Interlocking spirals as transverse reinforcement in bridge columns are being used especially in large rectangular cross sections not only because they provide more effective confinement than rectangular hoops but also because interlocking spirals make the column fabrication process is easier. The behavior of columns with interlocking spirals has been studied only to a limited extent. The University of Nevada, Reno is conducting a study on the seismic behavior of interlocking spirals columns. The study is funded by the California Department of Transportation (Caltrans). The study consists of experimental and analytical parts. The UNR shake table system is being used to test six large-scale models with interlocking spiral columns in the experimental part of the study. Two 1/4 scale flexure-dominated oval columns have already been tested in the strong direction. The spacing between center to center of the spirals (1.0 and 1.5 times the spiral radius) was the principal variable studied in the first two specimens. Preliminary analytical studies of the columns have been conducted. The bond slip and shear deflections were included to predicted the force-displacement response. The shake table tests showed that the distance between the spirals did not adversely affect the shear capacity and that both columns failed in a very ductile manner with a displacement ductility capacity exceeding 8. Good agreement was also found between predicted and measured response enveloped.
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