Stability Analysis Of Orthotropic Bridge Deck Of Cable-Stayed Bridge With Steel Box Girder

Based on the research of Chinese and foreign scholars,the dissertation uses theoretical analysis and finite element analysis to study the orthotropic sandwich plate stability(especially the sandwich plate which is formed by sandwiching the polyurethane core in the steel plate).The main works carried out in this dissertation are as follows:Firstly,the possible buckling failure modes of orthotropic sandwich plates and the relevant regulations on the local stability of orthotropic plates are introduced.Also,the static equilibrium equation of orthotropic sandwich plate is deduced based on Hoff theory,and the degenerate Reissner static equilibrium equation is obtained.In this dissertation,the energy method is used to deduce the bending stress of the orthotropic sandwich plate which is under the action of local uniform load and uniaxial axial pressure.As well,the expression of the critical buckling load of the orthotropic sandwich plate which is only under the action of unidirectional uniform pressure is deduced.Then,the multi-scale modeling method is used to extract the steel box girder section which is the most unfavorable to stability of the orthotropic bridge deck in the steel box girder cablestayed bridge,and finite element shell models of steel box girder sections with ordinary steel bridge panels and two different thickness of the SPS bridge deck are established respectively.Considering the effect of wheel local pressure on the orthotropic bridge deck under two different longitudinal loading conditions,the deflection distribution and the stress distribution of the bottom and the top of the normal orthotropic bridge deck(PT model)and the orthotropic sandwich bridge deck(SPS model)as well as its causes are compared and analyzed;Combining with the stress distribution and the buckling failure mode,the buckling stability of the orthotropic sandwich plate is studied by using the four sides simple boundary condition and the sub-model method to simulate the boundary constraint of the bridge deck in the actual engineering.The limitations of the hypothesis of the simply supported boundary constraint on the bridge deck are discussed too.The results show that the steel-polyurethane sandwich plate has no advantage in reducing the stress of the deck plate in the steel box girder of the cablestayed bridge,but it can reduce the stress concentration under the vehicle load and the stress and improve the stability of bridge deck.Next,the parametric analysis of main factors that affect the elastic critical buckling stress and buckling modes of the orthotropic sandwich plate such as the loading conditions,the spacing of the transverse partitions,the spacing of the longitudinal stiffeners,the thickness of the thickness of the laminated plate,the thickness of the core layer,and the thickness of the U-shaped stiffener is performed.Finally,the nonlinear analysis theory is introduced,and the causes of the initial defects of the orthotropic sandwich plate and the adverse effects of the initial defects on the structure are analyzed.At the end of this dissertation,the effects of material nonlinearity,geometric nonlinearity and other factors on the critical buckling load of of different sizes of orthotropic sandwich plates also are studied.