William C. Stone

Cumulative Seismic Damage of Circular Bridge Columns: Benchmark and Low-Cycle Fatigue Tests

An experimental study was undertaken to investigate cumulative damage in reinforced concrete circular bridge piers subjected to a series of earthquake excitations. Twelve identical quarter-scale bridge columns, designed in accordance with current American Association of State Highway and Transportation Officials specifications, were fabricated and tested to failure. This paper summarizes the results of Phase I testing that consisted of benchmark tests to establish the monotonic force-deformation envelope and the energy capacity under standard cyclic loads, and constant amplitude tests to determine the low-cycle fatigue characteristics of typical flexural bridge columns. A companion paper presents the results of variable amplitude testing that focused on the effects of load path on cumulative damage. Test observations indicate two potential failure modes: low cycle fatigue of the longitudinal reinforcing bars and confinement failure caused by rupture of the confining spirals. The former failure mode is associated with relatively large displacement amplitudes in excess of 4% lateral drift, while the latter is associated with a larger number of smaller amplitude cycles. A fatigue life expression is developed that can be used in damage-based seismic design of circular, flexural bridge columns.

CUMULATIVE SEISMIC DAMAGE OF CIRCULAR BRIDGE COLUMNS: VARIABLE AMPLITUDE TESTS

This paper presents the findings from an experimental study to investigate cumulative seismic damage in reinforced concrete circular bridge piers. Twelve identical quarter-scale bridge columns, designed in accordance with current American Association of State Highway and Transportation Officials specifications, were fabricated and tested to failure. Results from Phase I 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% lateral drift. A fatigue-based damage model, derived from the constant-amplitude tests completed in Phase I 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.