Aluminium Design and Construction John Dwight

Figure 8.11 Shear buckling stress for stiffened webs (without tension-field action).
When transverse stiffeners are fitted, an improved value of p v1 may
be read from Figure 8.11, in which a is the stiffener spacing. Alternatively
the designer may use the equations on which the figure is based:
(8.14a)
(8.14b)
For a web fitted with tongue plate or plates (Figure 8.10(b)), it is necessary
to sum the web and tongue contributions. This may be done as follows,
provided the tongue plates are properly designed (Section 8.6.2):
V c =V cw +V ct
(8.15)
where: V cw =value given by (8.12) taking d as the depth between tongues,
V ct =Σ A t p vt
� A t =total effective area of tongue plates,
p vt =limiting stress in shear for tongue material.
In a multi-web beam, V c may be taken as the sum of the values found
for the individual webs, using expression (8.12) or (8.15) as appropriate.
8.3.6 Web buckling, tension-field action
Very slender stiffened webs can often accept a great increase in shear
force above the initial buckling load before they finally fail. This results
from the development of a diagonal tension field as the buckles develop
(Figure 8.12). The designer can take advantage of this by using the treatment
below, based on the ‘Cardiff model’ of Rockey and Evans [15], which
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