Performance of concrete masonry shear walls with integral confined concrete boundary elements

Willis Bradford Cyrier

This project was funded by the National Institute of Standards and Technology as part of a joint study between researchers at the University of California at San Diego, the University of Texas at Austin and Washington State University to develop improved performance-based design provisions and methodologies for reinforced concrete masonry shear walls. The objective of research reported herein is to investigate the behavior of masonry walls incorporating integral confined concrete boundary elements under lateral loading. Results from this study also provide a basis for establishing prescriptive detailing requirements for designing masonry walls with integral confined concrete boundary elements. Four, fully grouted, concrete masonry shear walls with integral confined concrete boundary elements were designed according to the provisions of the 2011 MSJC and the 2011 ACI-318 codes. Performance measures investigated included peak load capacities; drifts at three limit states; drift components from shear, flexure and sliding; displacement and curvature ductilities; plastic hinge lengths; energy dissipation; and equivalent viscous damping values. The effects of incorporating the confined concrete boundary elements, axial compressive stress, boundary element geometry, and size of transverse hoops in the boundary elements were evaluated to determine their influence on wall performance. Test results in this research were compared to results from tests on two similar masonry walls without boundary elements performed by Kapoi (2012). Masonry walls with integral confined concrete boundary elements increased displacement ductility values by 48% and total energy dissipation was approximately 260% greater compared to similar masonry walls without boundary elements. Axial compressive stress increased peak load capacity and total energy dissipation. Peak load, displacement ductility, and total energy dissipated were greater in the wall with flanged boundary elements compared to the wall with rectangular boundary elements. These performance benefits were a result of the increased out-of-plane stability provided by the flanged boundary elements. One flanged wall used No. 3 hoops while the other employed ¼-in. round wire hoops. Wall responses were nearly identical. Walls with rectangular boundary elements failed when the boundary element core buckled out-of-plane. Walls with flanged boundary elements failed due to low-cycle fatigue fracture of the longitudinal reinforcing bars.

Performance of concrete masonry shear walls with integral confined concrete boundary elements

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