Test of High-Rise Core Wall: Effective Stiffness for Seismic Analysis

Abstract

A test was conducted on a large-scale model of a concrete shearwall from the core of a high-rise building. The wall was slender (height-to-length ratio of 7.2), had a flanged cross section, a low percentage of vertical reinforcement (0.45%), and was subjected to a constant axial compression of 0.1f c ' A g to simulate the effect of gravity loads. Approximately 70% of the flexural resistance of the wall was due to the applied axial compression. The main emphasis of the test was to investigate the influence of cracking on effective stiffness for seismic analysis. Of particular interest was recovery of uncracked-section stiffness due to axial compression from gravity loads closing flexural cracks in walls with a low percentage of vertical reinforcement. Extensive measurements were made of concrete strains over the cracked region of the wall, and these were used to calibrate a nonlinear flexural stiffness model for high-rise concrete shearwalls. The final failure mode was buckling of an unsupported vertical reinforcing bar leading to concrete spalling and bar fracture after a few post-buckling cycles. The maximum global drift of the wall was 2.4%.