Ultimate bearing capacity of concrete-filled double skin steel tubular (CFDST) columns under combined temperature and axial force

This research studies the axial mechanical behaviors of Concrete -Filled Double Skin Steel Tubular (CFDST) columns under thermal and mechanical coupling conditions. Through experiment and numerical simulation, the investigation assesses the impact of variables such as fire duration time, concrete cube compressive strength, yield strength of the outer steel tube, axial load ratio and hollow ratio on the residual bearing capacity of CFDST columns after fire. Results from the experiment and numerical simulation indicate that the columns' ultimate bearing capacity after fire improves with material strength enhancement but diminishes with fire duration time. Notably, applying initial loads before fire does not further reduce the ultimate bearing capacity of CFDST columns after fire. The study further reveals that a column with a hollow ratio of 0.52 significantly outperforms those with hollow ratios of 0.31 and 0.72 in terms of ultimate bearing capacity after fire. To carry out the mechanism analysis of columns under thermal and mechanical coupling conditions, Finite Element Analysis (FEA) models are developed, with their accuracy corroborated by experimental data. This research also elucidates the dynamic axial load distribution of the column components during the whole process of fire. In terms of fitting degree and safety, the T/CCES 7 - 2020 code emerges as a superior guideline for evaluating the ultimate bearing capacity of CFDST columns after fire, as compared to other relevant standards.