Fig.3.22 Average stress in the weld throat A simple approach to design is to assume uniform fillet weld strength in all directions and to specify a certain throat stress value. The average throat thickness is obtained by dividing the applied loads summed up in vectorial form per unit length by the throat size.
This method is limited in usage to cases of pure shear, tension or compression (Fig.3.23). It cannot be used in cases where the load vector direction varies around weld group. For the simple method, the stress is taken as the vector sum of the force components acting in the weld divided by the throat area.
Fig.3.23 (a) connections with simple weld design, (b) connections with Direction- dependent weld design Stresses Due to Individual forces - When subjected to either compressive or tensile or shear force alone, the stress in the weld is given by:
Indian Institute of Technology Madras
Design of Steel Structures
Prof. S.R.Satish Kumar and Prof. A.R.Santha Kumar
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3.27. These are called end returns. Most designers neglect end returns in the effective length calculation of the weld. End returns are invariably provided for welded joints that are subject to eccentricity, impact or stress reversals. The end returns are provided for a distance not less than twice the size of the weld.
Design of plug and slot welds:
In certain instances, the lengths available for the normal longitudinal fillet welds may not be sufficient to resist the loads. In such a situation, the required strength may be built up by welding along the back of the channel at the edge of the plate if sufficient space is available. This is shown in Fig. 3.28 (a). Another way of developing the required strength is by providing slot or plug welds. Slot and plug welds [Fig. 3.28 (b)] are generally used along with fillet welds in lap joints. On certain occasions, plug welds are used to fill the holes that are temporarily made for erection bolts for beam and
Indian Institute of Technology Madras
Design of Steel