Seismic behaviour of Exterior RC beam-column joints repaired and strengthened using post-tensioned metal straps

Abstract

Exterior beam-column joints are the most vulnerable part of substandard reinforced concrete (RC) buildings and are often the first to be damaged during earthquakes. This article presents an experimental and numerical investigation into the behaviour of exterior RC beam-column joints repaired and strengthened using Post-Tensioned Metal Straps (PTMS) for active confinement. The study focused on full-scale beam-column joints with an inadequate core zone detailing, thus emulating the deficiencies found in existing substandard RC buildings. Initially, four “bare” joints were subjected to cyclic tests to induce substantial damage within the core zone. Subsequently, the damaged core of the joints was repaired and recast with new concrete, and PTMS were applied to strengthen the joints, followed by another round of cyclic testing. The experimental findings were compared with predictions generated through established models from existing literature. The results revealed that ASCE/SEI 41–17 guidelines accurately predict the shear capacity of the bare joints. It is shown that recasting the core with new concrete significantly increased the joint’s shear capacity by up to 42% compared their bare counterparts. The use of PTMS strengthening further enhanced the capacity by up to 25%. A “scissors model” was employed for numerical simulations of both bare and PTMS-strengthened joints using DRAIN-2DX, which proved effective at predicting their nonlinear load-displacement envelope response. This article contributes towards the development of new cost-effective post-earthquake strengthening techniques for beam-column joints, with the potential to reduce the vulnerability of substandard RC buildings in developing countries.

Hysteresis Behavior of RC Beam–Column Joints of Existing Substandard RC Structures Subjected to Seismic Loading–Experimental and Analytical Investigation

“…In the experimental work of Garcia et al [37], three full-scale substandard exterior RC beam-column joint specimens with inadequate detailing in the joint core zone were tested under cyclic loading and, subsequently, the damaged concrete of the joint was replaced by high strength concrete and the specimens were strengthened with CFRP sheets, showing a significant improvement in their hysteresis performance. Helal et al [38] investigated, experimentally and numerically, the seismic response of full-scale exterior RC beam-column joints with poor reinforcement details strengthened using post-tensioned metal straps for active confinement. A high ductile metal strap confinement, for the strengthening of low strength concrete columns, was used by Ijmai et al [39].…”