Evaluation of the performance of seismically strengthened and prestressed exterior beam-column joints

Reinforced concrete (RC) beam-column joints (BCJs) are crucial in moment-resisting frames but are vulnerable to seismic damage. This study introduces a novel external diagonal prestressing technique using high-strength steel strands to improve the seismic performance of ductile-detailed exterior BCJs. The method is minimally invasive, cost-effective, and requires minor structural changes. Six full-scale BCJ specimens were tested under reverse cyclic loading: one control and five with varying prestressing levels (0-40%). The specimen prestressed at 30% showed a 70.37% increase in ultimate load and a 263% rise in initial stiffness. Prestressed joints had slower stiffness degradation and greater energy dissipation in early cycles. The failure mode shifted from brittle joint shear to ductile beam flexure, enhancing seismic resilience. The diagonal prestressing induced axial compression in the beam, improving joint shear strength. Overall, the technique provides a practical and effective alternative to traditional retrofitting methods for enhancing earthquake resistance in RC joints.