Composite Steel Highway Bridges

Corus Construction & Industrial

Composite steel highway bridges

Contents

Contents Acknowledgement of author

This guide is an update of a publication originally

Advantages of steel bridges

prepared by A.C.G. Hayward. Corus gratefully acknowledges the work of Mr Hayward and the

1

Design standards

2

Conceptual design

contribution made by D.C. Iles, The Steel Construction Institute, during this update.

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

4

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

Worked examples – use of charts 4.1 Continuous plate girder bridge 4.2 Simply supported universal beam bridge

5 6

References 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

1. Left: Waterside Bridge Newburgh, Scotland 2. Right: A1(M) Yorkshire, England

2


Advantages of steel bridges

Composite steel highway bridges The Author

Alan Hayward was continuously involved with the

Alan C. G. Hayward FREng CEng FICE FIStructE

development of bridge codes including BS 5400 and

Alan Hayward was a founding Partner of bridge

Eurocodes and has been National Technical Contact for

specialists Cass Hayward & Partners of Chepstow who

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

design and evolve construction methodology for all

education of engineers by lecturing at Universities on

types of bridges, particularly steel highway, railway,

behalf of industry, and has written numerous papers on

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

steel bridge construction. He was a long-standing

linkspans in the UK and overseas. He remains active in

member of the Steel Bridge Group who disseminate best

the firm as a Consultant.

practice through their published Guidance Notes.

Advantages of steel bridges Feature

Leading to

Advantages

Low weight of superstructure.

Fewer piles and smaller sizes of pile caps/foundations. Typical 30 – 50% reduction over concrete decks. Composite bridges 6.0 – 8.0kN/m2 typical.

Cheaper foundations.

Light units for erection.

Erection by smaller cranes. Delivery of long pieces. Launch erection with light equipment (skates or rollers).

Cheaper site costs.

Simple site joints.

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

Flexible site planning.

Maximum pre-fabrication in factory.

Quality control in good factory conditions avoiding outdoor site affected by weather and difficult access.

More reliable product.

Predictable maintenance costs.

Commuted painting costs can be calculated. If easy repainting is made possible by access and good design then no other maintenance necessary.

Total life cost known.

Low construction depth.

Depth/span ratio 1/20 to 1/30 typically. Lower depth achieved with half-through girders.

Slender appearance. Reduces costs of earthworks in approaches.

Self supporting during construction.

Falsework eliminated. Slab formwork and falsework also avoided using permanent formwork.

Falsework costs eliminated. Significant if more than 8m above ground.

Continuous and integral spans.

Continuity easy with bolted or welded joints. Most expansion joints eliminated. Number of bearings reduced. Compliance with BD57.

Better appearance. Improved durability. Improved running surface.

Adaptable details.

Pleasing appearance taking advantage of curves and colour.

Aesthetic gain.

Re-usable product.

Demountable structures and recyclable components which reduce manufacturing energy input.

Sustainable product.


3

1. M4/M25 Poyle Interchange

1. Design standards 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.

(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.

Part 3 (Design of Steel Bridges) is compatible with the workmanship standards and tolerances defined in Part

Use of the plastic modulus is permitted for stress

6, drawn up jointly with industry.

analysis of compact sections and where the slenderness is controlled by sufficient restraints, the effects of

The Code uses limit state principles. The ultimate

shrinkage and differential temperature can be neglected.

limit state (ULS) and serviceability limit state (SLS) must be satisfied.

For ‘compact’ sections, the entire load can also be assumed to act on the composite section even if the

In practice the ULS generally governs, exceptions being

steelwork is unpropped, provided that SLS checks

the checking at SLS for slip of HSFG bolts and the

are made.

design of shear connectors. While most rolled universal beams, columns and BS 5400 encourages the use of steel for a number

channels will be compact, plate girders will often be

of reasons:

non-compact and must be stressed elastically. (See also Section 3.2.4.)

(i)

Plastic stress analysis option offers the use of lighter members and extends the span range of

For structural analysis, elastic methods are utilised

rolled sections.

