Study On Some Key Problems Of Local Buckling Models Of Rectangular CFST Columns

Rectangular concrete-filled steel tubular(CFST)columns behave high bearing capacity,good ductility and excellent seismic behavior.Furthermore,rectangular CFST columns have more advantages,such as convenience in fabrication of the steel tube,better compatibility with the architectural requirements,which result in the extensive applications in engineering practice.However,local buckling occurs earlier for rectangular CFST columns than the circular ones,which influences the behavior of rectangular CFST columns significantly.The local buckling behavior of rectangular CFST columns has an important role in the research on the mechanical behavior and design method of rectangular CFST columns.Based on the energy method,this paper presents a theoretical study on the key problems of rectangular CFST columns.The main contents and results are as follows:(1)An elastic local buckling model and an elasto-plastic one local for normal rectangular CFST columns,which include the influence of the horizontal stress in the steel plate,were proposed,assuming that the loaded edges are clamped and the unloaded edges of the steel plate are elastically restrained against rotation.The proposed models were validated against the corresponding test results,showing that the results calculate by the proposed models agree well with the test results,better than the previous models in the literature.In addition,the proposed models can be respectively employed for the study on elastic and elasto-plastic local buckling behavior of the steel plate in contact with a rigid medium,which is subjected to combined loadings.(2)The influences of width-to-thickness ratio(b/t),the horizontal stress in the steel plate and elastically restraining factor of unloaded edges(?)on the local buckling behavior of rectangular CFST columns were investigated using the proposed elastic model.It is found that the local buckling stress increase with the width-to-thickness ratio decreasing or the horizontal stress in the steel plate increasing or elastically restraining factor of unloaded edges increasing.Furthermore,the influence of the width-to-thickness ratios on the local buckling behavior is the most significant while the influence of the horizontal stress in thesteel plate is the second most significant.The influence of elastically restraining of factor unloaded edges is the third most significant.(3)A brand-new elastic local buckling model and an elasto-plastic one of rectangular CFST columns with binding bars were proposed.Compared with the previous model,the proposed models can take into account the influences of the longitudinal spacing,horizontal spacing and the diameter of binding bars on the local buckling behavior of rectangular CFST columns with binding bars.The test results were validated against the proposed model,indicating that the proposed model is more reasonable than the previous model.Then,the proposed elastic model is used to investigate the local buckling behavior of rectangular CFST columns with binding bars.It is indicated that the influence of the longitudinal spacing of binding bars on the local buckling behavior of rectangular CFST columns with binding bars is the most significant while the influence on the horizontal spacing of binding bars is the second most significant.The influence is binding bar diameter is the third most significant while the influence of aspect ratios is the four most significant.(4)Based on the proposed models,the reasonable ranges for width-to-thickness ratio of steel plate in normal square CFST columns under axial compression at various types of steel were suggested for the reference of engineering design.