assembly of the panel bridgeproduces girders of uniform section through-out their entire length. Many individual panelmembers are therefore not stressed to fullcapacity when the bridge is under maximumload. Only chords of the center bays andvertical and diagonal members of the endbays are fully stressed. Any damage to thesemembers decreases the bridge class in directproportion. Lightly stressed verticals anddiagonals of the center bays, and chords ofthe end bays, can sustain considerabledamage without affecting the bridge class.

Since they can easily be replaced, the effect ofdamage to deck, transoms, sway braces,rakers, and bracing frames is not consideredhere.

RESIDUAL STRENGTH OFDAMAGED PANEL MEMBERS

Table 21-2 (page 280) gives the residualstrength of panel vertical and diagonalmembers expressed as percent maximumcapacity of the complete cross section. Thefigures apply to both tension and compressionmembers.

Residual strength of damaged panel chordsis given in Table 21-3 (page 268). The twochannels of a panel chord act as one member.Damage to one channel is indicated in the leftcolumn of the table and damage to the otherchannel is shown in the top row. Combined

result of damage to the two channels ex-pressed as a percentage of the strength of theundamaged chord is found at the intersectionof the appropriate column and row. In Tables21-2 and 21-3, darkened portion indicatesdamage. When length of damage exceeds 15inches, values must be reduced to 0.

SHEAR AND MOMENTDISTRIBUTION

To simplify calculations, shear and momentin single-story bridges are assumed to betaken equally by all trusses. Shear in adouble-story bridge is taken equally by bothstories except in end bays, where the bottomstory takes 60 percent of the total shear. Topand bottom chords of double-story bridgesprovide all resistance to bending. Damage tointermediate chords can be disregarded if itdoes not reduce shear capacity of web-memberconnections.

Shear in a triple-story bridge is taken equallyby all three stories except in end bays, asfollows:

Only bottom and middle stories resistshear when deck is in the bottom story.

Only middle and top stories resist shearwhen deck is in the middle story.

Stress in top and bottom chords of triple-story bridges is about three times that inintermediate chords. However, to simplifycalculations, it can be assumed that top andbottom chords provide all bending resistance.

279

FM 5-277

Damage to intermediate chords causing lossof chord capacity up to 50 percent need not beconsidered, but cases of more extensivedamage should be investigated and correlatedwith any damage in top or bottom chords ofthe same bay.

SHEAR AND MOMENT TABLETable A-16, Appendix A, gives maximumshear and bending moment in each bay of allspans of fixed-panel bridges expressed aspercentages of maximum capacity. Dead-load shear and moment values (DL) showpercentage of shear and moment capacity ofeach bay required to support dead weight ofthe bridge itself. Live-load values (LL) showpercentage of shear and moment capacity ofeach bay required to support a tank load ofthe weight class of the bridge. Tank loads areplaced at maximum eccentricity against onecurb, increased 10 percent for impact, andmoved along bridge to point of maximumeffect for each bay.

2 8 0

FM 5-277

EVALUATION OF DAMAGEThe two main girders of a bridge are inde-pendent of each other and each must becapable of taking at least half the total bridgeloads. If one girder is damaged it cannot behelped by any reserve capacity of the other.

ChordsThe members at a given section of a bridgewhich have an identical function and acttogether must be considered as a unit. Forexample, each main girder of a triple-doublebridge consists of three trusses. If a chord ofone truss is completely severed, the remainingundamaged construction of that girder isdouble-double and capacity of the bridge isthat of a double-double bridge of the samespan. Moreover, if the damaged truss isincapable of supporting itself, the double-double capacity must be further reduced byhalf the weight in tons of the damaged truss.If the chord in one panel of a single-singlebridge is completely severed, the capacity ofthe girder and bridge is reduced to zero.

Web membersEffects of damage to diagonals and verticalsdepend partly on the condition of adjacentmembers. When both diagonals at a verticalsection of a panel are seriously damaged,shear strength of the panel at that section isreduced to 30 percent because shear is resistedonly by bending in the chords. Any damageto the chords or other diagonals in the samehalf of the panel reduces the shear strength tozero. When one of the diagonals at a verticalsection is completely severed, panel shearstrength at the section is reduced to 50 per-cent. Each diagonal takes half the shear, one

in compression and the other in tension.Residual shear capacities of panels withdamaged verticals in percent of undamagedcapacity are shown in Table 21-4.

Deformed membersWhen a member struck by flying metal isdeformed and not severed, it must be watchedas loads pass over the bridge. If furtherdeformation takes place, it must be treated asif it were severed.

EXAMPLE:Given:

A 90-foot (27.4 meters) span, class 40double-single bridge damaged as follows:

Case 1. In the third bay from one end, aflange of one channel in the bottomchord of one truss is missing.

Case 2. In the second bay from the end, aflange of one diagonal channel issevered.

Case 3. In the end bay, the center verticalof one panel is completely severed.

Required:What is the load class of the damagedbridge without repair or reinforcement?

Solution:Case 1. From Table 21-3, the residual

strength of the damaged chord is 60percent. As there are two trusses, theresidual strength of the girder is—

281

FM 5-277

From Table A-16, Appendix A, bendingstresses in the third bay are-

The damaged girder section is capableof taking on 80 percent of its originalcapacity. Therefore, the rated bridgecapacity must be lowered to reducestresses at this section from 89 to 80percent. Dead load remains the same.Therefore, live load must be reduced by 9percent.

Reduction in live load is approximatelyproportional to the lowering of the loadclass.

Case 2. From Table 21-2, residual strengthof the diagonal with one flange severedis 25 percent.

From Table A-16, Appendix A, totalshear in the second bay is 67 percent ofmaximum capacity, so this damage hasno effect on the bridge class.

Case 3. The center vertical of one panelbeing completely severed reduces shearcapacity in that panel to zero (Table 21-4) with one truss carrying zero percentshear and the other 100 percent shear.Therefore, the girder shear capacity is50 percent. From Table A-16, AppendixA, shear in the end bay is—

Total load must therefore be reduced 29percent to the girder shear capacity of 50percent. With dead load remaining con-stant, allowable live load becomes—

Load class of the bridge is thereforedetermined by this damage to a centervertical in an end bay and must belowered to class 20.

