Design of multi-cell T-shaped concrete-filled steel tubular columns under compression and bending

Abstract

To date, a number of studies have been done on the calculation methods for predicting bearing capacities of multi-cell special-shaped concrete-filled steel tubular (MS-CFST) columns under axial, pure bending, and eccentric load. However, most of the existing methods only apply to a specific combination form of cross-section and have not been established in a unified formulation. In this study, finite element (FE) models were established to predict the performances of the four common combination forms of multi-cell T-shaped concrete-filled steel tubular (MT-CFST) sections subjected to axial, eccentric, and pure bending loads, and verified with the available test data. The parametric analyses were conducted to investigate the effects of steel thickness t, concrete strength fck, steel yield strength fy, aspect ratio of the web c/b, and slenderness ratio λ on the flexural and eccentric compressive performance based on the FE models. The study results demonstrated that the four common combination forms of MT-CFST sections showed the same changing trends of flexural capacity with different parameters, and the flexural capacity rose almost linearly with the increase of the parameters. The parameters (t, fy, fck, c/b, and λ) had a definite effect on the N/Nu-M/Mu correlation curve, especially c/b and λ. Furthermore, by analyzing the stress distribution of mid-span cross-section at ultimate state, the simplified calculation model for asymmetric flexural capacity applicable to different combination forms of MT-CFST section was put forward. The reduction factor of 0.9 for positive flexural capacity (WC) and the restricted width-to-thickness ratio 60235/fy are recommended. Based on the study of the constraint stress of steel tube to core concrete and the concrete constraint region distribution for the columns subjected to compression, the calculation method for predicting the axial bearing capacity applicable to different combination forms of MT-CFST section was proposed. According to the parametric analysis and shape of N/Nu-M/Mu correlation curve, the simplified method for N/Nu-M/Mu correlation curves applicable to different combination forms of MT-CFST sections was developed, which simultaneously took the influence of slenderness ratio into consideration. Besides, the calculation methods for MT-CFST members proposed in this paper have been verified with available test results and FE ones.