| Compared with circular CFT columns, T-shaped, as well as square, rectangular and L-shaped etc, concrete-filled steel tube (CFT) columns attract more attention in engineering practice due to their merits such as convenience in steel tube manufactured, simple joint construction, meeting with beams and requirement of architectural plane easily and larger inter of cross-section to resist bending moment. However, the bearing capacity and ductility of T-shaped CFT columns is much lower than circular CFT columns due to that the confinement effect of concrete core of T-shaped CFT columns is weaker than that of circular CFT columns. The confinement of T-shaped CFT columns at the external corners is more obvious than that both at the internal corners and beyond the region of corners. Additionally, the lateral confining pressures on the concrete core provided by broad faces are different from those provided by narrow faces, which results in the difference of confinement effect between T-shaped CFT columns and other special-shaped CFT columns. And the steel plate of each side is subjected to a state of longitudinal compression and lateral compression so that it is liable to local buckling leading to failure. Furthermore, the local buckling tends to occur earlier and more extensively on the broad faces of the steel tube. Aiming at such shortcomings of T-shaped CFT column, setting level binding bars at certain spacing along the height of the column at the cross section respectively along the narrow faces is an effective measure to strengthen the cross section. The binding bars constrain the lateral deformation of concrete core and improve the concrete confinement at the region of middle side and act as a lateral inward constraining and thus improve the behavior of the outward local buckling of the steel plate. Based on the analysis above, an extensive study on axial load and eccentric load behavior of T-shaped concrete-filled steel tube columns with binding bars (TCFT-WB) is conducted, including the following main aspects.(1) Tests on TCFT-WB, including 11 specimens with binding bars and 5 without binding bars under axial compression were carried out. The main parameters in tests are binding bar horizontal spacing, binding bar vertical spacing, binding bar diameter, the materials of steel plates and the depth-to-wall thickness ratio. The effects of parameters on the behavior of specimens such as failure mode, bearing capacity and ductility are analyzed to provide experimental data for the following research.(2) Tests on TCFT-WB, including 16 specimens with binding bars and 11 ones without binding bars under eccentric compression were carried out. The main parameters in tests are binding bar spacing, load eccentricity ratio and load angle. The effects of parameters on the behavior of specimens such as failure mode, bearing capacity and ductility are analyzed to provide experimental data for the following research.(3) The formulae to calculate ultimate strength of TCFT-WB columns under axial compression are deduced from the constitutive relationship of TCFT-WB. Furthermore, the simplified formulae are brought out. These formulae are used to calculate the ultimate strength of TCFT-WB stub columns and those without binding bars under axial compression. The calculated results are compared with those calculated by various design codes, showing the proposed formulae can give reasonable predictions on the ultimate strength of TCFT-WB stub columns under axial compression.(4) Basic on the formulae for local buckling strength of the steel plate in rectangular CFT columns under axial compression, assuming that the unloaded edges of the steel plate are elastically restrained against rotation, whereas the loaded edges are clamped, the study of local buckling of the steel plate in T-shaped CFT columns under axial compression is carried out, which results in appropriate spacing of binding bars, appropriate limitation for aspect ratio(D/B) and corresponding appropriate limitation for width-thickness ratios(B/t). |
