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AGR1CULIURE LIBRARY

LUMBER RIGID FRAMES FOR FARM BUILDINGS By J . O. Curtis and E. L. Hansen

CIRCULAR 812

UNIVERSITY OF ILLINOIS COLLEGE OF AGRICULTURE

EXTENSION SERVICE IN AGRICULTURE AND HOME ECONOMICS

Lumber rigid frames for farm buildings

BASIS FOR THE DESIGNS

"

For your next farm building, consider using the lumber rigid frame system of construction. With this system the joints of two studs and two rafters are made rigid by gluing and nailing plywood gussets on each side of each joint, doing away with the need for posts and ties.

The rigid frame system has several features to recommend it. Its use results in a structure completely free of interior obstructions, which means it is well suited for many types of farm buildings, such as poultry houses, hog houses, garages, and machinery storages. Construction is simple since individual frames consist of a relatively small number of different sizes and shapes of framing members. The cost is no greater than for other systems of clear-span con­struction and usually less.

Rigid frames for farm buildings are not new, but for the most part they have been steel and laminated wooden frames, fabricated in factories. There has been a need for designs for rigid frames that could be fabricated by local lumberyards, local builders, or by home labor. Such designs are presented in this circular, along with suggestions for building and erecting the frames.

The designs presented here are based on a study made by the authors in which load tests were made, tentative designs formulated, and these designs then tested. The following loads were assumed:

1. A combined snow load and dead load of 25 pounds per square foot of horizontal projection of the roof surface.

2. A wind velocity pressure of 20 pounds per square foot at a height of 30 feet (equivalent to a velocity of 88 miles per hour at this height ) . A cor­rection was then applied for the actual height of the building, based on "Wind and Snow Loads on Farm Structures," ARS 42-5 of the U. S. Department of Agriculture. The frames were designed for a load result­ing from the wind blowing toward the open side of a building closed on the other three sides.

The allowable working stresses assumed were as follows:

1. A stress in extreme fiber in bending of 2,000 pounds per square inch.

2. A stress in compression parallel to the grain of the lumber of 1,600 pounds per square inch.

3. A stress in shear parallel to the glue line of the plywood of 90 pounds per square inch.

By J. O. Curtis, Assistant Professor of Agricultural Engineering, and E. L. Hansen, Professor of Agricultural Engineering

Urbana, Illinois December, 1959

Cooperative Extension Work in Agriculture and Home Economics: University of Illinois, College of

Agriculture, and the United States Department of Agriculture cooperating. lOUIS B. HOWARD,

Director. Acts approved by Congress May 8 and June 30, 1914.

[ 2 ]

FLEXIBILITY IN DESIGN

7b 30. \C XT(0( 10. ? (">1 •

The designs presented here vary in size of lumber from 2 x 4 to 2 x 12, in span from 12 feet to 40 feet, in side-wall height from 6 feet to 12 feet, and in recommended maximum spacing from about 1 foot to 14 feet, 6 inches.

All follow the general pattern shown in Figure 1. All have a gable roof with a 4: 12 slope and vertical side walls. Each is designed as a two-hinged arch in which the joints at the eaves and at the ridge are assumed to be rigid and must be fabricated so they will be rigid. Plywood gusset plates, nailed and glued to the framing members, are used to make these rigid joints.

GU~5£T PLA.TE E.~C~ ~\DE. ~LOC.~ F"LLE.~ ~EQUI~ED

FO~ .3/& GU55~TS Fig. 1. Typical layout of a rigid frame.

SPA.Nl~ ~ Table 1. - MAXIMUM SPACING OF FRAME

Side-wall Maximum spacing when span is-Framing height,member 12 ft. 16 ft. 20 ft. 24 ft. 28 ft. 32 ft. 36 ft. 40 ft.feet

2x4 6 3'-8" 2'-0" 1'-2" 8 2'-8" 1'-1 0" 1'-2"

10 2'-0" 1'-6" 1'-2" 12 1'-8" 1'-4" 1'-0"

2x6 6 9'-2" 5'-0" 3'-2" 2'-2" 1'-6" 1'-2" 8 6'-6" 4'-8" 2'-10" 2'-2" 1'-6/1 1'-2"

