Study On Long-term Deformation Of Prestressed Continuous Concrete Box-girder Bridge

In recent years,with the development of economy and the improvement of technology,variable cross-section prestressed concrete box girder bridge is widely used.However,with the growth of service life,all kinds of diseases of the old bridges are also reflected,among which the midspan deflection and cracking diseases are the most prominent.For prestressed box girder bridge,due to the uneven solar radiation and the lag of concrete heat conduction,it is inevitable that there is temperature difference inside and outside,and the structure is constrained,so the structure will produce temperature stress.Studies have shown that the temperature stress even exceeds the live load stress.At the same time,the prestress in the structure will continue to decrease with time passes,and the loss of prestress is closely related to the crack resistance of the structure,bearing capacity,deflection and other properties.The temperature effect and prestress loss are related to the structural crack damage.After the structural crack,the stiffness reduction has a negative impact on the bearing capacity and durability of the bridge.Therefore,based on the variable cross-section prestressed concrete box girder bridge,this paper uses the comparative analysis method of theoretical analysis,finite element simulation and real bridge monitoring to study the influence of temperature effect,prestress loss and crack damage on the bridge structure.(1)This paper describes the current situation of concrete variable cross-section box girder bridge,the typical diseases of continuous box girder bridge and the current main bridge reinforcement methods.In addition,the research status of temperature effect,prestress loss and the influence of bridge structure crack on deflection at home and abroad are summarized.(2)This paper summarizes and deduces the analysis theory of temperature field and temperature effect,establishes the finite element model of two-dimensional temperature field by using ABAQUS thermal analysis function,and then analyzes the influencing factors of temperature field.And this paper determines the convective heat exchange coefficient and atmospheric temperature,introduces the concept of radiation temperature,transforms the second type boundary condition into the third type boundary condition,determines the boundary condition of temperature field,and then the numerical simulation of temperature field is carried out.The simulation results of temperature field are imported into the solid model,and the influence of temperature effect on deflection and stress is analyzed.(3)Combined with the code and monitoring data of the real bridge,this paper calculates and analyzes the instantaneous loss and long-term loss of prestress loss,and the time history analysis results of prestress loss are obtained.In this paper,the finite element analysis software ABAQUS is used to analyze the influence of three-dimensional prestress and different longitudinal prestress loss on the deflection of prestressed concrete continuous box girder bridge before and after reinforcement.(4)This paper summarizes the mechanism of concrete box girder cracks,the classification of concrete box girder cracks and the analysis methods of concrete cracks,and discusses and analyzes the finite element analysis theory of cracks.Based on the distribution of cracks in the real bridge,this paper uses ABAQUS finite element analysis software and the life and death element method to respectively analyze and discuss the influence on the structure and its dynamic characteristics of different height and number of cracks in 1 / 4 section web and midspan bottom plate of the real bridge.