Experimental performance of concrete masonry shear walls under in-plane loading

Christina Marie Kapoi

This study was conducted as part of a joint effort between the University of California at San Diego, the University of Texas at Austin, and Washington State University. The objective of the overall project is to develop improved performance-based design methodologies and provisions for reinforced masonry shear walls under seismic loading. The primary objective of the research reported in this thesis was to investigate the behavior of reinforced masonry shear walls subjected to in-plane lateral loading while varying wall aspect ratio, level of applied axial stress and reinforcement ratio. The secondary objective was to examine the effects of concentrated reinforcement at the ends of the walls (jambs) compared with evenly distributed reinforcement on shear wall performance. Eight, fully grouted, concrete masonry shear walls were designed according to the 2011 MSJC Code. Walls were tested to failure under cyclic in-plane lateral loading. The walls had three height-to-length aspect ratios (0.78, 1.0 and 2.0), two magnitudes of axial compressive stresses (0 and 158 psi), and two vertical reinforcement ratios (0.0033 and 0.0072). In addition, two of the walls compared the effects of jamb reinforcement vs. evenly distributed reinforcement. Wall performance was evaluated by comparison of failure modes, predicted vs. actual load capacity, drift capacity, displacement ductility, height of plasticity, equivalent plastic hinge length, amount of energy dissipation, and equivalent hysteretic damping. The walls exhibited either a flexural failure or a complex flexure/shear/crushing failure which depended upon the aspect ratio and amount of vertical reinforcement. Results showed that the amount of drift at failure was highly dependent upon the aspect ratio but was not influenced by the amount of axial compressive stress or the vertical reinforcement ratio. The displacement ductility was sensitive to the amount of vertical reinforcement but not the amount of axial compressive stress. There were no apparent correlations between the plastic hinge length and any of the design parameters. The performance of walls with jamb reinforcement was similar to that of walls with evenly distributed reinforcement. Large-diameter vertical reinforcement bars with lap splices at the base of the wall should be avoided because of their propensity towards abrupt failure.

Experimental performance of concrete masonry shear walls under in-plane loading

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