Research On Construction Control Theory Of Stress-free Status Methods For Concrete-filled Steel Tube Arch Bridge

The construction of CFST rigid-framed tied arch bridge with long span is a self-erection structure, and divided into many working procedures, which are completed step by step. Though in terms of structure system, rigid-framed tied arch bridge belongs to an arch bridge without thrust, and its load path is clear, the construction process is long and complex. So, a rigorous control of construction is greatly required to guarantee the arch rib and deck alignment. Currently, the forward analysis or inverse analysis or both interactive iteration method is used to achieve an ideal finished state in CFST bridge, whose analysis process is very complicated. By contrast, the construction control theory of stress-free status method aims at a relatively stable unstressed state amount of structure elements, making the monitoring problem on component erection more intuitive under the premise of meeting structure’s strength and security in stages. In the advantage of clear concept, small amount of calculation and strong adaptability,this method has a wider application prospect.Taking Xiazhongba Jialing River Bridge in Nanchong city as an instance, many problems on unstressed state control method for CFST bridge are discussed in this thesis, including:the calculation of rod and tie bar unstressed length in a reasonable finished dead state of arch rigid-framed bridge, analysis method of simulating construction phase, ascertainment of cable force in cable-stayed hoisting method, control of tie member tensioning and hanger rod installation.A simplified analysis model for long span truss CFST arch bridge is presented. The fractional-step iterative go-ahead method is introduced to the calculation of stayed-buckle-cable forces in the process of steel rib assembling and adjusting construction error. The calculated cable forces with high precision can always guarantee the assembling process in safe state and ensure the line shape of the arch after releasing cables according with design requirement.Based on the theory of unstressed state method, a comparison is made between non-stress closure and forced closure during the rib construction in stages. A general exploration for arch bridge is also made in order to achieve non-stress closure by adjusting displacements. The discussion about temporary load indicates that cable force does not affect the final structure’s inner forces and line shape.According to the characteristic of stiffness formed in stages of concrete filled steel tube arch bridge, a fractional-step algorithm to ascertain the unstressed length of rod and tie members in the final structure state is put forward.The calculated results can offer the basis for construction monitor and control. In this way, the initial unstressed length can be derived from the finished dead state of bridge regardless of concrete shrinkage and creep. Then, it will be revised in consideration of concrete shrinkage and creep, as well as live load, finally further be revised after considering the effect of stiffness variation of rib section.The feasibility and rationality are verified by simulation analysis with combination of the final unstressed length. The deck pre-camber capacity is considered during the installation of rod and the pier deviation is controlled by tie members tensioning for several times. The measured data shows that the performance of finished bridge state and design state are in good agreement.