Composite steel highway bridges 2005

Composite steel highway bridges

Corus Construction & Industrial

ContentsAcknowledgement of author

Advantages of steel bridges

1 Design standards

2 Conceptual design

2.1 Spans and component lengths

2.2 Cross sections

2.3 Intermediate supports

2.4 Bracings

2.5 Steel grades

2.6 Further guidance

3 Initial sizes and overall unit weight

3.1 Introduction

3.2 Use of charts

3.2.1 Plate girder flange sizes

3.2.2 Plate girder web sizes

3.2.3 Overall unit weight

3.2.4 Universal beams

3.2.5 List of symbols

4 Worked examples – use of charts

4.1 Continuous plate girder bridge

4.2 Simply supported universal beam bridge

5 References

6 Figures

Figure 4 – Simply supported bridges

Figure 5 – Continuous bridges – span girders

Figure 6 – Continuous bridges – pier girders

Figure 7 – Girder spacing factors

Figure 8 – Overall unit weights – plate girder bridges

Figure 9 – Universal beams – elastic stress analysis

Figure 10 – Universal beams – plastic stress analysis

2 Composite steel highway bridges

Contents

1. Left: Waterside BridgeNewburgh, Scotland

2. Right: A1(M)Yorkshire, England

This guide is an update of a publication originally

prepared by A.C.G. Hayward. Corus gratefully

acknowledges the work of Mr Hayward and the

contribution made by D.C. Iles, The Steel Construction

Institute, during this update.

Composite steel highway bridges 3

Advantages of steel bridges

The Author

Alan C. G. Hayward FREng CEng FICE FIStructE

Alan Hayward was a founding Partner of bridge

specialists Cass Hayward & Partners of Chepstow who

design and evolve construction methodology for all

types of bridges, particularly steel highway, railway,

footbridges, movable bridges and Roll-On/Roll-Off

linkspans in the UK and overseas. He remains active in

the firm as a Consultant.

Alan Hayward was continuously involved with the

development of bridge codes including BS 5400 and

Eurocodes and has been National Technical Contact for

the composite bridge code EC4-2. He contributes to the

education of engineers by lecturing at Universities on

behalf of industry, and has written numerous papers on

steel bridge construction. He was a long-standing

member of the Steel Bridge Group who disseminate best

practice through their published Guidance Notes.

Advantages of steel bridges Feature Leading to Advantages

Low weight of Fewer piles and smaller sizes of pile caps/foundations. Cheaper foundations.superstructure. Typical 30 – 50% reduction over concrete decks.

Composite bridges 6.0 – 8.0kN/m2 typical.

Light units for erection. Erection by smaller cranes. Delivery of long pieces. Cheaper site costs.Launch erection with light equipment (skates or rollers).

Simple site joints. Bolted joints: easy to form larger pieces from small Flexible site planning.transported components taken to remote sites.

Maximum Quality control in good factory conditions avoiding outdoor More reliable product.pre-fabrication in site affected by weather and difficult access.factory.

Predictable Commuted painting costs can be calculated. If easy repainting Total life cost known.maintenance costs. is made possible by access and good design then no other

maintenance necessary.

Low construction Depth/span ratio 1/20 to 1/30 typically. Slender appearance.depth. Lower depth achieved with half-through girders. Reduces costs of earthworks

in approaches.

Self supporting Falsework eliminated. Falsework costs eliminated.during construction. Slab formwork and falsework also avoided using permanent formwork. Significant if more than 8m

above ground.

Continuous and Continuity easy with bolted or welded joints. Most expansion Better appearance.integral spans. joints eliminated. Number of bearings reduced. Improved durability.

Compliance with BD57. Improved running surface.

Adaptable details. Pleasing appearance taking advantage of curves and colour. Aesthetic gain.

Re-usable product. Demountable structures and recyclable components which Sustainable product.reduce manufacturing energy input.

Composite steel highway bridges


The current bridge code BS 5400 (Ref. 1) was conceived

in 1967. Its ten parts cover the more common structural

media. The 1980 conference in Cardiff introduced the

Code relating to steel and made use of research carried

out since 1970.

Part 3 (Design of Steel Bridges) is compatible with the

workmanship standards and tolerances defined in Part

6, drawn up jointly with industry.

The Code uses limit state principles. The ultimate

limit state (ULS) and serviceability limit state (SLS) must

be satisfied.

In practice the ULS generally governs, exceptions being

the checking at SLS for slip of HSFG bolts and the

design of shear connectors.

BS 5400 encourages the use of steel for a number

of reasons:

(i) Plastic stress analysis option offers the use of

lighter members and extends the span range of

rolled sections.

(ii) Design clauses are easier to use than

previous Codes.

(iii) Workmanship requirements, including tolerances,

are rationalised.

(iv) Longitudinal web stiffeners to girders are

rarely needed.

