Question: Table J2.5 of the AISC 360-10 Specification, for fillet welds loaded in shear, indicates that two limit states are pertinent – failure of the weld metal and failure of the base metal. Does that mean that weld design in HSS joints is based on checking weld failure through the effective throat, plus base metal shearing along the fusion face?

Answer: No. Fillet weld strength is determined on the basis of failure of the weld metal, in shear, along the weld effective throat. The note in Table J2.5 about shear failure on the base metal being governed by Section J4 is meant as a reminder that shear through the thickness of the connected wall may need to be checked. Hence, for a stepped HSS-to-HSS T-connection, fillet-welded all around, the weld is only proportioned on the basis of failure along the effective throat. This requirement is the same in the current Canadian standard for steel structures too (CSA S16-09). Note that the prior Canadian standard (S16-01) did require a check for shear failure along the fusion face. All of the foregoing is based on weld filler metal with a strength level equal to, or less than, “matching filler metal”. If over-matching filler metal is used then it would still be prudent to perform an additional check for shear failure along the fusion face.