Pre-tensioned steel straps for seismic retrofit of reinforced concrete columns under combined loading of flexure, shear and torsion

Abstract

Confinement is a sustainable and cheap approach to strengthen the older deficient or inadequate design columns in seismic zones. There are many confinements proven to be effective for retrofitting the columns. However, the studies of strengthening the reinforced concrete columns using active confinement are scarce. This paper presents an extensive experimental work on examining the use of steel straps tensioning techniques (SSTT) in retrofitting the reinforced concrete (RC) columns. Nine reinforced concrete columns specimens were prepared and tested. Seven out of nine of the columns were retrofitted with SSTT under different confinement ratio (layers and clear spacing). The columns were loaded under quasi-static cyclic lateral load with constant axial load. The loading point of cyclic lateral load were slightly altered to create different torque-to-moment ratio (T/M). The seismic performances of columns before and after retrofitting were evaluated through load deformation curve, torque twist curve, energy dissipation, equivalent viscous damping coefficient, column cross-section curvature, strain value of longitudinal reinforcement bars and steel straps. From the laboratory results, SSTT managed to alter the failure mode and avoid sudden failure. Seismic behaviours of SSTT-confined columns, such as load carrying capacity, ductility, and energy dissipation improved. Load carrying capacity was increased up to 75.35% while ductility was increased up to 268.25%. High ductility of SSTT-confined columns resulted in with less crushing damage as it will be more deformable. It is believed that the proposed SSTT active confinement can aid structural engineers in the retrofitting the older deficient or inadequate design columns into a strong and ductile structures especially in the seismic region.