Use of the plastic modulus is permitted for stress

analysis of compact sections and where the slenderness

is controlled by sufficient restraints, the effects of

shrinkage and differential temperature can be neglected.

For ‘compact’ sections, the entire load can also be

assumed to act on the composite section even if the

steelwork is unpropped, provided that SLS checks

are made.

While most rolled universal beams, columns and

channels will be compact, plate girders will often be

non-compact and must be stressed elastically. (See also

Section 3.2.4.)

For structural analysis, elastic methods are utilised

using gross sections (i.e. not allowing for shear lag or

effective width).

1. M4/M25 Poyle Interchange

1. Design standards


Redistribution of moments arising from the formation of

plastic hinges is not permitted, but redistribution due to

cracking of concrete over intermediate supports may be

assumed using Part 5.

Combined bending and shear is dealt with using

interaction formulae. This is sometimes critical at

intermediate supports.

The Code contains no specific limits on slenderness of

members or proportion of plate panels. Longitudinal web

stiffeners are usually only necessary for very deep

girders or those with curved soffits.

For rolled sections the full shear yield stress can

generally be used without the need for intermediate

stiffeners. Bearing stiffeners are virtually mandatory at

supports, together with lateral bracing or a system of

bracing to maintain verticality.

Fatigue is checked to Part 10, although for highway

bridges this rarely demands a reduction in working

stresses provided good detailing practice is used.

For example:

(i) Do not locate welded attachments close to or on

flange edges (class 'G').

(ii) Re-entrant corners should be radiused.

(iii) Use HSFG bolts for permanent bolted connections.

(iv) Restrict doubler flange ends to areas of low stress

(class 'G').

(v) Avoid single sided partial penetration butt welded

joints which are subject to tensile stress.

(vi) Avoid welded cruciform joints, which are subject to

significant tensile stresses. An example is when

using integral crossheads (see Figs. 1B & 1F)

where fillet welds should be used in preference to

full penetration butt welds. If butt welds are

necessary, the use of steel with through-thickness

quality (Z-grades to BS EN 10164 – Ref 14) may be

considered in view of the strains which will be

caused during welding.

1. This page: A69 Haltwhistle Viaduct(Photo courtesy of Cleveland Bridge (UK) Ltd.)Northumberland, England

2. Right: Festival Park FlyoverStoke, England

3. Far right: Simon De Montford BridgeEvesham, England


Conceptual design

2.1 Spans and component lengthsSpans are usually fixed by site restrictions and

clearances. Where freedom exists, budget costing –

including foundations – is desirable to determine the

economic span. A range of 25m to 50m is likely.

Where deep piled foundations are needed, cost will

encourage the use of longer spans, thus keeping

foundations to a minimum.

Multiple spans

Multiple spans of approximately 24m suit universal

beams, this being the longest readily available length and

because continuous spans are convenient and economic.

Site splices may be bolted with HSFG bolts or welded

near points of contraflexure. The length of end spans

should ideally be about 0.8 of the penultimate span.

Continuous spans

The optimum for using plate or box girders for

continuous spans is about 45m, because 27m long

‘span girders’ can be spliced with ‘pier girders’ of a

single plate 18m long. For longer spans, more shop or

site splices are needed. Component lengths for shop

fabrication should be the maximum possible consistent

with delivery and site restrictions to reduce the amount

of on-site assembly. The maximum length for road

delivery without restrictions is normally 27.4m although

longer lengths can readily be transported by

arrangement. A minimum number of shop butt welds

should be used consistent with plate sizes available. The

decision whether to introduce thickness changes within

a fabricated length should take account of the cost of

butt welds compared with the potential for material

saving (Ref. Documents in Section 2.6).

Curved bridges

Curved bridges in plan may be formed using straight

fabricated girders, with direction changes introduced at

each site splice. However, steel girders can be curved in

plan which simplifies the cantilever formwork and

permits the use of standard systems. An example is the

A69 Haltwhistle Viaduct (radius 540m)

Skew and plan tapered bridges may also be built in

steel. Ideally, plan layout should be as simple as

possible (Ref. Documents in Section 2.6).

Integral bridges

The Highways Agency requires consideration of integral

bridge forms for spans up to 60m with the objective of

improved durability by elimination of bridge deck

movement joints (Ref. 4 & 5). Girders may then be

required to develop a degree of continuity with

substructures at end supports such that axial forces and

reverse moment effects need to be considered in the

design of the composite deck. Design principles remain

the same but girder sizes and bracing provision may be

influenced. Further guidance is available from the Steel

Construction Institute (Ref. 8, 9, 10 & 10a).

2.2 Cross sections Deck type construction

Deck type construction is common and is suitable for

highway bridges as shown in Fig. 1. A span-to-girder

depth ratio of 20 is economic although 30 or more can

be achieved. A half-through bridge (‘U’ frame) can be

appropriate in cases of severely limited depth, such as

where approach lengths are restricted. Footbridges and

rail under-bridges are common examples.