EXAMPLE:Given:

The 90-foot, US class 40 double-singlebridge of the example above has the chordof one truss in the third bay from one endcompletely severed.

Required:What is the load class of the damagedbridge without repair or reinforcement if—

Case 1. The damaged truss is capable ofsupporting its own weight?

Case 2. The damaged truss is not capableof supporting its own weight?

Solution:Case 1. We know from above that capacity

is reduced to that of a single-singlebridge of the same span or class 12.

Case 2. We also know from it that capacityof the corresponding single-single bridgemust be further reduced by half theweight of the damaged truss. Table 1-2shows the difference in weight of the twotypes of bridge bay as—

282

FM 5-277

The damaged truss, therefore, weighs—

Capacity of the 90-foot single-singlemust be reduced by half this weight.

REPAIR METHODSDamaged deck and bracing parts can beeasily replaced with spares. However, re-placing damaged panels is almost impossiblewithout first relaunching bridge, which isdifficult and time-consuming. If paneldamage results in greater loss of capacitythan can be tolerated, the bridge can berepaired by reinforcement or welding. Rein-forcement is preferred because welding cancause serious added damage unless it is donein favorable conditions by experiencedpersonnel.

REINFORCEMENTDamaged panels and chords are reinforced inseveral ways.

Shear capacity lost by damage to panelvertical and diagonal members is restored byadding complete trusses or partial stories orby replacing damaged bays, as follows:

Repair damaged single-single bridges byadding complete trusses.

Use a complete truss when damage ex-tends through several bays of double-truss bridges.

Add a partial story when damage is con-fined to one or two bays on long spans.The partial story must extend two baysbeyond both ends of damaged panels. Incase of damage to first or second endbays, the partial story extends from endof bridge to two bays beyond the damagedpanels.

If the end bay of double or triple-storybridges is seriously damaged it must bereplaced. Jack the bridge onto launchingrollers and build a new bay at the un-damaged end of bridge. Roll the new bayover the gap, dismantle the damaged bay,and lower the bridge onto its originalbearings.

If chord and web damage occur together,make repairs according to the above rules.Damage to exterior chords alone can berepaired with supplementary chords ex-tending two bays on both sides ofdamaged panel. Modified bracing framesmust be used with supplementary chordsplices of top chords of double- and triple-truss bridges to maintain a continuousbracing system.

CLASSThe posted class of the bridge must be reducedby the dead weight of the partial story orsupplementary chord.

The capacity of a girder reinforced with acomplete truss is determined by the methodfor assessment of damage in terms of reduc-tion of load class.

WELDINGAll panel-bridge parts can be repaired bywelding. Damaged parts which can be re-moved, however, preferably are replaced withspares. Repair work must be carefully done toprevent distortion and ensure proper fit of allparts.

Splice plates secured by fillet welds are morereliable than butt welding alone. Splicematerial should be mild steel plate about 50percent greater in cross-sectional area thanthe damaged section of the member beingrepaired. Splice plates should be arranged tomatch as closely as possible the shape andposition of the damaged section they replace.The minimum length, in inches, of a ¼-inch(.64 centimeters) fillet weld required on eachend of a splice plate is 10 times the cross-sectional area of the plate in square inches(Figure 21-1, page 284).

2 8 3

FM 5-277

Before making welded repairs, clear the areaaround the fracture by cutting all jaggededges. Always do straightening cold.

Both mild- and high-tensile low-alloy steelsof American parts can be repaired by eitherelectric-arc or oxyacetylene welding. Forelectric-arc welding, the heavy-coated mild-steel shielded-arc electrode (Lincoln FleetweldNo. 5 or equal), included in the electric arc-welding set No. 1, is the most satisfactory. Ifwelding is done by the oxyacetylene process,use a copper-coated mild-steel rod.

Cases of typical chord damage with correctrepair are shown in Figure 21-2. Figure 21-3shows typical damage repair of panel-webmembers. It is possible to use a standard setof strips in many cases, the more useful sizesbeing 3½ by ¼ by 12 inches (8.9 by .64 by 30.5centimeters), and 1 ½ by ¼ by 12 inches (3.8 by.61 by 30.5 centimeters). The choice of stripsizes is determined by the requirement ofusing downhand welding wherever possible.

Removable parts can be repaired using thesame general procedure as for panel members.Splice plates on transoms must not interferewith stringers or with positioning the tran-som seats on the girders. Welding of thelighter parts must be done carefully to preventdistortion and loss of interchangeability.

DISMANTLING OF BRIDGEPanel bridges are temporary structures andshould be replaced as soon as possible withsemipermanent bridges. A panel bridge isdismantled in reverse of the order in which itwas assembled. After dismantling, the panel-bridge parts are returned to the depot forreuse at another site.

The proper sequence of operations in dis-mantling a panel bridge is—

1

2

3

4

Take up ramps, jack up bridge, and placerocking rollers under each end and plainrollers on near-bank assembly site.

Remove end posts and assemblelaunching nose or counterweighted tail.

Pull bridge back on near-bank plainrollers.

Dismantle bridge and nose parts.

REPLACING OF BRIDGEWhile the new bridge is being constructed,some provision must be made to allow trafficto cross the gap. This can be done by buildinga bypass, by building the new bridge directlyunder the panel bridge, or by building thenew bridge alongside the panel bridge andrelocating the approaches.

Traffic can be diverted over a nearby bypass,such as a temporary bridge or culvert, whilethe panel bridge is being dismantled and thenew bridge is being built.

When a new two-lane bridge is being built,one lane is completed before the panel bridgeis removed. This completed lane carries thetraffic while the panel bridge is dismantledand the second lane is built.

When the new bridge is built directly underthe panel bridge, traffic is interrupted onlyfor a short time while the panel bridge isdismantled and the finishing touches areadded to the new bridge deck and approaches.The new bridge can be either a timber trestleor a culvert with solid fill.

Timber trestle bridges can usually be con-structed beneath the panel bridge and can beused as a working platform for driving pilesor erecting trestle. Culverts can be constructeddirectly underneath the panel bridge and anearth fill built up to the underside of the panelbridge. This fill is compacted, if only a shallowfill, and surfaced after the panel bridge isremoved.

