Ductility and Detailing Requirements of Bearing Wall Buildings

An analytical procedure to determine the need for concrete confinement at the boundaries of structural walls in a building subjected to earthquakes is described. The procedure is based on comparing directly the expected displacement capacities and displacement demands for the building. For bearing wall buildings, relatively simple expressions are derived that enable the need for confined boundary elements to be evaluated. The expressions are verified using observations from the laboratory and from postearthquake response studies. The primary variables that determine the need for confined boundary elements are found to be the ratio of wall cross-sectional area to the floor-plan area, the wall aspect ratio and configuration, the wall axial load, and the wall reinforcement ratio. The study concludes that concrete confinement in walls of bearing wall buildings may be necessary at the extremities of walls having T, L, or other similarly shaped cross sections. Confinement is typically not required for symmetrically reinforced, rectangular wall cross sections. Current U.S. code requirements for confinement do not properly discern those cases where concrete confinement is or is not required, and are generally quite conservative.