Nonlinear Analysis of Transversely Reinforced Concrete-Filled Square Tubular Columns Using Fiber-Based Model

  • Dr Jinho Kim, Korea Railroad Research Institute, Korea
  • Miss Minjung Shin, University of Science & Technology, Korea
  • Mr Jinho Hur, University of Science & Technology, Korea

In the conventional Concrete Filled Steel Tubular (CFT) system, local plastic buckling may occur at ends of the steel tube followed by the crushing of internal concrete as demonstrated in the previous research studies. In the new CFT column, named as transversely reinforced CFT (TRCFT) column with carbon-fiber-reinforced plastics (CFRP), additional transverse reinforcement is designed for the potential plastic hinge regions to achieve improved lateral performance. The study for cyclic load-displacement relationship and seismic characteristics of TRCFT columns is experimentally and analytically conducted. Nine TRCFT column specimens were tested under constant axial loading and monotonically increasing lateral loading. The parameters in the test include the width-thickness (b/t) ratio and the axial load level. For predicting the strength and ductility of TRCFT columns, fiber analysis technique is used. The simplified constitutive steel and concrete model, and cyclic stress-strain relationship for fiber elements are proposed. The analytical results show reasonable agreement with experiment results. The influence of the steel tube on the lateral response of TRCFT columns is studied for the evaluation of seismic performance. Because of the increase in ultimate compressive strain of concrete by the steel tube and strain hardening of the steel tube, the curvature ductility factor is increased up to 30 from 10. The lateral stiffness increased by 35-60 % and is fairly sensitive to the increase in the steel tube thickness ratio. The moment capacity of TRCFT columns is predicted with reasonable accuracy using the fiber model.