RC Structural Walls: Seismic Design for Shear

Abstract

Provisions of 1982 UBC, ACI 318‐83, and ATC 3‐06 pertaining to seismic shear design of slender walls in mid‐rise construction are evaluated. In the event of major ground shaking in regions of high seismic risk, the actual shear strength demand is expected to equal that associated with the axial‐flexural supply. Thus, the codes' minimum design requirements ought to insure that flexure, and not shear, will control the seismic response during the expected rare, major seismic event in the western U.S. The codes do not implement this condition. Expressions suggested by design documents for computing the shear strength of walls were evaluated by comparing the predicted and measured strengths of 10 wall specimens tested at Berkeley. Although generally conservative, since code expressions do not incorporate the actual shear resisting mechanisms of walls under seismic effects, it is possible for the expressions to mislead the designer to poor shear design. Recommendations are formulated to improve the current shear design procedures by: (1) Relating the shear strength demands to the actual axial‐flexural supply; and (2) incorporating the actual shear resisting mechanisms in predicting shear strength supply of walls.