Calculation Method Of Torsional Moment Of Inertia For Plate-truss Stiffening Girder

With the rapid development of bridge construction,plate-truss stiffening girder has become a common form of cross section in long-span Bridges.Plate-truss stiffening girder is made up of the orthotropic plate and truss as a whole,with light weight,large bending and torsional stiffness,good wind resistance stability,strong spanning capacity and less limit of construction.Torsional moment of inertia is one of the important parameters that is used to evaluate mechanical performance and wind resistance stability.If the torsional moment of inertia of plate-truss stiffening girder can quickly and accurately be calculated,especially can be calculated by a formulation,it will provides more proofs at the conceptual design of plate-truss stiffening girder,and saves a large amount of computing time and material costs.When the torsion moment of inertia is calculated based on the formula,a simplified modeling method of plate-truss stiffening that is put forward can greatly be improved calculation efficiency,and provide a new way for dynamic and static analysis of the plate-truss stiffening girder.The research results were summarized in this paper about torsional moment of inertia of the plate-truss stiffening girder at home and abroad.In view of the current research and all sorts of problems to be solved,and connecting with the actual project,some works were done as follow:1)reviewing of the existing calculation method of torsional moment of inertia of a truss,and establishing numerical model of space truss based on the finite element software—ANSYS,the accuracy of the existing calculation methods were verified.The main truss was split into the diagonal pole and the frame system composed of vertical pole and chord pole.Based on the principle of equivalent of shear deformation,the equivalent thickness of diagonal pole was calculated by the existing calculation formula,and · the equivalent thickness of frame system was calculated by the formula that was deduced,then a new formula of the equivalent thickness that considering the frame system was got.Through the establishment of numerical model,it was found that the new formula could significantly improve the accuracy of calculation for the torsional moment of inertia of space truss.2)Based on an equivalent principle of horizontal shear deformation between the bridge panel and U rib,the calculation method of the equivalent thickness of an orthotropic plate was improved.According to the thin-walled beam theory,the calculation formula of torsion moment of inertia were deduced for different types of plate-truss stiffening girder,then detailed numerical model was established,and the accuracy of the formulas was verified.Based on the formula that was deduced,the influence and trend of various parameters on the torsion moment of inertia were analyzed.It can provide some basis for the conceptual design of a plate-truss stiffening girder.Study found that there was an optimal Angle between the diagonal pole and the chord pole,and it made the torsional moment of inertia which became the largest.3)Based on the finite element software—ANSYS,a simplified modeling method of bridge decking with a diagonal pole was put forward.Through the establishment of a detailed model,the accuracy of the proposed simplified modeling method was high when the dynamic characteristics was analyzed.