Cohesive Zone Model With Dilation And Its Application In Numerical Analysis Of Composite Members

The composite members composed of steel and concrete are widely used in civil structures,and the two materials are combined by the interaction of the interface to bear the load together.Previous studies have shown that the microscopic mechanical properties of the steel-concrete interface have a great influence on the overall behavior(such as deformation,internal force distribution,failure mode,etc.)of the members when bearing external loads.Therefore,research on the behavior of the interfacial fracture process zone quantitatively is of great theoretical and engineering value to study on the mechanical behavior of composite members composed of steel and concrete.The mechanical property of the interface between steel and concrete is usually depicted by the bond-slip relation.The existing studies introduced parameters such as section type,member size and stress state of components,which lacks physical meaning.In addition,normal force and displacement of the interface are not considered in most studies of bond-slip behavior of steel and concrete interface.Using the cohesive zone model(CZM)to describe the mechanical property of the interface is a feasible way to solve the above problems.Although the cohesive zone model,combined with numerical methods,has been successfully applied in composite material interface simulations,it has not yet been applied to simulate the interface of steel and concrete.Based on the S?rensen model,this paper presents the method of constructing the cohesive zone model with dilation at first.Then the general concerns,such as parameters and modeling method,of simulating steel and concrete interface by cohesive zone model with dilation are studied.And finally,cohesive zone model with dilation is applied in simulating the steel and concrete interface when numerically analyzing composite components.The main achievements of the study are as follows:(1)The link between potential-based method and non-potential-based method is established,which provides a new way to study the non-potential-based tractionseparation laws by mathematical analysis method.And a general method to construct cohesive zone model with dilation is presented.This method explains the reason why the tangential traction-separation law of S?rensen model is discontinuous and why the S?rensen model does not satisfy the consistently coupled rule.Above all,this method fundamentally eliminates the deficiencies of S?rensen model.(2)By introducing the damage parameters into the traction-separation laws,the application scope of cohesive zone model with dilation is extended to the study of brittle and quasi-brittle cracking interfaces subjected to reversed loading.The interfacial tangential traction is decomposed into bonding and friction,and the effect of friction is counted from the initial damage of interface.The disappearance of bonding and the appearance of friction are progressive processes.The strength of friction depends on the level of interfacial damage and the normal pressure.(3)By applying the presented method to construct cohesive zone model with dilation,traction-separation laws applicable to monotonic and reversed loading problems are obtained,containing three groups of equations for each load type.At the same time,the method to calculate the interface stiffness matrix is given.The ABAQUS user subroutine UINTER is coded for the implementation of these traction-separation laws.(4)According to the mass conservation of interface layer material,it is found that the steel and concrete interface dilation caused by the damage of transition layer is about 2~16?m.The experimental and numerical results of the steel plate pull-out tests and the experimental data given in other studies are analyzed.Based on these data,the reasonable values of the parameters of the cohesive zone model with dilation in simulating the interface of composite members are discussed.By simulating the pull-out tests of plain rebar and the push-out test of concrete-filled steel tube,the extensive applicability of the cohesive zone model with dilation in simulating steel and concrete interface is displayed.Using the cohesive zone model with dilation to simulate the steel-concrete interface,it not only considers the interface interaction in tangential and normal direction,but also avoids the dependence of parameters on the section type,member size and stress state of components.Thus,the problems existing in current studies on bond-slip behavior of steel and concrete interface are successfully solved.(5)The cohesive zone model with dilation is applied to simulate the steel-concrete interface in numerically analyzing hollow section steel reinforced concrete short columns subjected to axial compression.The factors considered in finite element models,modeling methods and calculation results are discussed in detail.It is shown that even if the loading process of the model on the component level is monotonic,the separation on the interface may still exist unloading process.Therefore,the steel-concrete interface should be modeled by a model containing unloading and reloading behavior.The interaction between steel and concrete changed the distribution of axial force between the two materials.The out-of-plane displacement of the tube walls are confined by concrete,which improves the local stability of the tube walls.Although different interface models may change the calculated failure modes,they change the calculated axial bearing capacities negligibly.Finally,the equations predicting axial compressive bearing capacity of hollow section steel reinforced concrete short columns are given based on the finite element calculation data,which can be used as a reference for experimental research and engineering application.