Prediction And Analysis Of Deflection Of Prestressed Concrete Structure Based On Measured Temperature Field

The prestressed concrete continuous rigid frame bridge is widely used in the construction of mountain highways because of its smooth driving,wide view and convenient construction.At the same time,the construction methods such as cantilever casting and cantilever assembly are becoming more and more mature,which makes the bridge’s spanning capacity and construction speed faster.Therefore,it is necessary to provide more refined control measures at the construction stage as a guarantee.During the construction process,the pier and the girders are affected by the sunshine temperature,which causes the verticality of the pier and the line shape of the girders to shift,which makes the actual position deviate from the expected state.If the influence of the temperature gradient on the bridge structure is not identified and corrected in the construction control,it will be difficult to ensure the design and specification requirements.This paper is based on the construction control project of a continuous rigid frame bridge in a provincial expressway in Yunnan province.Through the actual measurement of the temperature gradient inside the pier and the girder,ANSYS software is used to establish the full-bridge solid element model,analyze the structural deformation and correct the girder at the mean time.The positional deviation enables the purpose of precise control.At the same time,by analyzing the deflection of the girder under the temperature gradient,the purpose of predicting the elevation of the girder is finally achieved.The research content of this paper is as follows:1.Briefly introduce the research history of temperature gradient and temperature stress in various countries.At present,the assumptions and methods often used in temperature gradient and temperature stress research.2.According to the existing concrete temperature field theory,several methods for solving the temperature gradient are introduced.By comparing and analyzing the advantages and disadvantages of several methods,the semi-empirical and semi-theoretical method is used to solve the temperature gradient distribution formula of the pier and the girder.Finally,the provisions on structural temperature gradients in relevant domestic and foreign specifications are introduced.3.Selecting the representative weather to measure the temperature gradient of the pier and the girder of the continuous rigid frame bridge.According to the measured temperature data,the temperature gradient inside the pier and the girder is analyzed,and the least squares method is used.The temperature gradient distribution formula of the pier body along the thickness direction and the temperature gradient distribution formula of the girder along the beam height are fitted.4.Analyze the influence of the temperature gradient of the specification on the elevation of the girder.The deflection prediction analysis of the girder during the construction stage is proposed.Based on this,the active control method for considering the elevation of the girder under the influence of the measured temperature gradient is proposed.The full-bridge solid finite element model is established by ANSYS.The principle,flow and precautions of the active control method are introduced in detail.Then the actual control data and feedback information are combined to verify the effectiveness of the method.5.The effects of temperature variations on precast,prestressed concrete bridge girders are analyzed in detail,and the reason for the deflection of the structure under the temperature variations is divided into the prestressing level reduction and the uneven heating of the concrete structure.The ANSYS finite element model is used to load the temperature gradients of different specifications to find the distribution law of the ratio.It can be seen that the maximum cantilever state in the construction phase is affected by the most unfavorable sunshine temperature difference,The decrease in the level of prestressing results in a maximum proportion of structural deflections of 6.9%~8.3%.Under the condition of bridge formation,it is affected by the most unfavorable sunshine temperature difference.The maximum pre-stress level is reduced,which results in a maximum proportion of structural deflection of 8.9%~10.4%.