Aluminium Design and Construction John Dwight

Figure 8.13 Beam with inclined shear webs.
8.3.7 Inclined webs
For a beam with inclined webs, as in Figure 8.13, the various expressions
for obtaining the shear force resistance of the section need to be adapted
as follows:
1. Yield check, method 1. Equation (8.9) remains valid taking D as the
overall section depth, t 1 is based on the actual metal thickness t, or
k z1 t if welded.
2. Yield check, method 2. Expressions (8.10) and (8.11) for V c should be
multiplied by cos �, where � is the angle of inclination of the webs,
and t 2 is the actual metal thickness (or the effective thickness if welded).
3. Buckling check. Expression (8.12) or (8.16) for finding V c should be
multiplied by cos �. In either expression, the depth d of the web
plate is measured on the slope, and t is the actual metal thickness.
Also d and t are defined in this way when obtaining p v1 , v 2 , v 3 , or m 1
It is necessary to multiply S f by cos � when calculating m 2 .
4. Web with tongue plates. In applying equation (8.15), the expression
defining V ct should be multiplied by cos �.
8.4 COMBINED MOMENT AND SHEAR
8.4.1 Low shear
At any given cross-section of a beam, it is usually found that moment
and shear force act simultaneously. Obviously the designer must consider
possible interaction between the two effects. In most beams, the moment
is the critical factor, and the problem is to find whether or by how
much the moment resistance is eroded by the presence of the shear.
If the applied shear force is reasonably small, the effect on the moment
resistance is negligible and can be ignored. This is referred to as the
‘low shear’ case, and can be assumed to apply when the shear force V
arising under factored loading does not exceed half the factored shear
force resistance V /�
c m without moment.
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