| With the rapid development of highway and Bridge in our country,prestressed bridge become an important part of the bridge construction.its safety has been paid more and more attention.There are more or less problems exist in the active prestressed concrete bridge,such as the premature cracking of the bridge deck,the serious bumping at bridge head,the corrosion of the steel bar and the damage of the rubber bearing.For the long span prestressed concrete bridge,the main problems are the midspan deflection and box girder cracking.The cause of the disease is not only related to the material of the bridge,but also related to the prestress can not be accurately applied to the structure.In this paper,based on the current calculation theory of friction loss I study on the main prestress loss in the prestressed tensioning stage.Based on the existing method of prestressed tension I study on the tension control of prestress.1?I tested the prestress friction loss of the selected steel beam by the prestress friction loss test and calculated the model of continuous rigid frame bridge by using MIDAS CIVIL.The comparison between the experimental results and the theoretical results of MIDAS shows that the theoretical values are large.2?Through the derivation and analysis of the theoretical formula,it is found that there are three defects in the current formula:The efect of friction on tensile force is neglected in engineering calculation;The pressure distribution of the prestressed curved channel is uniform,which is inconsistent with the actual situation;In the calculation of the bending angle,the formula is obtained by the uniform distribution of the curved channels.In order to solve the above problems,this paper optimizes the calculation of the friction loss of prestressed steel beam,and reduces the computational load by MATLAB programming.3?The contrast between the elongation of the test and the calculated elongation show that the change trend of the actual elongation is different from the theoretical arithmetic.Based on the three stages of material friction,this paper makes the assumption that the coefficient of friction is changed in the process of prestress tension and defines the new parameters which is include the two factors affecting friction coefficient.The fact that the friction coefficient changes has been confirmed by the relation schema of the new parameter and the percentage of the tension error,the variation offriction coefficient corresponds to the three stages of material friction.It is considered that it is not accurate to control the tension of prestressed steel beam by the standard of ±6%.4.According to the fact that the friction coefficient changes,I statistics the equivalent ratio and prestress stretching elongation.According to the relationship of the two parameters,the relation graph is drawn and the upper and lower limits are simulated.We can control the tension of prestressed by using the upper-lower limit.At the same time,based on a large amount of measured data,this paper puts forward the control standard of theoretical elongation under different construction levels.Through the study of this paper,a more accurate calculation method of the prestress friction loss is obtained and the computational complexity of this method is avoided by programming.Based on the test results,the paper puts forward the viewpoint that the coeffcient of friction is varied,based on it,i put forward a method for prestressed tension control. |
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