Seismic response of low aspect ratio reinforced concrete walls for buildings and safety-related nuclear applications
Luna, Bismarck N.
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Low aspect ratio reinforced concrete (RC) walls are widely used for low- and medium-rise buildings and safety-related nuclear structures. Studies have demonstrated that the seismic performance of conventional low aspect ratio walls cannot be estimated accurately using existing predictive equations or hysteretic models. To improve the profession’s understanding of the cyclic response of low aspect ratio walls, the US National Science Foundation funded a Network for Earthquake Engineering Simulation (NEES) research project on shear walls of conventional and composite construction. Twelve large-size, low aspect ratio, rectangular, RC shear wall specimens were designed, constructed and tested at the NEES facility at the University at Buffalo. The primary objective was to gather and analyze data to better characterize the performance of low aspect ratio RC walls during earthquake shaking. The global force-displacement relationships are analyzed and discussed. Deformation of the reinforced concrete panels was computed from a dense array of 3D non-contact transducers, and used to estimate a) contributions to total displacement of flexure, shear and sliding, and b) principal compressive and tensile strains, and shear strains, as a function of total displacement. The initial stiffness of the test specimens was substantially smaller than values calculated using equations in design standards and revisions are recommended. Restrained shrinkage at the foundation-wall junction is identified as the primary cause for the differences in stiffness. The concrete cracking patterns and rebar and concrete strain distributions are presented and used to identify how forces flow from the centerline of loading to the foundation. The traditionally assumed failure modes of diagonal tension (rebar yielding) and diagonal compression (concrete crushing) are coupled. New equations for the peak shear strength of low aspect ratio walls with and without boundary elements (contained within the web of the wall) are proposed for possible inclusion in codes and standards of practice.