Aluminium Design and Construction John Dwight

e less; while in the assumed HAZ a reduced thickness of k z t is taken,
where k z is the HAZ softening factor (Section 6.4).
For design purposes the effective block width b e1 can be obtained
from the following general expression:
b e1 =� 1 �t (7.4)
in which � 1 is a function of ß/� and � is as defined by equation (7.3). The
value of � 1 may be calculated from the formula:
(7.5)
where �=ß/� and P 1 and Q 1 are given in Table 7.2.
Figure 7.6 shows curves of � 1 plotted against � covering non-welded
and edge-welded plates. Note that this design data, if expressed in
terms of � m, would produce curves appropriately located (low down) in
the scatter band in Figure 7.3, taking advantage of post-buckled strength
at high ß. It is based on the results of a parametric study by Mofflin,
supported by tests [24], and also those of Little [31].
The above treatment contrasts with the effective thickness approach
in BS.8118. This is a less realistic model, in which the plate is assumed
to be effective over its full width, but with a reduced thickness. When
applied to non-welded plates, it gives the same predictions as ours. But
for welded ones it tends to be unsafe, because it makes an inadequate
correction for HAZ softening, or none at all at high ß.
7.2.4 Slender outstands
We now turn to outstands, again under uniform compression. For a
slender non-welded outstand the stress pattern at collapse will be of
the typical form shown by curve 1 in Figure 7.5, with the load mainly
carried by the material at the inboard edge. The idealized pattern used
in design is indicated by curve 2, with a fully effective stress block next
to this edge and the tip material assumed ineffective. Our effective
section is therefore as shown in figure diagram N (non-welded) or W
(with an edge weld).
The effective block width b eo may generally be obtained using a similar
expression to that for internal elements, namely:
b eo =� ° �t (7.6)
where � ° is again a function of the plate slenderness and � is given by
equation (7.3). Here � ° can be calculated from:
where �=ß/e, and P ° and Q ° are as given in Table 7.2.
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(7.7)