Aluminium Design and Construction John Dwight

Figure 11.3 Interaction diagram for combined shear and tension on a fastener.
11.1.8 Interaction of shear and tension
When a bolt has to transmit simultaneous shear and tension, one has to
consider possible interaction of the two effects. The check for failure of
the bolt may be made by using the data plotted in Figure 11.3 in which:
P – s , P– t =shear and tensile components of force transmitted by any
one bolt when factored loading acts on the structure;
P – cs, P– ct =calculated resistances to bolt shear failure and bolt tension
failure on their own, per bolt;
� m =material factor.
The suggested rule, using straight lines, is near enough to the BS.8118
rule, the curve of which is also shown in Figure 11.3. It is more convenient
than the latter, in that a designer does not have to bother with an
interaction calculation when P – s or P– t is small.
The check for bearing failure of the ply is performed in the usual
way with the bolt tension ignored.
11.1.9 Comparisons
Our suggested limiting stresses for a selection of materials are given in
Tables 11.1 (fastener material) and 5.4 (plate material). These values,
which are based on the expressions in Sections 11.1.4 and 11.1.7, differ
from those in BS.8118. The reason for not following the British Standard
is that the stress values it employs seem inconsistent, and sometimes
rather low when compared with other codes. Table 11.3 compares the
various expressions used in the two treatments, while Table 11.4 lists
some actual stress values calculated for typical materials. The following
points affect these comparisons:
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