Report No.: CCEER-00-2

Title: A Comparison of Confinement Requirements in Different Codes for Rectangular, Circular, and Double-Spiral RC Bridge Columns

Authors: N. Wehbe and M. Saiidi

Date: January, 2000

Sponsoring Agency: Nevada Department of Transportation (NDOT)

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557


This report presented the results of a an analytical study to evaluate the effect of confinement steel designed based on various United States seismic codes on the curvature and displacement capacities of reinforced concrete bridge columns. The codes that were included in the study were: the American Concrete Institute, the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges, the California Department of Transportation (Caltrans), the 1994 AASHTO Load and Resistance Factor Design (AASHTO-LRFD), and the Applied Technology Council panel 32. Note that the confinement steel design provisions in the 1998 version of AASHTO-LRFD were the same as those of AASHTO Specifications.

The column cross sections were round spiral columns, square tied columns, and rectangular columns with two interlocking spirals. The parameters that were varied consisted of the cross section size, the longitudinal steel ratio, the axial load, and the column aspect ratio. For double spiral columns, the aspect ratio was not changed but the spacing of the two spirals was treated as a variable. Both curvature and displacement ductilities were evaluated.

The results showed that the 1994 AASHTO-LRFD confinement steel design provisions led to the largest curvature ductility capacities for spiral columns while the Caltrans provisions led to the smallest values. In tied columns, the AASHTO and LRFD design generally led to the highest and the Caltrans design generally led to the lowest ductility capacities. The calculated curvature ductility capacities were relatively low for spiral and double spiral columns while they seemed to be adequate for tied columns. (by authors)