10 5'-4" 3'-10" 2'-10" 2'-0" 1'-4" 1'-0" 12 4'-2" 3'-4" 2'-6" 1'-10" 1'-4" 1'-0"

2x8 6 13'-4" 8'-8" 5'-6" 4'-6" 2'-10" 2'-2" 1'-10" 1'-6" 8 11'-10" 8'-0" 5'-2" 3'-6" 2'-6" 2'-0" 1'-6" 1'-4/1

10 9'-2" 6'-10" 5'-0" 3'-4" 2'-6" 1'-10" 1'-6" 1'-2/1

12 7'-2" 5'-8" 4'-4" 3'-4" 2'-4" 1'-10" 1'-6" 1'-2/1

2 x 10 6 14'-6" 9'-0" 6'-4" 4'-8" 3'-8/1 3'-0" 2'-6" 8 13'-0" 8'-2" 6'-0" 4'-2/1 3'-2" 2'-8/1 2'-2"

10 10'-10" 8'-0" 5'-6" 4'-0" 3'-0" 2'-6/1 2'-0/1

12 9'-2" 7'-0" 5'-4" 3'-10" 3'-0" 2'-4" 2'-0"

2 x 12 6 13'-6/1 9'-6" 7'-2" 5'-6/1 4'-6/1 3'-8/1

8 12'-4/1 8'-6" 6'-4" 4'-10" 4'-0" 3'-4" 10 11'-10" 8'-2" 6'-2/1 4'-6" 3'-8/1 3'-0" 12 10'-4" 8'-0" 5'-10" 4'-6" 3'-6" 3'-0"

[ 3

A suitable frame design for a given set of conditions may be found in Table 1, in which size of framing, wall height, span, and frame spacing are related. If, for example, you are considering a building 24 feet wide and 8 feet high at the side wall, you can choose from four frame sizes and spacings: 2 x 6 frame and 2'-2" maximum spacing; 2 x 8 frame and 3'-6" maximum spacing; 2 x 10 frame and 6' maximum spacing; and 2 x 12 frame and 8'-6" maximum spacing. In deciding which to use, you need to consider other features of construction, such as the wall covering or roofing to be used. In general, the wider the spacing of the frame, the more economical the construc­tion will be.

Details of the plywood gussets are given in Figure 2. Notice that two different thicknesses are called for, depending on the size of the lumber. A thickness of % inch is used for 2 x 4 and 2 x 6 frames, and a thickness of % inch for 2 x 8, 2 x 10, and 2 x 12 frames.

Fig. 2. Details of plywood gussets for different sizes of framing.

Eave gusset Ridge gusset Eave gusset Ridge gusset

~~:-\~ z· x 4" F=P-.AMING~~\y ~ ~~-'--""""'"'---.;...;...-C~ 2:' X 10" ~~AMING

DI~ECTlotJ O~F~4N FA.CE: G~AI~ ~ ~ ~4

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O/S" PLYWOOD l!1 I 28" . I C

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[ 4 ]

1

MATERIALS FOR

RIGID FRAMES

Fig. 3.

In preparing these designs, specific grades and types of materials were assumed. For the frames to perform satisfactorily, they must be constructed of materials at least equal in strength and quality to those assumed.

Lumber. The designs were based on the use of construction-grade Douglas fir lumber or other grades and species having at least equal strength. To insure a satisfactory job of gluing, the lumber must be dry (moisture content no more than 15 percent).

In addition to using the correct grade and moisture content of lumber, it is important to locate knots and other defects wisely when cutting out the framing members. Where possible, avoid locating knots and other defects in the region of highest stress in the lumber. In a rigid frame, this region of highest stress is in the vicinity of the eave gusset (see Figure 3) .

Plywood. The designs were based on the use of C-C exterior-grade Douglas fir plywood. Other grades and species may be used if they are at least equal in strength to the grade on which the designs were based.

Glue. The type of glue must be carefully selected so that it will be suitable under farm-type construction conditions. It must set at normal air tempera­tures, give strong joints when only nail pressure is used, and be reasonably easy to use.

Two basic types of glue satisfy these requirements - Grade A casein glue and resorcinol-resin glue. The choice should be made on the basis of the degree of resistance to moisture required. Resorcinol-resin glue is a waterproof glue and so is more resistant to moisture. It should be used in fabricating frames that will be subjected to damp conditions. Grade A casein glue IS

water-resistant and may be used when a waterproof glue is not required.