2 8 4

FM 5-277

2 8 5

FM 5-277

CHAPTER 22

EXPEDIENT USES OF PANEL-BRIDGE EQUIPMENT

Panel bridge parts are often used in the fieldto build improvised structures. To aid in theirproper use, the capacities of the parts aregiven here. In all cases, allowance must bemade for impact and load-distribution fac-tors. Table 22-1 (page 287) gives the strengthof M2 panel-bridge parts, and Table 22-2(page 289) gives the strength of panel-bridgeerection equipment.

EXPEDIENT DECKINGFOR PANEL BRIDGE

If stringers and chess are not available, anexpedient deck can be laid on the transoms ofa panel bridge. Timber or steel stringers witha wood floor can be used, or steel treadwayscan be laid on the transom.

EXPEDIENT WIDENINGOF PANEL BRIDGE

The normal panel-bridge roadway width is150 inches (381.8 centimeters). The roadwaycan be widened to accommodate wider ve-hicles. Some wide vehicles will have verylittle roadway clearance and require cautionin entering the bridge; however, it has beenfound that the ribbands should be retainedon the bridge for these wide vehicles. Theribbands help guide the vehicles across thebridge and prevent damage to the bridgetrusses.

Certain non-US vehicles are more than 150inches (381.8 centimeters) wide. By removingthe ribbands, a roadway width of 165 inches(419.1 centimeters) may be obtained. Normalchess, used for a guard rail, should be boltedto the panels just below the top chord of thebottom story as protection against damagingthe truss panels. To secure the chess to thepanels, use carriage bolts with washers, witheither steel plates or an added plank behindthe truss to bolt through. Limiting the weartread to the normal width between curbs willallow the curbs to be replaced promptly afterthe wide vehicles have crossed. Promptreplacement of these curbs is necessary toensure the bridge’s normal operatingcapacity. (A few crossings by tanks mayquickly loosen the nails so that the treadsmust frequently be renailed. The guard railsmay be left on the truss panels either with thewidened roadway or with the normal bridge.)

The capacity of the widened bridge may varysome from the standard bridge due to theincreased eccentricity possible in the widenedbridge. Use normal capacities under cautionrestrictions at all times when the curbs areremoved.

286

FM 5-277

2 8 7

FM 5-277

2 8 8

SPANS WITHOUT END POSTSSingle-story bridges can be built without endposts or bearings, the bridge resting on timbercribbing under the end vertical member of theend panels. However, this method of construc-tion is not recommended unless absolutelynecessary. When this is done, the transomssupporting the ends of the last bay ofstringers must be supported by one of thefollowing methods:

When the end transom is not supportedby trusses, place it outside the verticals ofthe panels and on grillage. Place an extratransom in the seating just inside the

verticals of the end panel. Wedge blockingbetween these two transoms and lashthem together. The ends of the stringersand ramps rest on and engage with thelugs of the end transom. Bolt bracingframes between the trusses at the end ofthe bridge. Table 22-3 lists the maximumspans that can be built with ends of thebridge supported in this way.

When the end transom is supported bytrusses, add an extra panel to the innertruss on each side of the bridge, and placea transom in this panel on the seatingnearest the bridge proper. This transom

FM 5-277

supports the ends of the stringers andramps. Place rakers on this transom andbracing frames between the trusses at theend of the bridge proper. Extend grillageunder the end vertical 2 feet (61.1 centi-meters) on each side of the panel joint. Abridge of this assembly can carry thesame load as a corresponding bridge withits end transom not supported by trusses.If the extra panel is added to all thetrusses, the bridge can carry the sameload as a corresponding bridge with endposts. In both cases, place cribbing underthe center of the end transom when loadsare over 30 tons (27.3 metric tons).

289

FM 5-277

CAUSEWAYSPanel-bridge decking can be used to build anexpedient causeway over the soft mud of atidal riverbed. The causeway described here(Figure 22-1) has a capacity of 45 tons (41metric tons) and can be used at all stages oftide to load heavy vehicles such as mediumtanks on rafts. Its roadway can have a slopeup to 1 in 5 and is not affected by heavytracked vehicles that would normally cause aroadway of landing mats on corduroy mate-rial to break up. Use of panel bridge equip-ment or causeways is expensive in equipment,however, and should be controlled carefullyto prevent a shortage of panel-bridge parts.

Preliminary workThe causeway consists of a normal panel-bridge deck of chess, ribband, and stringerssupported on transoms set in ramp pedestals.To prevent scour and to distribute the load,rest the pedestals on a foundation of landingmats and sapling mats (chess paling orsimilar material). Place two pedestals undereach transom and space the transoms 5 feet(1.5 meters) center to center. Use precut 4- by3-inch (10.2 by 7.62 centimeters) timberspacers, or rakers with timber wedges, be-tween the pedestals to take longitudinalthrust. Thread sway bracing through theoutside holes in the transom webs and hold inplace by bolts. Wire the button stringers tothe transoms to prevent the decking frombeing lifted by the tide. Provide a nonskidsurface by nailing down landing mat to thechess or wear treads. Use steel ribbands forcurbing. Use holdfasts at each side of thecauseway to anchor bays having a steepslope.

290

FM 5-277

ErectionAbout 100 man-hours are required to erect100 feet (30.8 meters) of this causeway. If theprecut timber spacers are used instead ofrakers with wedges, erection time can bereduced 25 percent. Place spacers at the sametime as the pedestals, before transoms arelaid. Do not tighten sway braces untilstringers have been placed.

The maintenance party keeps wedges, swaybraces, and anchor lines tight.

OperationAt low tide, and at high tide during construc-tion of the causeway, vehicles generally canbe loaded and unloaded at the end of thecauseway. The overhanging deck or adjust;able ramp of the raft rests on the end bay ofthe causeway so vehicles pass directly fromthe raft deck to the causeway. Where thecauseway is begun at high tide, bays can beadded at the rate of one bay in about 20minutes as the tide lowers.

At high tide, the lower end of the completedcauseway is submerged and rafts are loadedand unloaded at the higher bays. Use anadjustable landing ramp hinged to the raft to

bridge the gap between the causeway andshore end of the raft. The shoreward pontoncan be grounded on the submerged causeway,but care must be taken to position the raft sothe water is deep enough to permit maximumdisplacement when the shoreward pontongrounds.

