Mechanism And Effect Of Arch Rib Disease And Suspender Replacement For Concrete-filled Steel Tube Arch Bridge

Concrete-filled steel tube (CFST) arch bridges are widely used in our country, because of their advantages such as long-span, high bearing capacity, convenience construction and beautiful shape. However, in their maintaining stage, many diseases occur such as separation, arch rib deflection etc. It has brought a negative impact to the development of CFST arch bridge. So it is necessary to summarize and analyze the existing problems in order to take effective measures to avoid these problems during the new bridge design and construction. There are three key technical problems need to be solved urgently. The first is the mechanism of these diseases. The second is the effect of these diseases on the ultimate bearing capacity of the bridge. The third is the suspender replacement method of the bridge. All of them are studied detail in this dissertation. The main research work covers the following aspects:1. Mechanism of separation problems and arch rib deflection of CFST arch bridge.Based on plane strain theory, this dissertation derived the calculation formulations for calculating the tensile stress on the interface between the steel tube and concrete under the axial pressure, temperature load and shrinkage strain of the filled-concrete. A practical formula for calculating the tensile stress on the interface under low axial stress level is fitted. The result shows that if no measures were taken, appearance of partial separation is inevitable.According to the sealing properties of concrete filled in the steel tube the basic creep component of RELEM B3 model is proposed to predict the creep of it. Preconditioning conjugate gradient (PCG) was employed to fit the equation of RELEM B3 model for concrete creep as a common degenerate-kernel Dirichlet series expression. Based on it the creep recurrence formula is established. The user creep model is implemented through UPFs secondary exploitation technique of ANSYS software, and with step by step method, the calculation of creep effect for CSFT structure is carried out. The reasons cause arch rib deflection are studied detailed. Using the creep prediction model and the creep calculation method proposed in this paper, the arch rib deflection caused by creep of filled concrete is calculated, and the result shows good agreement with the measured ones which demonstrate that creep is the main reason caused arch rib deflection.2. Research the diseases influence on mechanical properties and ultimate bearing capacity of CFST arch bridge.According to the ratio of eccentric confining force with axial confining force, a modified constitutive relation for filled concrete under eccentric load is proposed. A simplified model for bond-slip constitutive relationship was also proposed, and nonlinear spring element using this constitutive model was adopted to simulate the bond-slip behavior between steel tube and concrete. Then computer simulation of the whole process for ultimate bearing load in the plane of CFST bridge considering separation effect is carried out on the platform of the universal finite element software ANSYS.In this dissertation, concepts of steel concrete interface separation ratio and height separation ratio are proposed. The effects of separation ratio on mechanical properties of CFST arch bridge with different steel ratio, rise-span ratio and load type are also studied. Then, selecting Sanshanxi bridge, Yajisha bridge and Guijiang bridge as examples, the effects of separation on ultimate bearing capacity of truss rib and single tube CFST arch bridge are studied. The results show that the separation will significantly reduces the ultimate bearing capacity of truss rib CFST arch bridge, but has no influence on the ultimate bearing capacity of the single tube CFST arch bridge.3. Research on the suspender replacement method of CFST arch bridgeWith Sanshanxi bridge reinforcement project as background, suspender replacement method of CFST arch bridge is studied. First, the baseline finite element model of Sanshanxi bridge is established to calculated the theoretical results. Second, with finite element method, the cable tension estimation approaches which are based on macro search method and optimization theory are implemented with ANSYS program. Third, to ensure the structural more safety during the suspender replacement, a variable step length replacement method is recommended in the Sanshanxi bridge reinforcement project. Last, two constrained optimization methods one using tension uniform as objective function and the other using arch ribs bending moment squares as objective function are used to optimize the cable tension of Sanshanxi bridge. Through comparative analysis, the optimized cable tension using tension uniform as objective function is more reasonable.