Concrete filled tube (CFT) columns have been increasingly used as the load-bearing systems in engineering applications. The fact that the CFT column has steel plate restrained by infilled concete and the availability of high strength structural steel leads to the application of thin steel plates in CFT columns. However, this gives rise to the local instability problem of thin steel plates under axial loadings. Furthermore, most of the studies on the local buckling of steel plates in contact with concrete reported in the literature were concerned with the cases where the four edges of the steel plate were assumed to be clamped or simply supported. This cannot reflect the real state of steel plate in CFT columns, where the unloaded edges of steel plate is more appropriate to be regarded as elastically restrained. This paper presents an analytical study of local buckling of steel plates in CFT columns. The steel plate, subjected to uniform axial compression, is assumed to be elastically rotationally restrained along loaded and unloaded edges. The approximate solution is obtained by Rayleigh-Rize method. The solution of rotationally restrained plates is verified by comparing with available experimental and theoretical data in the literature. Good agreement is found between them for local buckling stress of the steel plate. This research provides basis for capacity design of CFT columns under axial compression.
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