PANEL BOX ANCHORSAn expedient heavy rubble box anchor can bemade from four panels welded into a box withheavy wire net and filled with rock. Com-pletely filled with rock, the anchor weighsabout 10 tons. Heavy anchors of this type areused to anchor heavy floating bridges inswift currents and in streambeds in whichthe standard anchor will not hold.

OTHER EXPEDIENT USESPanel-bridge parts can be used to buildgantries (Figure 22-2), anchor-cable towers,high-line towers, towers for suspensionbridges (Figure 22-3), truck-loading traps,and other structures when building materialsare not available. Angles and I-beams can besalvaged from damaged panel-bridge partsto be used for expedient construction.

2 9 1

FM 5-277

CHAPTER 23

DEMOLITION OF BRIDGE AND PARTS

The success of these demolition methodsdepends on the use of a uniform procedure byall units in the theater. All ranks must beimpressed with the importance of followingthe principles stated in this chapter. Thedestruction must prevent both enemy use ofthe bridge as a unit and use of its parts fornormal or improvised construction.

ORDER AND METHODSOF DESTRUCTION

To prevent use of existing bridge, cut tressesso bridge drops into gap, and destroy abut-ments. To prevent reconstruction of a com-plete bridge, destroy one essential componentnot easily replaced or improvised. This com-ponent must be the same throughout thetheater so replacements cannot be obtainedfrom other sectors. The panel is the onlycomponent fulfilling these conditions.Always destroy all panels first. To make apanel useless, remove or distort female lug inlower or tension chord. Destruction of bothfemale lugs is unnecessary.

Also destroy certain other components, suchas transoms and decking, useful to the enemyfor improvised bridging. Destroy componentssuch as stringers, ramps, jacks, rollers, anderection tools only if time allows and explo-sives are available. Because the relativeimportance of these components varies con-siderably, follow the order of destructiongiven just below.

After the bridge is collapsed and the abut-ments destroyed, and if time permits, destroyindividual components in the order used fordestroying stacked equipment female lugs inlower chord of all panels; transoms andpanels (Figures 23-4 and 23-5, pages 295 and296); chess; stringers and ramps; jacks,rollers, and erection tools; and remainingsmall parts.

DESTRUCTION OF BRIDGECut bridge in one or more places by cuttingpanels on each side of the bridge and swaybraces in the same bay (Figure 23-l). Staggerthe line of cut through the panels (inset,Figure 23-l). Otherwise the top chords mayjam and prevent the bridge from dropping. Indouble or triple-story bridges, increase the

2 9 2

charges on the chords at the junction line ofthe stories.

For further destruction, place charges oncomponent parts of the bridge, such as panels,transoms, and stringers (Figures 23-2 and23-3). Stack and bum decking.

Charges and methods of placing variousexplosives are given in Table 23-1 (page 294).Wedge all charges in place. Use methods andcharges described in FM 5-25 for destroyingabutments.

FM 5-277

2 9 3

FM 5-277

DESTRUCTION OFSTACKED EQUIPMENT

Destroy panels and transoms in stacks. Todispose of stringers, ramps, jacks, rollers,small parts, and erection tools, dump themover large areas in places such as the sea,rivers, or woods. Bum decking. Methods ofdestruction are described in Table 23-2, andshown in Figures 23-4 and 23-5 (page 296).Tamp all charges.

294

DESTRUCTION OF CABLEREINFORCEMENT SET

When capture or abandonment of the cablereinforcement set is imminent, the respon-sible unit commander must make the decisioneither to destroy the equipment or to make itinoperative. Based on this decision, thatcommander orders how much should bedestroyed. Whatever method of demolitionused, it is essential to destroy the same vital

parts of all cable reinforcement sets and allcorresponding repair parts.

For demolition by mechanical means, usesledgehammers, crowbars, picks, axes, orany other heavy tool available to destroy thepost assemblies, fixtures, and braces; thecable-connection beams and span junctionposts; the cable assemblies; and the cable-tensioning or manual hydraulic-pump assem-

FM 5-277

blies. For demolition by explosives, place asmany charges as the situation permits.Detonate charges simultaneously with deto-nating cord and suitable detonator. Place atleast one ½-pound (.2 kilo) charge on eachcable and each cable-connection beamassembly. For demolition by weapons, fire onthe cable-connection beams and vertical postswith the heaviest suitable weapons available.

All operators should be thoroughly trained inthe destruction of the cable reinforcement set.Simulated destruction, using all methodslisted above, should be included in theoperator training program. It must be empha-sized in training that demolition preparationsare usually made in critical situations withlittle time available for destruction. For thisreason, operators must be fully familiar withall methods of destruction of equipment andbe able to carry out demolition instructionswithout reference to this or any other manual.

295

FM 5-277

296

APPENDIX A

O V E R S I Z E D T A B L E S

See pocket envelope inside back cover foruneven-numbered pages 297.1 through 321.Even-numbered pages 298 through 322 are blank.

297

APPENDIX B

C A B L E R E I N F O R C E M E N T S E T

Tables B-1 and B-2 of this appendix list itemswhich accompany the cable reinforcementset for installation or crew maintenance, aswell as supplies needed for initial operationof the set. Figure B-1 (page 324) shows the fivebasic issue items listed in Table B-1. FiguresB-2 through B-5 (pages 325 through 328) andTables B-3 (page 329) and B-4 (page 330),show maintenance and troubleshooting pro-cedures for the set, as described in Chapter15. Table B-5 (page 331) lists the repair partsneeded to maintain the set, while Figures B-6through B-12 (pages 332 through 336) show anumber of these parts separately.

