Fillet welds around circular hollow sections

An experimental and numerical research program was conducted to evaluate the safety of North American design rules for fillet welds around the perimeter of steel circular hollow sections (CHS). This assessment was performed in the context of the current American Institute of Steel Construction (AISC) steel building specification, AISC 360. Specifically, the appropriateness of the fillet weld directional strength-enhancement factor in AISC 360-16 Clause J2.4b was investigated for fillet welds to CHS branches, and the effect of non-uniform connection flexibility on the strength of welds in CHS-to-CHS connections was studied. A total of 24 large-scale, weld-critical experiments were tested, and a further 290 non-linear finite element models were used to parametrically expand the database. It was found that if the directional-strength factor is used, the target reliability (or safety) index prescribed by AISC for connectors, even when the welds are fully effective, is not achieved; hence, a recommendation to prohibit this factor for all fillet welds around the perimeter of CHS is made. With this restriction, it is then shown that AISC 360-16 Clause J2.4a fillet weld design provisions meet AISC’s 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 strength-enhancement factor (1.0 + 0.5sin1.5θ) is not used.