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Steel Designers' Manual - 6th Edition (2003)
Design of steel bridges to BS 5400: Part 3 485
(a) Two or three vertical stiffeners should be provided, at a spacing of approximately
one times the girder depth, close to the bearings; thereafter their spacing
should be increased to 1.5 times the girder depth.
(b) In general horizontal stiffeners should be avoided. In long span continuous plate
girders they may be necessary in locations close to the piers.
(c) It is desirable to provide vertical stiffeners on one side and horizontal stiffeners
on the other side, where possible.
(d) Initial values for web thickness are suggested in Table 17.3, if it is intended to
provide web stiffening. Consideration should also be given to the economy of
providing thicker webs, without any intermediate stiffening.
(e) Compact girders are more economical for most simply supported spans and for
shorter continuous spans; economical plate girders for longer continuous spans
will be non-compact.
17.6 Design of steel bridges to BS 5400: Part 3
17.6.1 Global analysis
The Code requires that the global analysis of the structure should be carried out
elastically to determine the load effects, i.e. bending moments, shear forces etc. The
section properties to be used will generally be those of the gross section (see clauses
7.1 and 7.2 of the Code 2 ).
Plastic analysis of the structure, i.e. redistribution of moments due to plastic hinge
formation, is not allowed under BS 5400: Part 3.
Analysis should be carried out for individual and unfactored load cases. Summation
of the load effects in different combinations and with different load factors can
then be carried out in tabular form, as required by the design process.
17.6.2 Design of beams at the ultimate limit state
17.6.2.1 Basis of design
Table 17.3 Initial values of web thickness
Beam depth (mm) Web thickness (mm)
Up to 1200 10
1200–1800 12
1800–2250 15
2250–3000 20
Consideration should also be given to the economy
of providing thicker webs, without any intermediate
stiffening.
In the design of beam cross sections at the ultimate limit state the following need
to be considered.