Estimation of Resistance Factors for Reliability-Based Design of Shallow Foundations in Cohesionless Soils Under Earthquake Loading

In areas with significant seismic activity, earthquake-induced loading effects may constitute the major portion of the design loads on foundations. However, very few attempts have been made to apply reliability-based design concepts on footings under seismic loads. Therefore, this study aims at contributing to the reliability-based design methodology by estimating the resistance factors for shallow foundations in cohesionless soils under earthquake loads for the ultimate limit state (ULS), which is defined as the condition in which the seismic bearing capacity is equal to the design load including dynamic effects. The uncertainties in both the load and the capacity are considered. To evaluate the variation of the reliability index ( ) with respect to each significant design parameter, a parametric study was conducted using First Order Reliability Method (FORM) and Markov Chain Monte Carlo simulations. These results were used to select the appropriate domains within the most influential design parameters for the calibration of the simplified RBD equations that can be presented for general use. The target reliability index for calibration, which turned out to be significantly smaller than that for static loading conditions, is selected after examining the range of reliability levels implicit in existing deterministic foundation designs. The resulting resistance factors are presented in the form of design charts that can be readily applied in foundation engineering practice.