The response of bridges when subjected to seismic excitation can be evaluated by a number of analysis methods. The traditional approach to seismic analysis focuses on forces (so-called force-based methods of analysis) while current design practice is moving towards an increased emphasis on displacements (so-called displacement-based methods of analysis). The primary objective of this research project was to evaluate the effectiveness of various commercially available computer programs for performing practical displacement-based seismic analysis of highway bridges. A secondary objective was to identify the fundamental differences between force-based and displacement-based methods of analysis, particularly as they apply to highway bridges. The objectives of the project were met by utilizing four different computer programs to evaluate the seismic response of a simple two-span highway bridge. The seismic response was evaluated using two force-based methods of analysis (response spectrum and time-history) and two displacement-based methods (capacity spectrum and inelastic demand spectrum). Furthermore, the effects of two different abutment and bent foundation support conditions were evaluated. The experience gained by utilizing the computer software revealed that some programs are well suited to displacement-based analysis, both from the point-of-view of being efficient and providing insight into the behavior of plastic hinges. The results of the seismic analyses demonstrated that force-based methods of analysis may be conveniently used to prioritize cases under which displacement-based methods of analysis should be applied. Furthermore, the displacement-based methods of analysis that were used produced different predictions of nonlinear response with neither method being regarded as producing accurate results due to a number of simplifications inherent in the methods. Finally, the displacement-based methods of analysis appear to be attractive to practicing engineers in the sense that they emphasize a graphical evaluation of seismic performance.
Washington State Transportation Center (TRAC)
Analysis, Bridge design, Computer programs, Dislocation (Geology), Dynamic structural analysis, Earthquake resistant design, Earthquakes, Evaluation, Highway bridges, Static structural analysis.