Post-Fire Seismic Performance of Lightweight RC Beam-Column Joints: Hysteresis, Energy Dissipation and Ductility

Abstract Fire exposure can substantially alter the post-fire seismic response of reinforced-concrete (RC) beam–column joints, whose performance strongly influences the integrity of moment-resisting frames. This study uses sequential thermal and mechanical finite-element analyses in Abaqus to examine lightweight aggregate concrete (LWAC) joints exposed to 200, 600, and 800 °C and subsequently subjected to cyclic loading. The response is evaluated in terms of hysteresis, backbone curves, load capacity, stiffness, displacement ductility, and hysteretic energy dissipation. Relative to the ambient-temperature model, the peak load decreases from approximately 117 kN to 101, 74, and 48 kN at 200, 600, and 800 °C, respectively, corresponding to reductions of 14%, 37%, and 59%. Displacement ductility also decreases, with reductions of approximately 6.6%, 9.4%, and 40.8%. The energy-based results indicate an even greater loss: cumulative hysteretic energy decreases by 18.3%, 46.5%, and 75.6% at the same temperatures. These findings suggest that energy dissipation may be more sensitive to thermal damage than displacement ductility. Because direct experimental validation for the specific LWAC joint configuration was unavailable, the model was compared with published experimental results for normal-aggregate concrete joints; the predictions should therefore be interpreted as a numerical assessment of relative trends rather than definitive absolute predictions for LWAC joints.