~WO~ST PO&~Ie,LE. IQQQQj L..OC~TION 1=0'"' ""'NO'T~

O~ OT~E~ DEFECT!i

Areas where defects in P'777J OTI-{E.~ A~E"~ W~E.FI\t: ~ IT l~ DE.'5I~A&L TOframing lumber are most seri­ AVOID LOCATIN~ ""NOTS

ous in fabricating rigid joints. O~ OT'-'E:~ DEFE.CTS

[ 5 ]

BUILDING AND Several satisfactory procedures can be used in building the rigid frames for a given structure. The one described here, however, will probably workERECTING THE FRAMES as well as any.

Precut all members. Cut the studs, rafters, gussets, and blocking (if re­quired ) for all the frames to be built before beginning to assemble the frames. It is best to first cut one set of members very accurately and then to use this set as a pattern for all the rest of the members.

Table 2. - RAFTER LENGTHS FOR VARIOUS SPANS AND SIZES OF FRAMES

Rafter length when span is-Framing member 12 ft. 16 ft. 20 ft. 24 ft. 28 ft. 32 ft. 36 ft. 40 ft.

2x4 6'-4%" 8'-6" 10'-6!h" 2x6 6'-5Ya" 8'-6Y2" 10'-73,4" 12'-9" 14'-10%" 16'-11%" 2x8 6'-5%" 8'-6Va" 10'-81,4" 12'-9Y2" 14'-10%" 17'- Ys " 19'-1¥s" 2 x 10 8'-7%" 10'-8%" 12'-10" 14'-111,4 " 17'­ % " 19'-1Va " 21 '-3Ys " 2 x 12 10'-9Ys" 12'-10%" 14'-11 % " 17'-1 " 19'-2%" 21 '-30/& "

The basic information needed for laying out the first set of members is given in Figures 1 and 2 and Table 2. The stud is, of course, very simple to layout since it has only a right-angle cut at each end. To layout the rafter, select the over-all length from Table 2 and then follow the details in Figure 1.

Fig. 4. Typical cutting dia­ Layout the gussets as shown in Figure 2. Note that it is necessary to orient gram for plywood gussets.

the gussets correctly with respect to the angle of the grain of the plywood. A typical diagram for laying out the gussets on a 4- by 8-foot plywood sheet is shown in Figure 4.

A power saw is almost a necessity in order to do an efficient job of cutting the members. The best place to do the cutting is therefore either in a local fabrication plant or in some building on the farm such as a shop or machine shed where there is electric power.

Fig. 5. A simple jig made from plywood and 2 x 4's.

b Co

4'-0"

[ 6 ]

Fig. 6. Applying glue to the surfaces of the mem­bers being joined.

Fig. 7. Recommended arrange­ment of nails in the nailed and glued joints.

Assemble the half-frames. The half-frames, consisting of a stud, a rafter, and the eave gussets, can best be assembled inside a building, either at a local plant or on the farm. This works much better than trying to assemble them out from under cover at the site where the building is to be erected. The half­frames are not difficult to carry or haul.

Use a jig when assembling the half-frames. It does not need to be elaborate. Any arrangement that will hold the members in their correct positions while the gusset is placed on one side of the eave joint is satisfactory. Figure 5 shows a simple jig consisting of a sheet of plywood and two 2 x 4's placed to hold the members in position. The use of a jig speeds up the assembly and insures that all the half-frames will be identical in shape. After the jig is built and you are ready to assemble the half-frames, proceed as follows:

1. Place the stud and rafter in their correct position in the jig. Since either end of the stud can go next to the gusset, remember to place the end containing the smallest and fewest defects next to the gusset.

2. Apply glue to both the stud and rafter and to the gusset plate (Figure 6) . Mix the glue carefully according to the manufacturer's directions and spread on with a fiber brush or a stiff-bristle brush. Apply enough glue so that a

little squeezes out when pressure is applied.

3. Nail the gusset into place. Use 4d common nails for %-inch gussets and 6d common nails for %-inch gussets. Follow the general pattern of nailing shown in Figure 7. In order to be sure that enough pressure is being applied, drive the nails until the head of the hammer dents the plywood.

