Axial compressive behavior of stone encased concrete-filled square steel tube stub columns

A novel type of stone prism encased concrete-filled steel tube (SCFST) column is proposed by inserting waste stone prisms into the cavity of a concrete-filled steel tube (CFST) column to effectively enhance the axial compressive loading capacity of CFST columns and save construction resources. Axial compressive tests were conducted on 9 square SCFST stub columns and 3 square CFST stub columns. Test results show that the outward local buckling of the steel tube and the crushing of the infilled concrete and stone prism is the primary failure mode of SCFST columns. Compared with the CFST column, the axial compressive loading-carrying capacity of SCFST columns with the same steel ratio increased by 3.8 % to 29.1 %. A small-sized stone prism (β  ≤ 0.14) does not significantly improve the axial compressive loading–carrying capacity of SCFST columns. Based on the test results, the finite element (FE) model of the SCFST column under axial compression is established, and the FE parameter expansion analysis is carried out. Furthermore, the confinement mechanism of the square steel tube on the infilled concrete and stone prism is further revealed based on both test and FE results of SCFST columns. Accordingly, a simplified approach to calculate the axial compressive loading–carrying capacity of square SCFST columns is proposed, and the calculation results are in better agreement with test and FE results in comparison with the results predicted according to the current design code.