Seismic Strengthening of RC Exterior Beam-Column Joints Using Local Confinement and 45° Steel Haunches: A Comparative FE Study

This study investigates the influence of local confinement and the introduction of metallic haunches on the mechanical and seismic behaviour of reinforced concrete beam–column joints. A numerical comparative approach is adopted to assess the performance of several strengthening configurations relative to a reference unstrengthen joint. Three confinement configurations are examined notably the confinement of the column in the joint region, confinement of the beam, and simultaneous confinement of both the beam and the column. A fourth configuration incorporates two metallic haunches inclined at 45°, acting as an external strengthening system applied to the unconfined reference configuration. The results indicate that confinement generally enhances the strength, ductility, and energy dissipation capacity of beam-column joints under seismic loading. Among the confined configurations, simultaneous confinement of the beam and the column provides the best overall performance. This is followed by confinement of the column alone, while confinement of the beam alone exhibits comparable load-bearing capacity but slightly inferior performance due to less favourable failure mechanisms. In contrast, the introduction of metallic haunches inclined at 45° leads to a very significant increase in mechanical and seismic performance, clearly exceeding the improvements achieved through conventional confinement. These findings highlight the critical role of external strengthening devices in enhancing the seismic behaviour of beam– column joints and emphasize the strong potential of metallic haunches for the seismic design and retrofitting of reinforced concrete structures.