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Evaluation of the Performance of a Conventional Four-Span Bridge During Shake Table Tests
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A conventional four-span bridge model was tested by Nelson et al. (2007) on three shake tables and two actuator-controlled abutments at the University of Nevada, Reno (UNR). This was part of a George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) study to investigate the seismic performance of fourspan bridges using conventional and advanced materials. In the present study, the seismic performance of the conventional four-span bridge model was evaluated during shake table tests. This bridge comprised a continuous prestressed concrete superstructure, drop-cap bents, seat-type abutments, and reinforced two-column bents For the purpose of this evaluation, the seismic behavior of the columns, cap beams, and abutment seats were studied. Generally, minimal damage was observed in the superstructure, abutments and footings during the shake table tests, and all damage was concentrated in the plastic hinge zones in the columns. The bridge model was ‘Serviceable' after the Expected Earthquake (EE), the earthquake with a 50% probability of exceedance in 75 years, and provided ‘Life Safety' after the Maximum Considered Earthquake (MCE). The MCE has a 3% probability of exceedance in 75 years. Furthermore, the bridge model provided ‘Life Safety' during the Design Earthquake (DE which has 7% probability of exceedance in 75 years as required by AASHTO LRFD Specifications. The measured rotations in the column plastic hinges indicated that the limits of plastic rotation used to define ‘Immediate Service' and ‘Life Safety' are overestimated by the NCHRP 12-49 Guidelines and are not consistent with damage levels. The measured relative displacements at the abutment seats showed that the support length provisions in the AASHTO Specifications provide a high level of safety against the superstructure being unseated at the abutments during the MCE.
Report No. CCEER-13-02