TUB 2765 SHS Welded Joints - Tata Steel

13 Design of SHS welded joints
4 Parameters affecting joint capacity
4.1 General
The effect that the various geometric parameters of the joint have on its load capacity is dependant
upon the joint type (single bracing, two bracings with a gap or an overlap) and the type of loading on
the joint (tension, compression, moment). Depending on these various conditions a number of different
failure modes, see section 4.2, are possible.
Design is always a compromise between various conflicting requirements and the following notes
highlight some of the points that need to be considered in arriving at an efficient design.
1) The joint
a) The joint capacity will always be higher if the thinner member at a joint sits on and is welded to
the thicker member rather than the other way around.
b) Joints with overlapping bracings will generally have a higher capacity than joints with a gap
between the bracings, all other things being equal.
c) The joint capacity, for all joint and load types (except fully overlapped joints), will be increased if
small thick chords rather than larger and thinner chords are used.
d) Joints with a gap between the bracings have a higher capacity if the bracing to chord width ratio
is as high as possible. This requires large thin bracings and small thick chords.
e) Joints with partially overlapping bracings have a higher capacity if both the chord and the
overlapped bracing are as small and thick as possible.
f) Joints with fully overlapping bracings have a higher capacity if the overlapped bracing is as small
and thick as possible. In this case the chord has no effect on the joint capacity.
g) On a size for size basis, joints with CHS chords will have a higher capacity than joints with RHS
chords
2) The overall girder requirements
a) The overall girder behaviour, e.g. lateral stability, is increased if the chord members are large and
thin. This also increases the compression chord strut capacity, due to its larger radius of gyration.
b) Consideration must also be given to the discussion on fabrication in section 3.3.
4.2 Joint failure modes
Joints in structural hollow sections can fail in a number of different failure modes depending on the joint
type, the geometric parameters of the joint and the type of loading. These various types of failure are
described in figures 11 to 16.
If the relevant geometric parameter limits given in section 5 are adhered to then the number of failure
modes is limited to those defined there; however, if this is not the case then other failure modes may
become critical.