Fillet welds around circular hollow sections

Abstract

A research program was conducted to evaluate the safety of design rules for fillet welds around the perimeter of steel circular hollow sections (CHS) in the current American Institute of Steel Construction (AISC) steel building specification, AISC 360. Specifically, the appropriateness of the fillet weld directional strength-enhancement factor was investigated for fillet welds to CHS branches, and the effect of non-uniform connection flexibility on fillet-weld strength in CHS-to-CHS connections was studied. A total of 24 large-scale, weld-critical experiments was tested and a further 290 nonlinear finite element models were used to parametrically expand the database. It was found that if the directional strength-enhancement factor is used the target reliability index prescribed by AISC for connectors is not achieved. A recommendation to prohibit this factor for fillet welds around the perimeter of CHS is made. With this restriction, it is shown that AISC 360-16 fillet weld design provisions meet the target safety index for welds in CHS-to-CHS X-connections, where a weld effective length phenomenon exists. It is therefore recommended that AISC advocate 100% weld effective lengths for fillet welds in CHS-to-CHS X-connections, provided that the directional strengthenhancement factor is not used.