2. Conceptual design


Conceptual design

Where permanent formwork is envisaged, the slab

should be made sufficiently thick to accommodate the

details taking account of reinforcement cover and

practical tolerances (Ref. 7). When using composite part

depth planks such as Omnia then a minimum thickness

of 250mm may be needed.

Universal beams and plate girders

Universal beams may be appropriate for bridges up to

25m span and above when continuous, or when use can

be made of the plastic modulus. For spans above 22m,

plate girders, especially if continuous, can be economic

because lighter sections can be inserted in mid-span

regions. Costs per tonne of painted and erected

universal beams were traditionally lower but, more

recently, automated fabrication and less expensive plate

material has allowed economic supply of plate girders

for the shorter spans.

A girder spacing of 3.0m to 3.5m is usual with a deck

slab of about 250mm thick (see Figs. 1A and 1B). Edge

cantilevers should not exceed half the beam spacing

and to simplify falsework should, where possible be less

than 1.5m. Shorter cantilevers are usually necessary

with a locally thickened slab where very high

containment parapets are specified, e.g. over rail tracks.

An even number of girders achieves better optimisation

of material (ordering) and allows bracing in pairs. For

wide girder spacings, the slab may be haunched, but

use of standardised permanent formwork is unlikely to

be possible and construction depth is increased (see

Fig. 1C). Where spans exceed 40m, twin plate girders

with a central stringer have been used on some single

carriageway decks up to about 13m wide (see Fig. 1D).

Twin girders and cross beams (often referred to as

ladder decks) have proved economic for a wide range of

spans (Ref. 10b). They can be used for single

carriageway decks (see Fig. 1E) and for wider decks

supporting more lanes.

Box girders

Where spans exceed 100m box girders are likely to be

more economic than plate girders with which flange sizes

would be excessive. Other reasons for using box girders

include aesthetics (where justifiable), aerodynamic

stability, severe plan curvature, the need for single column

supports or very limited depth. Other than in the cases

noted, box girders – being heavier than plate girders – are

more expensive because although less flange material

may be demanded due to inherent torsional properties,

this is usually more than offset by the amount of internal

stiffening and extra costs for workmanship. Fabrication

costs are higher because the assembly/welding

processes take longer and more shop space is needed.

However, erection work is often reduced because box

girders require little or no external bracing.

Multiple box girders have in the past proved to be

economic for spans of around 50m in particular

situations. Using narrow cross sections eliminates the

need for longitudinal stiffeners (see Fig. 1F). An example

of which is the M25/M4 Poyle Interchange.

For box girders, consideration of the safety of personnel in

confined spaces is essential during fabrication, erection and

for maintenance. Detailing must recognise the need to avoid

internal welding as far as possible and to allow sufficient

ventilation and openings for access and recovery in

emergency situations.

Open-topped trapezoidal and rectangular shaped box

girders have been used efficiently, but provisions are

needed to preserve stability during erection, for example the

Forrest Way Bridge, Warrington.

Plate girder flanges

Plate girder flanges should be as wide as possible but

consistent with outstand limitations in BS 5400 (i.e. 12t in

compression if fully stressed and up to the 20t robustness


Conceptual design

1. Far Left: Nene BridgePeterborough, England

2. Left: Forrest Way BridgeWarrington, England

3. Right: M20 Road BridgeFolkstone, England

limit), to give the best achievable stability during erection

and to reduce the number of bracings. For practical

reasons a desirable minimum width is about 400mm to

accommodate detailing for certain types of permanent

formwork, especially precast concrete. A maximum flange

thickness of 63mm is recommended to avoid heavy welds,

minimise pre-heating requirements and also limit the

reduction in design yield strength. Limiting the thickness

also has benefits in terms of notch toughness specification.

2.3 Intermediate supports Piers can take the form of reinforced concrete, leaf,

column or portal. Steel columns are also used. For

example, tubular steel columns (concrete filled

composite), were used in the M5 Almondsbury

Interchange and deserve consideration. Leaf piers or

multiple columns supporting every girder are convenient

but where fewer columns are demanded for aesthetic

reasons, integral steel crossheads provide a solution. The

popularity of these crossheads has recently increased

following earlier examples on M25 bridges including

Brook Street Viaduct, Mar Dyke Viaduct and South

Mimms Interchange Bridges (see Figs. 1B and 1F). They

were extensively used for the Second Severn crossing

approach roads and for the new Thelwall Viaduct.

It should, however, be recognised that the introduction

of these additional members is only likely to be

economic where the use of fewer supports is essential.

Costs can increase especially if column spacing is not

arranged to allow balanced erection and temporary

trestles become necessary. Care is also needed detailing

cruciform welded joints at the crosshead/main girder

connection (Ref. Section 1 (vi)).

2.4 Bracings For most universal beam or plate girder bridges, lateral

bracings are needed for erection stability and during

deck concreting.

