Reliability-based design of foundations for transmission line structures. Final report

Abstract

The application of reliability methods to foundation design constitutes a significant improvement over the traditional deterministic approach. However, the number of reliability-based design (RBD) procedures that are suitable for practical use is limited. This study was undertaken to develop practical RBD equations for drilled shafts subjected to uplift, compression, and lateral-moment loading and spread foundations subjected to uplift, with emphasis on application to transmission line structure foundation design. All of the above categories were subdivided further according to the limit state (ultimate or serviceability) and drainage conditions (drained or undrained). The basic goal of RBD is to calibrate the resistance or deformation factors in some simplified design formats until a selected target reliability index is achieved. The Load and Resistance Factor Design format and a multiple resistance factor format were selected for calibration. The reliability index was computed using the First-Order Reliability Method. The reliability indices implicit in existing designs were used as a basis for the selection of the target index.