Application of reliability based design concepts to transmission line structure foundations

A procedure is proposed for the design of power transmission line structure foundations using a probability-based load and resistance factor design (LRFD) format. This procedure involves the determination of a foundation strength factor, φ_F, which is used as a multiplier of the calculated nominal design strength to estimate the 5% exclusion limit strength required in the LRFD equation. Statistical analysis of the results from full-scale load tests are used to obtain φ_F values applicable to various nominal design strength equations for drilled shafts subjected to uplift loads. These results clearly illustrate the significant economic benefits of conducting more detailed subsurface investigations for the design of transmission line structure foundations. A design example is presented