Intermediate bracings require to be spaced at about

20 x top flange width and need to be adequate to

prevent lateral torsional buckling. Bracing is necessary

at supports if only to prevent overturning during

erection. At abutments this can be a channel trimmer

composite with the slab and supporting its free end. Over

piers a channel section can be used between each pair

of girders of up to about 1.2m deep. For deeper girders

triangulated angle bracings are usual (see Fig. 1B).

Intermediate lateral bracings are usually necessary in

hogging regions with a maximum spacing of about

12 x bottom flange width. If the bridge is curved they

should be close to the site splices where curvature

induces torsion. Bracings may be of a triangulated form

or of single channel sections between each pair of

girders of up to 1.2m deep (see Fig. 1A). Alternatively,

bracings can take the form of inverted 'U' frames, but

for spans exceeding around 35m it may be necessary to

interconnect all the girders by bracings during erection

so that transverse flexure from wind is adequately

shared. Although plan bracing systems are uneconomic

and should be avoided, they may be required for spans

exceeding 55m for temporary stability, especially if

launch erection is used (Ref. Documents in Section 2.6).

Use may be made of bracings in distributing live loads

between girders. This may offer reduced flange sizes

under HB loading but the uniformity of current loading to

BD37 across the carriageway (HB + 2 lanes HA + 0.6 HA

other lanes) tends to discourage this. An optimum design

is likely to include bracings only between pairs of girders,

such discontinuous bracings attracting minimal effects

under deck loading except in cases of heavy skew or

curvature where a different system may be appropriate.

Bracings should be included in the global analysis to

check for possible overload or fatigue effects.


Conceptual design

1. Left: Humber Road BridgeImmingham, England

2. Right: Thelwall Viaduct M6, Warrington, England

DECK WIDTH

230 TO

250 mm

2.5 TO 3.5

1.0 TO 1.75

TYPICAL

300 TO 350 mm

1.0 TO 3.3 4.0 TO 5.5

W

230 TO

250 mm

D

D

D

1BMultiple P.G.(N=4)

1CTwin P.G.Haunch Slab(N=2)

1AMultiple U.B.(N=4)

AT MID-SPAN AT PIERFigures 1A – 1FTypical deck type cross-sections


Conceptual design

230 TO 320 mm

6.0 TO 7.0

3.0 TO 3.5 c/c

0.9 TO 1.2 2.5 TO 3.5

AT MID-SPAN AT PIER

1.0 TO 3.3

>7.0

230 TO

250 mm

230 TO

250 mm

D

D

D

1DTwin P.G.& Stringer(N=2)

1ETwin P.G.& Cross Girders(N=2)

1FMultiple Box(N=6)


2.5 Steel gradesBS EN 10025-2: 2004 Grade S355 steels (Ref. 12) are

usual for bridges as they offer a lower cost-to-strength

ratio than Grade S275. BS 5400 requires all steel parts to

achieve a specified notch toughness, depending upon

design minimum temperature, stress level and

construction features (e.g. welding details). Subgrades J2

and K2 will be most common.

Composite bridge decks are specifically categorised in

the composite version of BS 5400: Part 2 (implemented

by BD37), to allow a range of effective bridge

temperatures to be determined from isotherms of

minimum and maximum shade air temperature for a

particular site location. Limiting thicknesses for steel

parts are prescribed in BS 5400: Part 3, as implemented

by BD13 (Ref. 3), as appropriate to these effective bridge

temperatures, and the other factors mentioned above.

Weathering steel

To eliminate the need for painting, weathering steels to

BS EN 10025-5: 2004 (Ref. 13) should be considered.

Although it can be shown that the commuted costs of

repainting are less than 1% of the initial bridge cost,

weathering steel bridges can be more economical on a

1. Above: Findhorn ViaductInverness, Scotland

2. Left: Westgate BridgeGloucester, England

3. Right: Slochd Beag BridgeInverness, Scotland


first cost basis and are particularly useful in eliminating

maintenance where access is difficult – over a railway,

for example.

Weathering steel is not suitable at or near the coast, (i.e.

within about 2km from the sea) due to the chloride laden

environment or in areas of severe pollution.

The Highways Agency requires sacrificial thickness to be

added to all exposed surfaces for possible long term

corrosion (1.5mm per face in a severe marine or industrial

environment, 1mm in mild environments and 0.5mm

inside box girders) and detailed guidance is given in

design standard BD 7 (Ref. 6) and Corus Publication

‘Weathering steel bridges’ (Ref. 11).

2.6 Further guidanceParticularly relevant information for initial (and detailed)

design is included within two publications:

• BCSA Publication No. 34/02 ‘Steel Bridges’

Alan Hayward, Neil Sadler and Derek Tordoff, 2002.

• SCI-P-185, Steel Bridge Group: Guidance notes on

Best Practice in Steel Bridge Construction.


