Development of a Reliability-Based Design Framework for Transmission Line Structure Foundations

This paper presents the reliability-based design (RBD) initiative sponsored by the Electric Power Research Institute for transmission line structure foundations. The role of RBD is presented within the context of geotechnical limit state design. Design parameters that are amenable to statistical description can be propagated systematically to a consistent measure of design risk using reliability techniques such as the first-order reliability method (FORM). Less quantifiable factors are incorporated approximately into RBD by judicious selection of the target reliability level. A simplified RBD approach based on the load and resistance factor design (LRFD) and multiple resistance factor design (MRFD) formats is proposed for practical implementation. The resistance factors for the LRFD and MRFD formats are calibrated rigorously using FORM to produce designs that can achieve a known level of reliability consistently.