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

4


Redistribution of moments arising from the formation of

For example:

plastic hinges is not permitted, but redistribution due to cracking of concrete over intermediate supports may be

(i)

assumed using Part 5.

Do not locate welded attachments close to or on flange edges (class 'G').

(ii)

Re-entrant corners should be radiused.

Combined bending and shear is dealt with using

(iii) Use HSFG bolts for permanent bolted connections.

interaction formulae. This is sometimes critical at

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

intermediate supports.

(class 'G'). (v)

The Code contains no specific limits on slenderness of members or proportion of plate panels. Longitudinal web

Avoid single sided partial penetration butt welded joints which are subject to tensile stress.

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

stiffeners are usually only necessary for very deep

significant tensile stresses. An example is when

girders or those with curved soffits.

using integral crossheads (see Figs. 1B & 1F) where fillet welds should be used in preference to

For rolled sections the full shear yield stress can

full penetration butt welds. If butt welds are

generally be used without the need for intermediate

necessary, the use of steel with through-thickness

stiffeners. Bearing stiffeners are virtually mandatory at

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

supports, together with lateral bracing or a system of

considered in view of the strains which will be

bracing to maintain verticality.

caused during welding.

Fatigue is checked to Part 10, although for highway bridges this rarely demands a reduction in working stresses provided good detailing practice is used.


5

1. This page: A69 Haltwhistle Viaduct (Photo courtesy of Cleveland Bridge (UK) Ltd.) Northumberland, England 2. Right: Festival Park Flyover Stoke, England 3. Far right: Simon De Montford Bridge Evesham, England

Conceptual design

2. Conceptual design 2.1 Spans and component lengths

Curved bridges

Spans are usually fixed by site restrictions and

Curved bridges in plan may be formed using straight

clearances. Where freedom exists, budget costing –

fabricated girders, with direction changes introduced at

including foundations – is desirable to determine the

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

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

plan which simplifies the cantilever formwork and

Where deep piled foundations are needed, cost will

permits the use of standard systems. An example is the

encourage the use of longer spans, thus keeping

A69 Haltwhistle Viaduct (radius 540m)

foundations to a minimum. Skew and plan tapered bridges may also be built in Multiple spans

steel. Ideally, plan layout should be as simple as

Multiple spans of approximately 24m suit universal

possible (Ref. Documents in Section 2.6).

beams, this being the longest readily available length and because continuous spans are convenient and economic.

Integral bridges

Site splices may be bolted with HSFG bolts or welded

The Highways Agency requires consideration of integral

near points of contraflexure. The length of end spans

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

should ideally be about 0.8 of the penultimate span.

improved durability by elimination of bridge deck movement joints (Ref. 4 & 5). Girders may then be

Continuous spans

required to develop a degree of continuity with

The optimum for using plate or box girders for

substructures at end supports such that axial forces and

continuous spans is about 45m, because 27m long

reverse moment effects need to be considered in the

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

design of the composite deck. Design principles remain

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

the same but girder sizes and bracing provision may be

site splices are needed. Component lengths for shop

influenced. Further guidance is available from the Steel

fabrication should be the maximum possible consistent

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

with delivery and site restrictions to reduce the amount of on-site assembly. The maximum length for road

2.2 Cross sections

delivery without restrictions is normally 27.4m although

Deck type construction

longer lengths can readily be transported by

Deck type construction is common and is suitable for

arrangement. A minimum number of shop butt welds

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

should be used consistent with plate sizes available. The

depth ratio of 20 is economic although 30 or more can

decision whether to introduce thickness changes within

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

a fabricated length should take account of the cost of

appropriate in cases of severely limited depth, such as

butt welds compared with the potential for material

where approach lengths are restricted. Footbridges and

saving (Ref. Documents in Section 2.6).

rail under-bridges are common examples.


