Seismic Collapse Risk Assessment and FRP Retrofitting of RC Coupled C-Shaped Core Walls Using the FEMA P695 Methodology

摘要

Despite the frequent use of C-shaped reinforced concrete (RC) cores as the primary force-resisting system in multistory buildings, there are still challenges in estimating their inelastic seismic response, especially when they are used as a coupled wall system. Recent studies showed the inadequacy of old code provisions in predicting the seismic shear demands of these systems. This means that many existing RC cores are structurally deficient and need to be retrofitted. One alternative is to retrofit RC shear walls using FRP composite materials to enhance the capacity and ductility of the system. The current paper focuses on two aspects of coupled C-shaped RC core systems: (1) seismic collapse of the system for different torsional sensitivities, and (2) effect of FRP retrofitting on the seismic response of the structure. Modifications are proposed to the wide column model recently proposed by other researchers to accurately capture the inelastic torsional behavior of RC cores, including different modes of failure. Moreover, a simplified spring model is proposed to consider the effect of fiber reinforced polymer (FRP) retrofitting with vertical strips along with X-bracing. The proposed modeling approach is validated against available experimental data. Nonlinear incremental dynamic analysis (IDA) of a typical 12-story RC building structure located in Eastern North America was performed using OpenSEES, following the FEMA P695 methodology. It was shown that, although torsional sensitivity has no significant effect on the interstory drift ratios of the building, it can significantly decrease the collapse margin ratio (CMR). Combined shear/flexural failure was found to be the most common failure mode. Observed results also confirmed that FRP strengthening can be used as an efficient method for enhancing the collapse resistance of RC core wall systems. By using a proper strengthening scheme with FRP material, a more than 60% increase in the CMR can be achieved for the structural system. (C) 2017 American Society of Civil Engineers.