Multiple Resistance Factor Design for Shallow Transmission Line Structure Foundations

TLDR

The study focuses on loading and foundation characteristics pertinent to the electric utility industry. The paper develops simplified reliability‑based design equations for spread foundations subjected to uplift. A general reliability calibration procedure derives robust resistance/deformation factors for LRFD and MRFD formats. The authors propose target reliability indices of 3.2 and 2.6 for ultimate and serviceability limit states, showing that the RBD factors consistently achieve desired reliability across diverse conditions and that MRFD calculations effectively incorporate parametric uncertainties.

Abstract

This paper presents the development of simplified reliability-based design (RBD) equations that are suitable for spread foundations subjected to uplift. Emphasis is placed on the loading and foundation characteristics relevant to the electric utility industry. A general reliability calibration procedure is used to derive robust resistance/deformation factors for load and resistance factor design (LRFD) and multiple resistance factor design (MRFD) formats. Two target reliability indices of 3.2 and 2.6 are proposed based on an extensive study of existing designs for ultimate and serviceability limit state, respectively. The main advantage of using these RBD factors is that a known level of reliability can be consistently achieved over a wide range of design conditions. Simple design calculations using the MRFD format are shown to demonstrate their ability to account for parametric uncertainties in a rational manner.