PhD Oral Exam - Mohammed Lotfy Albutainy, 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

There is a global drive to promote and optimize the design of higher building performance at low cost and minimum environmental impact. Although reinforced masonry construction is known for its better fire protection, structural durability, energy efficiency and cost reduction, its use is hindered by the lack of knowledge of its resistance to earthquake loads. The main objective of this research is to quantify the effect of influential parameters on the seismic performance of Reinforced Masonry Shear Walls with Boundary Elements (RMSW+BE). The parameters to be investigated are the size of the boundary element, the spacing between the transverse reinforcement hoops and the vertical reinforcement ratio in the boundary elements.

This research is divided into experimental and numerical investigations. A new system/configuration for RMSW+BE with C-shaped units to form the BE is proposed and implemented, and a new experimental setup is designed and built to capture the response of the lower panel of RMSW+BE in a 12-storey building subject to quasi-static loading protocol. Experimental and numerical research study intended to improve reinforced masonry shear walls' structural performance and constructability. A testing system capable of testing RMSW+BE with a high aspect ratio was developed along with the control system. For this investigation, six half-scale RMSW+BE defined by flexural dominance under continuous axial stress and reversed cyclic top moment and lateral loading were built and tested. The tested walls represent the lower storey panel of a reinforced masonry shear wall in a 12-storey building to simulate the plastic hinge zone for these walls. The boundary elements were constructed using C-shape masonry units rather than stretcher units. This study considered the size, vertical reinforcement ratio, and boundary element confinement ratio of the wall's boundary elements as variables. An experimentally validated model was created to assess the effect of changing the confinement reinforcement ratio in reinforced masonry wall boundary elements. The model was validated using the outcomes of three different experimental programs. To examine the influence of the boundary element's eccentricity on the accuracy of the 2D model findings, the results from the 2D model and the 3D model were compared. Furthermore, the effect of the loading strategy (cyclic vs monotonic) on wall curvature was investigated. The model was used to investigate the effect of modifying the confinement ratio in the boundary element by adjusting the spacing between the confinement hoops on the RMSW's behaviour.

The results showed that the proposed experimental setup and control system could represent the loading conditions on the plastic hinge zone of a 12-storey high masonry wall. From the constructability point of view, it was proven that the C-shaped units provided the lateral strength as designed and provided design engineers with the option of increasing the vertical and confinement reinforcement and the flexibility to change the boundary element length. Additionally, it is anticipated that using C-shaped masonry units to form the boundary elements can reduce the required manpower and the time needed to build the wall compared to the walls constructed using regular stretcher units. The proposed system could provide the lateral strength and ductility required to resist earthquake events. The tested walls were dominated by a flexural failure mode. The enhanced C-shaped boundary element did not change the out-of-plan stability required by the CSA S304-14 'Design of Masonry Structures' design standard. Additionally, it was demonstrated that when subjected to quasi-static reversed cyclic loading, RMSW with C-shaped boundary elements can provide a high level of ductility with minimal strength degradation.

The developed and validated numerical 2D and 3D models showed that eccentricity of the boundary elements is not affecting the predicted lateral force capacity, initial stiffness, stiffness degradation and energy dissipated in each cycle. In addition, reducing the spacing between the confinement hoops does not affect the yield and the ultimate lateral resistance and stiffness degradation. However, reducing the spacing between the confinement reinforcement leads to an increase in the number of cycles to failure and delays/prevents the vertical reinforcement buckling, which reflects the increase in the ductility of the wall. It also increases the amount of energy dissipated by the wall, which enhances the seismic behaviour of the structure and shifts the failure to the next weaker area (i.e., the web).