Seismic Behaviour of Reinforced Concrete Columns

Appropriate transverse confinement can significantly improve strength, ductility and energy dissipation capacity of reinforced concrete columns, therefore enhancing their seismic resistance. This study is conducted to evaluate the seismic behaviour of concrete columns transversely confined by steel spirals, ties or fiber reinforced polymer (FRP) wrapping. In the experimental program of this study, fifteen circular concrete columns of 356 mm (14 in.) diameter and 1473 mm (58 in.) length were tested under lateral cyclic displacement excursions while simultaneously subjected to constant axial load thus simulating earthquake loads. Eight columns were solely confined by various amounts of steel spirals, while seven other columns containing only minimal steel spirals were retrofitted by external FRP wrapping. Test results revealed that the increased transverse confinement can improve the energy dissipation capacity, ductility, deformability and flexural strength of concrete columns. The required transverse confinement should also be enhanced with the increase of axial load level to satisfy certain seismic design criterion. A computation program was developed to conduct monotonic pushover analysis for confined concrete columns, which can predict the envelope curves of moment vs. curvature and shear vs. deflection hysteresis loops with reasonable accuracy for columns subjected to simulated seismic loading. Based on extensive numerical analysis, expressions were developed for the relationships between the amount of transverse confinement and different ductility parameters, as well as the strength enhancement of confined columns. Finally, design procedures to determine the amount of transverse confinement were developed for concrete columns to achieve a certain ductility target. The enhancement of flexural strength of columns due to transverse confinement was also evaluated.Ph