1 Master’s Student, Department of Civil Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada, brook.robazza@civil.ubc.ca
2 Associate Professor, Department of Civil Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada, elwood@civil.ubc.ca
3 Professor Emeritus, Department of Civil Engineering, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada, dla@civil.ubc.ca
4 Faculty, Department of Civil Engineering, British Columbia Institute of Technology, Vancouver, BC, V5G 3H2, Canada, Svetlana_Brzev@bcit.ca
ABSTRACT
Reinforced concrete block masonry shear walls (RMSWs) often constitute the principal seismic force resisting system of masonry structures. During an earthquake, these walls experience the combined effects of gravity axial loading and in-plane overturning moments due to lateral seismic forces. This may precipitate an out-of-plane instability, especially when the vertical reinforcement in the wall end zones is subjected to cycles of high tensile strain. This failure mechanism forms the basis of the current height-to-thickness (h/t) ratio limits (ranging from 14 to 20) for ductile RMSWs stipulated by the Canadian masonry design standard CSA S304.1-04. A comprehensive two-phase research program is being conducted to investigate the key parameters associated with out-of-plane instability in RMSWs subjected to in-plane loading. The first phase involved the experimental testing of five full-scale reinforced masonry column-like specimens subjected to uniaxial cyclic tension-compression loading, which provided a valuable insight into the instability failure mechanism. The second phase of the program is currently in progress, and it consists of reversed cyclic testing of full-scale RMSW specimens. The paper focuses on the key findings of the experimental study for the first wall specimen, characterized by an (h/t) ratio of 27 exceeding CSA S304.1 limits, and its possible implications on the CSA S304 seismic design provisions.
KEYWORDS: reinforced masonry, concrete blocks, shear wall, out-of-plane stability, ductile performance, seismic loading
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