Research On Flexural Behavior Of Reinforced Concrete Sandwich Segments

With the rapid development of urban underground rail transit,the vibration and noise problems caused by rail trains have become increasingly prominent,which need to be solved urgently.The traditional vibration reduction and noise reduction is mainly realized by track vibration reduction and isolation or setting functional layer.The research on the use of lining structure vibration reduction layer is still in its infancy.The traditional vibration and noise reduction layer has limitations,so innovating the structural type of tunnel lining components and integrating load-bearing,vibration and noise reduction is a new idea to solve the problem.Reinforced concrete sandwich segments are composed of inner,outer concrete layers and intermediate functional layers,and the upper and lower concrete layers are connected through connectors.The reinforced concrete sandwich segments have dual functions,which can not only bear the load,but also reduce vibration and noise by placing flexible materials in the sandwich layer.In this paper,the flexural properties of half scale concrete solid segments and three kinds of scale concrete sandwich segments are studied.Firstly,the flexural capacity of different types of segments is analyzed and studied from the aspects of mid-span displacement,concrete strain,reinforcement strain and connector strain.Then the corresponding parameter analysis is carried out,and the influence of key parameters on the flexural performance of concrete sandwich segments is studied.Finally,an optimized scaled concrete sandwich segments are proposed,and reasonable suggestions are provided for developing the prototype sandwich segment structure.The main results and conclusions are as follows:(1)Referring to the research on the mechanical properties of shield segments,concrete sandwich panels and shear connectors at home and abroad,this paper designs concrete sandwich segments with three different types of connectors,carries out bending performance tests on various segments,observes the development and failure of segments cracks in the test process,and obtains the data of segments mid-span displacement,concrete strain,reinforcement strain and connector strain.The research shows that the three kinds of connectors can participate in the stress,the curved truss connector and curved steel plate connector can provide a certain bending stiffness for the segments,and the corresponding sandwich segments JXQ1 and JXQ3 have the same cracking resistance as the solid segments.The bending stiffness of curved grid connector is low,so the anti-cracking ability of segments are weak.The ultimate bearing capacity of the sandwich segments(JXQ1)of the curved truss connector is close to that of the solid segments(SXQ).The ultimate bearing capacity of the sandwich segments(JXQ3)of the curved steel plate connector is the largest,but the segments support are easy to be damaged.(2)The concrete sandwich segment model is established by using ABAQUS finite element software for numerical simulation.The vertical displacement,reinforcement strain,concrete strain and connector strain in the middle of the segment span are output and compared with the experimental data.The research shows that the simulation results are in good agreement with the experimental results,which proves the reliability of the model.Based on the reliable model,the effects of sandwich layer thickness,number of connectors and concrete strength grade on the flexural capacity of concrete sandwich segments are studied.The results show that: 1)with the increase of the thickness of the sandwich layer,the bearing capacity of the concrete sandwich segments decreases,and the ultimate bearing capacity decreases greatly.It can be seen that the thickness of the sandwich layer has a significant impact on the flexural performance of the concrete sandwich segments,but has no significant impact on the cracking resistance of the sandwich segments;2)When the thickness of sandwich layer is constant,the flexural capacity of concrete sandwich segments increases with the increase of the number of connectors;and 3)With the increase of concrete strength grade,the tensile strength of concrete increases,and the cracking resistance of sandwich segments increases.However,because the reinforcement setting in the segment remains unchanged,the bending bearing capacity of the segment is controlled by the reinforcement.When the reinforcement yields,the segment approaches the ultimate bearing state and the ultimate load is basically the same.(3)Through the analysis of key parameters,it is concluded that the thickness of the sandwich layer of the optimized scaled concrete sandwich segments are 60 mm,the number of shear connectors is 3,and the concrete strength grade is C50.According to the scaled sandwich segment,the design reference opinions of the prototype concrete sandwich segment are as follows: the thickness of the segment sandwich layer is120 mm,the number of shear connectors is 3,and the concrete strength grade is C50.