Analysis Of Ultimate Load-bearing Capacity Of Through Steel Box Arch Bridge Based On Multi-scale Finite Element Method

Under live loads,the rib of arch bridge bears bending moment and axial compressive forces at the same time.So,the stability is one of the most important problems.Taking a three-span through steel box arch bridge,Kongli bridge over Huaihe River in Huainan City,Anhui Province,as an example,the three-dimensional finite element model is built to carry out the structural linear elastic buckling and nonlinear ultimate load-carrying capacity.As the steel bridges are made up of various steel plates,they are likely to buckle under compressive forces.So,the local buckling of the arch rib is calculated based on plate buckling theory and stiffened plate buckling theory.Finally,the multi-scale finite element models that aim at different parts of the rib to be locally buckled are built to perform the local-overall interactive buckling ultimate load-carrying capacity,which can be a reference for the analysis of local failure.The main research work and conclusions of this thesis are as follows:1.The analysis of the structural linear elastic buckling of Kongli bridge is carried out based on the structure-level finite element model.The results indicate that the main arch is more likely to buckle,and the stability coefficient is greatly influenced by vertical load.Meanwhile,the out-of-plane buckling is largely influenced by out-of-plane rigidity,while the in-plane buckling is largely influenced by in-plane rigidity,and torsional rigidity has a little influence on the two kinds of buckling.2.Considering both geometric nonlinearity and material nonlinearity,the ultimate load-carrying capacity Kongli bridge is investigated.It is demonstrated that the geometric nonlinearity has a little impact on the ultimate load-carrying capacity,while the material nonlinearity controls the ultimate load-carrying capacity.Arch rib locations at L/6 and L/2 sections are found to be yielded first with the loads increase.The yielding of key rib sections causes the change of the bending rigidity and large deformation,which leads to internal force redistribution and moment unloading.3.When the bridge arrives at the ultimate load-carrying capacity state,the huge load will make local plate to be buckled.But the traditional finite element model of whole bridge cannot consider the local buckling.According to the results of the analysis of ultimate load-carrying capacity and theoretical local buckling,the target areas that need more detail simulation are decided.Then the target areas are modeled by shell elements,and the other areas are modeled by beam and truss elements.Finally,the equations that make the deformations to be coincident realize the connecting between different level elements.This modeling process of the multi-scale finite element model can be a reference for other research of local-overall interactive buckling of steel box arch bridge.4.The analysis of the local-overall interactive buckling ultimate load-carrying capacity of Kongli bridge is carried out based on the multi-scale finite element models.The results show that this multi-scale finite element model can realize the cooperative computation of local plate and overall structure,consider the interaction between local plate buckling and overall structure buckling,and reveal the failure process of local plate in detail.It is demonstrated that the local plate buckling does not mean the losing of the ultimate load-carrying capacity of the whole structure.The different area local buckling has the different influence on ultimate load-capacity capacity of whole bridge.