Seismic Retrofit of Non‐Seismically Designed 3D Beam‐Column Joints With Post‐Installed Steel Haunches

ABSTRACT The paper presents experimental results on two‐dimensional and three‐dimensional full‐scale exterior reinforced concrete beam‐column joints subassemblies retrofitted with the Fully Fastened Haunch Retrofit Solution. The specimens were non‐seismically designed with no transverse reinforcement in the joint core, thus making them vulnerable to joint shear failure. Three different beam‐column joint configurations were investigated. The first one was a two‐dimensional subassembly serving as a reference. Two unloaded transverse beams were added in the second specimen, while the third one additionally incorporated a monolithically cast slab. The specimens were subjected to unidirectional, quasi‐static cyclic loads. In this retrofit solution, steel diagonals are post‐installed onto the column and beam to create a new force path around the joint and thereby relocate the plastic hinge away from the joint to the beam. The haunch elements were connected to the column and beam with bonded anchors. The results showcased an upgraded seismic performance of the beam‐column joints in terms of stiffness, strength, and ductility compared to their as‐built counterparts. The results were evaluated in terms of cyclic load‐displacement behaviour, energy dissipation, crack development in concrete, strain development in reinforcing bars and in steel diagonals, as well as qualitative force distribution within the anchor group. The redistribution of forces within the anchor group, an increase in anchorage capacity when the slab was present, as well as the vulnerability of a shear failure in the column due to the slab's participation in flexure constituted the main findings of this study. It was concluded that the performance and efficacy of this retrofit solution strongly depend on the anchorage performance.