Confinement behavior of rectangular reinforced concrete prisms simulating wall boundary elements

Abstract

Observations following recent earthquakes, and from structural testing, indicate numerous brittle compression failures in rein-forced concrete seismic-resisting walls. This is unexpected, as most seismic-resisting walls are designed to be tension-controlled. The prob-lematic compressive response led to two independent studies, each individually aimed at identifying design and loading parameters that affectthe seismic deformability of the compression regions (or boundary elements) of seismic-resisting walls. These experimental studies arecombined here for a more complete understanding. Both studies used axially loaded, rectangular reinforced concrete specimens that simulateseismic-resisting wall boundary elements. The rectangular prisms were tested under cyclic axial loading or monotonic compression, with afocus on the following parameters: boundary element detailing classification, detailing of transverse reinforcement, maximum tensile strainpreceding compressive demand, and cross-sectional aspect ratio. Test results indicate that expected strength and deformation capacity can beoverestimated unless a rectangular hoop restrains every longitudinal reinforcing bar; use of crossties does not guarantee stability of thelongitudinal reinforcement. Tensile strains of 2 and 5%, imposed prior to reaching the compressive capacity, resulted in compression strengthreductions of 20 and 50%, respectively, indicating that load-history can also be important.