Research On The Numerical Simulation Method Of Building Structure Progressive Collapse

In order to simulate the nonlinear dynamic process of progressive collapse of building structure,considering the coupled nonlinearity of geometrical,material and contact from continuum to non-continuum,a particle element method(PEM) was proposed to simulate the nonlinear dynamics process of building structure collapse after the principles of nonlinear dynamical mechanics were studied systematically. Then the beam and shell element with the large displacement and large rotation capability were researched.Finally, the dynamic relaxation method was studied to apply the initial stress.The detailed research contents are as follows:(1)Research on the present state of the progressive collapse of building structure.Firstly,the present state of structure progressive collapse was analyzed from theory research,code research, numerical simulation and the software application respectively.Then considering material,geometrically and contact nonlinearity, the present state of nonlinear dynamics analysis was studied.(2)Research on the principles of nonlinear dynamical mechanics. Considering the coupled nonlinearity of geometrical, material and contact of building progressive collapse, the nonlinear dynamical mechanics principles of the implicit finite element method, the explicit finite element method and the discrete element method were studied. Then the advantages and disadvantages of those methods to simulate the process of building progressive collapse were compared.(3)Research on the particle element method(PEM) which was proposed to simulate the nonlinear dynamics process of building structure collapse from continuum to non-continuum. Based on the theory of particle dynamics, this method unifies the explicit finite element method and discrete element method to the same computation framework by defining the generalized link modal, constructing the conversion law of the link modal and creating the contact collision algorithm. The particle element method,which has the computation accuracy of finite element method during the continuum phase and the computation capability of discrete element method during the non-continuum phase, could be used for strong nonlinear dynamics simulation of building structure collapse.(4)Research on the explicit geometrical beam element.In order to achieve the nonlinear dynamic analysis of the beams and columns during structure collapse, the realization procedure of a nonlinear dynamic beam with explicit algorithms was researched.Based on the updated Lagrange formulation,the finite rotation method was adopted to consider the rotation non-swappable, which was used to determine the element coordinate. Combining with the Co-Rotational method, the exact element internal force was calculated after the deformation and rigid displacement was separated. A nonlinear dynamic procedure of beam element with explicit algorithms, which could be used for the structure dynamic analysis, was presented. The numerical result shows that the beam element has very good performance.(5)Research on the explicit geometrical shell element. In order to achieve the nonlinear dynamic analysis of the walls and plates during structure collapse, the realization procedure of a nonlinear dynamic shell with explicit algorithms was researched. The shell, which is combined by the membrane and plate element, is based on the mindlin theory. The detailed realization techniques such as the local element coordinate, element formulations, the mass matrix calculation and the element broken criterion were studied. Finally, a nonlinear dynamic procedure of shell element with explicit algorithms was presented. The numerical result shows that the shell element has very good performance.(6)Research on the dynamic relaxation method. Considering the implementation method of implicit finite element stiffness damp, a stress stiffness damp was realized in the explicit finite element framework by the stress updated procedure. The influence rule of stiffness damp to the stability time step was studied through a three dimensional beam dynamic analysis. The numerical result shows that the stiffness damp coefficient will reduce the stability time step length greatly. Therefore, the application of the stiffness damp coefficient is not suggested in the explicit dynamic analysis, while the mass damp coefficient is recommended when the damp should be considered.