7

Conceptual design

Where permanent formwork is envisaged, the slab

Box girders

should be made sufficiently thick to accommodate the

Where spans exceed 100m box girders are likely to be

details taking account of reinforcement cover and

more economic than plate girders with which flange sizes

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

would be excessive. Other reasons for using box girders

depth planks such as Omnia then a minimum thickness

include aesthetics (where justifiable), aerodynamic

of 250mm may be needed.

stability, severe plan curvature, the need for single column supports or very limited depth. Other than in the cases

Universal beams and plate girders

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

Universal beams may be appropriate for bridges up to

more expensive because although less flange material

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

may be demanded due to inherent torsional properties,

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

this is usually more than offset by the amount of internal

plate girders, especially if continuous, can be economic

stiffening and extra costs for workmanship. Fabrication

because lighter sections can be inserted in mid-span

costs are higher because the assembly/welding

regions. Costs per tonne of painted and erected

processes take longer and more shop space is needed.

universal beams were traditionally lower but, more

However, erection work is often reduced because box

recently, automated fabrication and less expensive plate

girders require little or no external bracing.

material has allowed economic supply of plate girders for the shorter spans.

Multiple box girders have in the past proved to be economic for spans of around 50m in particular

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

situations. Using narrow cross sections eliminates the

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

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

cantilevers should not exceed half the beam spacing

of which is the M25/M4 Poyle Interchange.

and to simplify falsework should, where possible be less than 1.5m. Shorter cantilevers are usually necessary

For box girders, consideration of the safety of personnel in

with a locally thickened slab where very high

confined spaces is essential during fabrication, erection and

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

for maintenance. Detailing must recognise the need to avoid

An even number of girders achieves better optimisation

internal welding as far as possible and to allow sufficient

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

ventilation and openings for access and recovery in

wide girder spacings, the slab may be haunched, but

emergency situations.

use of standardised permanent formwork is unlikely to be possible and construction depth is increased (see

Open-topped trapezoidal and rectangular shaped box

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

girders have been used efficiently, but provisions are

with a central stringer have been used on some single

needed to preserve stability during erection, for example the

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

Forrest Way Bridge, Warrington.

Twin girders and cross beams (often referred to as ladder decks) have proved economic for a wide range of

Plate girder flanges

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

Plate girder flanges should be as wide as possible but

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

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

supporting more lanes.

compression if fully stressed and up to the 20t robustness

8


Conceptual design

limit), to give the best achievable stability during erection

Intermediate bracings require to be spaced at about

and to reduce the number of bracings. For practical

20 x top flange width and need to be adequate to

reasons a desirable minimum width is about 400mm to

prevent lateral torsional buckling. Bracing is necessary

accommodate detailing for certain types of permanent

at supports if only to prevent overturning during

formwork, especially precast concrete. A maximum flange

erection. At abutments this can be a channel trimmer

thickness of 63mm is recommended to avoid heavy welds,

composite with the slab and supporting its free end. Over

minimise pre-heating requirements and also limit the

piers a channel section can be used between each pair

reduction in design yield strength. Limiting the thickness

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

also has benefits in terms of notch toughness specification.

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

2.3 Intermediate supports

Intermediate lateral bracings are usually necessary in

Piers can take the form of reinforced concrete, leaf,

hogging regions with a maximum spacing of about

column or portal. Steel columns are also used. For

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

example, tubular steel columns (concrete filled

should be close to the site splices where curvature

composite), were used in the M5 Almondsbury

induces torsion. Bracings may be of a triangulated form

Interchange and deserve consideration. Leaf piers or

or of single channel sections between each pair of

multiple columns supporting every girder are convenient

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

but where fewer columns are demanded for aesthetic

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

reasons, integral steel crossheads provide a solution. The

for spans exceeding around 35m it may be necessary to

popularity of these crossheads has recently increased

interconnect all the girders by bracings during erection

following earlier examples on M25 bridges including

so that transverse flexure from wind is adequately

Brook Street Viaduct, Mar Dyke Viaduct and South

shared. Although plan bracing systems are uneconomic

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

and should be avoided, they may be required for spans

were extensively used for the Second Severn crossing

exceeding 55m for temporary stability, especially if

approach roads and for the new Thelwall Viaduct.

