One-Way Shear Strength of Large Beams and Foundation ElementsContaining High-Strength Longitudinal Reinforcement

Mat foundations for high-rise buildings have traditionally been constructed as relatively thick members without shear reinforcement and with relatively low longitudinal reinforcement ratio. Laboratory tests demonstrate that unit shear strength decreases with increasing depth and with decreasing longitudinal reinforcement. These effects are represented in the one-way shear strength design equations of ACI 318-19, which results in significantly reduced nominal strength compared with design strengths that were successfully used for foundation mats for decades. The introduction of high-strength longitudinal reinforcement raises further questions about the effects of increased longitudinal reinforcement strains on one-way shear strength. To explore the effects of depth, reinforcement ratio, and high-strength reinforcement on one-way shear strength, a series of seven one-way shear laboratory tests were conducted. The tests were supplemented by nonlinear finite element studies to extrapolate the test results to alternate member geometries and boundary conditions. Design recommendations are proposed based on the findings of the experimental and analytical studies.