Axial compressive behavior of GFRP composite spiral ties-reinforced ECC-encased HCFST columns

Aiming to solve the issues of conventional concrete-encased high-strength concrete-filled steel tube (HCFST) columns, a novel GFRP composite spiral ties (GC)-reinforced engineered cementitious composite (ECC)-encased HCFST column was proposed and tested under axial compression in this study. The test variables included encasing cement-based materials, the thicknesses of ECC and steel tube, the compression strength of HSC, and the tie configuration. The test results indicated that the failure mode of the composite columns changed after replacing the outer concrete with ECC, showing that the ECC-encased HCFST columns had excellent integrity. When ECC with the same compression strength was used instead of concrete, the bearing capacity, strength index (SI), ductility ( μ ) and energy dissipation ( E d .) of the composite columns were increased by 14.2%, 7.7%, and 81%, respectively. Increasing the thicknesses of ECC and the steel tube significantly improved the composite columns' bearing capacity, and the latter was superior in enhancing the μ and E d . of the columns. Compared with other tie configurations, GC had an outstanding performance in improving μ and E d ., reflecting the excellent restraint performance of GC. Furthermore, a calculation method for the axial compressive bearing capacity of GC-reinforced ECC-encased HCFST columns was proposed based on the composite constraint model and the unified theory of strength.