Experimental Study On UHPC "T-Shaped" Wet Joints In The Negative Moment Zone Of Continuous Concrete Beams After Simple Support

In order to improve the crack resistance and durability of wet joints in the negative moment zone of continuous concrete beam bridges with simple support and then structure,and simplify the construction process,a new type of high-performance concrete(UHPC)wet joints in the negative moment zone of concrete beam bridges was proposed.Program.Due to the low tensile strength of conventional concrete,it is necessary to ensure the crack resistance of the concrete in the negative bending moment zone of the pier by prestressing,which not only increases the difficulty of on-site construction,but also difficult to ensure the long-term effects caused by its shrinkage and creep.UHPC has excellent mechanical properties and durability.After using UHPC at wet joints with negative bending moments,it uses its outstanding tensile toughness in order to cancel the prestressing of the concrete through the negative bending moment zone at the top of the pier.At the same time,UHPC’s good bonding performance with steel bars will be eliminated in order to eliminate the welding connection of steel bars on site and greatly simplify the construction process of concrete in the negative moment zone of the pier.Based on UHPC as the joint material,the new wet joint scheme proposed in this paper eliminates the negative moment bundle at the top of the pier,eliminates the welding of steel bars,and changes the structure of the traditional joint in the negative moment zone.The design of the transverse wet joint as "T" makes the structure of the wet joint in the negative moment area more reasonable,and it is expected to improve the crack resistance and durability of the structure itself.Whether the new type of wet joint structure can meet the engineering requirements,is there any obvious advantage over the traditional simple supported to continuous negative moment zone wet joint scheme,and it is necessary to study its mechanical performance.The research work in this paper is as follows:(1)Trial design is carried out with a simple beam supported by a continuous concrete beam bridge with a main span of 30m as the background,and a new wet joint structure design scheme is proposed to replace the traditional wet joint structure scheme.The finite element software is used to calculate the new joint construction scheme to control the design stress of the cross section under the normal use limit state and the load capacity limit state.The French UHPC code and the "Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts" are used to control the normal use limit state.Under the crack width,a preliminary reinforcement design for the new wet joint structure is proposed,and a preliminary reinforcement formula for the wet joint structure is proposed.(2)A bending test of a 1:2 scale test model of a new type of wet joint structure with known reinforcement is conducted.The tests show that the crack stress and bearing capacity of the new wet joint structure meet the engineering requirements,and UHPC The introduction of can effectively limit the crack width of NC and improve the stiffness of NC section within a certain range of bending moment.When the bending moment of the section is between 220kN·m and 500kN·m,the stiffness increase range of the UHPC-NC composite section compared to the full NC section is 20%～58.5%.Under normal use limit state,the internal force and deformation redistribution coefficient of the new wet joint structure are reduced to the same span and the same reinforcement.About 50%.(3)Numerical analysis was performed on the new wet joint scale model using MATLAB software,and the results showed that the test values and the simulated values fit well.Based on the comparison and analysis of the stress test values and numerical calculation values of the reinforced bars in various sections,a calculation formula for the reinforced bar stress of the UHPC-NC composite section was proposed.》The NC crack width calculation formula was modified,and it was found that the calculated value of the crack width fits the test value well.Comparing the UHPC crack widths calculated by the codes,the results show that the crack width formula in the French UHPC code fits well,which shows the reliability of the French code.(4)The test analysis of the new wet joint structure by numerical analysis software shows that under normal use limit states,when the control crack width is 0.05mm and 0.1mm,the reasonable lengths of UHPC along the longitudinal bridge direction are 0.27 l and 0.22l.l is the calculative span.When the thickness of the UHPC is 60mm,the crack resistance requirements of the section have been met.At this time,the reasonable steel bar diameter that meets the engineering requirements is unified to 20mm,and the redistribution coefficients of the internal force and deformation caused by the stiffness reduction of the section in the negative bending moment area are less than 20%,The reduced displacement meets the requirements of the specification.(5)The finite element simulation of the experimental scale model was carried out using ABAQUS,and the influence of different parameters on its mechanical performance was obtained through the finite element calculation.The results show that the ABAQUS nonlinear finite element analysis results of the experimental scale model are in good agreement with the experimental results,indicating that the material The constitutive model and modeling method are basically consistent with the actual situation,and it is reasonable to use the finite element model to analyze the test beam parameters.The analysis of the test beam parameters shows that:properly increasing the diameter of the steel bar can increase the initial crack load of the test beam,controlling the cracking stress of the cross section,controlling the residual coefficient of the stiffness after cracking,and limiting the bearing capacity.Properly increasing the thickness of the UHPC layer can improve the UHPC-NC combination,the cracking stress of the cross-section and the residual coefficient of post-crack stiffness at the combined cross-section and interface,but it is not obvious to increase the cracking load,ultimate bearing capacity and interface cracking stress of the test beam.Increasing the axial tensile strength of UHPC can improve the UHPC-NC combined cross-section Cracking stress and combined section,residual coefficient of post-crack stiffness at the interface,increase the ultimate load of the test beam,but not significantly increase the cracking load of the test beam and the interface cracking stress.