Study On Shrinkage And Creep Effects Of Stiff Skeleton Arch Bridge With Prefabricated Box Bottom Floor

The stiff skeleton concrete arch bridge has been widely used in China due to its advantages of good mechanical properties and large span capacity.However,traditional construction methods for stiff skeleton arch bridges suffer from difficulties in hanging the formwork for the bottom floor,long construction periods for the outer concrete,and high construction risks.To overcome these issues,the engineering community has proposed a method of using stiff skeleton with prefabricate box bottom floor.While this method overcomes the difficulties in constructing the box bottom floor,it also results in a significant difference in the age of the concrete between the bottom floor and the web and top slabs,as well as differences in the strength of the outer concrete and the concrete inside the tube,as well as differences in the humidity of the environment.Therefore,it is necessary to conduct in-depth research on the shrinkage and creep effects of the stiff skeleton arch bridge with prefabricate box bottom floor.In this thesis,we focus on the Guizhou Yutang Bridge and use the shrinkage and creep model from the " Specification for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts(JTG3362-2018)" to study the shrinkage and creep effects of stiff skeleton with prefabricate box bottom floor.The main content is as follows:(1)Using the finite element analysis software Midas Civil,a construction stage model of the entire bridge was established to analyze the effect of shrinkage and creep on the deformation and stress of the Yutang Bridge.Based on the construction characteristics of the bridge and the factors affecting concrete shrinkage and creep,the influence of different prefabricate box bottom floor ages and different relative environmental humidity on the long-term effects of the rigid frame arch bridge was studied.(2)Reinforcing steel has a constraining effect on concrete shrinkage and creep,but current mainstream prediction models for shrinkage and creep are based on a large amount of experimental data for plain concrete and do not take into account the influence of steel reinforcement.Therefore,this thesis derives a formula for the long-term deformation of little eccentrically compressed reinforced concrete members and uses a segmented overlay method to consider the stress unloading process and the aging of the concrete modulus of elasticity during long-term deformation.A solid rectangular section example is designed,and a solid model is established in Midas FEA to verify the correctness of the calculation results.(3)Based on the formula for the long-term deformation of little eccentrically compressed members,this study investigates the influence of reinforcement ratio on concrete long-term deformation under different stress levels and proposes a calculation formula for the shrinkage and creep strain reduction factor considering reinforcement ratio.The validity of the reduction factor for calculating the shrinkage and creep deformation of the external concrete section(box section)of the arch foot of the Yutang Bridge is verified using a solid model established in Midas FEA.