Construction Controlling And Cable Tension Testing Of Long Span Steel Box Girder Cable-stayed Bridge

The cable-stayed bridge is highly redundant complex structure.The girder geometry and internal forces state of cable-stayed bridge are highly coupled with the construction process.Therefore,the construction monitoring and control of cablestayed bridges must be carried out.The elevation of main girder and cable tension are the key parameters in the construction monitoring and control of long-span steel box girder cable-stayed bridges.The influence of the variety of temperature on the control parameters cannot be ignored.In addition,the cable tension determines the internal force state of cable-stayed bridges.The influence of the installation of internal and external vibration damping device on the conventional frequency method cannot be ignored.Based on this,this paper takes the practice of construction monitoring and control in South Dongting bridge as the background.The research is carried out from three aspects: temperature field of steel box girder cable-stayed bridge,construction monitoring and control of main girder and cable tension measurement of stay cable,so as to make guiding significance for construction control and cable tension measurement of long-span steel box girder cable-stayed bridge.(1)The temperature field distribution and numerical simulation of cable-stayed bridge.During the construction of the steel box girder without paving,the temperature field changes with time under the action of daytime temperature and solar radiation.Compared with the concrete girder,the heat capacity of the steel box girder is lower,the temperature changes rapidly and varies greatly by the solar radiation.while the rigidity of the steel box girder is smaller,the effect of temperature influences on the key parameters of the girder construction greatly.Based on the ASHRAE clear-sky model,the solar radiation heat flux of the component surface is simulated,and the temperature field simulation method of the three main components of the cable-stayed bridge,tower,girder and stay cable is proposed in this article.The characteristics of the simulated temperature field calculated by heat conduction finite element method with ABAQUS software are compared with the measured temperature field characteristics,which proves the rationality of the temperature field simulation method in this article.The construction control of girder of cable-stayed bridge.Based on the actual construction control data,the key parameters of the construction predicted by Kalman filter and grey system theory are calculated and contrasted with each other,aiming at evaluating the prediction accuracy of two methods.Based on the temperature field simulation method proposed in this paper,taking the longest cantilever condition as an example,the influence of variety of temperature field on cantilever end elevation and cable tension is calculated by transient thermal-mechanical finite element analysis.A construction parameter adjustment system considering the effect of temperature field is put forward.The results show that the Kalman filter method performs better in this practice.The change of temperature field of steel box girder and stay cable have great influence on the elevation of cantilevered end.The temperature effect of steel box girder plays the most important role in the variation of cable tension.And the change of temperature field of tower has less effect on either of them.(2)The measurement of cable tension.Based on the stay cable system with damper and the stay cable system with spring,the influence of modal damping,equivalent supporting stiffness and installation location on the converting first order frequency of stay cable is clarified in this article.The relationship between the supporting stiffness of the absorber and the converting first order frequency of the cable is summarized and simplified,and the parameters related to the equivalent supporting stiffness of the absorber are defined.An approximate method of cable tension measurement for cables with built in and external vibration damping devices is derived.This method is convenient for engineering application by using the existing conventional cable tension measurement instrument.The data of the South Dongting Bridge show that the vibration damping device in the form of high damping rubber ring makes the actual maximum deviation to 22.4% using the conventional cable tension measurement method.And the VSD external vibration damping device makes the actual maximum deviation to 2% using the cable tension measurement method with built-in vibration damping device.Using the cable tension measurement method of this article to account for the impact of internal and external vibration damping devices can effectively reduce the deviation of cable tension measurement.