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

It should, however, be recognised that the introduction

Use may be made of bracings in distributing live loads

of these additional members is only likely to be

between girders. This may offer reduced flange sizes

economic where the use of fewer supports is essential.

under HB loading but the uniformity of current loading to

Costs can increase especially if column spacing is not

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

arranged to allow balanced erection and temporary

other lanes) tends to discourage this. An optimum design

trestles become necessary. Care is also needed detailing

is likely to include bracings only between pairs of girders,

cruciform welded joints at the crosshead/main girder

such discontinuous bracings attracting minimal effects

connection (Ref. Section 1 (vi)).

under deck loading except in cases of heavy skew or curvature where a different system may be appropriate.

2.4 Bracings

Bracings should be included in the global analysis to

For most universal beam or plate girder bridges, lateral

check for possible overload or fatigue effects.

bracings are needed for erection stability and during deck concreting.

1. Far Left: Nene Bridge Peterborough, England 2. Left: Forrest Way Bridge Warrington, England 3. Right: M20 Road Bridge Folkstone, England


9

Conceptual design

DECK WIDTH W

230 TO 1A Multiple U.B. (N=4)

250 mm D

2.5 TO 3.5

230 TO 1B Multiple P.G. (N=4)

250 mm D 1.0 TO 1.75 TYPICAL

300 TO 350 mm 1C Twin P.G. Haunch Slab (N=2) D

1.0 TO 3.3

4.0 TO 5.5 AT MID-SPAN

AT PIER

Figures 1A – 1F Typical deck type cross-sections

1. Left: Humber Road Bridge Immingham, England 2. Right: Thelwall Viaduct M6, Warrington, England

10 Composite steel highway bridges

Conceptual design

230 TO 320 mm 1D Twin P.G. & Stringer (N=2) D

6.0 TO 7.0

1.0 TO 3.3

230 TO 1E Twin P.G. & Cross Girders (N=2)

250 mm

D

3.0 TO 3.5 c/c

>7.0

230 TO 1F Multiple Box (N=6)

250 mm

D

0.9 TO 1.2

2.5 TO 3.5 AT MID-SPAN

AT PIER

Composite steel highway bridges 11

2.5 Steel grades

temperatures to be determined from isotherms of

BS EN 10025-2: 2004 Grade S355 steels (Ref. 12) are

minimum and maximum shade air temperature for a

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

particular site location. Limiting thicknesses for steel

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

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

achieve a specified notch toughness, depending upon

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

design minimum temperature, stress level and

temperatures, and the other factors mentioned above.

construction features (e.g. welding details). Subgrades J2 and K2 will be most common.

Weathering steel To eliminate the need for painting, weathering steels to

Composite bridge decks are specifically categorised in

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

the composite version of BS 5400: Part 2 (implemented

Although it can be shown that the commuted costs of

by BD37), to allow a range of effective bridge

repainting are less than 1% of the initial bridge cost, weathering steel bridges can be more economical on a

1. Above: Findhorn Viaduct Inverness, Scotland 2. Left: Westgate Bridge Gloucester, England 3. Right: Slochd Beag Bridge Inverness, Scotland


first cost basis and are particularly useful in eliminating

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

maintenance where access is difficult – over a railway,

‘Weathering steel bridges’ (Ref. 11).

for example.

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

Particularly relevant information for initial (and detailed)

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

design is included within two publications:

environment or in areas of severe pollution. • BCSA Publication No. 34/02 ‘Steel Bridges’ 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

Alan Hayward, Neil Sadler and Derek Tordoff, 2002. • SCI-P-185, Steel Bridge Group: Guidance notes on Best Practice in Steel Bridge Construction.

environment, 1mm in mild environments and 0.5mm inside box girders) and detailed guidance is given in


Initial sizes and overall unit weight

3. Initial sizes and overall unit weight

(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.

