Study On The Key Problems Of Construction Control Of Extradosed Cable-stayed Bridge

Extradosed cable-stayed bridge takes the advantage of continuous girder bridge(rigid frame bridge) and the traditional cable stayed bridge. Extradosed cable-stayed bridge has three prominent characteristics as short tower,the girder is stiffnessly and with the cable which is fixed toghter.On the part of stiffness,extradosed cable-stayed bridge is fallen in between continuous girder bridge(rigid frame bridge)and the traditional cable stayed bridge.On the part of the form of the section, the grider section of extradosed cable-stayed bridge is similar to the section of continuous girder bridge which use the variable cross-section of continuous box grider.On the part of the structual characteristic,extradosed cable-stayed is a type of bridge which is fall in between the continuous girder bridge(rigid frame bridge) and the traditional cable stayed bridge.The paper approaches a grand extradosed cable-stayed bridge(named ShaWan extradosed cable-stayed bridge) on the DongXing highway in guangzhou as the project background.To study the static and dynamical characteristics of the extradosed cable-stayed bridge during the construction process and the in the process of operation systematic.The specific contents in this paper is list as the following:(1)According to the characteristics that the high rigidity of the main beam and the cable force is insensitiveness for the linear,it point out that the principle in construction monitoring of the extradosed cable-stayed bridge shoud be the dual control of the linear cable force.It means in the installation of cable stage the cable tension tonnage should be controlled . The pattern level and linear can be controled throught adjusting the elevation before the concrete pouring.(2)The camber can be divided into construction camber and camber in-service phase, construction camber is to offset the cumulative deformation of the main beam cause by various reasons during construction process. The camber in-service phase is to offset the cumulative deformation cause by shrinkage and creep, and live load during the service phase. According to this understanding,the bridge alignment is the design linear plus the camber in-service phase.The common method of camber in-service phase setting is to cross the largest pier top to zero by the second curve of distribution,it is proved that the setting of this method will generate a cusp in the top of the pier, meanwhile,the linear does not comply with the law of the finite element method. According to finite element calculation, use the cosine curve to distribute the camber in-service phase of the extradosed cable-stayed bridge and increase it appropriatly according to experience.(3)Study the parameters identification in the self-adaption monitoring, the dichotomy method is given to self-adaption, this method is based on existing structural analysis software as the basis for iterative calculations to determine the interval of the parameters.and then minish the interval of the parameters by iterative calculation, thereby, the parameters which meet the accuracy requirement is identified.(4)Two methods is proposed on tension adjustment,one is Iterative calculation method,this method can calculate the cable force accurately,but it need to operate by the order specified of the cable construction.and ensure the accuracy of the tension in the construction process;The other method is control the cable force by elongation, this method only needs to calculate the stress-free length before and after the cable stretching,then adjust the cable tension by the difference on stress-free length until satisfied with the accuracy requirements.this method do not need to consider the order of the tension but also do not exist coupling errors.(5)Study the impact of temperature on the frequency of cable force of Shawan bridge ,it solve the temperature impact in the cable force testing process.Use the test calibration coefficient to identify the relationship between the cable force and frequency of the extradosed cable-stayed bridge,the calibration coefficient can automatically included the impact of boundary conditions, bending rigidityof the cable during the tension process. It can considere the factors after the tension complete by the method of coefficient conversion.