The National Building Code of Canada, NBCC-15, has recently added a new Seismic Force Resisting System (SFRS) category, ductile shear walls, for Reinforced Concrete Masonry (RCM) buildings. Although it is given a higher ductility-related force modification factor, Rd=3.0, compared to that of moderately ductile walls Rd=2.0, NBCC-15 assigned the same building height limits for the ductile and moderately ductile RCM walls. The research work outlined herein contributes to the understanding of the seismic performance and collapse capacity of ductile RCM shear wall buildings with boundary elements. The main objective is to develop component and system levels, solutions and design recommendations to enhance the overall seismic performance of RCM buildings.
At the component (structural element) level, it is proposed to utilize RCM shear walls with boundary elements built using C-shaped masonry blocks. To quantify the component’s seismic performance, six half-scale high-rise RCM shear walls were constructed and tested under high constant axial compressive load, along with in-plane fully reversed cyclic loading synchronized with top moment. The tested walls represented the plastic hinge region of prototype 6- and 12-storey RCM structural walls. The studied parameters are the boundary element’s length, the boundary element’s vertical reinforcement ratio, the wall’s shear span-to-depth ratio, the type of masonry blocks used in constructing the boundary elements (stretcher or C-shaped), and the lap splicing of vertical rebars in the plastic hinge region.
At the system (building) level, a hybrid structural system composed of ductile and gravity walls is proposed. The ductile walls are RCM shear walls with boundary elements, whereas the gravity walls are conventional rectangular RCM walls with no special seismic detailing. Several archetype buildings were designed according to NBCC-15 and the Canadian masonry design standard CSA S304-14 with varying heights, location’s seismicity, ductile shear wall ratios and cross-sectional configurations. Validated macro-modelling approaches were utilized to simulate the nonlinear response of the buildings. A series of linear and nonlinear, pseudo-static and dynamic time-history analyses were performed to quantify the influence of the studied parameters on the seismic response and collapse capacity. Besides, the possibility of increasing the height limits of ductile RCM shear walls was evaluated. Finally, the potential for reducing and terminating the specially detailed boundary elements over the building’s height was investigated.
The results of the experimental testing confirmed that the presence of the well-detailed and confined boundary elements is capable of mitigating the impacts of the high axial compression load. Using the C-shaped masonry blocks instead of the regular stretcher blocks in constructing the boundary elements enhanced the construction and performance of the walls. Lap splicing of vertical rebars increased the initial lateral stiffness, the rate of stiffness and strength degradation, and slightly limited the displacement ductility. However, with proper detailing of the splice and confinement of the end zones, the premature tensile bond failure was prevented.
Based on the findings of the numerical simulations, it was suggested to increase the height limits of RCM buildings with ductile shear walls with boundary elements. In addition, the results emphasized that utilizing the ductile walls with boundary elements, instead of the traditional rectangular walls, in the proposed hybrid structural system enhanced the structural response and optimized the design. Furthermore, the results demonstrated the possibility of vertically reducing and terminating the specially detailed boundary elements. Therefore, the experimental and numerical results of this research form a step forward in presenting RCM shear walls with boundary elements as a practical and competitive SFRS
