Bi-diaphragm elastoplastic haunch retrofit solution for ill-detailed RC beam-column joints
Abhay Gujar, Sachin Pore
Department of Civil Engineering, DBATU, Lonere, Maharashtra, India
Failure of ill-detailed connections is a primary cause of catastrophic, cascading failure of Reinforced cement concrete (RC) frame subjected to seismic loading. A performance based, 3 dimensional (3D), Bi-Diaphragm bolted metallic haunch retrofit solution is proposed, to avoid brittle shear damage to the connection panel zone. Welding is avoided in fabrication of the proposed device to avoid brittle failure in any part of the assembly. The haunch is designed to alter the strength hierarchy of connection subassembly, ensuring plastic hinge formation in beam before any other type of failure occurs. Assessments reveal that, 3D geometry improves torsional stiffness (+277%) and resilience (+94%) over those of an equivalent planer haunch. Numerical analysis is done to estimate the stiffness of haunch. A flow-chart illustrating procedure to design the proposed haunch is presented. The efficacy of proposed solution is evaluated by performance comparison of a Parking+6 storey frame, with and without retrofit solution, subjected to push-over (+87% rise in lateral load at yield, resilience increased by +37 %) and non-linear seismic analysis (Max. roof displacement reduced by -106% and storey drift by -154%). Masonry walls in habitable floors are modeled as equivalent diagonal struts to replicate much essential soft-storey effect. This study is focused on retrofitting exterior beam-column connections owing to their vulnerability reported in the literature. Analytical and numerical assessments confirm the efficacy of proposed solution in mitigating failure during seismic excitations.
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