Resistance factor calculations for LRFD of axially loaded driven piles in sands

Abstract

This paper presents the development of Load and Resistance Factor Design (LRFD) of axially-loaded driven piles in sands. The resistance factors of base and shaft resistances were calculated separately to account for their different uncertainty levels. The ratios of dead-to-live load and ultimate base resistance to limit shaft resistance change the uncertainty levels of total load and total pile capacity, respectively; thus, those ratios should be reflected in the calculation of base and shaft resistance factors. For the development of LRFD for axially-loaded driven piles in sands, the ultimate limit state for an axially-loaded driven pile was established based on the Imperial College Pile (ICP) design method; the uncertainties of loads and resistance were accessed; reliability analyses were performed using the First-order Reliability Method (FORM); and finally, reasonable resistance factors of base and shaft resistances were calculated based on the results of reliability analyses for different target reliability index levels. The load factors used for the calculation of resistance factors are the ones proposed by AASHTO and ASCE/SEI 7-05. From the results of extensible reliability analyses using FORM, the resistance factors for base and shaft resistances were found to be highly dependent on the ratios of the dead-to-live load and the ultimate base resistance to the limit shaft resistance. Resistance factors are proposed for different combinations of these ratios within their possible ranges.