Axial Compressive Properties of Prefabricated Circular Steel Tube Confined Concrete Columns

A finite element analysis based on test results was carried out to study axial compressive performances of the prefabricated circular steel tube confined concrete columns connected with steel sleeve and straight thread sleeve. First, finite element models of cast-in-situ and prefabricated circular steel tube confined concrete columns were established. Then, axial compressive performances of the cast-in-situ and prefabricated columns were compared in terms of the bearing capacity–average longitudinal strain curves, steel tube stress, rebar stress, and concrete stress; the deformation pattern and mechanism of prefabricated columns were analyzed. Finally, a calculation method of axial compressive capacity of prefabricated columns was proposed. Results show that the cast-in-situ columns and the prefabricated columns both have good mechanical and ductility properties; the steel tube and steel sleeve have strong confinement effect on the core concrete and the axial compressive bearing capacity was increased by 1.94%−6.17%. Increasing the thickness of steel tube can effectively improve the axial compressive bearing capacity by 59.15% at most, while increasing the stirrup spacing has little effect on the axial compressive bearing capacity, merely a reduction of 2.91%. The longitudinal stress of the steel tube is larger in the area near the connection between the steel tube and steel sleeve, while the circumferential stress of the steel tube is larger in the area near the upper and lower circular sutures of steel tube and is also larger at the assembly of steel sleeve. The average ratio of calculated value (N_uc) to finite element value (N_uf) and the average ratio of N_uc to test value (N_ut) is 0.964 and 1.014, with variance of 0.003 5 and 0.002 9, respectively, where N_uc, N_uf and N_ut denote respectively the values from formula calculation, finite element calculation, and test of the prefabricated column axial compressive bearing capacity.