Mat foundations for high-rise buildings must resist immense overturning moments and associated shear forces. When design shear strengths of existing mats are calculated with the new one-way shear equations in ACI 318-19, the nominal one-way shear strength is much lower relative to design checks with prior versions of ACI 318, raising concerns about shear strength in existing concrete elements without shear reinforcement. This prompted the experimental work described in this dissertation, where seven unique one-way shear tests were conducted on a range of member depths, with depths representative of simple spread footings to full-depth mat foundations. These tests served to illustrate the shear strength of beams and foundations when subject to the size effect.

The dissertation is separated into the experimental work (Chapter 2 and Appendix A) and the analytical work (Chapters 3 and 4). The experimental tests investigated the effects of low reinforcement ratio associated with the use of high-strength longitudinal reinforcement on shear strength. These tests also investigated the difference between foundation shear strengths and beam shear strengths. Experimental results showed that the ACI 318-19 one-way shear equations significantly underpredict the shear capacity of members with large depth and low reinforcement ratio, and that use of high-strength longitudinal reinforcement provided adequate one-way shear strengths even at high steel strains. Analytical studies were undertaken using finite element simulations to extrapolate the experimental results to conditions related to a mat foundation. These models revealed that foundations can have higher one-way shear strengths than beams, but the magnitude of the improvement depends on member geometry and the boundary conditions.