Analysis Of Stability And Ultimate Load-Bearing Capacity Of Railway Concrete-Filled Steel Tubular Continuous Beam-Arch Bridge Under Construction And Completed Stage

The stability of arch bridges is one of key issues that need to be focused on and studied in the engineering design,construction process and service,especially for the long-span arch bridges.The Concrete-filled steel tubular(CFST)arch bridges are widely used in long-span bridges because of their excellent bearing capacity.Taking a(90 + 180 + 90)m CFST arch bridgein He An high-speed railway as an example,this thesis establishes the finite element models for both construction stage and completed bridge stage tocarry out the linear elastic stability analysis of the construction stage,the linear elastic stability analysis of the completedbridge,the ultimate bearing capacity analysis of the structure,and the failure paths when the bridge reaches the ultimate bearing capacity state.The influences of the construction errors of the arch rib on the ultimate bearing capacity are also investigated.The main contents and conclusions of this thesis are as follows:1.The concept and basic theory of structural stability analysis and structural nonlinear analysis are introduced.The method and iteration convergence criterions used in the analysis of ultimate bearing capacity of CFST arch bridge are explained.2.By using finite element method,the linear stability analysis of continuous beam arch bridge in the construction stage located at He An high-speed railwayhas been carried out,and the stability coefficients and corresponding instability mode are obtained accordingly.The results show that the bridge has enough linear elastic stability in the construction process.The cross brace can greatly improve the stability of the bridge and the concrete pouring condition in the steel tube has a certain impact on the stability of the structure.The first nine instability modes of the bridge are the instability of the arch rib,whilethe continuous concrete beams are not unstablein the first ten modes.3.The ultimate bearing capacity of CFST arch bridge is analyzed including both geometric nonlinearity and material nonlinearity.It is demonstrated that the ultimate bearing capacity of such a CFST arch bridge is mainly controlled by the material nonlinearity.When considering the dual nonlinearities,the calculation results are more in line with the actual carrying capacity of the bridge.Regarding the failure path of the bridge,the critical position of the arch rib determines the ultimate bearing capacity where the material yielding at 1/8L and 1/2L of the arch rib are reached.4.The influence of the initial geometric imperfects caused by the installation deviation of the arch rib and the cavity of concrete filled steel tubecaused by the insufficient concrete pouring in the steel tube and the shrinkage creep on the ultimate bearing capacity of the bridge are investigated.In order to study the influence of initial geometric imperfects on the ultimate bearing capacity,the initial geometric imperfects are fed back to the finite element model to carry out re-analysis.The calculation results show that the installation error of the bridge has a certain influence on the ultimate bearing capacity of the bridge.The influence of different initial geometric defects on the ultimate bearing capacity of the CFST arch bridge is also discussed.Compared with the concrete void of the upper chord and the concrete void of the lower chord and the batten web,it can be observed that the concrete void of the arch rib will have the more significantinfluence on the ultimate bearing capacity of the bridge.