Research On Mechanical Behavior Of Prefabricated Deck Slab With UHPC Joint

With the rapid progress of Bridge Technology in our country,bridge assembly construction technology has gradually become the main development direction of bridge technology.The application of prefabricated structures can speed up construction speed,improve construction quality,and reduce environmental pollution.At present,prefabricated assembly technology has been widely used in bridge superstructures.Prefabricated bridge deck components meet the national requirements for prefabrication,standardization and industrialization in the field of bridge construction.In order to better transfer the shear and bending moment,the prefabricated bridge decks are usually connected by in-situ cast joint.However,it has been found in a large number of engineering practices that the width of in-situ cast joint of bridge decks is large and the construction is complicated,which directly affects the construction speed of prefabricated bridge decks.Diseases such as cracking and water leakage are most likely to occur in the in-situ cast joint area of the bridge deck,which seriously affects the safety and durability of the bridge structure.Ultra high performance concrete(UHPC)provides a better choice for in-situ cast joint materials with its excellent mechanical properties and super durability,and has a broad application prospect.In this paper,according to the bending resistance of UHPC in-situ cast joint of precast assembled bridge deck,the finite element model of precast assembled bridge deck with UHPC in-situ cast joint is established,the width of in-situ cast joint,section form of in-situ cast joint and reinforcement ratio of in-situ cast joint are analyzed,and the parameter of UHPC in-situ cast joint is optimized.According to the optimized parameter of the in-situ cast joint,the experimental study on the flexural performance of the UHPC in-situ cast joint is carried out,and the flexural capacity of the in-situ cast joint is calculated according to the strut-and-tie model and the stress characteristics of the longitudinal reinforcement discontinuity in the UHPC in-situ cast joint area.The main work and research results of this article are as follows:(1)Optimize UHPC in-situ cast joint construction parameters.The finite element model is established on the basis of the bending performance test of UHPC in-situ cast joint in China.The reliability of the finite element model is verified by comparing with the crack development,failure mode,load midspan deflection curve of the test results.On this basis,the parameters of the width of the in-situ cast joint,the section form of the in-situ cast joint and the reinforcement ratio of the in-situ cast joint are analyzed.The results show that the width of the in-situ cast joint can be reduced to 15 cm when the UHPC in-situ cast joint is used for the precast assembled bridge deck,which can ensure the connection effect and mechanical properties of the in-situ cast joint.Wedge-shaped or funnel-shaped joint sections can solve the problem of weak crack resistance at the interface of rectangular joint sections.Increasing the reinforcement ratio has little effect on the cracking load,and the maximum reinforcement ratio in in-situ cast joint should not exceed 2.6%.(2)Based on the test of the flexural performance of the bridge deck with UHPC in-situ cast joint,the influence of the cross-section form of funnel-shaped and wedge-shaped joint,the U-shaped reinforcement and arc-shaped reinforcement on the crack development,flexural capacity and joint mechanical performance of the structure is studied,and compared with the integral concrete slab.The test results show that there is no crack in UHPC at the in-situ cast joint,and the interface bond strength between the cast-in-place UHPC and the ordinary concrete of precast slab is high,and the main crack is located in the ordinary concrete of precast slab beside the joint.The flexural capacity of the bridge deck with the width of the in-situ cast joint of 15 cm is basically the same as that of the whole concrete slab.The UHPC in-situ cast joint with funnel-shaped joint section should adopt arc reinforcement connection.(3)The calculation method of flexural capacity of UHPC in-situ cast joint is studied.Taking the funnel-shaped and wedge-shaped joint section of the U-shaped reinforcing bar as an example,the force transmission mechanism of discontinuous steel bars in the in-situ cast joint is explained based on the strut-and-tie model,and the bending resistance of the UHPC wet joint is calculated,which provides reference for design.