Cumulative Seismic Damage of Circular Bridge Columns: Variable Amplitude Tests.
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899