323

FM 5-277

324

FM 5-277

325

FM 5-277

326

FM 5-277

327

FM 5-277

328

FM 5-277

329

FM 5-277

330

FM 5-277

331

FM 5-277

332

FM 5-277

333

FM 5-277

334

FM 5-277

335

FM 5-277

336

FM 5-277

APPENDIX C

U S E O F S A L E C H A R T S I N D E T E R M I N I N G M O M E N T A N D S H E A R

When a simple horizontal beam is loaded, itdeflects, or bends downward, and the hori-zontal fibers in the lower part of the beam arelengthened (tension) and those in the upperpart are shortened (compression). The exter-nal forces act to produce a bending moment.The moment of the internal forces (stresses)resisting this bending is called the resistingmoment. In Figure C-1, in that part of thebeam to the right of section C, the counter-clockwise bending moment produced by theexternal force P and Rr is resisted by theclockwise resisting moment produced by thetensile and compressive stresses in the beamat section C. Within the strength of thematerial, the resisting moment at any sectionis equal to the betiding moment at thatsection. When abeam is designed, the dimen-sions must be such that the maximumresisting moment that the beam can developis at least equal to the greatest bendingmoment that may be imposed on it by theexternal loads.

BENDING MOMENTThe following procedures, formulas, andother data are relevant to the determinationof maximum allowable bending moment:

The bending moment at any section(point) of a beam for an external load in aspecific position is found as follows:

Determine reactions caused by load inthis position.

1

337

FM 5-277

(Load W partially distri-

2

3

Take either reaction and multiply it bydistance of that reaction from sectionunder consideration.

From this product, subtract product ofeach load applied to beam betweenreaction and section times the distancefrom that load to section.

In Figure C-2, external bending momentat C equals Mc = (RL x 20) - (8,000 x 10) =260,000 - 80,000 = 180,000 foot-pounds, orMc= 18,000 x 12 = 2,160,000 inch-pounds.This may also be found by taking forcesfrom the right end.

The bending moment at any point in abeam due to a moving load varies with theposition of the load. For design, it isnecessary to know the maximum momentthat is caused by the load as it movesacross the bridge.

Maximum bending moment caused by a

WhereP= 30 tons (60,000 pounds)1 = 20 feet (240 inches)

single concentrated axle load occurs at

338

center of span when load is at center ofspan.

Maximum bending moment produced bya uniformly distributed load occurs atcenter of span when distributed loadcovers entire span.

If distributed load is shorter than span,maximum bending moment occurs atcenter of span when center of load is atcenter of span.

The following formulas are useful indetermining maximum bending momentscaused by single loads on simple beams:

(Concentrated center load P)

(Total load W uniformly distri-buted over span 1)

M = w12 (Load w per linear foot distri-buted over span 1)

buted over span 1)

WhereM=

P=

W=

w=

1=b=

Moment in inch-pounds atcenter of beamConcentrated load inpoundsTotal distributed load inpoundsDistributed load per linearfoot in poundsSpan in inchesLength of load in inches

EXAMPLES: What is the maximumbending moment produced in a 20-footspan by a single concentrated axle loadof 30 tons? By a total load of 5 tonsuniformly distributed over the span(dead load)? By a 30-ton tank that has147 inches of track?

SOLUTIONS:

For a single concentrated axle load of30 tons:

= 3,600,000 inch-pounds

FM 5277

For a uniformly distributed load of 5tons:

= 300,00 inch-pounds

For a 30-ton tank:

= 2,497,500 inch-pounds

For a series of axle loads on a span,maximum moment may occur under theheaviest load when that load is at thecenter of the span, or it may occur underone of the heavier loads when that loadand the center of gravity of all the loadson the span are equidistant from thecenter of the span.

Further details on computing maximumbending moment produced by two or moreloads on a span can be found in engi-neering handbooks.

For the design of military bridges thecomputation of maximum bending pro-duced by a series of axle loads or thatproduced by a uniformly partially distri-buted load, such as a tank, has beensimplified by the use of single-axle loadequivalents (SALE). The SALE is thatsingle-axle load that, when placed atmidspan, will cause the same maximummoment as the maximum moment caused

by the actual vehicle. From the formulaabove for a concentrated center load P,and substituting SALE, we have

RESISTING MOMENTMaximum allowable resisting moment that abeam can develop is the product of maximumallowable fiber stress for the material andsection modulus of the beam, which is ameasure of the capacity of the cross section ofthe beam to resist bending. Where M is themaximum allowable resisting moment that abeam can develop; f, the allowable extremefiber stress for the material; and S, the sectionmodulus, their relationship is expressed bythe formula M = fS.S depends solely on shapeand size of the cross section and f on thematerial of the beam. For rectangular beams,such as timber stringers,

S for I-bems and other structural steelshapes may be found in tables in standardengineering handbooks. Values of S forselected I-beams and WF (wide flange) beamsare given in Tables C-1 and C-2 (page 340).The stress f is ordinarily expressed in pounds

per square inch, and band din inches, givingM in inch-pounds. Values of f will varyaccording to type of stress and type ofmaterial. For this text and the majority offield design, values as given in the nextsection are used. For example, if the extremeallowable fiber stress (f) in bending of thewood in a rectangular beam 6 by 12 inches is2,400 pounds per square inch, then themaximum allowable bending moment thatbeam can resist is:

= 345,600 inch-pounds.

339

FM 5-277

SHEAR AND SHEARING STRESSAny load applied to a beam induces shearingstresses. There is a tendency for the beam tofail by dropping down between the supports(Figure C-3 (A)). This is called vertical shear.There is also a tendency for the fibers of thebeam to slide past each other in a horizontaldirection (Figure C-3 (B)). The name given tothis is horizontal shear.

The following procedures, formulas, andother data are relevant to the determinationof maximum allowable shearing stress:

For beams supported at both ends, theshear at any section (point on the beam) isequal to the reaction at one end of thebeam minus all the loads between thatend and the section in question. To cal-culate maximum shear, it is necessary tofind the position of the loads that producesthe greatest end reaction. This usuallyoccurs when the heaviest load is over onesupport.

In timber we find that because of the layereffect of the grain, the stringers areweaker horizontally along the member.But the stress numerically equal to thehorizontal direction is numerically equalto the vertical direction, so design is onthe basis of the stress in the verticaldirection. In military bridge design ashear check must be made if the spanlength in inches is less than 13 times thedepth of the stringer.

The average intensity of shear stress(horizontal and vertical) in a beam isobtained by dividing maximum externalshear by cross-sectional area of the beam.However, shear is not evenly distributedthroughout the beam from top to bottom,so maximum shear intensity is greaterthan the average. Maximum shear inten-sity occurs at the midpoint of the verticalsection.