3.1 Introduction

(ix)

due to buckling criteria.

area (A f) web thickness (t w) and overall unit weight of steelwork (kg/m2) for typical composite bridge cross

Sufficient transverse bracings are included such that bending stresses are not significantly reduced

Charts are given to provide initial estimates of flange (x)

Top flanges in sagging regions are dictated by the maximum stress during concreting allowing for

sections as shown in Fig. 1.

formwork and live load – to BS 5975 (Ref. 15). Continuous or simply supported span plate girders and

Continuous bridge mid-span regions are concreted

simply supported universal beams are included. The

in turn followed by portions over the piers.

charts were derived from approximate BS 5400 designs

(xi)

HA loading (BD37).

distribution and to achieve correlation with modern bridges. The charts take account of the latest highway

Live loading HA (assuming 3.5m wide lanes), or alternatively 45 units of HB loading with co-existent

using simplifying assumptions for loads, transverse

(xii) Continuous spans are approximately equal.

loading requirements in BD37.

3.2 Use of charts It is emphasised that the sizes obtained do not represent final designs, which must always be executed to take

3.2.1 Plate girder flange sizes

account of all factors, such as bridge configuration and

Flange areas (Af in m2) are read against the span L.

loading. Adjustments will need to be made to take account of the likely effects of end continuity if integral

(a)

For simply supported bridges – (refer Fig. 4)

construction is intended.

(b)

For continuous bridges – Size of span girder (refer Fig. 5)

The charts are based on the following assumptions: (i) (ii) (iii)

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

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

Superimposed dead loads equivalent to 100mm of

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

surfacing (2.40 kN/m2).

K af which is multiplied by the flange areas, obtained

Permanent formwork weight 0.50 kN/m of slab

above, to give values appropriate to the actual average

soffit area.

girder spacing.

2

(iv)

Steel grade S355.

(v)

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

(vi)

Size of pier girder (refer Fig. 6)

i.e. Top Flange A ft = A ft (Figs. 4, 5 or 6) x K af (Fig. 7)

Plate girder webs have vertical stiffeners at approx. 2.0m centres where such stiffening is required.

i.e. Bottom Flange A fb = A fb (Figs. 4, 5 or 6) x K af ( Fig. 7)

(vii) Elastic stress analysis is used for plate girders. If however the plastic modulus is used for compact

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

cross sections, then economies may be possible.

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

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

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

girder depth (D) within that span.

Flange area of pier girders of continuous unequal spans

For box girder bridges a rough estimate may be

can be estimated by taking the greater of the two

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

adjacent spans.

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

End spans of continuous bridges may be estimated

For continuous bridges the end spans should be assumed

using L = 1.25 x actual span.

as 1.25 x actual span, following which the mean span for use in Fig. 8 may be determined as follows:

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

4

Mean span L =

L14 + L24...Ln4 n

average girder spacing 's' is obtainable from Fig. 7 using girder spacing factor k tw. i.e. Web thickness t w = t w (Figs. 4, 5 or 6) x k tw (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 k w. i.e. Unit weight kg/m2 = kg/m2 (Fig. 8) x k w (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-

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 28t w, 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.

1. Left: Milton Bridge Lesmahagow, Scotland 2. Right: Fossdyke Bridge (Photo courtesy of Cleveland Bridge (UK) Ltd.) Lincoln, England



Reference figures 9 & 10

Universal beam size

Actual depth (mm)

3.2.5 List of symbols

Serial size (mm)

Mass per metre (kg/m)

914 x 419

388

921.0

343

911.8

289

926.6

253

253

918.4

HA

224

224

910.4

HB

388 343 289

914 x 305

201 226

838 x 292

201

903.0

226

850.9

194

194

840.7

176

176

834.9

197

769.8

173

762.2

197

762 x 267

173 147 170

686 x 254

152

147

754.0

170

692.9

152

687.5

Af

Flange area (m2)

A fb

Bottom flange area (m2)

A ft

Top flange area (m 2)

D

Girder or beam overall depth excluding slab or finishes (m) Standard highway loading defined in BD37 Abnormal highway loading defined in BD37, 45 units assumed

K af

Girder spacing factor for flange area

K tw

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/m

2

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)

140

140

683.5

125

125

677.9

238

635.8

n

Number of spans

179

179

620.2

N

Number of girders (refer to Section 3.2.3 for

149

149

612.4

140

617.2

125

125

612.2

113

113

607.6

101

101

602.6

238

140

610 x 305

610 x 229

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.


