Research and outlook of steel beam‐to‐column joints retrofitted by welding haunches

A critical issue in structural retrofitting is to enhance the moment resistance of steel beam‐to‐column joints. The authors have investigated the cyclic behaviour and design of existing welded unreinforced flange‐bolted web (WUF‐B) joints, in which welding haunches were utilised to retrofit weak panel zones. In this study, three full‐scale joint specimens were retrofitted by haunches and stiffeners after applying axial column compression load. Then, cyclic tests, numerical simulations, and finite element parametric analyses were conducted. Results indicated that the retrofitted joints exhibited increased moment resistance and satisfactory seismic performance, meeting the ductility requirement of Special Moment Frames in the AISC 341 provision. The force‐transferring mechanism was substantially changed after adding haunches, and thus, a simplified mechanical model has been established to predict the force distribution. Furthermore, parameters influencing the joint behaviour (i.e., haunch geometries and axial column load before retrofitting) were involved in parametric analyses. Based on the above experimental and numerical results, the design method has been proposed, including the recommended configurations, calculations of the moment resistance and initial rotational stiffness, and detailed seismic checking procedures. This study reports a feasible solution to retrofit weak panel zones with column compression remaining and provides an outlook on retrofitting beam‐to‐column joints in future investigations.