Experimental Study On Replacing And Fixing Of The Joint Section Of Continuous Rigid Frame Bridge

China has built a great number of long span pre-stressed concrete continuous rigid frame bridges since 1970 s for their economic efficiency and adaptability.However,the limitations of the design theories of bridge structures and research on material properties and the lack of strict supervision in construction quality at that time,the development of society,the increased traffic and the inadequate maintenance and management are the main causes which lead to problems of bridge structures.It is mainly characterized in cracks in the girder and the deflection in the mid-span,which will affect the appearance and durability of bridges.What's worse,it can affect the safe use of the bridges.With the need of research on the project of China Communications Construction Company “the research and application of the changes in the structural system reinforcement and the whole span demolition technology of long span concrete box girder bridges”,this thesis proposes the reinforcement method by replacing concrete beam with steel structure in the mid-span of the girder,which is also based on the existing problems of pre-stressed concrete continuous rigid frame bridge and its reinforcement methods.In short,it means to reduce the self-weight of the girder to reduce the deflection in mid-span and improve bearing capacity of bridge.The research work of this thesis is as follows.Firstly,make a summary and conclusion on the main problems and causes of prestressed concrete continuous rigid frame bridges which have been built and the advantages and disadvantages of the existing maintenance and reinforcement methods,and then provide a new reinforcement method.The method is to replace the existing concrete beam with steel structure.Secondly,based on the design and research of the replacement and the reinforcement of bridge,the form of organization structure of steel-concrete joint and steel beam is determined,the technologies of the segmental demolition of girder,the hoisting and installation of steel-concrete joints,the pouring of concrete and the prestresses tensioning are improved.According to experimental models,two different models of steel-concrete joints are designed;and the mechanical behavior of steelconcrete composite segment in key parts is calculated and analyzed under the effects of specific load combination.Thirdly,the finite element models of the experimental bridge models of pre-andpost-replacement and reinforcement are established,the loading tests based on load grade are designed,cracking load of girder before replacement is calculated,the stress deformation of critical sections of pre-and post-replacement under different load is contrasted and analyzed.As a result,the practicability of using segmental replacement and reinforcement to solve the deflection in the mid-span can be verified theoretically.Fourthly,the experiments on replacement and reinforcement in mid-span are conducted,the measured data of experiments is summarized and calculated,the comparison and analysis based on pre-and post-replacement and reinforcement is conducted.On the basis of calculating data of stimulation models,the effects of reinforcement method by using steel structure to replace concrete beam are assessed and analyzed.