R-LRFD:RobustLoad and Resistance Factor Design

Abstract

In the modern design codes adopting load and resistance factor design (LRFD), the resistance factors for various models for the design of geotechnical systems were calibrated with the load factors that had been determined by structural engineers. Although the consistent performance or risk level was intended for LRFD, the uncertainty remains in the geotechnical design obtained with LRFD, as the variability of input parameters at a given site could be quite different from those variation levels assumed in the calibration of resistance factors. Thus, the question of how likely the completed geotechnical system meets the performance requirement does not vanish even with LRFD. A logical question then is “how can we perform LRFD so that the geotechnical system will remain feasible (i.e., being able to satisfy the performance requirement) in the face of uncertainties.” In this paper, we proposed an approach that integrates the robust design concept with LRFD, termed robust LRFD (R-LRFD) approach, to help solve this problem. We demonstrated this R-LRFD approach with a drilled shaft design example documented in ETC10. Comparison was made between the LRFD solution with that obtained using the proposed R-LRFD approach.