Designing the Concrete Dual System

Abstract

Assessment of building failures in recent earthquakes shows that shear walls are mandatory to make a structure earthquake resistant. Also, the hybrid “shear wall-moment resisting frame” should satisfy the criteria of strength, ductility, and stiffness. The structure should be designed as a dual system, as defined by the Uniform Building Code. In the dual system, the shear walls are to resist the total design base shear as dictated by a proper structural analysis. The moment resisting frame is to resist 25% of the total base shear, independently. The amount of shear wall area as a percentage of the floor plan area is derived by an upper-bound calculation of the total design base shear and a lower-bound calculation of shear strength of shear walls containing minimum steel percentage. A plastic analysis is performed to relate the displacement ductility ratio to the more readily obtainable curvature ductility ratio. The cross-sections of the shear walls are to be consecutively designed to provide the curvature ductility demands that are calculated.