Influence of Floor Diaphragm-Wall Coupling on the System-Level Seismic Performance of an Asymmetrical Reinforced Concrete Block Building

Understanding the inelastic seismic response of reinforced masonry shear walls (RMSW) is the first step to develop predictive models of the system-level (i.e.,complete building) response under different levels of seismic demand. Such predictive models will not only have to be capable of accurately accounting for the different system-level-specific aspects but will also have to be easy enough to be adopted by design engineers. In this respect, the influence of the floor diaphragms on a building's seismic response is typically recognized only through the role of the former in distributing the shear forces on the building's seismic force resisting system (SFRS) as a result of the diaphragms' in-plane stiffness. Subsequently, the current paper focuses on analyzing experimental data of a series of RMSW tested as individual components and within two asymmetrical building systems. The analyses showed that the out-of-plane stiffness of the floor diaphragms played an important role in flexurally coupling the RMSW aligned along the loading direction with those walls aligned orthogonally. This system-level aspect affected not only the different wall strength and displacement demands but also the failure mechanism sequence and the building's twist response. For the building system under consideration, the diaphragm-wall coupling resulted in doubling the building's initial stiffness, and also significantly increasing the building's strength. The results of the study show that neglecting diaphragm out-of-plane coupling influence on the RMSW at the system-level may result in unconservative designs and possibly undesirable component-level failure modes as a result of violating capacity design principles. To develop an analytical model that can account for the aforementioned influences, simplified load-displacement relationships were developed to predict RMSW component- and system-level responses under lateral seismic loads. In the current study, three approaches were proposed to account for the diaphragm coupling influences on the RMSW response. The developed analytical model presents a useful system-level response prediction tool for displacement- and performance-based seismic design of RMSW buildings.