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Cumulative Seismic Damage of Circular Bridge Columns: Variable Amplitude Tests.


pdf icon Cumulative Seismic Damage of Circular Bridge Columns: Variable Amplitude Tests. (939 K)
El-Bahy, A.; Kunnath, S. K.; Stone, W. C.; Taylor, A. W.

ACI Structural Journal, Vol. 96, No. 5, 711-719, September/October 1999.

Keywords:

bridges (structures); columns; cyclic loads; damage; ductility

Abstract:

The findings from an experimental study to investigate cumulative seismic damage in reinforced concrete circular bridge piers is presented. Twelve identical quarter-scale bridge columns, designed in accordance with current AASHTO specifications, were fabrzcated and tested to failure. Results from Phase 1 testing, which included constant amplitude tests to determine the low-cycle fatigue characteristics of the bridge column, were presented in a companion paper. This paper summarizes results of variable amplitude testing that focused on the effects of load path on cumulative damage. The imposed displacement histories were obtained from analytical simulations of the model column subjected to a sequence of earthquakes of varying duration and magnitude. Test observations indicate that failure is generally initiated by confinement inadequacy and the rupture of the transverse spiral reinforcement. The tests also demonstrated the potential for low-cycle fatigue fracture of the main longitudinal steel when the specimen was subjected to relatively larger displacement amplitudes, typically in excess of 4 percent lateral drift. A fatigue-based damage model, derived from the constant-amplitude tests completed in Phase 1 testing, was applied to the observed response of the six specimens tested in this phase. Findings from the study indicate that the energy capacity of members is ductility-dependent and that fatigue-based damage models offer a reliable means of assessing seismic structural performance.