PhD Oral Exam - Belal Ali Abdelhafeez Abdelrahman, 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

As a seismic force-resisting system (SFRS), reinforced masonry shear walls with masonry boundary elements (RMSW+BEs) were recently introduced and found to achieve enhanced strength, stability, and ductility levels compared to rectangular RMSWs. Thanks to the added confined reinforced masonry boundary elements (RMBEs) at the RMSWs' extremities (i.e., far edges), the wall’s compression zone depth is decreased, resulting in an enhanced stabilized and ductile response when subjected to seismic excitations. Moreover, these confined RMBEs alleviate the RMSW+BEs' reinforcement buckling under high drift levels, boost their displacement ductility, and improves their overall seismic response.

The seismic design of RMSW+BEs necessitates reliable experimental and analytical investigations of their RMBEs. The axial monotonic and cyclic stress-strain curves of RMBEs are essential to predict the lateral cyclic response of RMSW+BEs. This research aims to investigate, experimentally and analytically, the axial monotonic and cyclic behaviour of RMBEs built with C-shape masonry blocks. Moreover, this research proposes monotonic and cyclic stress-strain models for unconfined and confined RMBEs subjected to axial compression loading. Furthermore, a numerical study was performed to assess the nonlinear seismic response of RMSW+BEs having different wall configurations and various design parameters.

This research’s experimental work involved investigating various parameters affecting the compressive strength of fully-grouted concrete masonry prisms and the axial monotonic and cyclic behaviour of RMBEs. Forty-two concrete masonry prisms and 69 scaled RMBEs were tested. The studied parameters are the vertical reinforcement ratio, the transverse confinement ratio and configuration, the cross-section geometry (i.e., square RMBEs vs. rectangular RMBEs), the masonry bonding pattern, pre-wetting of dry RMBEs, various grout types, and the grout compressive strength. The results showed that increasing the vertical reinforcement ratio of the RMBEs resulted in a significant increase in the peak compressive stress and a reduction in the corresponding strain ductility. Moreover, as the RMBEs' confinement ratio increased, the strain ductility witnessed a remarkable enhancement, whereas the peak stress was slightly affected. RMBEs built with rectangular sections exhibited comparable peak stresses, smaller drops following the face shell spalling, better strain ductilities, and enhanced post-peak behaviours than square RMBEs. Besides, using low grout compressive strength significantly reduced the strain ductility of RMBEs. Pre-wetting of dry masonry shell before grouting was found to boost the peak stress of RMBEs; however, it negatively affected their strain ductility.

Comparisons of RMBEs tested under monotonic and cyclic behaviour revealed that the monotonic stress-strain curves form envelope curves of their cyclically tested counterparts. The proposed monotonic and cyclic stress-strain models showed good-to-excellent agreement with the experimental results, predicting the envelope stress-strain curve and the cyclic stress-strain curves' major characteristics.

The numerical study was performed to quantify the influence of the vertical reinforcement ratio of the RMBEs, the masonry strain at peak stress, the masonry compressive strength, and the masonry modulus of elasticity on the seismic performance of 135 RMSW+BEs with different wall configurations. The results showed that the walls' lateral yield and ultimate capacities are highly sensitive to the change of the vertical reinforcement ratio of the RMBEs, whereas their displacement ductility was highly sensitive to the change of the masonry strain at peak. The walls' lateral effective stiffness was greatly influenced by the vertical reinforcement ratio change and the masonry modulus of elasticity.

These research efforts were designed and implemented to address the literature gap of the RMBEs' cyclic response, propose monotonic and cyclic stress-strain curves for confined RMBEs, facilitate design tools to better quantify the RMSW+BEs' seismic response, and further enhance and promote the RMSW+BEs as an effective SFRS.