4. Remove the half-frame from the jig, turn it over, lay it back down on any flat surface, and apply the gusset to the other side.

5. After completing a half-frame, lay it flat without any bows in the members and leave it for about 24 hours while the glue sets. Temperatures around 65 0 or higher are required for the glue to set properly.

[ 7 ]

Erect the frames. After the frames have set for at least 24 hours, you may erect them in this way:

1. Move the half-frames to the build­ing site, lay two of them down flat near where they are to be erected, and connect them at the ridge (Figure 8 ) . Nail and glue the gussets to the framing members, following the same procedure as for the eave joint. Be sure that the lower ends of the studs are the correct distance apart

Fig. 8. Connecting the half-frames at the ridge. when making the joint.

2. Tip the frames up into positlon (Figure 9 ) . The frames are light enough that four men can easily handle even the heaviest ones.

3. Fasten the frames to the foundation (see next page for suggestions ) , plumb them, and apply either temporary or part of the permanent bracing and nailers to hold them in position (Figure 10 ) .

If the frames are erected during a windy period or are to be left overnight without all of the permanent bracing and wall and roof sheathing or stripping

in place, they should be thoroughly braced to pro­tect them against wind damage.

Fig. 9. Completed ridge frames being lifted into position.

Fig. 10. Applying bracing and nailers to the frames to hold them in position.

[ 8 ]

FOUNDATIONS Foundations for rigid frames must be carefully planned and constructed. Besides the normal vertical loads on the foundation that occur with any type of framing, rigid frames place large horizontal loads on the foundation. These loads tend to spread the foundation walls and to cause them to overturn.

There are two types of foundations most likely to be used - the flat-slab type and the more common concrete wall type with the wall extending 12 to 18 inches above grade and 24 to 30 inches below grade. The flat-slab type is probably the simplest to construct, but it is suitable only when there is to be a concrete floor in the building and when it is not necessary that a concrete wall extend above floor level. Detailed construction recommendations are given in Figure 11 for both types of foundations.

Q MINIMUM OF 6 " OT~~p..,WI~E. 6AME I ~ =IW1on-l OF FP.A.ME

Wh '%A~ NOMI~AL

Fig. 11. Details WIt:>T~ OF F~AM"

for the foundation. ~'10.~" NO, 10 ' )4" STEEL ~OD WELDED WI~E.

COt-JT I t.Juou5 AP-OUND ME6~ I=OUf\JDA, ION WALL

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p.,OD Yz.~ ~TE.E.L p..OD5 4 '-0 " SPACING IF f--rl. CO~Cp..E:TE. ~LOOp., 15 U~E.D LMI~IMUM WIDT~:: W

CONNECTIONS BETWEEN Special attention should be given to the connections between rigid frames

FRAMES AND and the foundations. Nailing alone is not enough to resist the large horizon­tal and uplift loads. With 2 x 4 and 2 x 6 frames, a wooden sill, anchor bolts,FOUNDATIONS and metal framing anchors will form a satisfactory connection; larger frames, however, require the use of a steel angle and bolts (Figure 12 ) .

,r F"AMING ANCI-IOJl. z r:p..AMING ANCIo{O"~ PL-U~ TO.N~ILING PLUS TOENAIL-ING

2 ")( 6· SIL-L 2"J{~· SILL

~"ANC~O" f>OL-T '1i'ANC~Op.." e,OLTe.. LONG 8" LOt..lG 4 '- 0 " SPA.CING 3 '-0· 5PAClt-JG

lfx e; AtJCa.tOP. -'---'lJ-------'- r,OLT5

Fig. 12. Details for anchoring 2: X 10 · !=~AME 2.."'1. 12." J=P-..AM~frames to the foundation.

1'-='=:::::::»--- 3 -~' )C z:t; e,OLT~

~~I 3 "~ 5 "" '/i. L 3·X~· ){~' L

9" L-ONG " " LONG

V; "/. roO' ANCI-K)" I/i: X 6 " ANC~O~ bOLTS &OLT5

[ 9 ]

BRACING Rigid frames require diagonal bracing in the direction of the long axis of the building to prevent racking by wind. Bracing for the side wall and roof is required as shown in Figure 13. The braces should be well nailed to the inside edge of the frames. The frames should not be notched for the braces under any circumstances.

