Research On Flexural-torsional Buckling Of Doubly Symmetric Dumbbell Shaped CFST Members Based Upon Plate-beam Theory

Concrete filled steel tubular structure is widely used in high-rise and large space structures due to its high bearing capacity,good plasticity and convenient for fabrication and construction.The in-plane bearing capacity of dumbbell shaped CFST is higher,the out of plane stability problem is obvious.The study of CFST mainly concentrate on mechanical behavior of axial compression,eccentric compression,there are few studies on flexural torsional buckling.In order to make the dumbbell shaped CFST easy to calculate and more widely used in practical engineering,based on Professor Zhang Wenfu’s "Plate-Beam theory",this paper analyzed out-plan buckling of single web dumbbell shaped section,double web dumbbell shaped section and solid web dumbbell shaped section of CFST members based upon “Plate-Beam Theory”.Finite element software ANSYS was used to establish different models to verify the theoretical solution.The main contents of this paper are as follows:(1)Based on the “Plate-Beam Theory”,the out of plane buckling of beams,columns and arches with rectangular section of single material under pure bending and pure compression is analyzed and studied.The total strain energy of bending and torsional buckling of rectangular section arch with single material is obtained.On the basis of above,the calculation formulas of bending stiffness,free torsional stiffness and restrained torsional stiffness of the section are obtained.The finite element models of eight rectangular section arches with single material are established and the correctness of section properties is verified by comparing the theoretical critical load of arch flexural torsional buckling with the finite element solution.(2)Based on the “Plate-Beam Theory”,the single web,double web and solid web dumbbell shaped CFST beams and columns are analyzed and studied.For the dumbbell section with double webs,the in-plane bending deformation of the plate satisfies Timoshenko beam theory,and the influence of shear deformation is considered.For the dumbbell section with single webs and solid webs satisfy the Euler beam theory,and the influence of in-plane shear deformation is not considered.Eight CFST beams and columns are established respectively,and the out of plane buckling loads under pure bending and axial compression are verified by finite element software.(3)Based on the above beam column model,the buckling critical load of dumbbell section arch under pure bending and axial compression is calculated by beam column method.The finite element software ANSYS is used to establish eight different size arch models with three different sections,and the theoretical solution is verified by finite element method.