Bridge Instrumentation and Post-Earthquake Evaluation of Bridges

by Patrick Hipley, Moh Huang and Anthony Shakal

Hipley, Patrick, Moh Huang and Anthony Shakal (1998). Bridge Instrumentation and Post-Earthquake Evaluation of Bridges. SMIP98 Seminar on Utilization of Strong-Motion Data, p. 53 - 62.

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As the number of large civil structures instrumented for strong motion is increasing, efforts towards utilizing the earthquake data collected from these structures is also increasing. The studies are geared towards verifying seismic engineering design assumptions by comparing the theoretical models to the actual readings. Efforts to utilize the data ranging from simple comparison of the estimated structural period of vibration with the recorded free vibration, to complex comparisons of non-linear time-history models are underway. Many more studies are needed to take full advantage of this valuable data.

Accurately monitoring bridge movements during a large earthquake is necessary to advance our understanding of how these massive structures are affected by seismic input. Bridges of different structure types react differently to the same seismic wave patterns. Dynamic soil-structure interaction can be studied and theories can be verified or disproved based on the actual readings. Before strong motion sensors were placed at ground sites or on civil structures, theories were based on very little data. Therefore, the data collected from large earthquakes with these sensors are invaluable to the seismic engineering community.

The California Department of Transportation (Caltrans) and the California Strong Motion Instrumentation Program (CSMIP) of the California Department of Conservation's Division of Mines and Geology have instrumented more than 50 Caltrans bridges throughout the State since the 1989 Loma Prieta earthquake. In addition, CSMIP and Caltrans are installing more near-real-time stations at selected bridge sites in the State. Consequently, more near-real-time strong-motion data will be available quickly after an earthquake. These data provide information on ground shaking and response of the bridge structure, and are useful not only for improving seismic design practices but for post-earthquake damage evaluation of bridges. This paper describes the current status and future plan of the Caltrans/CSMIP bridge instrumentation project, and discusses quick application of strong-motion data to post-earthquake evaluations of bridges. Cases of quick application of near- real-time data are presented and criteria for determining post-earthquake inspection of bridges are discussed.