Economical Placement of Shear Walls in a Moment Resisting Frame for Earthquake Protection

Abstract

Use of shear walls in RC buildings is one of the most commonly used strategies for earthquake mitigation. To avoid torsion in buildings, shear walls must be placed symmetrically in plan. In this paper, a five-storey RC building located in seismic zone-V is considered with four shear walls. Five different configurations of shear walls viz. bare frame, shear wall symmetrically placed at exterior bays (centrally), at core and adjacently placed in exterior of the building, were considered. These frames were analysed for seismic forces to assess performance in terms of base shear, storey drift, member forces and joint displacements. The frame with shear walls at core and centrally placed at exterior bays showed significant reduction of order 29% to 83% in lateral displacement. The reduction in bending moments was approximately 70% to 85% for interior and perimeter columns respectively. Shear and axial forces in columns have reduced by 86% and 45% respectively. Based on such results, the best placement of shear walls in building plan is suggested. Afterwards, frame with best shear wall configuration was chosen for further work. In order to reduce the cost of construction shear walls were curtailed first at the top one storey and top two storeys. The two frames were analysed for earthquake loads and their performances were compared in terms of bending moment, shear forces, storey drift and interstorey drift, etc. It was concluded that the best configuration is the one in which shear wall at the core is established till 2/3rd the height of the building. This configuration is found to be economical but not at the cost of protection against earthquake.