SEISMIC PERFORMANCE OF CIRCULAR COLUMNS WITH LOW LONGITUDINAL REINFORCEMENT RATIOS

Two large-scale circular columns with low longitudinal reinforcement r atios were tested under cyclic inelastic lateral displacements simulat ing seismic response. The first column had a longitudinal steel ratio of 0.5 percent, one-half that specified as a lower limit by ACI design rules, and was intended to investigate ductile flexural response of c olumns with low steel ratios. The second column, with 1.0 percent stee l ratio, was intended to investigate whether shear strength was influe nced by steel ratio. Both columns performed well. Column I exhibited s table flexural response at displacement ductilities lip to mu(Delta) = 10 before failing in shear, while Column 2 failed in shear at mu(Delt a) = 4, somewhat higher than the expected ductility level. Response of the two columns indicates that current lower design limits for steel ratio could be reduced without detrimental influence on flexural respo nse, and that shear strength of columns does not appear to be influenc ed by longitudinal steel ratio.