Analysis Of Shrinkage And Creep Effects Of Long-span Cable-stayed Bridges Based On New And Old Codes

Shrinkage and creep are inherent characteristics of concrete materials.Shrinkage is the phenomenon that the volume of concrete decreases with time,and creep is the effect that the strain increases with time under long-term load.Because of the long span of time,the great change of environmental humidity,the different theoretical thickness of each component and the compressive strength of concrete,the effect of shrinkage and creep on bridge structure is more obvious.In order to study the difference of the influence of shrinkage and creep on long-span cable-stayed bridges under the new and old bridge and culvert design codes,this paper analyses the effect of shrinkage and creep on the concrete pylon of Jiayu Bridge under construction and the concrete main girder of Jingzhou Bridge in operation for more than ten years through the new and old bridge and culvert design codes(1985 and 2018 editions).The specific contents are as follows:Firstly,the common calculation models of shrinkage and creep at home and abroad are classified and summarized,and the basic calculation formulas of finite element initial strain method and concrete initial strain method are deduced.Then,two codes promulgated by the Ministry of Communications of China,the former "Bridge and Culvert Design Code","JTJ 023-85"(abbreviated as "85 Code")and the recent "Bridge and Culvert Design Code" "JTG 3362-2018"(abbreviated as "18 Code")The exponential function of shrinkage and creep in the norm is fitted,and the influencing factors of creep coefficient and shrinkage strain in the new and old codes are compared and analyzed in detail.Secondly,The whole bridge model of Jiayu Bridge is established with the help of large-scale general software MIDAS,and the construction conditions and basic parameters of shrinkage and creep are introduced.The time-varying effect of the South Tower structural model is studied.The differences of the influence of shrinkage and creep between the new and the old codes are analyzed,and the differences in creep calculation between the new and the old codes are compared.The vertical displacement of the pylon is analyzed and studied by the loading age of soil components and different environmental humidity.Finally,the calculation model of Jingzhou Bridge is established by using the BDCMS plane bar finite element software,and the stress changes of the main girder after the completion of the long-span PC cable-stayed bridge are compared,and the influencing reasons are analyzed.Combining with the measured deflection values of concrete main girder in operation period obtained by health monitoring for more than ten years,and comparing with the theoretical values under the new and old codes,it is verified that the shrinkage and creep of the new codes are more practical than the old codes.On this basis,many useful suggestions on design,construction,monitoring and monitoring are put forward.