Effect of Subduction Earthquake-Based Loading History on Substandard RC Square Columns

Abstract

The cyclic behavior of RC bridge columns with a square cross section was experimentally evaluated using two types of quasi-static cyclic deformations, a conventional loading protocol and a loading protocol designed to assess the behavior or capacity of deficient bridge columns under subduction-zone earthquakes. The specimens and the laboratory arrangement were chosen to represent full-scale typical bridge columns constructed in the 195s to mid-197s as part of a typical multicolumn bridge bent in the Pacific Northwest. These columns included lap splices of longitudinal bars in the plastic hinge region and lacked sufficient transverse reinforcement details, making them vulnerable to major seismic events. The experimental results showed that the specimens achieved moderate to high displacement ductilities despite the detailing deficiencies, which can be attributed to the flexure-dominated response. More importantly, however, the experimental results illustrated that these types of substandard RC columns can exhibit a shift in the mode of failure and exhibit less strength and displacement capacity under the subduction earthquake-based cyclic protocol compared with more conventional cyclic protocols. A numerical modeling approach was also adopted with the aim of characterizing the response of the specimens. The numerical results show that the model provided a reasonable approximation of the nonlinear behavior of the columns, including stiffness and strength degradation.