Load and Resistance Factor Design Calibration for Bridge Pile Foundations

Abstract

In response to the documented advantage of the load and resistance factor design (LRFD) approach over the working stress design approach, FHWA issued a policy memorandum on June 28, 2000, requiring all new bridges initiated after October 1, 2007, to be designed according to the LRFD approach. This paper presents current design and construction practices for bridge pile foundations that were established through a survey of Iowa county engineers as well as consulting firms that design piles for the county offices. Conducted during the second and third quarters of 2008 as part of an ongoing research study centered on the LRFD approach for pile foundations in Iowa, this study highlights the benefits associated with a thorough description of regional deep foundation design and construction practices on successive LRFD resistance factor calibrations. The specific topics targeted in the study were current foundation practice; the extent of timber pile usage; pile analysis and design; and pile drivability, pile design verification, and quality control. Since this is the first study to have been conducted at the county jurisdictional level on the topic of pile foundation design after the FHWA mandate, the current status of the implementation of the LRFD approach for bridge foundation design was examined. The responses obtained from 44 Iowa county engineers and eight consulting firms revealed that (a) regional variation in pile foundation practice cannot be captured via a state-level investigation, inhibiting the performance of effective regional LRFD calibrations, and (b) the degree of implementation of the LRFD approach at the county level is about 84%.