Experimental study of cyclic behavior of retrofitted beam-to-column joints with welded haunches

Abstract

A critical demand in structural steel retrofitting situations is to retrofit beam-to-column joints, in which the weak panel zones can be retrofitted by welding haunches. This investigation focused on the retrofitting of weak panel zones in existing welded unreinforced flange-bolted web (WUF-B) joints with column compression remaining. Beam-to-column joints were designed as full-scale specimens with a weak panel zone whose moment resistance did not meet the standard requirement, and then retrofitted by welding haunches and stiffeners after axial loads were applied on the column. Cyclic tests were conducted with three retrofitted beam-to-column joint specimens and the resistance, stiffness, ductility, strain distributions and energy dissipation capacity were analysed. The results showed that the maximum story drift angle of each specimen was greater than 0.07 rad with high resistance, plump hysteresis loop and good ductility. The retrofitted panel zones developed large plastic deformation, and increasing the haunch height could significantly improve the loading capacity and stiffness. The moment resistance of the enlarged panel zones as determined by the American and Japanese codes showed good agreement with the test results, whereas the Chinese code overestimated the yield moment by 22.3%–31.1%. The three joints met the ductility requirement of a special moment frame (SMF) and had satisfactory seismic behavior, demonstrating that the use of welding haunches is feasible and effective for the retrofitting of weak panel zones with column compression remaining.