Initial sizes and overall unit weight

3. Initial sizes and overallunit weight 3.1 IntroductionCharts are given to provide initial estimates of flange

area (Af) web thickness (tw) and overall unit weight of

steelwork (kg/m2) for typical composite bridge cross

sections as shown in Fig. 1.

Continuous or simply supported span plate girders and

simply supported universal beams are included. The

charts were derived from approximate BS 5400 designs

using simplifying assumptions for loads, transverse

distribution and to achieve correlation with modern

bridges. The charts take account of the latest highway

loading requirements in BD37.

It is emphasised that the sizes obtained do not represent

final designs, which must always be executed to take

account of all factors, such as bridge configuration and

loading. Adjustments will need to be made to take

account of the likely effects of end continuity if integral

construction is intended.

The charts are based on the following assumptions:

(i) Deck slab 250mm average thickness (6.25kN/m2).

(ii) Superimposed dead loads equivalent to 100mm of

surfacing (2.40 kN/m2).

(iii) Permanent formwork weight 0.50 kN/m2 of slab

soffit area.

(iv) Steel grade S355.

(v) Span to depth ratios L/D of 20 & 30.

(vi) Plate girder webs have vertical stiffeners at approx.

2.0m centres where such stiffening is required.

(vii) Elastic stress analysis is used for plate girders. If

however the plastic modulus is used for compact

cross sections, then economies may be possible.

(viii) Steelwork is unpropped and therefore not acting

compositely under its own weight and that of the

concrete slab. The steel is however composite for

all superimposed loads after the concrete has cured.

(ix) Sufficient transverse bracings are included such

that bending stresses are not significantly reduced

due to buckling criteria.

(x) Top flanges in sagging regions are dictated by the

maximum stress during concreting allowing for

formwork and live load – to BS 5975 (Ref. 15).

Continuous bridge mid-span regions are concreted

in turn followed by portions over the piers.

(xi) Live loading HA (assuming 3.5m wide lanes), or

alternatively 45 units of HB loading with co-existent

HA loading (BD37).

(xii) Continuous spans are approximately equal.

3.2 Use of charts

3.2.1 Plate girder flange sizesFlange areas (Af in m2) are read against the span L.

(a) For simply supported bridges – (refer Fig. 4)

(b) For continuous bridges –

Size of span girder (refer Fig. 5)

Size of pier girder (refer Fig. 6)

Figures 4, 5 and 6 are applicable to an average girder

spacing ‘s’ of 3.5m. Fig. 7 gives a girder spacing factor

Kaf which is multiplied by the flange areas, obtained

above, to give values appropriate to the actual average

girder spacing.

i.e. Top Flange Aft = Aft (Figs. 4, 5 or 6) x Kaf (Fig. 7)

i.e. Bottom Flange Afb = Afb (Figs. 4, 5 or 6) x Kaf ( Fig. 7)

Two different span-to-depth ratios, L/D = 20 and L/D =

30, are included for either HB or alternatively HA loading.

Values for intermediate L/D ratios can be read

by interpolation.



The charts also show actual flange sizes using

400mm x 15mm to 1000mm x 75mm.

Flange area of pier girders of continuous unequal spans

can be estimated by taking the greater of the two

adjacent spans.

End spans of continuous bridges may be estimated

using L = 1.25 x actual span.

3.2.2 Plate girder web sizes Web thicknesses are similarly obtained using Figs. 4, 5

and 6 applicable to 's' = 3.5m. Adjustment for the actual

average girder spacing 's' is obtainable from Fig. 7 using

girder spacing factor ktw.

i.e. Web thickness tw = tw (Figs. 4, 5 or 6) x ktw (Fig. 7).

The thickness obtained may be regarded as reasonably

typical. However, designers may prefer to opt for thicker

webs to reduce the number of web stiffeners.

3.2.3 Overall unit weight Overall unit weight (kg/m2 of gross deck area) for plate

girders is read against the span L from Fig. 8 for simply

supported or continuous bridges with L/D ratios of 20 or

30, under HB or alternatively HA loading and applicable

to ‘s’ = 3.5m.

Adjustment for average girder spacing 's' other than

3.5m is obtainable from Fig. 7 using girder spacing

factor kw.

i.e. Unit weight kg/m2 = kg/m2 (Fig. 8) x kw (Fig. 7).

The unit weight provides an approximate first

estimate of steelwork tonnage allowing for all stiffeners

and bracings.

For continuous bridges with variable depth, Fig. 8 may

be used to provide a rough guide, assuming a span-to-

depth (L/D) ratio for each span based upon the average

girder depth (D) within that span.

For box girder bridges a rough estimate may be

obtained assuming that N = 2 x number of box girders in

the cross section (see Fig. 1F where N = 2 x 3 = 6).

For continuous bridges the end spans should be assumed

as 1.25 x actual span, following which the mean span for

use in Fig. 8 may be determined as follows:

Mean span L = L14 + L2

4...Ln4

n

where n = number of spans.

