Performance-Based Design of Drilled Shaft Bridge Foundations

The design of deep foundations for bridge structures should ideally consider the interaction between the soil and the foundation element to properly model the side and tip resistance components. A soil-structure interaction model, such as the $t\mathrm{\text{-}}z$ model method, can be utilized to develop a load-displacement curve for a deep foundation subjected to axial loads. The load-displacement curve represents the behavior of the deep foundation over a range of applied axial loads. More importantly, however, the load-displacement curve can be analyzed by using performance-based design criteria, such as a tolerable displacement corresponding to the service limit state. The tolerable displacement of an individual deep foundation element can be selected to correspond to a movement that would cause adverse performance, excessive maintenance issues, or functionality problems with the bridge structure. In this paper, a performance-based soil-structure interaction design approach for the strength and service limit state axial design of drilled shafts using the AASHTO-LRFD approach is presented. The approach explicitly incorporates field load test data into the design to increase design efficiency while satisfying the limit states. A design example using drilled shaft load test data acquired via the O-cell technology has also been included to demonstrate the developed methodology for use in day-to-day bridge foundation design.