PhD Oral Exam - Amgad Mahrous, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Reinforced masonry shear walls with boundary elements (RMSW+BEs) have gained an increased reputation as a reliable seismic force-resisting system (SFRS) since the Canadian Standards for the Design of Masonry Structures (CSA S304-14) and the National Building Code of Canada for 2015 (NBCC 2015) implemented the new guidelines for this category. On the other hand, reinforced concrete (RC) core walls are commonly used as an SFRS in RC structures due to their ability to allocate staircases and elevators conveniently. Despite improvements in reinforced masonry (RM) buildings' seismic performance, there is a gap in the literature of studies investigating the seismic performance of reinforced masonry core walls with boundary elements (RMCW+BEs). Furthermore, the in-plane shear strength calculated following the CSA S304-14 is conservative when designing RM ductile shear walls, which limits the use of these walls with the height limits specified by NBCC. However, there is a lack of studies that address the quantification of the shear strength of RM, considering different design parameters such as the vertical and horizontal reinforcement ratios and configurations.

In this respect, this research is divided into two main phases. Phase I, titled "Seismic Performance Evaluation of the System-level Response of RMCW+BEs", involves introducing the Applied Element Method (AEM) as a new modelling technique for capturing the cyclic behaviour of fully grouted RM shear walls and the dynamic response of RM buildings. Moreover, it proposes a new structural layout for RM buildings with RMCW+BEs as the main SFRS and partially grouted RM walls as the gravity load-carrying system. Furthermore, the seismic response of RMCW+BEs, designed following the CSA S304-14 standard, was analyzed. Nevertheless, this phase investigates the effect of higher modes of vibration on the seismic performance of RM buildings and the efficiency of utilizing the dual plastic hinge (DPH) design approach in mitigating these effects. Furthermore, this phase aims to quantify the ductility and overstrength of the proposed system through nonlinear pseudo-static pushover analysis following the guidelines of the FEMA P695 for the Quantification of Building Seismic Performance Factors. In addition, an incremental dynamic analysis (IDA) is carried out to assess the seismic collapse risk of RMCW+BEs by generating system-level-based fragility curves following FEMA P58-1 guidelines for Seismic Performance Assessment of Buildings. On the other hand, Phase II, titled "Experimental Investigation of the Component-Level Response of RMCW+BEs", involves carrying out diagonal tension tests on forty-one masonry assemblages to evaluate the effect of different the vertical and horizontal reinforcement ratios and configurations on the RM shear strength. Furthermore, one C-shaped RMCW+BEs was tested under a quasi-static along its major axis. The wall represented the first story of one of the core walls utilized as the main SFRS in a 12-story prototype building.

The analyses carried out in Phase I have demonstrated enhanced performance for the RMCW+BEs under the design-level earthquakes compared with the code limits of CSA S304-14 and NBCC. The results showed that the proposed RM system provides the needed ductility, overstrength, and deformation capacity for a ductile SFRS. The proposed layout of RM buildings showed negligible collapse probability values and high reserved collapse capacity at the maximum considered earthquake (MCE) design level. However, the higher modes of vibration showed an adverse effect on the seismic response of RM buildings, which requires the addition of a shear demand amplification factor in the next generation of North American design standards for masonry structures.

The experimental results of Phase II showed that adding vertical reinforcement to masonry assemblages improved the shear capacity and the corresponding shear strain. Furthermore, combining the vertical and horizontal reinforcement resulted in the most optimum configuration to enhance the diagonal tensile (shear) resistance of masonry assemblages. Moreover, the results of the quasi-static cyclic test on RMCW+BEs demonstrated the capability of the proposed wall's geometry to attain a high level of ductility without any reduction in the lateral capacity. Additionally, the wall showed a flexural dominant ductile response with enhanced distribution of cracks and sequence of damage with high levels of dissipated energy and gradual degradation in the lateral stiffness.

The experimental and numerical findings of this research will contribute toward adopting RMCW+BEs as an effective and competitive SFRS for typical RM buildings in the next generations of North American masonry design standards.