Performance of Confined Boundary Regions of RC Walls under Cyclic Reversal Loadings

Observed damages in reinforced concrete wall buildings following some recent earthquakes raised concerns about the seismic performance of rectangular RC walls. Damages in RC walls included spalling and crushing of concrete and longitudinal reinforcement buckling at boundaries as well as global buckling. Preliminary studies attributed these damages to the lack of adequate confinement and detailing in wall boundary regions and high axial load level. Prism specimens representing wall boundaries were tested to study the influence of reinforcement detailing, cross-section slenderness, and loading type on the damages, failure modes, and compressive capacity of isolated confined boundary regions of RC rectangular walls. It was found that the tensile strain prior to compressive strain affected the performance of thin wall boundaries and may lead to different failure modes when subjected to cyclic loading. It was also found that dense transverse reinforcement detailing in thin confined boundaries did not improve their compressive capacity. Design and detailing rules to prevent global buckling and reinforcement bar buckling were also evaluated. A Numerical model that takes into account buckling of reinforcement was proposed to simulate response curves of cyclically tested specimens. The model showed the influence of reinforcement buckling behavior on reducing the compressive capacity for elements with buckling of reinforcement failure.