I have a question regarding the plug weld design. Per AISC the base metal have to be checked per section J4. When I am checking the shear rupture for the base metal what area do I use?
Av = t x b
t = Thickness of the base metal
b = Perimeter of the plug weld hole?
A plug weld obviously has different modes of failure depending on the stress direction. Tension on a plug weld is not a good idea as the tension load does not engage the weld solution below the plug weld unless the perimeter shear area is large enough (with thickness of the top material being high enough to increase the shear area so that shear resistance is greater than the tension stress of the plug area). In most cases, the top material is relatively thin as compared to the base metal and the plug weld results in more of a clamping device than a weld failure mode.
The better mode of load resistance is in lateral shear between the two materials. In this case, all of the plug area needs to be mobilized for failure to occur.
Snippet source: https://www.eng-tips.com/viewthread.cfm?qid=475765