Uniaxial Monotonic and Cyclic Compressive Stress-Strain Model for Concrete-Filled Thin-Walled Helical Corrugated Steel Tubes

Concrete-filled thin-walled helical corrugated steel tubes (CFCST) are innovative composite members suitable for rehabilitating or reconstructing piers/columns under earthquake or long-term corrosion damage. The strength and ductility of the concrete can be effectively improved by the lateral confinement of the thin-walled corrugated steel tube (CST). However, for such a member, the previously proposed monotonic model is not applicable to large helical angles, and no existing cyclic model can be directly employed. Hence, some key indicators, including the nominal hoop stress, equivalent confining stress, peak stress, peak strain, plastic strain, and stress deterioration, are examined based on an enlarged experimental database and the working mechanism of CFCST. Subsequently, a systematic constitutive model with an updated monotonic stress-strain relationship and rational unloading/reloading rules was developed for the CST-confined concrete in this study. The accuracy of the proposed model was validated by the experimental results of both the monotonic and cyclic responses of CST-confined concrete specimens.