Strength Research Of Simply Supported Steel Box Girder Under Combined Bending And Torsion

With a wider application in architectural engineering, steel box girder is mainly used in steel framed structures, overhead crane, high-rise composite structures and other public buildings. Compared with other forms, box section beams are able to evaluate the utilization of steel and have a better bending and torsional stiffness of the two axes. However, there have been comparatively few studies on the carrying capacity of steel box girder under combined bending and torsion, which leads to a lack of an effective method to guide engineering design.In this thesis, the elastic-plastic load-deformation relationships and strength of simply supported steel box girder under combined bending and torsion is studied. Based on the theoretical analysis, this thesis investigate the characteristics of load-deformation relationships of steel box girder with no lateral bracings by taking account of the effects of large deformations, material nonlinearities, and geometric imperfections. According to different loading process showed by load-deformation curves, the thesis analyzes the stress distribution of different stage of steel box girder in detail. The study also finds that the rotation caused by torque may be amplified by bending and torsional deformation considering geometric nonlinearities, and it will reduce the torsional stiffness.The interaction between in-plane bending and torsion are studied in this thesis, considering the member span, the thickness of the flange and the web, the change of section size and other factors in the analysis. After analyzing a large number of models, a practical inelastic analysis procedure based on ANSYS program is proposed.Finally, the thesis makes a comparison of the various box girder bending-torsional related curve model. Considering all the analysis results above, when the steel box girder complies with the requirements of the overall stability and local stability in the current Code for design of steel structure (GB50017-2003) and beam span is within the span of commonly used, it is pointed out that circular interaction equation for steel box girder under combined bending and torsion studied by this thesis is reasonable and has a good applicability. It is indicated that this equation has a certain significance on engineering project and provides a reference for engineering design.