Aluminium Design and Construction John Dwight

Figure 8.14 Moment/shear interaction: (a) method A; (b) method B; (c) with tension-field
action.
8.4.2 High shear, method A
For the ‘high shear’ case (V > 0.5V c /� m ), the moment resistance must be
suitably reduced to allow for the coexistent shear force. One method is
to use a simple interaction diagram of the form shown in Figure 8.14(a),
which gives the reduction in M c as a function of V. In entering this, M co
is taken as the calculated moment resistance in the absence of shear.
Such a diagram gives a reasonable result for solid bars (for which shear
force is seldom a factor anyway), but is over-safe for typical beams
containing thin webs.
8.4.3 High shear, method B
Figure 8.14(b) shows a more favourable form of interaction diagram,
from which the reduced Mc may generally be found for members in
which the shear is carried by webs. In entering this figure, Mco is again
the value of Mc without shear, while Mcf is that part of Mco which is
contributed by the flanges with web (and tongue plates) excluded.
When tension-field action has been included in the determination of
Vc , Figure 8.14(b) becomes invalid and a diagram of the form shown in
Figure 8.14 (c) should be employed instead. In this, we take Vcw as the
value of Vc that would be obtained by putting m=0 in equation (8.16).
8.5 WEB CRUSHING
8.5.1 Webs with bearing stiffeners
At any position where a concentrated load or reaction acts on a beam,
it is obviously desirable to provide a properly designed transverse stiffener,
to prevent crushing of the web. The design of such stiffeners, known as
‘bearing stiffeners’, is covered in Section 8.6.3 below.
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