340

FM 5-277

For a rectangular section, maximumhorizontal shear intensity equals 3/2times average intensity, or—

WhereS h=

V =b =d =

maximum shear intensity(unit shear stress) induced inthe beam, in pounds persquare inchmaximum shear, in poundsbreadth of beam, in inchesdepth of beam, in inches

Over short spans where shear rather thanbending may control, beams warrantspecial means of analysis. In computingmaximum horizontal shear intensity, usethe formula given above. In determiningV for use in this formula, neglect all loadswithin a distance equal to or less than thebeam height from either support, andplace the design moving load at a distancethree times the height of the beam fromthe support.

For a circular section, maximum horizon-tal shear intensity equals 4/3 timesaverage intensity, or—

Whered = s diameter of beam, in inches

CLASSIFICATION OFVEHICLES AND BRIDGES

The purpose of this paragraph is to outlineoffice and field procedures for classifyingvehicles and bridges in accordance with thevehicle and bridge classification system andto explain the field design of simple bridges.It explains vehicle and bridge classificationprocedures in sufficient detail to enable engi-neers who are familiar with the classificationsystem to determine the proper classificationof vehicles and bridges. It also explains howto select stringers for simple-span bridgesand to design the substructure using timbertrestle intermediate supports.

STANDARD CLASSESA group of 16 standard classes ranging from4 to 150 has been established at the intervalsshown in Figure C-4 (pages 343 and 344). Foreach of the standard classes two hypotheticalvehicles are assumed: a tracked vehicle whoseweight in short tons is the standard classnumber, and a wheeled vehicle of greaterweight which induces about the same maxi-mum stresses in a given span. For example,in standard class 4 the tracked vehicle weighs4 tons, the wheeled vehicle 4.5 tons; in class 8,8 tons and 9 tons, respectively. The hypo-thetical vehicles and their characteristics areshown in Figure C-4. Although these vehiclesare hypothetical, they approximate actualUnited States and United Kingdom armyvehicles.

For each standard class both a moment classcurve and a shear class curve are drawn.These curves are determined by computingthe maximum moment and maximum shearinduced in simple spans by the two hypo-

thetical vehicles for each standard class,converting these values to single-axle-loadequivalents (SALE), in short tons, and plot-ting the SALE against the simple-beam spanin feet. The envelope curve is then drawnthrough the maximum moment and shearvalues as shown in Figures C-5 and C-6 (page345). The standard class curves are shown inFigures C-7 through C-12 (pages 345 through348). In computing maximum moment andshear, space the vehicles at normal convoyspacing, with an interval of 30 yards from thetail of one vehicle to the front of the nextvehicle.

SPECIFICATIONSThe basic assumptions and specificationsused here for design and capacity estimationdata are as follows:

As regards bending stress: steel—27,000pounds per square inch; timber—2,400pounds per square inch.

As regards shear stress: structural steelsections—16,500 pounds per square inch;steel pins and rivets—20,000 pounds persquare inch; timber—150 pounds persquare inch.

As regards impact: steel—15 percent oflive load moment; timber—none.

As regards the lateral distribution factortheoretically, two stringers are twice asstrong as one, four are twice as strong astwo, and so on; actually, this is true only if

341

FM 5-277

each stringer carries an equal share of the As regards the distance between roadtotal load. A stringer directly under a contacts of vehicles following in line: 100wheel load is more highly stressed and feet.carries a greater portion of the load thanthose farther to the side. Because of this OFFICE DETERMINATIONnonuniform lateral distribution of a wheel Use the following method to determine ve-load among stringers, the total width (or hicle class number in the office:number) of stringers required to carry aparticular load is greater than the total width (or number) that would be requiredif all stringers carried an equal share ofthe load. This requires an increase instringer width (or number of stringers)and is expressed as a ratio called lateraldistribution factor. For design of two-lanemilitary bridges with vehicles on thecenterline of each lane, the factor is 1.5.

As regards roadway widths: a minimumclear width between curbs of 13 feet 6inches for single-lane bridges and 22 feetfor two-lane bridges.

1 Compute the maximum moment producedby the vehicle in at least six simple spansof different length.

2 Convert maximum moment to SALEusing the formula,

in which M = maximum moment in foot-tons, and L = span length in feet.

3 Plot SALE against corresponding spanlength.

4

5

6

Draw curve through the points plotted.This is the moment class curve for thevehicle.

Superimpose the curve over the standardclass curves for moment (Figures C-7, C-8,and C-9).

Determine the class of the vehicle by theposition of the vehicle class curve withrespect to the standard class curves.Round off any fraction to the next largerwhole number.

Repeat the last three steps for maximumshear, using the formula, SALE = shear.

The class of the vehicle is the maximum classdetermined from either the moment or shearcurve. In most cases, moment will govern.

342

FM 5-277

343

FM 5-277

344

FM 5-277

345

FM 5-277

346

FM 5-277

347

FM 5-277

EXAMPLES:Single vehicle

Figure C-13 shows the moment curve for a2 1/2-ton, 6x6 dump truck superimposed onthe standard class curves. From the figure

348

it is seen that the curve for this vehicle liesbetween the class 4 and the class 8 curvesand from its position with respect to thesecurves the vehicle is class 8.

Combination vehicle over class 40Figure C-14 shows the moment curve for aM26A1 tractor with transporter M15A1,loaded, superimposed on the standardclass curves. From the figure it is seenthat at a span length of 100 feet thesuperimposed curve crosses the standardclass 70 curve and begins to level off. Itdoes not cross the class 80 curve. From itsposition with respect to the standard classcurves, the class of the vehicle is 77.Figure C-14 shows that the vehicle haslower classes at shorter span lengths. Ata span length of 70 feet, for example, thevehicle’s class curve crosses the standardclass 60 curve, and for this span the classof the vehicle is 60. The other classes ofthe vehicle for shorter span lengths are

similarly determined by inspection of thecurves, and this information is placed ona cab plate. The section of the cab platefor this vehicle, loaded, shows the classrestrictions for the various spans, listedin Table C-3.

