Bridge Foundations: Modeling Large Pile Groups and Caissons for Seismic Design

摘要

The report synthesizes and summarizes current FHWA-sponsored bridge and related technical reports on the seismic design of large pile groups and caissons into one design-oriented guideline report on seismic design,suitable for applications to the retrofit of existing long span bridges or for new design. The characterization of ground motions for analyses, including a discussion on methods of generating spectrum compatible time histories, spatial variations of ground motion, and effects of local soil conditions on site response, is presented. Modeling approaches for large pile groups focusing on the use of the sub-structuring approach are discussed. The use of p-y curves and associated pile groups, development of linearized Winkler springs, and the assembly of pile group stiffness matrices is discussed in detail and illustrated with examples. Modeling approaches such as the linear stiffness matrix, nonlinear lumped springs and nonlinear distributed springs are discussed for large caissons, which can be employed as foundation piers in many over-water bridges. Case histories of the San Francisco-Oakland Bay Bridge East Span Project and the Tacoma Narrows Bridge are presented to illustrate the modeling approaches.