Aluminium Design and Construction John Dwight

provided, to which the equation is (valid for a > r):
0.1 < r/b < 1 K=1.2 {1+ (1-e -0.7a/r )(1-r/b) 2 }
r/b > 1 K=1.2 (12.2)
Other non-linear effects which become significant in fatigue are the
secondary stresses in trusses, due to joint fixity, and the effects of shear
lag, distortion and warping in plated structures. The increased stress
levels resulting from these must be allowed for.
12.4.2 Method B
This is used for fillets and partial penetration butt welds transmitting
load from one plate to another. A notional value is assumed for f obtained
as follows:
(12.3)
where F – =force transmitted per unit length of joint at the position
considered, g=nominal throat dimension (Figure 11.7), and n=number
of welds.
Here F – can be a force transverse to the weld, a longitudinal one, or
a vectorial sum of the two. It is normally found in the same general
way as for P – when considering static resistance (Section 11.3.3), except
that we are now considering the force transmitted under nominal, and
not factored loading.
When a single weld suffers bending about its longitudinal axis, f should
be taken as the elastic flexural stress at the root, based on a linear stress
distribution through the (nominal) throat. If necessary, this component of
f should be added vectorially to the value found using equation (12.3).
Table 12.2 Classification of fatigue details (non-welded)
Notes. 1. Use K for cases 2, 3, 4.
2. An open hole having d/t in the range 2–3 may be treated as either case 4 (using actual stress
concentration factor K), or case 5 (putting K=1).
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