FIELD DETERMINATIONIf time, information, or a qualified engineer isunavailable, and the office methods cannotbe used, substitute one of the followingmethods:

Compare characteristics such as dimen-sions, axle loads, and gross weight withcharacteristics of the hypothetical ve-hicles shown in Figure C-4.

EXAMPLE:An unclassified wheeled vehicle has agross weight of 27 tons and a length ofabout 27 feet. By interpolation in FigureC-4, it is class 23. If, however, because of

FM 5-277

axle spacing and weight distribution themaximum single-axle load for this vehicleis 12.5 tons (greater than Figure C-4 showsas allowable for class 23), the maximumsingle-axle load is used as the classifyingcriterion. By interpolation in the maxi-mum single-axle load column (Figure C-4), the vehicle is then class 26.

Compare the characteristics of an un-classified vehicle with those of a similarclassified vehicle.

EXAMPLE:An unclassified single vehicle has threeaxles, is about 166 inches long, and weighsabout 8 1/2 tons. By comparison with astandard 2 1/2-ton truck 6x6-LWB, whichweighs 8.85 tons, it is class 8.

Compare the ground-contact area of anunclassified tracked vehicle with that of aclassified tracked vehicle. Tracked ve-hicles can be assumed to be designed withabout the same ground pressure.

EXAMPLE:An unclassified tracked vehicle has aground contact area of about 5,500 squareinches. By comparison with an M4 tank,which has a ground contact area of 5,444square inches, it is class 36.

Compare the deflection in a long stealspan caused by an unclassified vehiclewith the deflections caused by classifiedvehicles. In this method the span must beat least twice as long as the vehicles andthe vehicles must be placed for maximumdeflection. Measuring apparatus must beaccurate to at least one thirty-second ofan inch.

EXAMPLE:Select two vehicles of known class whichare estimated to bracket the unknownvehicle class. Measure the deflections of along steel span when loaded individuallyby each of the three vehicles. Move eachvehicle on the span three times and readthe deflection. Then average the threereadings.

349

FM 5-277

DeflectionVehicle Class (average of three loadings)

A 62 2 13/32 in, or 2.406inB 42 1 11/16 in, or 1.688 inC unknown 2 3/32 in, or 2.094 in

Class is considered proportional to deflectionso—

Unknown class = lower class +(Upper class–lower class) xdeflection of unknown classminus deflection of lower class

Deflection of upper classminus deflection of lower class

= 42+ 11.31 = 53.31, or class 53

350

FM 5-277

GLOSSARYACRONYMS AND ABBREVIATIONS

AARassyBBPBSSCC-Ccad pltdcirc

cmd

pcs

ptQDQSQT

DLDDdiam

DQDS

R

DTD5ETO

FSgalH

sq

hex (hd)hrhyd

inLllblgLHLiLLLRmaxmessmin

anchor spanas requiredassemblybridgebase plateBritish standard specificationcantilever span, cautioncenter to centercadmium platedcircularcenterlinecentimeter(s)distance from center of gravity

to tail of bridgedouble-doublediameterdead loaddouble-quadrupledouble-singledouble-tripledouble-five storiesEuropean theater of operationsfar shorefoot, feetgallon(s)horizontalhexagonal (head)hourhydraulicimpactinch(es)length of bridgelength of span of bridgepound(s)longleft-handedlength, initiallive loadlift requiredmaximummeasureminimum

MkMOPPmphNNATOnoNPTNPTFNS

qty

refreinfRHRRTSSALESBC

SSTt/sfTDthdTSTTT5T6VW

wwowtyd

Mark (model)mission-oriented protection posturemiles per hournormal, noseNorth Atlantic Treaty Organizationnumbernational pipe threadnational pipe thread finenear shorepiecespanelpointquadruple-doublequadruple-singlequadruple-triplequantityrisk, rocking rollerreferencereinforcedright-handedrocking-roller templatesimple suspended spansingle-axle-load equivalent(s)soil-bearing capacitysquaresafety setback, single-singletracked-load classtons per square foottriple-doublethreadtriple-singletriple-tripletriple-five storiestriple-six storiesverticalwheeled-load class, wide-flange

beam (formerly WF)withwithoutweightyard(s)

351

FM 5-277

DEFINITIONS

Angle of repose

Backspace

Bailey bridge Ml

Bailey bridge M2

Bailey bridge M3

Bay

Bays

Beam, distributing

Blocking

For field design, assumed to be an angle of 45 degrees from the horizontal. The base of thisangle starts at the toe of slope and proceeds upward to ground level. Placement of any load infront (toward the gap) of this angle would probably result in bank failure.

The amount of space available for construction of the bridge.

The original US design of the British prefabricated Bailey bridge.

The revised US design of the Bailey bridge Ml, with a greater roadway width of 121/2 feet. Alsocalled the Panel Bridge.

The revised, wider, British design of the Bailey bridge M2. It is often referred to as theextra-widened Bailey bridge and is not stocked by the US Army.

One complete section of a Bailey bridge, equivalent to the length of one panel 10 feet (3.04meters) wide. The term bay is used regardless of the truss type.

Floating: Interior bays of a floating bridge that are located between the near- and far-bankend floating bays.End Floating: Those which form the continuation of the bridge between the floating and thelanding bays.Landing: Those which form the connection between the end floating bay and the bank. Thereare two types:Variable-slope - these span the gap between the bank and the landing bay, or the intermediatelanding bay if a fixed-slope landing bay is used.Fixed-slope - these span the gap between the intermediate landing bay and the landing bay.

Rigid: A steel beam securely attached to the top of a pier or abutment which is designed tospread the weight applied to it over a large area.Rocking-bearing: A steel beam attached to the bottom chord of Bailey bridge panels. It isused to prevent excessive local bending of the bottom chord.

Timber used to support the junction of the first and second bays of bridge when buildingdeck-type bridges without end posts. Also, any timber used under girders during jacking downof deck-type bridges.

352

FM 5-277

Bridge

Chords

Cribbing

Decking

Grillage

Harmonious vibration

Node points

Packing

Panel bridge

Panel points

Through-type truss: A bridge with a roadway between the main load-carrying girders.Deck-type: A bridge with the roadway on top of the main load-carrying girders.Broken-span: A multispan bridge with the top chord broken and the bottom chord eitherbroken or pinned at the piers.Continuous-span: A bridge of which both upper and lower chords are continuous overintermediate piers between abutments.

