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Steel Designers' Manual - 6th Edition (2003)
410 Columns and struts
The above process should be used for all types of rolled section, including those
reinforced by the addition of welded cover plates for which Fig. 14 should be used
to supplement Table 23 when deciding which curve of Table 24 to use for determining
pc. When sections are fabricated by welding plates together, however, the
pattern of residual stresses produced by the heating and cooling of the welding
process will be rather different from that typically found in a hot-rolled section 3 as
illustrated in Fig. 15.4. This tends to produce lower buckling strengths. It is allowed
for in BS 5950: Part 1 by the modification to the column curves shown in Fig. 15.5
in which the basic curve of Fig. 15.3 is replotted for a reduced material design
strength. This has the effect of reducing the basic curve down to the level of that
for the welded member in the important medium slenderness region. Clause 4.7.5
thus requires that when checking the axial resistance of a member that has been
fabricated from plate by welding, the value of pc be obtained using a py value of
20 N/mm 2 less than the actual figure.
BS 5400: Part 3 is intended to cover a wider range of construction than BS 5950:
Part 1. Specifically in this context it recognizes the greater likelihood that struts may
contain slender elements (other than outstands) and so it defines compression resistance,
Pc,as
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rolled universal beam rolled universal column
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Fig. 15.4 Distribution of residual stresses
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welded box