Research On Reinforcement Technology Of External Prestressing On Variable Cross Section Continuous Girder Bridge

Since China's reform and opening up,traffic volume developed rapidly with the fast-developing of economic construction in China and the boom of transportation.There are quite a part of the bridge builded earlier is now can not meet the requirement of the use under the influence of many factors,such as shrinkage and creep,prestress loss and overload,etc.The bridge began to show the trend of the development of the disease and have seriously affected the normal use of the bridge.So,it is urgent for the bridge reinforcement.Comparing with other reinforcement method,external prestressing made the damage of the bridge structure smaller,which can reduce or avoid cracks,and make some of these cracks to get closed,to improve the durability of bridge.In addition,the increasement of gravity is small with the method and can save the reinforcement cost and also does not affect traffic construction process.It can be used as a temporary reinforcement measures as well as a permanent reinforcement measures,which improve the bearing capacity of the bridge structure.Although both theoretical and experimental studies on the technology of external prestressing can be found at home and abroad,the study of technologies about variable cross section continuous girder bridge are not as common.Relying on the bridge strengthening project in a city in Jiangsu province,this paper analyses and summarizes the experimental studies at home and abroad and relevant literature,conducting a study of external prestressing reinforcement of variable cross section continuous girder bridge with theoretical analysis,finite element modelling and the data of reinforcement construction supervision.The analysis includes the tendon configuration,structure of deviator device and anchor device,which has an influence on the reinforcement of the continuous girder bridge with variable cross section.The conclusion of the paper and main research work is as following aspects:(1)Introduced the present situation of the domestic and foreign bridges,sketched the significance and necessity of the strengthening technology with external prestressing,and briefly introduced the trait and basic method of the reinforcement of the variable cross section continuous girder bridge.(2)Based on the reinforcement of the bridge,for the cross crack in the mid-span,kinds of methods of reinforcement are compared and choice the method of external prestressing to reinforce the bridge.A conclusion that the disease is related to the loss of prestress and the over load by the analysis of the disease cause.According it,the key point of the design is introduced,such as the analysis of the bearing capability of the bridge,the additional area of the tendons,the profile of the tendon,the form and position of the deviator and anchor.(3)Introduced the calculation of the effect of the external prestressing,compared different tendon configurations through the finite element modeling,which concluded the equivalent effect on variable cross section continuous girder bridge.It verifies the correctness of the tendon configurations,and solve the technology of tendon configurations on variable cross section continuous girder bridge.It introduces the idea of structure optimization,and made an optimization of the tendon configuration through the ANSYS optimization module.With the optimization target of bending moment in the midspan,the optimized scheme has resulted in a increasement of negative bending moment,which solve the optimization techniques of tendon configurations with external prestressing.(4)Base on the engineering background,made a study of deviator and anchor with the form of steel structure.On the one hand,it selects truss structural form through the finite element analysis method,and chose a relatively reasonable double channel cross section using the iterative analysis method for the stress analysis of different cross section steel members,and carries on the calculation of truss,which solved the technology of selection of deviator device structure form and cross section,and it is advantageous to promote the steel structure deviator device.On the other hand,it analysed the local stress of the joint between the concrete and the deviator or the anchor,which verified the position of the anchorage block and connection and the feasibility of the steel structure anchor device through the analysis of the finite element modeling method.(5)Base on variable cross-section continuous box girder bridge,it introduces the methods and content of the construction scheme,and the tensioning construction is completed successfully through the monitoring data and the theoretical data by the finite element model to guide every step of the construction.It verified the rationality of the externally prestressed reinforcement design and the feasibility of reinforcement for the partial or whole control in the process by finite element model with the load test,which is helpful to promote the use of the similar projects in the future.