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Seismic Time History Analysis and Instrumentation of the Galena Creek Bridge
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The behavior of complex and irregular structures during construction and in a seismic event is often not well understood by practicing design engineers. The focus of this research is centered around a comprehensive examination of the Galena Creek Bridge, both during construction and under seismic loading. The original arch design of the Galena Creek Bridge featured an innovative steel pilot truss, which supported the arch during construction and supplied the supporting framework for concrete casting. To examine its behavior during construction, an instrumentation plan was developed that consisted of a series of strain gages attached to the pilot truss, conventional arch reinforcing, and embedded in the pilot truss grout and arch concrete. The instrumentation plan allows researchers to monitor the arch in real-time through the construction sequence. The instrumentation plan also featured accelerometers attached to the arch frame to monitor the response of the structure to dynamic loading. To further understand the behavior of the structure to earthquake loading, a non-linear time history analysis of the structure was performed, and then compared to traditional elastic response spectrum techniques. Peak structure displacements, moments, and base shears formed the basis for the comparison. Seismology experts were consulted to select seven acceleration time histories from earthquake records with similar seismology as the active faults located near the Galena Creek Bridge. Recommendations by the Federal Emergency Management Agency (FEMA) were used to scale the seven earthquake acceleration records which were used for the non-linear time history analysis. The results of the analysis show reasonable agreement between the non-linear time history analysis and the elastic response spectrum analysis. With the proper selection of input ground motions, the non-linear time history analysis is effective as a performance-based evaluation tool for better understanding global bridge behavior and interactions.
Report No. CCEER-08-02