3.2.4 Universal beams An indication of beam size for simply supported spans

may be obtained from Figs. 9 and 10 for elastic or

plastic stress analysis respectively. BS 5400 permits the

use of either option, provided that the cross section is

‘compact’; this condition being satisfied for all sections

shown in Fig. 10. Sufficient ductility is also required. It is

apparent that plastic stress analysis can achieve

significant economy in extending the span range of

universal beams. In practice, a serviceability stress

check (SLS) must be made including the effects of shear

lag. There is advantage also in using the plastic design

option for continuous spans but some universal beams

may need to be classed as 'non-compact', requiring

elastic analysis in hogging regions because the web

depth between the (elastic) neutral axis and its

compressive edge may exceed 28tw, depending upon

the amount of longitudinal slab reinforcement.

An overall unit weight for universal beam bridges may be

estimated at the conceptual stage by adding an

allowance of approximately 8% to the weight of the

main beams to allow for any bracings and stiffeners etc.

Figs. 9 and 10 refer to mass per metre of universal beams.

4

1. Left: Milton BridgeLesmahagow, Scotland

2. Right: Fossdyke Bridge(Photo courtesy of Cleveland Bridge (UK) Ltd.)Lincoln, England



Reference Universal beam size Actual depth (mm)figures 9 & 10

Serial Mass per size (mm) metre (kg/m)

388 914 x 419 388 921.0

343 343 911.8

289 914 x 305 289 926.6

253 253 918.4

224 224 910.4

201 201 903.0

226 838 x 292 226 850.9

194 194 840.7

176 176 834.9

197 762 x 267 197 769.8

173 173 762.2

147 147 754.0

170 686 x 254 170 692.9

152 152 687.5

140 140 683.5

125 125 677.9

238 610 x 305 238 635.8

179 179 620.2

149 149 612.4

140 610 x 229 140 617.2

125 125 612.2

113 113 607.6

101 101 602.6

Table 1 (with reference to sizes in Figs. 9 and 10)

Table 1 above defines the referencing system for the

serial sizes in Figs. 9 and 10, which is based on the

mass per metre of universal beams. Larger sizes are

available (e.g. 1016), but are unlikely to be economic

compared to fabricated plate girders.

3.2.5 List of symbolsAf Flange area (m2)

Afb Bottom flange area (m2)

Aft Top flange area (m2)

D Girder or beam overall depth excluding slab

or finishes (m)

HA Standard highway loading defined in BD37

HB Abnormal highway loading defined in BD37,

45 units assumed

Kaf Girder spacing factor for flange area

Ktw Girder spacing factor for web thickness

Kw Girder spacing factor for unit weight

L Span centre to centre of bearings

(taken as 1.25 x span for end span of

continuous bridges)

kg/m2 Unit weight of steelwork in bridge expressed as:

total steelwork weight (kg)

W x overall bridge length

s Average girder spacing defined as W/N (m)

tw Web thickness (mm)

W Overall deck width including parapets (m)

n Number of spans

N Number of girders (refer to Section 3.2.3 for

box girders)

Notes

(i) Where relevant, symbols correspond with

BS 5400 Part 3.

(ii) Units where relevant are shown in parentheses.


Worked examples – use of charts

4.1 Continuous plate girder bridge A composite highway bridge has 3 continuous spans –

A, B and C of 24, 40 and 32m.

Overall deck width is 12m and it carries 45 units of HB

loading (as shown in figure 2).

There are 4 plate girders in the cross section of

1.75m depth.

Estimate the main girder sizes and the total weight of

structural steel.

Average girder spacing 's' = W/N =12m/4 No. = 3.0m

Figure 2 Worked example

Flange and web sizes

Girder spacing factors: for 'S' = 3.0m

From Fig. 7: Kaf = 0.87, Kaf = 0.85*, Ktw = 0.95

(*top flange span girders only).

Span girder Pier girderPier girder Span girderSpan girder

W = 12m

24m 40m 32mSpan A Span B Span C

D = 1.75m

1. Left: Trent ViaductNewark, England

2. Right: A69 Haltwhistle Viaduct(Photo courtesy of Cleveland Bridge (UK) Ltd.)Northumberland, England

4. Worked examples – use of charts



Span A: 24m This is an end span so take L = 1.25 x 24m = 30m

Therefore L/D = 30m/1.75m = 17, so assume L/D = 20

Top flange Aft = Aft (from Fig. 5) x Kaf

= 0.006 x 0.85 = 0.0051m2

400 x 15 top flange

Bottom flange Afb = Afb(from Fig. 5) x Kaf

= 0.014 x 0.87 = 0.012m2

500 x 25 bottom flange

Web tw = tw (from Fig. 5) x Ktw

= 10 x 0.95 = 9.5mm

Use 10mm web

Span B: 40m Span girder

L/D = 40m/1.75m = 22.9


= 0.009 x 0.85 = 0.0077m2

400 x 20 top flange

Bottom flange Afb = Afb (from Fig. 5) x Kaf

= 0.020 x 0.87 = 0.017m2



= 10 x 0.95 = 9.5mm

Use 10mm web

Span C: 32m This is an end span so take L = 1.25 x 32m = 40m

therefore sizes as 40m span.

