CCEER-07-04: Experimental Evaluation of Performance of Conventional Bridge Systems
As part of a multi-university research project utilizing the Network for Earthquake Engineering Simulation (NEES), a quarter-scale 110 ft (33.5 m) long asymmetric conventional reinforced concrete bridge model was tested using the shake table system at the University of Nevada, Reno. The model consisted of four spans supported on three, two-column bents of a drop-cap design and two abutment seats driven by hydraulic actuators capable of dynamic excitation. The objective of shake table testing was to study the response and performance of a contemporary reinforced concrete bridge model subjected to biaxial horizontal earthquake excitation. This included the effects of inplane rotation, force distribution among bents, and abutment interaction.
The model was designed in accordance with the provisions of the National Cooperative Highway Research Program (NCHRP) document 12-49. It represented an assumed prototype located in the Los Angeles area. The ground motion that was simulated was the Century City record of the 1994 Northridge earthquake. It was applied in six test runs with increasing amplitudes. At the end of Test 6, with a PGA of 1.00 g in the transverse direction and 1.20 g in the direction, some of the columns showed sign of imminent failure. A seventh test was conducted repeating the same amplitudes as those of Test 6.
The model met all performance requirements for both the expected and rare earthquakes when subjected to equivalent excitations. Failure occurred during Test 7 in bent 1. The bent failed in flexure with rupture of both longitudinal and transverse steel reinforcement and crushing of core concrete in the bottom plastic hinge of the east columns. Bents 2 and 3 only exhibited spalling and cracking of the cover concrete in the plastic hinge regions, revealing some of the reinforcing bars in bent 3. Displacement ductilities of 11.7, 3.4, and 8.3 were reached in bents 1, 2, and 3 respectively. Closing of the abutment backwall superstructure gap occurred first during Test 2, which somewhat limited the longitudinal displacement of the superstructure.
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