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 AASHTO 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 will present 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 due to rupture of the confining spirals. The former failure mode is associated with relatively large displacement amplitudes in excess of 4 percent lateral drift, while the latter is associated with a larger number of smaller amplitude cycles. A fatigue life expression is developed that call be used in damage-based seismic design of circular, flexular bridge columns.