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Report No.: CCEER-04-3

Title: Impact of Aspect Ratio on Two-Column Bent Seismic Performance

Authors: Khaled Moustafa, David Sanders, and M. Saiid Saiidi

Date: February 2004

Sponsoring Agency: California Department of Transportation (CalTrans)

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557

Abstract:

The design of structural bridge elements like columns, beam-column joints, and cap beams has evolved in the past 20 years. Many experimental tests have been done in order to determine the behavior of bridge columns under seismic loading. Most of those tests were static performed with monotonic cyclic loading. Only a few of those tests were dynamically performed on shake tables to simulate the actual earthquakes. Based on the literature review, few studies were concerned about testing the seismic behavior of newly designed models; in particular, two-column bent models with hinged bases. Therefore, the objective of the present study was to test two-column bridge bents dynamically by subjecting them to actual time earthquakes. Three models with columns aspect ratios of 6.64, 4.5 and 2.5 and scale ratio of 0.3 were designed according to the updated Caltrans design criteria. The aspect ratio is the height of the column divided by the column diameter. The shake table was able to exert the record of the Sylmar earthquake, 1984 on the three specimens with various amplitudes. All deformations, rebar strains and mass accelerations were recorded during shaking. The three specimens behaved strongly and resisted high levels of the Sylmar earthquakes after experiencing high ductility levels. The two long specimens had a similar flexural behavior, whereas the short specimen had a hybrid between flexural and shear behavior. The data from these specimens will be used to understand joint, column and base hinge behavior to develop analytical models and to propose design recommendations.

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