Resistance factor contour plot analyses of load and resistance factor design of axially-loaded driven piles in clays

This paper presents a framework for calculating the resistance factors of load and resistance factor design (LRFD) for axially-loaded driven piles in clays that can fully account for all necessary reliability-related parameters. The Imperial College Pile (ICP) design method was adopted to determine the resistance factors. The ICP design method was selected because it has been widely verified and has produced close matches to measured pile load capacities. A high-quality database, originally employed to develop the ICP design method, was used to assess the uncertainties of base and shaft capacities. The uncertainties of dead and live loads were determined from previously reported results. The challenge of this paper was to identify the effect of base-to-shaft capacity ratios on resistance factors, which has not been considered in previous methodologies. The resistance factors, compatible with the load factors given in the American Association of State Highway and Transportation Officials (AASHTO) LRFD design specifications and those provided in the American Petroleum Institute (API) LRFD recommended practice, were calculated and proposed for different levels of target reliability index. The effect of base-to-shaft capacity ratios on resistance factors was noticeable, while the effect of dead-to-live load ratios on resistance factors was relatively small.