Pier girders

Take L as the greater of the two adjacent spans, i.e.

assume L = 40m at both supports, hence, L/D =

40m/1.75m = 22.9


= 0.017 x 0.87 = 0.015m2

400 x 40 top flange

Bottom flange Afb = Afb(from Fig. 6) x K af

= 0.033 x 0.87 = 0.029m2



= 16.8 x 0.95 = 16mm

Therefore use 18mm web

Steel tonnage Girder spacing = 3.0m

for end span A: L = 1.25 x 24m = 30m

for centre span B: L = 40m

for end span C: L = 1.25 x 32m = 40m

Therefore mean span

4

L14 + L2

4...Ln4

n

4

304 + 404 + 404 = 37.5m

3

L/D = 37.5m/1.75m = 21

= kg/m2 (from Fig. 8) x Kw (from Fig. 7)

= 145kg/m2 x 1.04 = 151kg/m2

Hence, steel weight

= 151 kg/m2/1000 x (24m + 40m + 32m) x 12m wide

= 174 tonnes



4.2 Simply supported universal beam bridgeA composite bridge has a simply supported span of

24m. (as shown in figure 3). Overall deck width is 9.6m

and it carries HA loading only. Estimate the beam size

and total weight of structural steel assuming there are 4

beams in the cross section.

Figure 3 Worked example

(a) For an elastic stress analysis refer to Fig. 9

For 4 beams

'S' = 9.6m/4No. = 2.4m. Use 388

i.e. 914 x 419 x 388kg/m Universal Beam

Total weight approx.

(388kg/m/1000) x 4No. x 24m x 1.08

(the 1.08 factor allows for 8% bracing + stiffener

allowance)

= 40.2 tonnes (i.e. 174kg/m )

(b) For a plastic stress analysis refer to Fig. 10

For 'S' = 2.4m. Use 289

i.e. 914 x 305 x 289kg/m universal beam

Total weight approx.

(289kg/m /1000) x 4No. x 24m x 1.08

= 30 tonnes (i.e. 130kg/m )

Thus, plastic stress analysis offers a significant

reduction in beam size but SLS checks must be made.

W = 9.6m

24m

2

2

1. Left: A9 BridgePitlochry, Scotland

2. Right: A1(M)Yorkshire, England


References

5. References

1. BS5400, Steel, Concrete and Composite Bridges. British Standards Institution.

Design Manual for Roads and Bridges (DMRB):

2. DMRB 1.3 BD37 Loads for Highway Bridges.

3. DMRB 1.3 BD13 Codes of Practice for Design of Steel Bridges.

4. DMRB 1.3 BD & BA 57 Design for Durability.

5. DMRB 1.3 BA 42 Design of Integral Bridges.

6. DMRB 2.3 BD7 Weathering Steel for Highway Structures.

7. DMRB 2.3 BA36 The Use of Permanent Formwork.

Steel Construction Institute Publications

8. P163: Integral Steel Bridges – Design Guidance.

9. P180: Integral Steel Bridges – Design of a Single Span Bridge.

10. P250: Integral Steel Bridges – Design of a Multi Span Bridge.

10a. P340: Technical Report on Integral Steel Bridges.

10b. P339: Design Guide for Ladder Deck Bridges.

11. Corus Publication – Weathering steel bridges.

Material Standards (EN)

12. BS EN 10025-2 – Non-alloy structural steels.

13. BS EN 10025-5 – Structural Steels with improved atmospheric corrosion resistance.

14. BS EN 10164 – Steel products with improved deformation properties perpendicular

to the surface of the product.

Other Standards (BS)

15. BS 5975 Code of Practice for Falsework.

BS 5400 Title DMRB MCDHW

Part Document* Document**

1 General Statement BD15 –

2 Specification for Loads BD37 –

3 Code of Practice for Design of Steel Bridges BD13 –

4 Code of Practice for Design of Concrete Bridges BD 24 –

5 Code of Practice for Design of Composite Bridges BD16 –

6 Specification for Materials & Workmanship, Steel – Volume 1 Series 1800

7 Specification for Materials & Workmanship, Concrete, Volume 1 Series 1700Reinforcement & Prestressing Tendons –

8 Recommendations for Materials & Workmanship, Concrete, Volume 2 Series NG1700Reinforcement & Prestressing Tendons –

9 Bridge Bearings BD20 –

10 Code of Practice for Fatigue BD9 –

* Design Manual for Roads and Bridges published by the Stationery Office for the Overseeing Organisations.** Manual of Contract Document for Highway Work published by the Stationery Office for the Overseeing Organisations.


