Towards more efficient shallow foundations for low-rise concentrically braced frame buildings

Abstract

Earthquakes pose a significant threat to communities, necessitating ongoing efforts to evaluate and mitigate potential damages. Current seismic design codes are intended to protect building occupants during severe earthquakes, and the performance of code-compliant structures in past events indicates their general effectiveness. However, these codes permit a certain level of damage, which can lead to considerable economic losses and prolonged recovery times. Consequently, decision-makers are increasingly emphasizing objectives that not only ensure individual safety but also enhance building performance and community resilience, aiming to exceed minimum code requirements. Recently, economic loss and recovery time have emerged as critical metrics for assessing seismic resilience. Among lateral force-resisting systems, concentrically braced frames (CBFs) are recognized for their efficiency and cost-effectiveness. Despite the strong performance of low-rise CBF buildings during real earthquakes, some analyses suggest a higher collapse probability under high-intensity seismic events, particularly as the structural period decreases. This discrepancy, known as the short-period building seismic performance paradox, may be partially addressed by incorporating soil-foundation-structure interaction (SFSI) into numerical analyses. Effective SFSI implementation requires careful consideration of soil and foundation modeling methods, uncertainties in soil characteristics, and variations in footing design philosophy across different codes. This thesis addresses several key research gaps. First, it evaluates how including soil and foundation effects in numerical analyses influences the computed performance of CBF buildings regarding displacement, acceleration, and economic loss, considering various footing sizes and site classes. Second, it explores efficient foundation designs for Canadian short-period buildings using Latin Hypercube Sampling to examine uncertainties and their impact on performance and repair costs. Third, it develops analytical equations to predict the sliding and rotation of shallow rectangular footings during seismic events. A practical design guide for engineers is provided as an appendix, featuring examples for calculating foundation movement by applying the new equations.