Seismic Performance of Coupled Shear Walls Designed according to Old and New Codes and Retrofitted with Eb-CFRP Composites

ABSTRACT

Coupled shear walls (CSW) are an efficient lateral load-resisting system. Their seismic performance depends primarily on their coupling beams (CBs) ability to provide adequate stiffness and strength. However, many existing buildings with CSW resisting system were designed and constructed according to old codes and standards with insufficient requirements for seismic design. These systems feature unsatisfactory behaviour and prematurely collapse in case of major earthquake events. Therefore, their seismic retrofit is urgently needed. The main objectives of this study are, i) evaluate and compare the seismic performance of CSWs designed to old and new codes; ii) highlight the deficiencies of CSWs designed to old codes; iii) investigate a retrofit method using externally bonded (EB) carbon fibre reinforced polymer (CFRP) composites to enhance the seismic response of deficient CSWs. To that end, a 20-story CSW is considered with different design details including one according to old National Building Code of Canada (NBCC) before the 1970s and the other one designed consistent with the new NBCC 2015 and the Canadian Standard Association, CSA A23.3–14, for Eastern seismic Canadian zone. The nonlinear analyses of CSWs under earthquake records are conducted in two steps. At first, the nonlinear time-history analyses of two types of CSWs are carried out using RUAUMOKO program and the deficiencies of old-designed CSW are identified through the comparison of obtained results. In the second step, the old design CSW is retrofitted using CFRP sheets and reanalysed to investigate the benefits of the retrofit technique in mitigating the shortcomings. The results indicate that CFRP retrofitting is an efficient method to enhance the seismic performance of deficient old CSWs in terms of story displacement, inter-story drift, CBs rotation, and ductility demand.

KEYWORDS:

• Coupled shear wall
• coupling beam
• CFRP retrofit method
• non-linear time history analysis
• old code
• new code