The upper and lower horizontal members of a Bailey panel.

Grillage placed in alternating layers under the roller templates and bridge baseplates toprovide the correct horizontal plane on which the bridge is built, launched, and positioned fortrafficking.

Laminated: Timbers laid on edge and nailed together horizontally, and then positioned ontop of Bailey panels to form a type of roadway for deck-type bridges.Layered: Roadway on deck-type bridges comprised of timbers laid across the trussesperpendicular to the bridge centerline. The second layer is placed diagonally to the first, and athird layer (optional wear tread) is placed parallel to centerline. Sometimes referred to as deck,or flooring.

Standard: Square-cut timber positioned under the Bailey bridge to spread the weight of theridge over a large area. The Bailey grillage set has a fixed number of two sizes of standardgrillage.Non-standard: Timber other than that supplied in the Bailey set. This timber must be at leastas large as standard Bailey grillage.

Vibration in a bridge caused by the loads crossing it.

Critical-load centering points used for exact alignment of components bearing on each other.

Timber used during raising and lowering, which the bridge rests on while jacks are reposi-tioned.

See Bailey bridge M2.

Points under panel verticals and junctions of diagonals that must be supported by a rocker-bearing distributing beam.

3 5 3

FM 5-277

Pier

Placement control lines

Point of contraflexure

Roller clearance

Safety setback

Skidding

Spacing

Span

Supplementary chords

Temporary launching pier

Toe of slope

Underslung story

Wear tread

Floating-bay: Supports the floating bay in the interior of the Bailey bridge.Landing-bay: Supports the shore end of the floating bay and riverward end of either thefixed-slope or the variable-slope landing bay.Intermediate landing-bay: Supports the shore end of the fixed-slope landing bay and theriverward end of the variable-slope landing bay.

Used to ensure that the rollers are placed and leveled accurately.

The point where the downward sag of a girder changes to an upward bend as it approaches anintermediate support.

The distance between the center of the rocking rollers and the center of the bearing on whichthe bridge end posts will rest.

The minimum distance that a rocking roller is placed from the edge of the gap.

Moving the bridge or a single girder over greased timbers or steel beams.

Lateral: Spacing of the rollers in rows across the centerline of the bridge.Longitudinal: Spacing of the rollers in a line parallel to the centerline of the bridge.

Lift: Connects two adjacent floating bays and provides a span that can be lifted vertically toallow passage of water traffic.Draw: Connects two adjacent floating bays and provides a span that can be split in themiddle and the two parts pivoted upward to allow passage of water traffic.Connecting: Connects two adjacent floating bays where barges are grounded.

Upper or lower chords used to reinforce a Bailey bridge.

A pier used during the building of bridges with an underslung story.

The point in the gap considered to be the base of the bank.

One story of a through-type truss bridge that is below the level of the roadway.

Lumber laid across the chess of the Bailey bridge to prevent damage by vehicles crossing it.

354

FM 5-277

REFERENCESREQUIRED PUBLICATIONS

These are sources that users must read in order to understand or comply with this publication.Department of the Army Pamphlet (DA Pamphlet)

736-750Field Manuals (FMs)

5-345-134

Tables of Organization and Equipment (TOEs)05077H20005077J200

Technical Manuals (TMs)5-3129-2320-260-109-2320272-109-2330-287-14&P740-90-1750-244-3

The Army Maintenance Management System (TAMMS)

Engineer Field DataPile Construction

Engineer Panel Bridge CompanyEngineer Panel Bridge Company

Military Fixed BridgesOperators Manual for Truck, 5-Ton, 6 x 6, M809 Series (Diesel)Operators Manual for Truck, 5-Ton, 6 x 6, M939 Series (Diesel)Operator’s, Organizational, Direct Support and General Support MaintenanceAdministrative Storage of EquipmentProcedures for Destruction of Equipment to Prevent Enemy use

RELATED PUBLICATIONSThese are sources of additional information. They are not required in order to understand this publication.Department of the Army Form (DA Form)

2258 Depreservation Guide for Vehicles and EquipmentFederal Supply Group (FSG)

9100 Identification List (IL): FSG 9100, Fuels, Lubricant, Oils, and WaxesField Manuals (FMs)

5-1 Engineer Troop Organizations and Operations5-25 Explosives and Demolitions5-36 Route Reconnaissance and Classification55450-1 Army Helicopter External Load Operations101-5-1 Operational Terms and Symbols

9-2320-260-12 Truck Chassis 5-ton, 6 x 6, M809

5-210 Military Floating Bridge Equipment5-232 Elements of Surveying36-230-1 Packaging of Materiel: Preservation (Vol I)43-0139 Painting Instructions for Field Use

Lubrication Order (LO)

Technical Manuals (TMs)

355

FM 5-277

INDEX

356

FM 5-277

357

FM 5-277

358

FM 5-277

359

FM 5-277

360

FM 5-277

361

FM 5-277

362

FM 5-277

363

FM 5-277

364

FM 5-2779 MAY 1986

By Order of the Secretary of the Army:

JOHN A. WICKHAM, JR.General United States Army

Chief of Staff

Official:

R. L. DILWORTHBrigadier General United States Army

The Adjutant General

DISTRIBUTION:Active Army, USAR, and ARNG: To be distributed in accordance with DA Form 12-34B,Requirements for Bailey Bridge (Qty rqr block no. 658).

✰ U.S. GOVERNMENT PRINTING OFFICE 1994-367-927

APPENDIX A

OVERSIZED TABLESPages 297.1 through 322

FM 5-277 297.1

297.1

FM 5-277 299

299

This change supersedes page 301.FM 5-277 301

301

FM 5-277 303

303

FM 5-277 306

305

FM 5-277 307

307

FM 5-277 309

309

FM 5-277 311

3 1 1

FM 5-277 313

*Capacities are those assigned to the bridge in the field; actual capacities may be greater

313

FM 5-277 315

315

FM 5-277 317

317

FM 5-277 319

319

FM 5-277 321

3 2 1

PIN: 059910-000