United States Department of Transportation
i
Accelerating Bridge Construction to Reduce Congestion
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2011-05-01
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[PDF-1.85 MB]
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TRIS Online Accession Number:01680160
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Edition:Final Technical Report
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Abstract:The magnitude of the “residual” displacements at the end of an earthquake can affect the amount of time needed to restore a bridge to service. It may be possible to reduce these displacements (and downtimes) by introducing prestressing forces into the bridge columns. However, before such systems can be designed, it is necessary to be able to estimate the residual displacements with analytical models. The accuracy of the numerical models needed to be established. In this study, tests of sixteen reinforced concrete columns provided the opportunity to observe experimental trends in residual displacements, and to evaluate the ability of a modeling methodology proposed by Berry and Eberhard (2007) to reproduce the observed behavior. Since the columns were subjected to cyclic loading with imposed displacements rather than an actual earthquake, it was not possible to extract a true residual displacement from the test data. Instead, the results are expressed in terms of cross‐over displacements, which are the displacements when the applied effective force is equal to 10% of the effective yield force. The test results indicate that the normalized cross‐over ratio (cross‐over displacement divided by peak cycle displacement) increases with increasing drift ratio. The normalized cross‐over ratio decreases with (a) increases in span‐to‐depth ratio, (b) decreases in reinforcement ratio, (c) increases in axial‐load ratio, and (d) increases in the re‐centering ratio. (The re‐centering ratio defines the relative quantities of post‐tensioned and mild steel reinforcement. As the name implies, it influences the extent to which the column re‐centers when the lateral load is removed). The model did reproduce the expected trends in span‐to‐depth ratio, axial‐load ratio and re‐centering ratio, but it did not reproduce the observed trend in longitudinal reinforcement ratio. The corresponding analytical estimates of the cross‐over ratios consistently exceeded the measured displacements by approximately 20%.
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