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. Worked examples – use of charts 4.1 Continuous plate girder bridge

Flange and web sizes

A composite highway bridge has 3 continuous spans –

Girder spacing factors: for 'S' = 3.0m

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

From Fig. 7: K af = 0.87, Kaf = 0.85*, K tw = 0.95

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

(*top flange span girders only).

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

W = 12m

D = 1.75m

Span girder

Pier girder

24m Span A

Span girder

40m Span B

Pier girder

Span girder

32m Span C

Figure 2 Worked example

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



Span A: 24m

Pier girders

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

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

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

assume L = 40m at both supports, hence, L/D = 40m/1.75m = 22.9

Top flange A ft

= A ft (from Fig. 5) x K af = 0.006 x 0.85 = 0.0051m2

Top flange A ft

= A ft (from Fig. 6) x K af = 0.017 x 0.87 = 0.015m2

400 x 15 top flange

400 x 40 top flange Bottom flange A fb

= A fb(from Fig. 5) x K af Bottom flange A fb

= 0.014 x 0.87 = 0.012m2

= A fb(from Fig. 6) x K af = 0.033 x 0.87 = 0.029m2

500 x 25 bottom flange

500 x 60 bottom flange Web t w

= t w (from Fig. 5) x K tw Web t w

= 10 x 0.95 = 9.5mm

= t w (from Fig. 6) x K tw = 16.8 x 0.95 = 16mm

Use 10mm web

Therefore use 18mm web

Span B: 40m Span girder

Steel tonnage

L/D = 40m/1.75m = 22.9

Girder spacing for end span A:

Top flange A ft

= A ft (from Fig. 5) x K af = 0.009 x 0.85 = 0.0077m

2

= 3.0m L = 1.25 x 24m = 30m

for centre span B:

L = 40m

for end span C:

L = 1.25 x 32m = 40m

400 x 20 top flange Therefore mean span Bottom flange A fb

= A fb (from Fig. 5) x K af

4

L14 + L24...Ln4

= 0.020 x 0.87 = 0.017m2

n

500 x 35 bottom flange 4

Web t w

= t w (from Fig. 5) x K tw = 10 x 0.95 = 9.5mm

304 + 404 + 404 = 37.5m 3

Use 10mm web L/D = 37.5m/1.75m = 21

Span C: 32m

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

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

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

therefore sizes as 40m span. Hence, steel weight = 151 kg/m2/1000 x (24m + 40m + 32m) x 12m wide = 174 tonnes



4.2 Simply supported universal beam bridge A 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.

W = 9.6m

24m

Figure 3 Worked example

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

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

For 4 beams

For 'S' = 2.4m. Use 289

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

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

i.e. 914 x 419 x 388kg/m Universal Beam Total weight approx. (289kg/m /1000) x 4No. x 24m x 1.08

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

= 30 tonnes (i.e. 130kg/m 2) (the 1.08 factor allows for 8% bracing + stiffener Thus, plastic stress analysis offers a significant

allowance)

reduction in beam size but SLS checks must be made. 2

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

1. Left: A9 Bridge Pitlochry, 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

Part

DMRB

MCDHW

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, Reinforcement & Prestressing Tendons

–

Recommendations for Materials & Workmanship, Concrete, Reinforcement & Prestressing Tendons

–

9

Bridge Bearings

BD20

–

10

Code of Practice for Fatigue

BD9

–

8

Volume 1 Series 1700 Volume 2 Series NG1700

* 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.


