Object-oriented Interface Stress Element Method And Its Coupling With FEM In Time Domain Analysis

Collapse of infrastructure is one of the main reasons for casualties undersevere earthquake. Protection against collapse has always been a majorobjective of seismic design. In order to mitigate the damage, collapsemechanism needs to be studied theoretically and experimentally. In the meanwhile, accurate and efficient numerical simulation method also needs to bedeveloped.In mechanics view point, collapse is the transition from continuum stateto discrete state. In order to accurately simulate this progress, propernumerical method and analytical model needs to be proposed. Traditionalnumerical methods cannot solve collapse problem. There are severalnumerical analysis methods can solve growing crack program now, such asE-FEM, X-FEM, Discontinuous Galerkine method, mesh-free method and soon. These methods have several limitations, and the problem has not beenproperly solved and is still under development.The main objective of this study is the development ofcontinuum-discrete numerical analysis method for actual application purpose.Based on profound understanding of interface element method (IEM), theauthor proposes an analytical model by combining FEM and IEM in timedomain. The components of this research are as following:1. Based on the mechanical characteristics of the continuous-discreteproblems, the characteristics and applicability of several typical numericalmethods are compared and several helpful conclusions are drawn:(1) Thefinite element method is mainly applicable to continuum problems while thediscrete element method and DDA method are appropriate for discreteproblems; for the continuous-discrete problems, continuous discrete elementmethod can be used;(2) For the analysis of continuous-discrete problems,mesh-free method and numerical manifold method have great potential whileIEM has its own advantages.2. Supplement and amending of the IEM's theory have been proposed:(1)The assumption of interface element's mechanical characteristics has beensummarized;(2) The stress mode of constrained boundary has been proposed;(3) Based on principle of virtual work and ordinary dynamic equations, thegoverning equation of finite discretized element method with constrained effect has been derived;(4) A method dealing with constrain modelingwithout using virtual element is introduced;(5) The relationship betweenapplied element method(AEM) and rigid body spring model (RBSM) has beenillustrated.3. Based on the improved interface element theory, the first set ofobject-oriented interface element analysis program is designed and realized.The design of the overall framework of the program, the data interface and thecore class structure is completed; and solver for two-dimensional linearproblem is complied. Basic post-processing features are also realized.Pre-process program is developed for rectangular domain with openings, andthe data conversion program from ANSYS finite element model to theinterface element model is complied.4. Through several simple examples which have analytic solutions or iseasy to be compared and validated, calculation accuracy, convergence, andapplicability of the interface element method were studied, and theoreticalanalysis were made using the interface element analysis program. The resultsshow that the higher accuracy and convergency can be got, and more accurateresults can get in either static analysis or dynamic analysis when using thebeam or bar element. But computational results are not necessarily convergedwhen using plane element; and accuracy of analysis is effected by the shape ofsolving domain, the upload way, and the grid layout. Plane element can bedirectly used for stretch-based rod problem or bend-based beam or columnproblem; but for general plane problem, the calculation accuracy of interfaceelement method is difficult to be guaranteed, and should be carefully applied.5. The calculation results are not necessarily converged and the accuracyis difficult to be guaranteed in the coordination deformation stage when usinginterface elemenet method. In order to overcome these shortcomings, aFEM-IEM coupling analysis model in time domain is proposed. Thecomposition of the model, the process of analysis and implementation arediscussed. An implementation sample of the proposed analysis model is givenbased on object-oriented interface element analysis program. Feasibility andeffectiveness of this coupling analysis method is preliminarily verified.