A FEM-DEM Coupled Multiscale Analysis Method For Study Of Mechanical Behaviors Of Concrete

Concrete is a kind of multiphase composite material,whose mechanical behaviors are very complicated because of its inhomogeneous and anisotropy characteristics.As conctete is one of the most widely used materials in building structures,developing numerical simulation methods that can reliably and efficiently simulate its mechanical behaviors is of siginificant importance.The finite element method(FEM)is mainly focused on the simulation of macroscopic mechanical behaviors of concrete,but has difficulty to analyze the mesoscopic mechanical behaivor after crack because of its assumption of continuum media.The discrete element method(DEM)has advantages in simulation of mesoscopic crack and local failure behaviors of concrete,however,it is time-consuming which limited its applications to engineering problems.Therefore,this thesis aims to develop a numerical simulation method combining the advantages of both FEM and DEM to analyze mechanical behaviors of concrete in an accurate and efficient manner.Based on an exiting FEM-DEM coupled multiscale method for studying the microscopic and mesoscopic mechanical properties of sand[1],the thesis present a similar FEM-DEM coupled multiscale analysis method that is appropriate for studying the multiscale behaviors of concrete.The FEM-DEM coupled multiscale analysis method uses FEM to simulate the macroscopic element behavior,and DEM as the representative volume element to simulate the constitutive relationship of concrete of the Gaussian integration point of finite element.This thesis developed a "Coupled Multiscale DEM Material" in general finite element software OpenSees and establish the corresponding calculation process in the general discrete element software Yade through Client-Server software integration technique[2],then discussed how to select the appropriate parameters of the mesoscopic discrete element model in Yade.This thesis developed the OpenSees-Yade numerical simulation platform,through which the coupled FEM-DEM multiscale analysis method applying to the macroscopic and mesoscopic numerical simulation of the concrete is carried out.Then,the method is applied to the simulation of the experiment of concrete column under cyclic loading conditions,and by comparing with the result of experiment,the feasibility of the FEM-DEM coupled multiscale analysis method is shown.The efficiency of the method is proved by the study of the computation time of purely using discrete element software Yade.Then,the FEM-DEM coupled multiscale analysis method is applied to the analysis of the reinforced concrete simply supported beam under concentrated load.The macroscopic finite element mechanical properties and the mesoscopic damage and crack behaviors of the beam are studied.By comparing with the result of using finite element model truncated Drucker-Prager[3,4](DP)material,the accuracy of the FEM-DEM method is studied.Finally,this thesis present a large-scale parallel distributed computing method of the FEM-DEM coupled multiscale analysis method,which greatly improves the computational efficiency and provides the possibility for the method to be applied to engineering practice.The parallel distributed computing FEM-DEM coupled multiscale analysis method is applied to the simulation of reinforced concrete shear wall under vertical and horizontal loads.The macroscopic mechanical property and the mesoscopic cracking state are analyzed,and the comparison with the result of using truncated DP material demonstrate the accuracy and effectiveness of the method.The efficiency of the parallel distributed computing is verified by comparison of the calculation time of using the serial FEM-DEM coupled multiscale analysis method to simulation shear wall.The research shows that the newly developed coupled FEM-DEM multiscale analysis numerical simulation method provides an ideal tool for simulation of concrete members,such as concrete beams,columns or shear walls.It provides a practically useful tool for macroscopic and mesoscopic study of concrete mechanical behaviors.