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by P.K. Malhotra, M.J. Huang and A.F. Shakal
Malhotra, P.K., M.J. Huang and A.F. Shakal (1994). Interaction at Separation Joints of the 110/215 Bridge During Earthquakes. SMIP94
Seminar on Seismological and Engineering Implications of Recent Strong-Motion Data, p. 49 - 60.
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Abstract
A multi-span, curved, concrete box-girder bridge has been extensively instrumented by the
California Strong Motion Instrumentation Program (CSMIP) in cooperation with the California
Department of Transportation (Caltrans). On June 28, 1992, the bridge was shaken by the
magnitude 7.5 Landers and magnitude 6.6 Big Bear earthquakes in Southern California. The
epicenters of these earthquakes were 50 and 29 miles (81 and 46 km) from the bridge,
respectively. All thirty-four strong-motion sensors installed on the bridge recorded its
response to these earthquakes and provided an insightful set of response data. A striking
aspect of the response is the presence of intermittent sharp spikes in nearly all of the
acceleration records from sensors on the deck of the bridge. Among these the highest spike
was 0.80g for the Landers and 1.00g for the Big Bear earthquake. The peak ground acceleration
at the bridge site was only about 0.10g for both these earthquakes. With the aid of visual
examination and simple analysis it is deduced that: (i) the spikes were caused by forces
generated at separation joints between adjacent bridge segments by impacts and stretching of
the cable restrainers; and (ii) the forces of impacts and cable stretching are directly
proportional to the size of the spikes and can be estimated by the use of a simple formula.
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