Theoretical Study On Local Buckling Of Rectangular CFT Columns With Or Without Binding Bars Under Eccentric Compression

Rectangular concrete-filled steel tubular (CFT) columns are being extensively used as structure members for construction of High-rise Building and Super High-rise Building structures due to their merits such as convenience in steel tube manufactured, meeting with beams and requirement of architectural plane easily. The strength of rectangular CFT columns can’t be fully used if the local buckling occurs too earlier, which will cause construction accidents and economic waste. Hence, the local buckling behavior of steel plates in rectangular CFT columns has been a very important branch in study of rectangular concrete-filled steel tubular columns.This paper presents a theoretical study on the local buckling behavior of steel plates in eccentrically loaded rectangular CFT columns with or without binding bars subjected to eccentric compression based on the energy method. Contents and results are as follows.(1) The formulas for local buckling stress of the steel plates in rectangular CFT columns under eccentric compression are derived, assuming that the unloaded edges of the steel plate are elastically restrained against rotation, whereas the loaded edges are clamped. Subsequently, the formulas are calibrated with the experimental results and compared with calculated results by the empirical method, which exhibit good agreement. Then, these formulas are applied to investigate the local buckling behavior of steel plates in eccentrically loaded rectangular CFT columns. Studies have shown that the local buckling stress of steel plates in eccentrically loaded rectangular CFT columns is significantly influenced by the stress gradient coefficients, b/t and boundary conditions, while it is slightly influenced by cross-sectional aspect ratios(DIB); The half buckling wave length (a) is only influenced by the boundary conditions and DIB, while it is not influenced by the stress gradient coefficients ao. Then the reasonable ranges for width-thickness ratios (B/t) and depth-thickness ratios (Dlt) at various ao corresponding to different DIB are suggested for the steel plates in eccentrically loaded rectangular CFT columns, and the appropriate relationship for the thickness of the steel plates at various ao is suggested for design.(2) Based on the formulars for local buckling stress of the steel plates in rectangular CFT columns under eccentric compression and consider the reasonable influence of the binding bars, the formulas for local buckling stress of the steel plates in rectangular CFT columns with binding bars under eccentric compression are derived. Subsequently, the formulas are calibrated with the experimental results and compared with calculated results by the empirical method, which exhibit good agreement. Then, these formulas are applied to investigate the local buckling behavior of steel plates in eccentrically loaded rectangular CFT columns with binding bars. Studies have shown that with the bs decreasing, the critical elastic local buckling coefficient k and stress σcr increases considerably, and the calculated buckling strengths increase considerable as bs=D/3 or bs=D/2. The reasonable ranges for depth-thickness ratios (D/T) and bs at various α0 corresponding to different D/B are suggested for the steel plates in eccentrically loaded rectangular CFT columns with binding bars.(3) Finally, the formulas for local buckling stress of the steel plates in rectangular CFT columns under eccentric compression are optimized and simplified calculation formulas are obtained. Subsequently, the simplified formulas are calibrated with the calculated results by the derived formulas for local buckling stress of the steel plates in rectangular CFT columns under eccentric compression, which exhibit good agreement.