Impact of Axial Load on the Seismic Response of Rectangular Walls

Abstract

Experimental testing was conducted on four large-scale, flexure-yielding walls with rectangular cross sections to investigate the impact of imposed axial load ratio (1, 14, and 2% of axial compression capacity) and transverse reinforcement detailing on the seismic performance, including damage and deformability. Variations in detailing included the inclusion or exclusion of crossties on web longitudinal reinforcement, the confined length of the boundary element, and the effectiveness of using full hoops versus 18–18° crossties in boundary elements. Failure was characterized by simultaneous crushing of the boundary element core concrete and buckling of the longitudinal reinforcement, except for one wall that failed by out-of-plane instability of the wall boundary element. The plastic rotations at lateral strength loss of 2% were on average 3.3, 2.7, and 2.1% for walls with axial load ratios of .1, .14, and .2, respectively. These rotations exceeded the codified limits used for assessment of structures in the United States but were below the codified limits used for design in New Zealand for axial load ratios exceeding 1%. A model for determining the plastic rotation capacity of rectangular walls as a function of the axial load is proposed.