Research On Mechanical Behavior Of Steel Box Girder Under Combined Bending And Torsion

With the continuous development of steel structure and the producing process of component member improving and becoming more mature, steel box girder, due to its good bending stiffness of the two axis directions and torsional stiffness, compared with other forms, is more widely used in application now, especially in the high-rise building.In this paper, the elastic-plastic load-deformation relationships, ultimate strength and stiffness of steel box girder are investigated by using the finite element method (FEM) under combined bending and torsion. Taking into account the effects of large deformation, material inelasticity and geometric imperfections, the characteristics of load-deformation relationships are analyzed of steel box girder with no lateral supporting, and then compared with that of box girder with mid-point supporting, illustrating that steel box girder has a better overall stability. The study also found that the first-order rotation due to pure torque may be amplified by flexural-torsional buckling effects, which reduce the effective torsional stiffness. Then the amplified elastic twist rotation formula is suggested, taking into the effects.The study also found that the combined effects of bending moment and torque, due to bending and torsional deformation of the geometric nonlinearity arising in the corner across the beam increased, this increase in considering the impact of this proposed based on the beam as by the combined effects of the bending moment and torque are enlarged cross-section mid-point of the corner office of the second order formula.The interactions between in-plane bending and torsion are studied, considering the member span, section properties, the thickness of the flange and the web and other factors. A practical user-defined inelastic analysis procedure based on ANSYS program is proposed after analyzing a large number of models, and the ultimate strength formula for the design of steel box girder under combined bending and torsion is proposed. It is found that a commonly quoted circular interaction equation for combined bending and torsion dose not always provide a true lower bound for steel box girder.Finally, some research and discussion are conducted on the bending stiffness of steel box girder under combined bending and torsion and the carrying capacity formula of steel box girder under the control of stiffness conditions is obtained, which is a revised formula. The purpose of the formula is to calculate the mid-span deflection under concentrated load in elastic state, taking into account the effect of torsion at the same time and making some modification of the torque into appropriate bending moment, then to sum up to the two parts of moment to calculate the deflection of steel box girder.In this paper, some research on the carrying properties of steel box girder under combined bending and torsion is conducted, and the formulas proposed can be applied in Practical Engineering Design.