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Plate girders are sometimes designed with transverse web reinforcement
in form of corrugations or closely-spaced transverse stiffeners (extrusions).
Plate girders can be subjected to combinations of moment, shear
and axial loading, and to local loading on the flanges. Because
of their slender proportions they may be subjected to lateral
torsional buckling, unless properly supported along the length.
Failure (buckling) modes may be:
• web buckling by compressive stresses
• shear buckling
• interaction between shear force and bending moment
• buckling of web because of local loads on flanges
• flange-induced web buckling
• torsional buckling of flange (local buckling)
• lateral torsional buckling
68
7.3. Welded connections
7.3.1. General
The rules given in EN 1999-1-1,
clause 8.6, apply to structures
welded by MIG or TIG and with
weld quality in accordance with
EN 1090-3. Certified welders are
highly recommended.
Recommended welding consumables
can be found in:
• Chapter VIII, section 3.8
• EN 1999-1-1, section 3.3.4
• EN 1011-4
When welding hardened aluminium
alloys, part of the hardening
effect will be destroyed. In
a welded connection it can be
three different strengths:
• the one of the parent (not
heat affected) material (fo)
• the one in the heat affected
zone (fo,HAZ)
• the one of the weld metal (fw)
Normally it will be necessary to
check the stresses in the HAZ and
in the welds.
The strength in HAZ is dependent
on the alloy, the temper, the
type of product and the welding
procedure. Values are given in
Table 3.2 in EN 1999-1-1.
The strength in the weld (weld
metal) is dependent on the filler
metal (welding consumables)
and the alloys being welded.
Values are given in Table 8.8 in
EN 1999-1-1.
Single sided butt welds with no
backing is practically impossible
to weld in aluminium. If single
sided butt welds cannot be
avoided, the effective seam
thickness can be taken as:
• the depth of the joint preparation
for J and U type
• the depth of the joint preparation
minus 3 mm or 25%, whichever is
the less for V or bevel type
In addition to the single sided
butt weld, a fillet weld may be
used to compensate for the low
penetration of the butt weld.
When designing a welded connection
some few practical precautions
should be taken into account.
• Provide good access to the
welding groove. The “welding
head” of the equipment used for
welding aluminium is rather
large, so there must be enough
space around the weld.
• Good access is also needed for
checking the weld. All welds
shall be 100 % visually examined
in addition to some non-destructive
testing (NDT).
• Full penetration single sided
butt welds are impossible to
weld without any backing.
If possible, position the welds in
areas where the stresses are low.
7.3.2. Butt weld
Heavy loaded members should be
welded with full penetration butt
welds. The effective thickness of
a full penetration butt weld
should be taken as the thickness
of the thinnest connecting member.
The effective length should
be taken as the total length if
run-on and run-off plates are
used. If not, the total length
should be reduced by twice the
effective thickness. (Figure VI.3)
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VI DESIGN AND CALCULATION 68 | 69
 
  b
t
F, σ
F, σ
 
  b
t
F, τ
F, τ
Butt weld subject to normal stresses
Butt weld subject to shear stresses
FIGURE VI.3
69
EUROPEAN ALUMINIUM ASSOCIATION
Design formulas for butt welds:
Normal stress, tension or compression,
perpendicular to weld
axis:
σ⊥ ≤
fw
γMw
Shear stress:
τ ≤ 0,6 .
fw
γMw
Combined normal and shear
stress:
√σ2
⊥ + 3 . τ2 ≤
fw
γMw
7.3.3. Fillet weld
A fillet weld is defined with the
throat thickness “a” given in mm.
The Figure VI.4 shows how to
measure the throat thickness.
The effective length should be
taken as the total length of the
weld if:
• the length of the weld is at
least 8 times the throat thickness
• the length of the weld does
not exceed 100 times the throat
　
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