Abstract

Reinforced masonry (RM) shear walls are commonly used as a seismic force-resisting system (SFRS) in low and mid-rise buildings. Considerable progress has been made on the seismic performance of reinforced masonry shear walls with masonry boundary elements (RMSW+BEs). The integration of masonry boundary elements at the wall end zones of RM shear walls showed an enhancement in the lateral performance and curvature ductility compared to that of rectangular RM shear walls. The addition of masonry boundary elements increases the stability of the compression zone and preserves the flexural strength of the wall. This further increases the ductility of the walls, which in turn, increases the ductility modification factor of the wall that reduces the earthquake design load and thus achieves more economical masonry buildings. The research work outlined herein contributes to the understanding of the seismic behaviour and enhance the overall structural performance and competitiveness of RMSW+BEs.
The main objective of this research study is to investigate the seismic behaviour of RMSW+BEs, highlight the ability of boundary elements to enhance the seismic performance of reinforced masonry buildings with RMSW+BEs, and hence, provide the necessary data to support the recent codification of this system in masonry design codes (TMS 402/602 and CSA S304). In this study, seventy full-scale fully grouted flexure dominated reinforced masonry shear walls with C-shaped boundary elements are numerically modelled under reversed cyclic quasi-static lateral loading and constant axial load. The key design detailing parameters used to investigate the seismic performance of the studied walls are the type of reinforcement (steel and GFRP), the boundary element length, and vertical reinforcement ratio in the boundary element, transverse hoop spacing, aspect ratio, and axial stress. The overall performance of each wall is examined in terms of hysteretic response, strength capacity, level of deformation, stiffness degradation, effective stiffness, and response modification factor. Validated and calibrated macro-modelling approaches were developed and utilized to simulate the nonlinear in-plane response of the RMSW+BEs.
The obtained results demonstrated that decreasing the transverse hoop spacing in the masonry boundary element enhanced the wall’s lateral load and displacement, indicating the effectiveness of confining the masonry boundary element core in delaying failure. Besides, increasing the masonry boundary element’s length and vertical reinforcement ratio in the boundary element resulted in a significant increase in the lateral strength and displacement of the walls. Moreover, higher ductility related modification factor, Rd, values were suggested for steel-reinforced walls that could reduce the seismic demand on masonry buildings. The value Rd =3 for ductile walls specified by the Canadian standard CSA S304 (2014) seems to be conservative if adopted for this wall type. In addition, fragility curves at different damage states were developed according to the FEMA P-58 methodology, which can be adopted in future performance-based seismic design approaches. Furthermore, this study analyzed the experimental results of previously tested forty-three fully grouted flexure-dominated rectangular RMSWs under quasi-static cyclic loading that are available in the literature. An equation for the modified section reduction factor for the effective stiffness for both the Canadian and the American masonry standards was proposed using linear regression, taking into consideration the effect of axial stress, vertical and horizontal reinforcement ratios. The force-based design parameters in terms of seismic force response modification factor and deflection amplification factor were assessed, and refined values were suggested to be implemented in future design codes. The numerical and analytical findings in this research are expected to facilitate the practical implementation of RM shear walls with masonry boundary elements as a practical and competitive SFRS in the future masonry design standards.