Mechanical Analysis Of Arch Ring Construction Of Concrete-filled Steel Tube Arch Bridge

With the development of traffic routes in China,arch bridge of concrete-filled steel tube(CFST)was frequently applied in complex terrain due to its good material properties and mature construction technique.Arch ring is the main structure of CFST arch bridge,whose construction quality directly affects the final state of arch bridge.In this thesis,the construction process of the arch rib of a bridge is analyzed by finite element method(FEM)for supporting its construction,which includes the calculation of the buckle cable force in the hoisting construction of the arch rib segment.The comparison of the concrete injection schemes in the steel tube and the analysis of the structural stress states are done during the construction.Then,the comparison between the actual monitoring data and the finite element calculation results proves that the results of the mechanical analysis have a high guiding value for the actual construction.Before hoisting the arch rib segment with cable-stayed method,it is necessary to calculate the tension values of the cables to determine the cable arrangement.The mechanical model of the actual structure of the bridge was established.FEM with different elements was used to simulate the work states of the structures in the cable-stayed truss system,where the cable stiffness simulated by the truss elements was modified.And the weight of each arch rib segment in the model was adjusted to be consistent with the reality.Through the comparison and analysis of various methods of evaluating the cable forces,the unknown load coefficient method is applied to determine the cable arrangement plan together with finite element analysis.By using the present cable arrangement scheme,the arch rib alignment satisfies the requirements of closure of the bridge.Then the influences of wind loads and temperature loads are considered in the finite element analysis.According to the computed results,the corresponding strategies are put forward for actual construction of the arch rib hoisting.After the completion of the arch rib closure,the compaction of concrete in steel tube will directly affect the stress distribution of the arch ring of the bridge.Hence,it is very important to determine the optimal concrete compaction scheme.The double element method and the joint section method are used to simulate the construction of the concrete-filled steel tube structure,respectively.Initial four kinds of concrete-filled steel tube compaction schemes are analyzed by finite element method.By comparison of the computed results of the stress distribution under four schemes,the optimal scheme is determined.In the concrete injection scheme in the steel tube,the corresponding construction stages are set and calculated by FEM.Thus the construction schemes for removing the cables and casting the arch ring concrete are also given.In order to ensure that the stresses and deformations of the structures conform to the design and construction requirements,a monitoring system is arranged to control the stress status,cable forces and arch rib line shape of the arch bridge on site construction.According to the results of mechanical analysis,the steel string stress sensors are arranged at the key positions of the arch rib.It has been detected that the working stresses of steel string pipe are less than the allowable stress of material.The measuring stress values are in agreement with the result of finite element calculation during the hoisting constructions of arch rib segments.And the dynamic measuring instrument is used to measure the cable forces in each group.Then,the measuring values of cable forces are compared with the calculated values of cable forces.It not only guarantees the safety of the cable-stayed cable system,but also verifies that the unknown load coefficient method has a high computational accuracy in solving the cable forces.In the aspect of arch rib alignment monitoring,the prisms fixed at he upper chords of all the arch rib segments were used as the monitoring points of the line shape of the bridge.Thus,the line shapes on both sides of the arch ribs were monitored by the total station instrument at each construction stage.It was found that the line shapes in the construction of the bridge were consistent with the finite element calculation results.It is concluded by summarizing the monitoring data of the construction that the finite element analyses play beneficial guidance for the arch ring construction.In the present thesis,the finite element method is used to successfully analyze the construction process of the arch ring of CFST arch bridge.The mechanical analysis strategies and computed results also can provide some references for similar large-scale engineering construction.