SEISMIC DESIGN AND PERFORMANCE OF COMPOSITE COUPLED WALLS

The cyclic response of steel coupling beams embedded into reinforced concrete boundary elements was studied. Three half-scale subassemblies representing a portion of a prototype structure were designed, constructed, and tested. The main test variables were the amount of vertical tension/compression stresses in the boundary element, and presence of auxiliary bars attached to the beam flanges for a smoother transfer of bearing stresses. The steel coupling beams exhibited very stable hysteresis characteristics, and could develop the theoretical plastic moment when the boundary and, hence, the connection region were subjected to normal compressive stresses. Tensile stresses in the boundary element reduced the stiffness, and smaller moments could be developed. A significant amount of dissipated energy could be accounted by that energy dissipated in ''plastic hinges'' formed in the exposed portion of the coupling beam. The stiffness was found to be different depending on whether the boundary element was under compressive or tensile normal stresses. The initial stiffness of the coupling beams in all the specimens was smaller than the value computed assuming full fixity at the face of the wall. The ''effective fixed point'' of the coupling beam was found to be inside the wall at approximately one-third of the embedment length from the face of the wall. Analysis and design of composite coupled walls should account for the actual location at which the coupling beams are fixed in the walls.