Report No. CCEER-95-6A nonlinear computer program to predict the dynamic response of base isolated bridges to orthogonal, horizontal earthquake ground motions was developed. The computer program can model multi-span bridges with straight, continuous superstructures and multi-column bents. Hysteretic behavior of elastomeric or lead-rubber isolators, abutments, shear keys, and columns can be modeled. Nonlinear analysis of the six-span Verdi bridge near Reno, Nevada showed that column ductility demands can be eliminated using isolation. Contrary to linear elastic theory, the superstructure displacements were controlled. Studies were conducted to show that seismic isolation may not be effective in bridges with long columns and located on deep soil deposits. The AASHTO Guide Specifications for Seismic Isolation Design were evaluated. Results of the simplified linear methods compared well with nonlinear analysis in the longitudinal direction but were in error by 21% transversely (Abstract by authors)