45

50

55

75

60

50

45

35

25

30

35

25

30

35

40

45

55

50

40

60

55

45

40

65

70

75

600 x

60

65

70

75

650 x

75 70 65 60 55 50 45 40 35 30 25 20

500 x

Flange size (mm)

50

55

60

65

70

800 x

65

70

75

1000 x

S = 3.5m

400 x 75 70 65 60 55 50 45 40 35 30 25 20 15 0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

(m2)

Af

20

25

30

Figure 4: Simply supported bridges – flange (at mid-span) and web (at support)

6. Figures

35

Afb

40

Afb

Afb

Span (m)

45

Aft

50

Afb

HA

HB

HA

55

/HB

tw

tw

HB HA/

HB HA

Aft

60

30

30

30

D

30

L/

20

20

20

20

10

11

12

13

14

15

tw (mm)

Figures



70

65

65

60

25

30

35

40

45

50

25

30

35

40

45

50

55

60

75

70

55

600 x

650 x

75 70 65 60 55 50 45 40 35 30 25 20

500 x

400 x 75 70 65 60 55 50 45 40 35 30 25 20 15

Flange size (mm)

S = 3.5m

0

0.01

0.02

0.03

0.04

Af (m2)

0

25

30

Figure 5: Continuous bridges – flange and web sizes of span girders

35

Aft

40 Span (m)

Aft

tw

HA/HB

Afb HA/HB

Afb

45

tw

HA

Afb

50

Afb

HA

HB

HB

55

D

60

30

30

30

L/

30

20 20

20

20

10

11

12

13

14

15

tw (mm)

Figures

45

50

55

60

1000 x

35

40

45

50

55

60

65

70

75

800 x

25

30

35

40

45

50

25

30

35

40

45

50

55

60

65

55

70

70

65

75

75

60

600 x

650 x

75 70 65 60 55 50 45 40 35 30 25 20

500 x

Flange size (mm)

S = 3.5

400 x 75 70 65 60 55 50 45 40 35 30 25 20 15 0

0.01

0.02

0.03

0.04

0.05

Af (m2)

20

25

Figure 6: Continuous bridges – flange and web sizes of pier girders

30

35

Span (m)

40

HA/HB

B HA/H

H

B A/H

45

HB HA/

Afb

50

Aft

Aft

Afb

55

tw

tw

L / 30 D

60

30

30

20

20

20

10

11

12

13

14

15

16

17

18

19

20

21

tw (mm)

Figures


0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1

Kw

3

4

5 Haunch slab

Girder spacing - S (m)

Girders & slab

2

on

Stringer

6

ly Ka f

2.0

f Ka

p To

d mi ge Fla n

24 Composite steel highway bridges -sp an

Figure 7: Girder spacing factors

7

8

Cross girders

L=60

L=40

Ktw

Figures

Ka f

Kt

w

Kaf, Ktw, Kw

Kg/m2

80

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

20

m

s

ea

400

rs

al b

Un ive

25

30

35

HB

40 Span (m)

45

HA

50

HA

HB

55

HB

HA

HA

HB

60

30

30

30 L / D

20 20

20

20

Simply supported Continuous

Figure 8: Overall unit weights – plate girder bridges (S = 3.5)

Figures



7 19

1 20

17

12

13

14

15

28 9

17

17

6

3

1

79

14

2.2

4 19

2.3

38

2.4

4/2

2.5

19

2.6

8

2.7

/23

2.8

2.9

3.0

3.1

3.2

3.3

3.4

3.5

22 4 16

17

34

Beam spacing - S (m)

Figure 9: Universal beams – elastic stress analysis

18

28 9 Span (m)

19

20

21

22

23

24

HB

HA

25

Figures

8 38

3 34

8 38

3

3 25

6 22

253

224

201

6

173

7

28 26

27

HA

HB

29

Figures

25

8 38

3

23

24

34

8 38

3

21

34

9

22

28

3

6

22

1

20

4

19

6 22

38

7/2

19 4

22

16

1

20

6

17

3

17 38

15

4/2

19

79 0/1

197 176

12

2.2

2.5

2.6

2.7

3.1

125 113 101

125 2.8

3.2

3.3

3.4

3.5

0)

(61

140

2.3

86)

2.9

1

3.0

2

15

7

/14

14 40/

13

7 14

2

15

9(6

179

) 86 0(6 14 9 14 0) (61 140

2.4

173 170

14

17

Beam spacing - S (m)

Figure 10: Universal beams – plastic stress analysis

4 22

17

18

2

53

Span (m)

9

19

28

20

25


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CC&I:CD:3000:UK:04/2005/r

Composite Steel Highway Bridges

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