Effect of axial loads in the seismic behavior of reinforced concrete walls with unconfined wall boundaries

Abstract

About 2% of Reinforced Concrete (RC) buildings taller than nine stories suffered serious damage instructural walls during the 2010 Chile earthquake. The observed damage involved mostly crushing ofconcrete, buckling of vertical reinforcement, and opening of the horizontal reinforcement. This damageis attributed to poor concrete confinement in the web and boundaries, inadequate horizontal reinforcementdetailing, and high axial loads. This research aims to reproduce the observed damage and evaluatethe influence of axial loads in the seismic behavior of RC walls with unconfined boundaries. To achievethese objectives, three identical wall specimens were tested. The wall specimens were designed withcharacteristic wall detailing obtained from data of five damaged buildings. These wall specimens weretested under equal lateral displacement cycles and subjected to different axial load ratios. Theflexural-compressive failure mode exhibited by damaged walls during the earthquake was reproducedin these tests. Experimental results indicate that high axial load has a significant effect on the seismicperformance and failure mode of RC walls. Indeed, it triggers a dangerous brittle concrete crushing failurewhich occurs immediately after spalling of the concrete cover.