Aluminium Design and Construction John Dwight

Figure 8.15 Web crushing.
8.5.2 Crushing of unstiffened webs
In the absence of a bearing stiffener, either for economy or because of a
rolling load (Figure 8.15), it is necessary to consider the possibility of
localized web crushing. The designer must determine the calculated
resistance W c to such failure, and ensure that this is not less than � m times
the factored load W acting at the point considered, where W is the nominal
(working) load or reaction at that point multiplied by � f . The BS.8118
procedure for finding W c is to obtain two values, based on yield and on
buckling, and take the lower. Both assume a 45° dispersion angle.
1. Yield failure. The critical position for this will typically be either adjacent
to the flange or adjacent to a tongue-plate. For any given position,
W c may be calculated using the expression:
Wc =ctwPa (8.17)
where: c=width of dispersion zone at the level considered,
tw =actual metal thickness t at that level, if unwelded,
=kz1t in an HAZ region,
kz1 =HAZ softening factor (Section 6.4),
pa =limiting stress for the material.
If necessary, W c should be calculated at two or more levels, and the
lowest value taken.
2. Buckling failure. For this, it is assumed that the load is carried by a
vertical strip of the web acting as a strut, with cross-section c ° t where
c ° is the value of c at the neutral axis. W c is found thus:
W c =c ° tp b
(8.18)
where t=actual web thickness, and p b =limiting stress based on column
buckling of the assumed strip. p b may be read from a type C1 buckling
curve defined by p 1 =p ° (Section 9.5.2), taking the slenderness � as
follows:
�=�(d/t) (8.19)
where d is the web-plate depth between flanges or tongue plates if
fitted. When the loaded flange is held from out-of plane movement
relative to the other flange, � may be taken in the range 2.5–3.5,
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