PhD Oral Exam - Abdulelah Mansoor Mohammed Alahdal, 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 (RMSWs) are frequently used in seismic regions. The behaviour of fully grouted (FG) masonry shear walls is complex due to the composite nature of their materials, including masonry blocks, mortar, steel rebars, and grout. This complexity is even greater in partially grouted (PG) masonry shear walls, where stiffness discontinuities arise at the interfaces between grouted and ungrouted cells. The variability of these materials makes predicting their behaviour challenging. Additionally, the limited experimental data available has hindered the development of accurate analytical models for these structures. This research aims to improve the lateral performance of PG masonry shear walls and develop an analytical model to estimate their behaviour.

This research is divided into two main branches: analytical and experimental investigations. In the analytical investigation, an extensive study was carried out to establish simplified analytical models to simulate PG masonry walls’ behaviour. A nonlinear finite element model was employed and validated against experimental specimens from the literature. It was noticed that there is a shortage in the materials properites in the experimental work in literature; and therefore, some assumptions have been done to compensate this shortage. This model was then utilized to generate a comprehensive matrix of 196 numerical models covering a wide range of design and detailing parameters. These parameters included the aspect ratio, the spacing between vertical and horizontal grouted cells, the axial load, the ratio of vertical and horizontal reinforcement, and the compressive strength of grouted and ungrouted masonry units.

Then in the experimental part, to cover the shortage in quantifying of the materials properties’ values, a comprehensive investigation was conducted into the mechanical properties of masonry assemblages subjected to axial compression, shear, and tension loads. Eighty-four masonry prisms were constructed and tested to assess the compressive, shear, and tensile responses of fully grouted stretcher, stretcher ungrouted, and boundary element masonry assemblages. After that, utilizing the masonry components experimentally investigated in the previous phase, two half-scale PG shear wall specimens with C-shaped masonry boundary elements representing walls in mid- and high-rise buildings were constructed and subjected to high constant axial compressive loads and in-plane fully reversed cyclic loading that was synchronized with top moments. These walls represented the lower story panel (i.e., the first storey) of reinforced masonry shear wall prototypes for 6- and 12-storey RM buildings. The study examined parameters such as aspect ratio and the impact of full versus partial grouting by comparing the tested walls to their FG counterparts.

The analytical investigation resulted in three penta-linear load-displacement backbone models that were derived using linear regression analysis for flexural-dominated, shear-dominated, and flexure/shear walls, respectively. Five secant stiffness expressions were derived to define the backbone curve of each wall category. These analytical models were validated against additional numerical and experimental data, showing good prediction accuracy for PG masonry walls. Finally, the stiffness reduction factor in CSA S304-14 masonry, , was found to be imprecise for PG walls. Consequently, three new coefficients for PG wall categories were derived based on regression analyses comparing numerical stiffnesses at yielding with corresponding values calculated using the CSA S304-14 factor.

The experimental results provided full stress‒strain for the compressive, shear, and tensile responses of grouted, ungrouted, and C-shaped boundary element prisms. Stress‒strain curves were established and analysed to determine different mechanical properties, such as compressive strength, tensile strength, shear strength, modulus of elasticity, modulus of rigidity, ductility and toughness indices, and fracture energy. Moreover, the walls’ tests demonstrated a ductile performance primarily dominated by flexure, with both walls exhibiting symmetric and stable hysteretic responses characterized by wide loops, signifying high energy dissipation capacities. Notably, the walls sustain compressive strains in the masonry extreme fibers, exceeding the design value stipulated by North American masonry design standards before strength degradation initiates.