Research On Reinforcement Method Of Small And Medium-span Bridges Based On Vertically Tensioned Prestressed Method

As an important part of modern transportation system,bridge structures have a great effect on the development of national economic and the safety of people’s lives and property.However,as a functional building,in the actual long-term service process,the environment condition of bridges are very complex,the bridge structures will be affected by various factors,such as the aging of materials,environmental erosion,overload operation,natural disaster and so on.In addition,the long-term maintenance and management is improper.All of these will inevitably lead to the damage of bridge structure and reduction of service performance.When these effects reach a certain extent,they will directly threaten the safe operation of bridge structures.For small and medium-span bridges with damages,we should tap their potential and take reasonable and effective reinforcement measures to enhance their bearing capacity and extend their service life.Therefore,it is of great significance to study the reinforcement methods of bridge structures under loads for improving the operation status of damaged bridge structures.Compared with other reinforcement methods,external prestressing reinforcement method is an effective and reliable active reinforcement method.This method has many advantages: less damage to bridge structures;less increase in bridge deadweight;by closing the cracks in the bridge structure,the crack propagation can be effectively restrained and the stress condition of the bridge can be improved;improving the bearing capacity of Bridge structure effectively;the traffic is not affected in the process of reinforcement,and it is convenient to maintain after strengthening.Therefore,the external prestressing reinforcement method has been widely used in the bridge reinforcement engineering,and the research and analysis of the external prestressing reinforcement method for the bridge structures under load is still the front topic in the field of civil engineering.In the design of highway bridge structure in China,the proportion of small and medium-span concrete bridges is the largest.According to the structural characteristics of bridge structure,the traditional external prestressing reinforcement method requires the installation of tensioning equipment at both ends of the beam to be strengthened.However,this location usually has end diaphragm and near pier abutment,which limits the tension space and affects the construction operation.Therefore,the tension end is often moved to the mid-span direction for a certain distance,which will inevitably reduce the length of the prestressing steel bar,so that the loss of prestressing force is greater,resulting in poor reinforcement effect.For small and medium-span bridges,due to the limitation of bridge span,such bridges can only be strengthened by short external cables,which limits the application of traditional external prestressing reinforcement methods in small and medium-span bridges.Therefore,it is of great significance to study more reasonable and economical external prestressing reinforcement methods for the safety performance maintenance of bridge structures.In order to solve this technical bottleneck,Professor Tan of Jilin University introduced the idea of transverse prestressing into the reinforcement of small and medium-span bridges,and proposed a reinforcement technology of small and medium span bridges based on transverse prestressing method.In this paper,combined with Jilin Province Transportation Science and Technology Project "Research on Reinforcement Technology of Small and Medium Span Bridges Based on Transverse Prestressing Method",the research on strengthening methods of transverse prestressing is carried out theoretically.In this paper,the overall and local mechanical properties of the structure strengthened by transverse prestressing are taken into account.The purpose of this study is to provide theoretical support and guidance for the ultimate formation of a systematic and effective reinforcement method for small and medium-span bridges based on the idea of transverse prestressing.In order to slove the problems above,the main research has been carried out in this paper as follow:(1)Based on the basic principle of transverse prestressing,combined with the mechanical characteristics and structural characteristics of bridge structure,the reinforcement method of transverse prestressing is studied.The structure of reinforcement system was designed,and the reasonable layout of reinforcement components,the method of applying transverse prestressing force,the reinforcement steps and construction precautions were determined.Finally,ANSYS finite element analysis software is used to simulate and analyze the static characteristics of bridge structures strengthened by transverse prestressing.The effects of different tension control forces on the bearing capacity,concrete strain,internal non-prestressing tendon strain and external prestressing tendon stress of beams strengthened by transverse prestressing are discussed in numerical examples and the incremental calculation model of external prestressing tendon stress of beams strengthened by transverse prestressing is proposed.(2)Aiming at the dynamic characteristics of bridges strengthened by transverse prestressing,based on the free vibration equation of Euler-Bernoulli beams is derived by the distributed mass model of beams,and on the basis of considering the influence of quadratic effect,the increment of tension of external prestressing tendons is assumed to be proportional to the vibration displacement of the midpoint of beams,and then the natural vibration frequency formula of beams strengthened by transverse prestressing is deduced.The reliability and accuracy of this method are verified by finite element method.Finally,taking a box-section beam as an example,the effects of initial prestressing,eccentricity,deflection angle and cross-section size of external prestressing tendons on the frequency of beams strengthened by transverse prestressing are discussed.Taking a hollow slab beam as an example,the effects of different factors on the natural frequencies of the beams strengthened with different external prestressing conditions are discussed.(3)ABAQUS finite element software was used to establish a three-dimensional solid non-linear finite element model of the specimens to analyze the local weak parts of the beams strengthened by transverse prestressing.Based on the finite element model,the load-displacement curves,the failure mechanism of concrete,the structural stress characteristics of anchorage members and the structural stress characteristics of supporting members in the transverse prestressing reinforcement system are analyzed.The calculation method of structural dimension design for key parts is also given.