Study On The Prestress Loss Of Flexible Tie And Its Effect Of Flying-Swallow-Type CFST Arch Bridge

The flying-swallow-type CFST arch bridge has beautiful shape,light structure and large span capacity.The existence of prestressing reduces the requirements of CFST arch bridge on the foundation anti-thrust capacity,making it more competitive in choice of bridge scheme.As an important component to improve the foundation stress,the prestressing loss of flexible tie is a key concern.However,at present,the calculation method of prestressing loss of flexible tie is based on the calculation method of prestressing loss of prestressed reinforced concrete structure,and its applicability remains to be discussed.In this paper,the finite element analysis method is adopted to study the prestressing loss along the way and the influence of the prestressing loss on the structure,and the calculation method applicable to the prestressing loss of flexible tie is explored.The research is as follows:(1)Based on the detailed analysis of the main span,side span,main pier and flexible tie of flying-swallow-type CFST arch bridge,it is pointed out that the flexible tie can be regarded as the external prestressing to improve the stress of the main pier and side span,and according to the stress analysis,the method of drawing the reasonable value range of flexible tie tension in the construction stage is proposed to determine the flexible tie tension time and tension in the construction process.(2)Eight types of prestressing loss of flexible tie are put forward by using the method of partial calculation of prestressing.The differences and similarities between the prestressing loss of flexible tie and prestressed reinforced concrete structure are analyzed and the calculation method is deduced.This calculation method is used to calculate the prestressing loss of flexible tie of supporting engineering.The calculation results show that the prestressing loss of flexible tie of supporting engineering accounts for about 12%of the control tension,and the prestressing loss caused by pipe friction accounts for about80% of the total loss.(3)Analysis of structural stress changes based on the prestressing of flexible tie in supporting engineering when the loss is-5%(overtension),0%,10%,and 20%,the results show that the prestressing loss of flexible tie has little impact on the main span,but a great impact on the main pier,which will reduce or even eliminate the thrust reserve of the main pier to balance the live load thrust;The side span is the stress state of the curved beam,which is the most sensitive to the prestressing loss of the flexible tie.When the prestress loss of tie is close to 20%,the tension stress of side arch concrete only appears under the dead load;when the prestress of tie is over tensioned by 5%,the stress of structure is more favorable,so the over tensioned technology can be considered.(4)The finite element analysis method is used to analyze the stress of the common embedded steel tube steering device and the row of roller steering device;the contact area between the embedded steel tube steering device and the tie cable body is large,and the stress of each component is obviously dominant;the row of roller steering device has little influence on the prestressing loss of the tie,but its roller is prone to failure in the exposed air,which makes its friction resistance multiply,The advantages of the flexible ties for replacement are not obvious.(5)Through the finite element analysis method to verify the applicability of the standard calculation formula of prestressing loss caused by the friction resistance of the prestressed reinforced concrete structure pipeline to the flexible tie prestress,the analysis results show that there is a deviation between the standard calculation formula and the finite element analysis results;therefore,the finite element analysis results are taken as samples,and the nonlinear least square method based on the trust region is used to analyze the flexible tie from the pipeline.The calculation formula of prestressing loss caused by friction resistance is fitted,and the calculation formula which can better reflect the prestressing loss caused by friction resistance of flexible tie is obtained.