Fiber Model for Seismic Design of Bridges for California High Speed Rail

This study presents the use of a fiber model for the seismic design of ductile elements for several bridges on the California High Speed Rail (CAHSR) project. The application of a fiber model to represent plastic deformation was not traditionally used in the bridge design practice because of the large computational effort required. However, the fiber model can be used as a design tool to describe inelastic behavior more realistically than the conventional plastic hinge method. Specifically, the fiber model can capture loading and unloading of the different parts of the cross section with higher accuracy than the concentrated plastic hinge method. With the fiber model, non-linear evaluation of cracking and spalling of concrete can be directly observed for reinforced concrete structures without requiring an assumed composite behavior curve. For complex structures, such as bridges carrying track on the CAHSR project, non-linear time history analysis for several seismic records is required. A three-dimensional dynamic fiber model has been developed for several locations on the project to consider flexural hinging as well as a pushover model. Fiber nodes were included at the base of single column elements, and at top and bottom of columns for multi-column rigid bents. A comparison between the traditional plastic hinge method and fiber model is presented, noting that this higher-level analysis is still within the acceptable range for industry design.