The Stress Computation Research Of Orthotropic Deck System Of Suspension Bridge With Stiffening Steel Truss

On a suspension bridge with stiffening steel truss, while its longitudinal displacement is out of constraint, the deck system does not work as a part of system I , so the computation is mainly on system II. The Baling River Bridge is a typical long-span suspension bridge which adopts this structure. This thesis, taking the Baling River Bridge as a research subject, presents a study on the stress computation of orthotropic deck system.First of all, the thesis introduces the steel deck structure as well as the classification and computation methods of stress systems; then introduces the basic theory of commonly employed simple computation method—P-E method in the stress computation of system II and system III, based on which, computes the stress on the Baling River Bridge. Meanwhile, with the general used finite element analysis software ANSYS, 3-D finite element models, particularly deck models considering the effect of stiffening girder flexibility are set up to calculate the stress in all kinds of models and loading methods.A reasonable finite element model is set up based on analysis of the influence factors including loading methods, boundary conditions and panels length. By comparing the results of P-E method and FEM, the thesis studies the difference and regulation of the two computation methods. By the study of P-E method's applicability in a flexible structure like suspension bridge, it is easy to find that the calculation results of the two methods are in a great difference. So P-E method is not an ideal choice. However the maximal transverse stress of system III resulted from P-E method is quite close to the result of FEM. By comparing the differences between deck stresses with and without effect of the stiffening girder flexibility, we find their longitudinal rib stresses are close. So the deck model without effect of stiffening girder flexibility not only meets accuracy requirement but also simplifies the calculation. Based on this conclusion, the thesis studies the further simplification possibility. In the simplified finite element model obtained above, the thesis analyzes the following influence factors to the stress variation, including increasing the rigidity of longitudinal beams, enlarging loading areas, thickening deck slab and altering the spaces between floor beams. So far as the research object in this thesis, increasing the rigidity of longitudinal beams affects little on the stress while the other three factors have great effects which can be considered as the effective means to control the deck stress in practice.