Aluminium Design and Construction John Dwight

where a is the stiffener spacing and t the web thickness. At the outboard
side of an end stiffener, it should be taken as the lesser of a o and 6et
where a o is the distance to the free edge of the web.
(a) Strength
The effective stiffener is checked as a strut, buckling out of the plane of the
web, which is required to carry a notional load P under factored loading.
Bearing stiffener P=W+V/3 (8.23a)
Intermediate stiffener P=V/3 (8.23b)
where W=factored load or reaction applied to the beam at the stiffener
considered, and V=average shear force arising in the panels either side
of the stiffener, under factored loading.
The effective stiffener section, including the associated width of web
plate, must be such that its calculated resistance P c to column buckling
about an axis parallel to the web is not less than � m P. P c may be found as
in Section 9.5, with suitable allowance for any HAZ softening within the
effective section, and taking an effective strut length l generally as follows:
a/d � 1.5 l=d (8.24)
(8.25)
where d is the depth of the web plate between flanges or tongue plates,
if fitted. When the panel dimension is different on the two sides of the
stiffener, a should be taken as the mean value. If the applied load W
acts eccentric to the axis of the stiffener, due account should be taken
of the moment thereby introduced (combined axial load and moment).
(b) Stiffness
When a is less than 2.9d, the following requirement should also be satisfied:
(8.26)
where I s =inertia of the effective stiffener section, including the associated
part of the web, about an axis through its centroid parallel to the web,
with HAZ softening ignored.
8.6.4 End-posts
An ‘end-post’ is a special kind of transverse web stiffener that may be
needed at the ends of a deep slender beam: (a) to provide twist resistance
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