Fine Control Research And Parameter Sensitivity Analysis Of Self-anchored Suspension Bridge System Transformation Process

The self-anchored suspension bridge is a tower-beam-cable self-balance structure system.Because the main cable is anchored to the stiffening girder,the construction sequence is towers and girder first and then cable system,which makes the construction process very complicated.After the construction of tower and beam,it is necessary to accurately calculate the main cable shape and fine control the erection of datum strand.In order to reduce the influence of creep and shrinkage on the structure during operation,to save construction costs and shorten the construction period,and to reduce the influence of construction errors on the structure alignment and internal forces,a reasonable,economic,efficient and accurate system transformation scheme should be developed in the construction stage.Taking two self-anchored suspension bridges as the research background,which are the single-tower unequal-span steel box girder bridge in Tianshui,Gansu Province and the double-tower five-span prestressed concrete box girder bridge in Xining,Qinghai Province respectively,this paper focuses on the calculation and control of cable system,optimization of reasonable bridge completion state,formulation of system transformation scheme of non-lengthened hanger cables and sensitivity of influencing parameters in the process of system transformation.The main contents and achievements are as follows:Based on the theory of sectional catenary,according to the principle of non stress length of main cable and the balance condition of cable saddle along the sliding surface,the calculation method and process of main cable shape at bridge completion stage and cable finish stage,and the position of main cable at the tangent point of cable saddle are proposed.The calculation program of cable system of self-anchored suspension bridge is compiled with FORTRAN language.The unstressed length and the main cables shape of Luojiagou Bridge in Tianshui and Wenhui Bridge in Xining are calculated.The results show that the proposed method is correct and reliable,and can be used in the actual construction control and subsequent finite element analysis.Based on CEB-FIP 90 model,the parameters influencing creep coefficient and shrinkage strain are analyzed.The results show that the influence of average temperature on creep coefficient and shrinkage strain is positive correlation,and the influence of concrete loading age,fly ash content,average relative humidity and concrete strength on creep coefficient and shrinkage strain is negative correlation.Then,considering the meteorological data of the bridge site,site material parameters and construction plan,the long-term influence of creep and shrinkage effects on the structure is predicted by using finite element forward analysis.It can be seen that the creep and shrinkage effects make the internal deflection of the bridge tower,the deflection of the stiffening beam,the side span hanger cables force decrease more than the main span hanger cables force,and the support reaction at the auxiliary pier and bridge tower increases with the end time of calculation.Finally,according to the prediction results,the calculation process of optimizing the reasonable completed bridge state in the design stage is put forward,that is,according to the prediction results,the pre-deflection is set for the bridge tower and the unbalanced horizontal force component that causes the pre deflection is calculated.By increasing the side span hanger cables force and reducing the main span hanger cables force in the cable analysis program,the bridge hanger cables force is determined.Finally,the optimized reasonable state of completed bridge is checked by the combination of completed bridge actions.Based on the research of hanger cables tension method,the parameters affecting the main cable sag are analyzed based on the parabola theory firstly.It is known that the main controllable parameters in the process of system transformation are the span and length of main cable,that is,the sag of main span will increase significantly by increasing the elastic elongation of main cable and pushing the main cable saddle.Then,the system transformation scheme of three-stage and two-wheel tension hanger cables is proposed,and the numerical simulation method of cable saddle is studied.Finally,the conversion scheme of the bridge is compared with the original scheme.The results show that the new scheme can effectively avoid the hanger cables lengthening,shorten the construction period,save the construction cost and simplify the calculation and analysis process.The parameters that affect the system conversion accuracy of self-anchored suspension bridge during construction are divided into pre-tensioning parameters and post-tensioning parameters.When analyzing the parameters before tensioning,firstly,the cable shape at cable finish stage after the parameters change is calculated by analytical method,and then it is brought into the finite element model to analyze the construction process.For the parameters after tensioning,only the change values of corresponding parameters are modified in the finite element model,and the construction process is analyzed.The calculated results are compared with the original hanger cables force,main cable and stiffener beam alignment.The results show that the main cable shape is sensitive to the change of tensile stiffness of main cable and sensitive to the change of saddle height;hanger cables force,main cable and stiffening beam alignment are not sensitive to the bending stiffness of stiffening beam and the longitudinal position of splay saddle,so their influence can not be considered in the actual system transformation process.There is a negative correlation between the ambient temperature and the hanger cables force,that is,when the ambient temperature increases,the hanger cables force decreases.It is suggested that when the deviation between the ambient temperature and the design temperature is more than 10 ?,the tension of the middle and long cables should be properly corrected.The precise and multi-round tension can correct the hanger cables force deviation,main cable and stiffener line deviation caused by the change of tension of single hanger cable and the change of environment temperature during the tension hanger cable.It is suggested that each hanger cable should not be tensioned once when making system conversion scheme.The hanger cables force and the shape of main cable and stiffening beam are sensitive to whether the sliding boundary is considered in the numerical simulation and when the temporary constraint of the saddle is released during construction.The sliding boundary should be simulated when the simulation calculation and system transformation scheme are made,and the temporary state of the splay saddle should be restrained or released on time according to the system transformation scheme during construction.