Figures

20

75 70 65 60 55 50 45

75 70 65 60 55 50 45 40 35

S =

3.5

m

0.07

0.06

0.05

0.04

0.03

0.02

0.01 0

2025

3035

4045

5055

60101112131415tw

(mm

)

Sp

an (m

)

1000 x

800

x

650

x60

0 x

500

x

400

x

Flan

ge

size

(mm

)

75

75

75

75

70 65 60 55 50 45 40 35 30 25

70 65 60 55 50 45 40 35 30 25

70 65 60 55 50 45 40 35 30 25 20

70 65 60 55 50 45 40 35 30 25 20 15

L/

D30

tw

Afb

HB

Afb

HA

Afb

Aft

30

HB

20

Afb

HA

Aft

20

tw30

Af

(m2 )

30

20H

A/H

B

HA

/HB

FIG

. 2

FIG. 2

6. F

igur

esF

igur

e 4:

Sim

ply

sup

po

rted

bri

dges

– f

lang

e (a

t m

id-s

pan

) and

web

(at

supp

ort

)


Figures

Fig

ure

5: C

ont

inuo

us b

ridg

es –

fla

nge

and

web

siz

es o

f sp

an g

irde

rs

7075

75

75

0.04

65 60 55 50 45 40 35 30 25

70 65 60 55 50 45 40 35 30 25

70 65 60 55 50 45 40 35 30 25 20

70 65 60 55 50 45 40 35 30 25 20 15

0.03

0.02

0.01

0

S =

3.5

m

Af

(m2 )

650

x60

0 x

500

x

400

x

025

3035

4045

5055

60101112131415tw

(mm

)

Sp

an (m

)

L/

D30

Flan

ge

size

(mm

)

HB

Afb

HA

HB

Afb

HA

Aft

Aft

twtw

20 20 20

3030 30

20

Afb

Afb

HA

/HB

HA

/HB


Figures

6075

75

75

75

75

55 50 45

70 65 60 55 50 45 40 35

70 65 60 55 50 45 40 35 30 25

70 65 60 55 50 45 40 35 30 25

70 65 60 55 50 45 40 35 30 25 20

70 65 60 55 50 45 40 35 30 25 20 15

S =

3.5

Af

(m2 )

0.05

2010

Flan

ge

size

(mm

)10

00 x

0.04

0.03

0.02

0.01

0

2530

3540

4550

5560

1214 111315161718192021

800 x

650 x

600 x

500 x

400 x

Sp

an (m

)

L/

D30

Afb

Afb

tw

tw

20 20 20

3030

Aft Aft

tw (m

m)

HA/

HB

HA

/HB

HA

/HB

HA

/HB

Fig

ure

6: C

ont

inuo

us b

ridg

es –

fla

nge

and

web

siz

es o

f p

ier

gir

ders


Figures

Fig

ure

7: G

irde

r sp

acin

g fa

cto

rs

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

12

34

56

78

Gir

der

sp

acin

g -

S (m

)

Kaf, Ktw, Kw

Kw

Ktw

Kaf

Top Flange mid-sp

an only

L=40

L=60Kt

w

Kaf

Kaf

Gir

der

s &

sla

b

Hau

nch

slab

Str

ing

erC

ross

gir

der

s


Figures

80

20

ContinuousSimply supported

Kg/m2

L/ D

30

Sp

an (m

)

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

2530

3540

4550

5560

HB

HA

Univers

al bea

ms

20

HB

HA

3020

HB

HB

HA

HA

30

2020

Fig

ure

8: O

vera

ll un

it w

eig

hts

– p

late

gir

der

bri

dges

(S =

3.5

)


Figures

HA

HB

Beam spacing - S (m)

2.2

12

Sp

an (m

)

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

1314

1516

1718

1920

2122

2324

25

388

343

289

253

224

201

194/238

197176

173179

147

388

343

289

253

224

226

201

194/238

176

173

Fig

ure

9: U

nive

rsal

bea

ms

– el

asti

c st

ress

ana

lysi

s


Figures

HA

HB

2.2 12

Beam spacing - S (m)

Sp

an (m

)

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

1314

1516

1718

1920

2122

2324

2526

2728

29

388

343

289

253

224

226

201

194/238

179/147

170173

176197

152

140/149(686)

140(610)

125 113 101

388

343

289

253

224

226

201

194

197/238

176

173

170/179

147

152

140(686)

149

140(610)

125

Fig

ure

10: U

nive

rsal

bea

ms

– p

last

ic s

tres

s an

alys

is

Care has been taken to ensure that thisinformation is accurate, but Corus Groupplc, including its subsidiaries, does notaccept responsibility or liability for errors orinformation which is found to be misleading.

Copyright 2005Corus

Designed and produced by Orchard Corporate Ltd.

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Technology

Composite steel highway bridges 2005