Axial compression behavior of precast circular semi-continuous concrete-filled steel tube columns

To study the axial compression performance of precast circular semi-continuous concrete-filled steel tube (PCSCFST) column, a total of 17 specimens were prepared and tested, including 13 PCSCFST columns and 4 continuous CFST columns. This PCSCFST column is made up of upper and lower steel tubes and outer steel tubes connected by bolts, which has the advantages of easy factory production and convenient transportation. The results showed that shear failure occurred in continuous CFST columns, but not in PCSCFST columns, bolts had obvious influence on failure mode. Maintaining the consistency of the thickness of each steel tube on the specimen can not only improve the local buckling, but also avoid the short plate effect to give full play to the material performance. Moreover, with the increase of steel tube thickness, concrete strength, bolt diameter, reduction of specimen length and pure bolt connection instead of bolt and weld combination connection, the deformation resistance of bolts and axial compression performance of specimens had been enhanced. However, the increase of bolt diameter from 12 to 18 mm resulted in a better strength degradation rate, but worse bearing capacity and deformation resistance. Finally, the predictions of the ultimate bearing capacity of PCSCFST columns under axial compression agree well with the test results, the average value of N-exp/N-pre and the variance are 0.998 and 0.00111.