Research On Mechanical Properties Of Sandwich Shells Considering Partial Degree Of Composite Action

While solving urban traffic problems,urban rail transit brings inevitable environmental vibration and noise problems.The traditional solution to the problem of vibration and noise is to install vibration and noise reduction facilities,which will undoubtedly increase the construction process and fail to fully utilize the performance of the shield segment structure itself.Therefore,innovating the structural form of the lining,improving the energy absorption and energy consumption capacity of the component itself,meeting the dual requirements of structural safety and green environmental protection functions,integrating load-bearing and functionality(vibration reduction,noise reduction),is a new strategy.The concrete sandwich shells includes inner,outer concrete shell and an intermediate functional layer.The two-layer concrete shells are connected by connectors to achieve a composite action,and the intermediate function layer acts as a damping noise reduction.Considering that the connectors are not completely rigid,there will be limited slip between the inner and outer shell,which will lead to partial composite action of the sandwich shells.Due to the existence of the hoop connector,the stress distribution along the width direction of the segment will be uneven,which is called shear lag effect,the effective flange width is used to describe this shear lag effect.Therefore,this paper focuses on the research of mechanical properties of green multi-functional concrete sandwich shells,including the derivation of the analytical model and construction of finite element analysis model;and uses the finite element analysis results to verify the analytical results.The main work and research results are as follows:(1)Considering the internal typical arrangement of the connector,the analytical model was developed,and a finite element model was constructed to verify the analytical model.The research shows that the derived analytical model can accurately predict the stress and deflection of the sandwich segment,and the effective flange width is the smallest and the shear lag effect is the most significant under the full composite action.A parametric study was carried out using the validated analytical model to study the effects of concrete strength grade,the ratio of the thickness of the sandwich layer to the thickness of the single shell and the ratio of the arc length to the width of the sandwich segment on the effective flange width.The research shows that the influence of concrete strength grade on the effective flange width is negligible;the ratio of the thickness of the sandwich layer to the thickness of the single-layer shell and the ratio of the arc length to the width of the sandwich segment not only have a significant impact on the effective flange width ratio under the same degree of composite action,but also has a significant effect on the relative value of the effective flange width ratio between different degrees of composite action.According to the parametric study and based on the effective flange width under full composite action,a simplified calculation formula was derived.The research shows that this formula can be used for design purposes.(2)Considering the general arrangement of connectors,the analytical model was developed,and a finite element model was constructed to verify the analytical model.The research objects are single-chamber section,single-chamber with cantilever section,multi-chamber with cantilever section and wide flange section.In the process of analytical formula derivation and calculation,the strain continuity condition and the hoop shear flow distribution coefficient were successfully applied,and the analytical solution for the general arrangement of the connectors was obtained.The research shows that the hoop shear flow distribution coefficients of the single-chamber section,the single-chamber section with cantilever,the multi-chamber section with cantilever and the wide flange section areη_l=1、η_r=1,η_l=.0441、η_r=.0559,η_l=0 5.、η_r=.05,η_l=.0 5、η_r=.05,respectively.The arrangement of the connectors has an important influence on the value of the distribution coefficient of the hoop shear flow.For full composite action,the value of the effective flange width ratio under the arrangement of all the connectors is the smallest;the effective flange width ratio of the wide flange section is the smallest value for all connector arrangements.(3)Using the beam-spring model,this paper derived the internal force and displacement of the sandwich segment ring using the asymmetric calculation model that considers the position of the joint.At the same time,the effects of the joint bending stiffness,calculation of the radius and the thickness of the segment are considered for the bending stiffness reduction factor,and the simplified empirical calculation formula was obtained.The research shows that:within a given range of joint stiffness ratio,there is a linear relationship between the empirical calculation formula of the stiffness reduction factor and the joint stiffness ratio log(λ).As log(λ)increases,stiffness reduction factor will linearly increase and gradually approach 1;stiffness reduction factor will decrease with the increase of lining thickness;stiffness reduction factor will increase with the increase of the calculated radius.(4)Combined with engineering examples,and the segment reinforcement is calculated by considering the degree of composite action.The research shows that:with the increase of the degree of composite action,the composite action of sandwich shells segment will become higher and the area of reinforcement will gradually decrease.