Load and Resistance Factor Design for Serviceability Limit State of Laterally Loaded Drilled Shafts for Transmission Line Structures in Sands

Load and resistance factor design (LRFD) for serviceability limit state (SLS) of laterally loaded drilled shafts was explored for transmission line structures in sand, and the SLS resistance factor (RF) was proposed. Statistical characteristics of various load components, including transverse tension load (TTL), wind-on-structure load (WSL), and wind-on-conductor load (WCL), were considered and assessed. A database was established and adopted to calibrate RF for SLS of laterally loaded drilled shafts in sands. The hyperbolic model was introduced to quantify uncertainties in the lateral load-displacement curves for drilled shafts and adopted to determine the allowable load capacity. A Monte Carlo simulation was performed to calibrate RF for SLS. The effects of target reliability index (βT), allowable displacement (ya), ice thickness on conductor (Iz), and various load ratios were all considered in the RF calibration. The values of RF for SLS varied from 0.19 to 0.94 for βT in the range of 1.5-3.5. Equivalent factors of safety (FSeq) were obtained for the proposed RFs to evaluate and compare the safety margin of SLS to that of current design practice.