Local Buckling of Rectangular Concrete-Filled Steel Tubular (CFT) Columns with Binding Bars Subjected to Axial Compression Using the Rayleigh-Ritz Method.

In Concrete-Filled Steel Tubular (CFT) Columns with binding bars, horizontal binding bars arranged along the steel tubes are used to enhance the confinement effects on the core concrete and to postpone the initiation of local buckling. So, they have higher strength, more stiffness, better ductility and larger energy absorption compared to conventional CFT columns. In this paper, the unilateral buckling of steel plates in CFT Columns with binding bars under axial compression is investigated by the Rayleigh-Ritz method, using the shape functions of a rectangular plate with appropriate boundary conditions. It is assumed that the unloaded edges of the steel plate are elastically restrained against rotation. Trigonometrical functions that satisfy the boundary conditions of the rectangular plate are used to define the shape functions. In unilateral buckling, the folled concrete is described as an elastic foundation with high stiffness in compression and without tensile stiffness, such that buckling occurs in only one direction. The Lagrange multiplier technique is used to model the binding bars. The solution algorithms of the problems are written in MATLAB code. The solution of this process is used to obtain the elasto-plastic local buckling load of unilaterally-restrained steel plate with various numbers of binding bolts depends on spacing between them. Finally, the numerical results were compared with experiment results. The excellent agreements of the results verify the accuracy and efficiency of the method.