Seismic resistance of reinforced concrete-masonry shear walls with high steel percentages
Priestley, M. J. N.
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This paper summarizes test results of six heavily reinforced concrete masonry shear walls. The test programme was designed to investigate the necessity for the low ultimate shear stress specified by Masonry codes. Care was taken to accurately model good, but realistic design practice in detailing, and variables investigated in the series included steel percentage, influence of vertical load and confinement of potential crushing areas by mortar bed confining plates. Results are presented which clearly indicate that the maximum current code allowance for ultimate shear stress is unreasonably low. No wall suffered diagonal shear failure despite maximum shear stresses exceeding four times the maximum code level. All walls displayed stable hysteresis loops at a displacement ductility factor of 2, and the less heavily reinforced walls (designed to approximately twice code levels) were satisfactory at DF = 4. Degradation was never catastrophic and occurred due to slip of the entire wall along the foundation beam. Methods for reducing the degradation are discussed. Confining plates did not significantly reduce the degradation of the hysteresis loops, but substantially reduced damage to the walls at high ductility factors. Values of required ductility for walls designed to the Loadings Code are investigated, and on the basis of these and the experimental results, recommendations are made for relaxation to the ultimate shear provisions of the masonry code.