A Soil-Structure Interaction Procedure for the Design of Bridges on Drilled Shafts

This study presents a practical way to include deep foundation elements, such as drilled shafts and soil effects (through p-y, t-z, and q-z curves), in the modeling of bridges. Superstructure, substructure, and foundations are modeled using finite elements. Shafts are supported by a collection of horizontal (p-y) and vertical (t-z) springs along pile length; at the tip of the shaft a vertical spring (q-z) is included. The incorporation of the nonlinearity of p-y, t-z, and q-z curves is solved by an iterative process using secant stiffness. Our studies have shown that this is a simple process requiring only a few iterations. These iterations are performed using linear analysis with typical finite element software in conjunction with spreadsheet processing. The procedure has been used in the analysis and design of White River Bridge an 18-span bridge in a seismic region with large scour, and for several bridges of the California High Speed Rail project where liquefaction was included. The study includes a range of foundations to incorporate both single-shaft and multi-shaft foundations, and describes a process that can also be applicable to buildings and other deep foundations.