Research On The Time-varying Effects Of Curved Extradosed Cable-stayed Concrete Bridge

Curved extradosed cable-stayed concrete bridge has been widely applied due to its simplicity of construction and strong adaptability to geographical environment.But as time goes by,under the influence of environmental and internal factors,various distresses will occur which would affect its performance obviously.Besides,certain gap exists between the research results of time-varying structure effect and its actual engineering application.Therefore further study on curved extradosed cable-stayed concrete bridge about its time-varying structure effect has important theoretical significance and practical value.At present,the study about time-varying effect of curved extradosed cable-stayed concrete bridge is not yet mature.Derive a prediction model suitable for time-varying effect of curved extradosed cable-stayed concrete bridge according to the actual bridge engineering test is an important research direction.In this paper,analysis method of time-varying effect of curved extradosed cable-stayed concrete bridge was studied combining with Research of Key Techniques for Curved Extradosed Cable-Stayed Concrete Bridge and it was based on experiments of situ bridge.Practical time-varying effect prediction model was proposed,applied and promoted in practice as well.First of all,based on three-dimensional concrete bridge structure monitoring effect of situ bridge,five analysis methods of accuracy and stability was put forward through analyzing the influence rules of shrink and creep and three dimensional temperature field according to different prediction model respectively.Analyze the error between the calculated values and the measured ones,so as to obtain the calculation precision ranking of different prediction models.Based on three-dimensional measurement data,modify the models which have high precision to obtain the shrink and creep practical prediction model and temperature gradient practical prediction curve.Get prediction value through practical prediction model and compare it with measurement value of condition after closure.The results show that the prediction values and the measured ones have the same trend,which decreases the error(about 75% of the error calculated according to specifications).Secondly,coupled prediction model of shrink and creep and temperature was established based on structure effect of curved extradosed cable-stayed concrete bridge,considering time-varying coupled effect.This model was proposed combining with the practical shrink and creep prediction model and introducing the influence of temperature on the early concrete shrinkage as well.This prediction model,together with the shrink and creep practical prediction model and temperature gradient practical prediction curve proposed are called practical coupled prediction method.By using the main grider analysis method,box section girder is decomposed into three sub-units.By means of the displacement parameter transformation matrix,each sub unit is spliced into a composite box element.The time-varying effect of situ bridge was analyzed using space unit model,which was based on the practical prediction model while the temperature,shrink and creep were simulated with the equivalent joint load.The prediction values and measurement ones of condition selected were compared.The results show that predicted values and the measured ones of structure effect has the same change trend,which decreases the error from 35%(specification prediction model)to less than 15%.Then,the environmental parameter partition is determined by the change trend of the average environmental parameters.Based on the fitted temperature and humidity curve,the time-varying effect of curved extradosed cable-stayed concrete bridge is analyzed according to the practical coupled prediction method.The regions with small structural effects can be regarded as similar regions.Based on the comprehensive analysis of the spatial position and clearance above bridge deck of stay cables,the minimum bending radius of the curved extradosed cable-stayed concrete bridge is 600 m.The bending radius is chosen as?,1800 m,1500m,1200 m,900m and 600 m respectively.The structural effects of the curved extradosed cable-stayed concrete bridge and continuous rigid frame bridge are simulated and compared.It is concluded that with the increase of curvature radius,the temperature spatial effects of the two types of bridges also increase under the combined effect of bending radius and temperature variation.The mechanical effects of the two types of bridges are similar under the influence of the same environmental parameters.Compared with the continuous rigid frame bridge,the pier bottom reaction force of curved extradosed cable-stayed concrete bridge is larger and the counter force at the bearing is smaller.A method for determining the closure jacking force is proposed,which takes the displacement along the bridge of the pier top as the control target.Combined with environmental parameters,shrinkage,creep and temperature,the calculation formula of jacking force is obtained and verified by actual bridge.Finally,the whole stage structural mechanics effect of the actual bridge construction was calculated according to the time-varying effect practical prediction model derived and the environment measured parameters.Besides,error analysis methods was put forward to measure the accuracy and stability of the time-varying effect prediction model.The results show that the coupled calculation error is less than 10%,the combined calculation error is less than 15% and both of them are far less than calculation result according to Code JTG D62-2004.