Use 1 x 6 boards for frames spaced 4 feet or less, 2 x 4 lumber for frames spaced 4 to 8 feet, and aT-shaped brace consisting of two pieces of 2 x 4 (Figure 14) for frames spaced more than 8 feet. If the building is to be lined on the inside with a sheet-type material, no angle bracing is needed.

Fig. 13. Locations for diagonal bracing. Fig. 14. Details of T -shaped diagonal brace.

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Lio"""'" 1..1 io"""= I ~ Ia: V I ~ '" I ~ EAVE

K .,. " I' "" I I I Y F=OUNOA.TION T~.SE O~It.CI:5 ~E­ e,P\ACE: l=P\OM QUIP\&O IF= f!)UlL.OING e>A~E. OF 1= ~A.ME ,~ L.O~GEp.... T~AN TO E.A.VE: T- 5~A.P~D DIAGONkL e,~ACE~ Ae,OUT lOO F=EE, 2."lt4" C.UT TO I=IT e,E.TWE.E.N ~~A.ME

2"l!!4" SPI~~D TO UNOE.l'-.'l>IDE O~ Fp.,AME:.

WALL CONSTRUCTION The type of wall construction depends on the frame spacing and the type of wall surfacing material. Materials such as wood siding applied horizontally and corrugated sheet-metal siding applied with the corrugations horizontal may be attached directly to the frames if the spacing is not too great (Figure 15 ) . Wide spacings and the use of siding which is applied vertically require the use of horizontal nailing girts (Figure 16 ) .

Fig. 15. Wall construction with siding applied directly to frames.

Frame Type of siding spacing

1 " matched siding 4'- 0" applied horizontally

1~" corrugated 2'- 6" metal siding

2Yz" corrugated 4'- 0" metal siding I(Frame spacing is maximum GJIl-T 1=J1.-0M 2. -Z·x4" ,allowable)

ONE. I=LAT AGAINST FIV.Mt. ONE CUT TO I=IT BE.TWEEN ~~AME.5

Fig. 16. Wall construction with siding applied over horizontal nailing girts.

Girt Frame Girt spacing spacing

1x4 1'- 6" 2'- 0" 2'- 0" 1'- 6"

2 x 4 flat 1'- 6" 6'- 0" against 2'- 0" 5'- 0" frame 2'- 6" 4'-0"

Girt 1'- 6" 16'- 0" from 2'- 0" 14'- 6" 2- 2x4 2'- 6" 13'- 0"

[ 10 ] (Frame spacing is maximum allowable)

ROOF CONSTRUCTION The system of roof construction to be used depends primarily on the type of roofing material to be used. Roofing materials that require solid sheathing work well with frame spacings up to 4 feet (Figure 17 ) . Roofing materials that may be applied over spaced nailing girts work well with any frame spac­ing. The size of girt required, of course, varies with the spacing of the girts and of the frame (Figure 18 ) .

Fig. 17. Roof construction using solid sheathing.

Type of solid Fr ame sheathing spacing

1" matched boards 4'-0"

%6" plywood 1'-4"

%" plywood 2'-0"

12" p lywood 2'- 8"

Va " plywood 3'-6"

%" p lywooda 4'-0"

(Frame spacing is maximum allowable)

a Edges b locked with alu­minum clip designed for th is purpose.

Fig. 18. Roof construction using spaced nailing girts.

Girt Frame Girt spacing spacing

2x 4 1'-6" 6'- 0" flat 2'- 0" 5'- 0"

2'-6" 4'- 0"

2x 4 on 1'- 6" 11'- 0" edge 2'-0" 9'-6"

2'-6" 7'-6"

2x 6 on 1'-6" 16'-0" edge 2'-0" 14'- 6"

2'-6" 13'- 0"

(Frame spacing is maximum allowable)

Fig. 19. Transporting half-frames for a building 30 feet wide.

Fig. 20. Glued joints can be easily protected against rain until they are ready to be put up.

[ 11 ]

,...­

From the outside, buildings with lumber rigid frame construction look like building of conventional construction. Inside, however, the differences are obvious. As shown below, the entire floor space is left free of posts, and no ties are needed for the rafters. The gussets at the eaves can be seen along each side. The ridge gussets are partly hidden by the ventilating system in this building.

12M-12-59-69793