Non-linear time history analysis of reinforced concrete coupled shear walls: Comparison of old design, modern design and retrofitted with externally bonded CFRP composites

Abstract

When appropriately designed, coupled shear walls (CSWs) are very effective lateral load resisting systems for medium to high rise buildings. They reduce the deformation demands on the building and distribute the inelastic deformation between the coupling beams (CBs) and the wall piers. Their seismic performance depends mainly on the ability of their CBs to provide adequate stiffness and strength. Therefore, the design of the CBs and the walls at their base is of paramount importance. However, many existing buildings with CSWs feature unsatisfactory behaviour under lateral loading as they were designed and constructed according to old codes and standards with insufficient requirements for seismic design. Their seismic retrofit is therefore inevitable. Many conventional retrofit techniques have been attempted in the past to improve the seismic behavior of CSWs. Recently, an innovative technique using externally bonded fibre reinforced polymer (EB-FRP) composite to strengthen existing reinforced concrete (RC) structural elements has emerged. The current study focuses on two objectives related to CSWs: (i) evaluate the seismic performance of old designed CSWs and highlight their deficiencies by comparing its response with that of corresponding modern design CSWs; and (ii) evaluate the effectiveness of EB-Carbon FRP (EB-CFRP) retrofitting on the seismic response of deficient CSWs. To achieve these objectives, two 20-story CSWs located in Western seismic Canadian zone were considered. One CSW was designed according to old National Building Code of Canada (NBCC) 1941 and the other one designed in conformity with modern NBCC 2015 and Canadian Standard Association (CSA) A23.3-14. The nonlinear time-history analyses of the two types of CSWs as well as the CFRP retrofitted one under simulated earthquake motions are carried out using RUAUMOKO program. The observed results confirmed the effectiveness of CFRP retrofitting in enhancing the seismic performance of deficient old CSWs in terms of story displacement, inter-story drift, CBs’ rotation, and walls’ curvature.