Recorded seismic response of the Samoa Channel Bridge-foundation system and adjacent downhole array

A large set of earthquake records from the highly instrumented Samoa Channel bridge-ground system has been compiled and made available by the California Geological Survey. During six seismic events, more than 30 data channels have been documenting the seismic response of the bridge, abutments, and adjacent ground surface. Of special interest is the response of one of the bridge piers with records at the deck level, pile cap and within the underlying pile foundation. Response of this pile foundation is compared to that of the ground as documented by the nearby Eureka geotechnical downhole array. In this paper, records from the strongest to date 2010 Ferndale earthquake (PGA of about 0.16 g), along with other available low-amplitude events (2007-2014) are employed to evaluate the ground, pile foundation, and overall bridge seismic response. Spatial variation of the recorded motions is examined. Linear and nonlinear response of the ground and the bridge are assessed using system identification techniques. During the strong shaking phase of the 2010 Ferndale Earthquake, a clear and significant stiffness reduction was observed in the column as well as in the foundation of the instrumented pier.