Civil Engineering Reference
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s
s
⊥
t
t
⊥
Figure 3.39 Stresses on the throat section of a fillet weld specified in EC3 (BS EN 1993-
1-8) [2.13].
The design resistance of a fillet weld specified in EC3 (BS EN 1993-1-8)
[2.13] should be determined using either the directional method given or the
simplified method. In the directional method, the forces transmitted by a
unit length of weld are resolved into components parallel and transverse
to the longitudinal axis of the weld and normal and transverse to the plane
of its throat. The design throat area
A
w
should be taken as
A
w
¼
P
al
eff
. The
location of the design throat area should be assumed to be concentrated in
the root. A uniform distribution of stress is assumed on the throat section
of the weld, leading to the normal stresses and shear stresses shown in
pendicular to the throat) and
sk
(the normal stress parallel to the axis of the
weld). The shear stresses are denoted as
t?
(the shear stress, in the plane of
the throat, perpendicular to the axis of the weld) and
tk
(the shear stress, in
the plane of the throat, parallel to the axis of the weld). The normal stress
sk
parallel to the axis is not considered when verifying the design resistance of
the weld. The design resistance of the fillet weld will be sufficient if the fol-
lowing are both satisfied:
0
:
5
2
+3
t?
2
+
tk
2
s?
f
u
=
ð
b
w
g
M2
Þ
and
s?
0
:
9
f
u
=
g
M2
ð
3
:
125
Þ
where
f
u
is the nominal ultimate tensile strength of the weaker part joined
mended by EC3. Welds between parts with different material strength
grades should be designed using the properties of the material with the lower
strength grade.
EC3 (BS EN 1993-1-8) [2.13] also specifies a simplified method for
design resistance of fillet weld. In the simplified method of weld design,
the design resistance of a fillet weld may be assumed to be adequate if, at
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