Research On The Correlation Between Temperature And The Mid-span Vertical Displacement Of Girder For Cable-stayed Bridges With Semi-floating System

The vertical displacement of the girder is one of the important indicators for evaluating the structural stiffness and operational status of cable-stayed bridges.It is also an important indicator for structural health monitoring.It will vary appreciably with the temperature of the cable-stayed bridge components and environment.Studying the correlation between the mid-span vertical displacement and the temperature of environment and component can be used to eliminate the displacement caused by the temperature effect.It also can highlight the abnormal deformation of the girder caused by other loads.It has important research significance for accurating assessment and early warning of the operation status of cable-stayed bridges.This thesis takes two long-span cable-stayed bridges with semi-floating system as engineering backgrounds.Based on long-term monitoring data,the variation laws of member section temperature and the mid-span vertical displacement are studied.A Support Vector Regression(SVR)model is constructed to reflect the correlation between the two.A corresponding simplified analysis method is proposed.The main research work and conclusions of the thesis are as follows:(1)Based on one-year monitoring data of the Langqi Minjiang cable-stayed bridge,the variation laws of ambient temperature,uniform temperature of the girder and pylon section,gradient temperature of the girder and pylon section,and the mid-span vertical displacement are analyzed.The time-varying model of the ambient temperature and the uniform temperature of the girder and pylon section can be established with the 2nd-order Fourier series.The results show that the uniform temperature of the girder and pylon section has similar annual variation laws with the ambient temperature.The daily variation laws are obviously different.There is a time lag between the ambient temperature and the uniform temperature of the girder and pylon in summer.The lateral distribution of the temperature difference between the top and bottom plates of the girder of the steel box is quite different.The temperature difference at the center line is the smallest.The temperature difference between the two sides is the largest.The surface temperature on the sunny side of the pylon fluctuates significantly.(2)Selecting the DB10 wavelet and the appropriate decomposition level,the mid-span vertical displacement under the action of temperature is extracted by wavelet transform.Taking it as output,with ambient temperature,the uniform temperature of girder and pylon section,and the girder gradient temperature as input,2 SVR models(January and July)reflecting the temperature-mid-span vertical displacement correlation were trained.The results show that the predicted results are in good agreement with the measured results.The data goodness-of-fit R~2 is 0.89and 0.71 respectively.(3)A simplified plane geometric model of the cable-stayed bridges with semi-floating system is established.A simplified analysis method for the mid-span vertical displacement under the action of uniform temperature is proposed.The correctness of the simplified analysis method is verified by finite element analysis of Langqi Minjiang cable-stayed bridge and Huanggang Yangtze River bridge.The errors existing in the simplified analysis method are discussed.The results show that there is a linear relationship between the uniform temperature change of the girder,pylon,stay cables and the mid-span vertical displacement.The influence of the three on the mid-span vertical displacement is in the order of stay cables,girder and pylon.Compared with the finite element analysis results,the error of the simplified analysis method is less than 25%.