Civil Engineering Association

Load and Resistance Factor Design (LRFD) for Reliability Analysis/Design of Piles Axial Capacity

Resistance factors were developed for use as a part of the implementation of the Load and Resistance Factor Design (LRFD) method of driven piles’ axial capacity. Resistance factors were calibrated in the framework of reliability theory utilizing pile load test data available from North Carolina Department of Transportation (NCDOT). Resistance statistics were evaluated for each data case in terms of bias factors. Reliability analyses on the current practice of pile foundation design by the Vesic, Meyerhof, and Nordlund methods were performed to evaluate the level of safety and to select target reliability indexes. Two types of First Order Reliability Method, Mean Value First Order Second Moment method and Advanced First Order Second Moment method, were employed for the reliability analysis and the calibration of the resistance factors. Recommended resistance factors for the three design methods (Vesic, Meyerhof, and Nordlund) are presented for the target reliability indexes of 2.0 and 2.5. Seven design categories for which the resistance factors are recommended are coastal concrete square pile with N@Toe<=40, coastal concrete square pile with N@Toe>40, coastal steel HP pile, coastal steel pipe pile, coastal concrete cylinder pile, piedmont concrete square pile, and piedmont steel HP pile. The resistance factors were calibrated separately for total, skin and toe capacities in an attempt to develop a correlation between the three resistance factors for each design category. In many cases, however, the resistance factor for total capacity is larger than both the skin and toe resistance factors and only total capacity factors are recommended. The resistance factors developed and recommended from this research are specific for the distinct soil types of North Carolina and for the unique practice of pile foundation design in the NCDOT.