Aluminium Design and Construction John Dwight

depending on the estimated degree of rotational restraint at the ends
of the assumed strut. A value of �=3.5 would correspond to pinned
ends. If however the loaded flange is free to deflect laterally as the
web buckles,�� should be suitably increased.
In a multi-web beam, W c should be summed for all the webs. If the
webs are inclined (Figure 8.13), the values of W c given by equations
(8.18) must be multiplied by cos �, with the web-plate depth d measured
on the slope.
8.6 WEB REINFORCEMENT
8.6.1 Types of reinforcement
The following types of reinforcement may be used for strengthening
the webs of beams:
1. tongue plates;
2. bearing stiffeners (transverse);
3. intermediate stiffeners (transverse);
4. end-posts.
To be effective, these must be properly designed, the rules given below
being based on BS.8118.
8.6.2 Tongue plates
The provision of tongue plates (Figure 8.16) can be beneficial in various
ways. It enables web-to-flange welds to be moved in from the extreme
fibres, thereby locating the HAZ in a region of lower stress. It reduces
the d/t ratio of the web, thus improving the buckling performance in
both bending and shear. Also, when a rolling load has to be carried on
the top flange, it greatly increases the resistance to web crushing.
To be effective, a tongue should be proportioned so as not to be slender
in terms of local buckling. A safe rule is to make the ratio of its depth bt Figure 8.16 Tongue dimensions.
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