Fine Analysis And Collapse Of Cable-strut Structures Based On The Vector Form Intrinsic Finite Element Method

Under the externnal loading,the behaviors of the cable-strut tensile structures usually contain large deformation,elastoplastic nonlinear and complex discontinuous behaviors.The VFIFE is a new analysis method based on the vector mechanics theory.And this method is advantageous in the simulation of structural failure.Structural nonlinearities and discontinuities can be well handled by this method.Based on Vector Form Intrinsic Finite Element(VFIFE),this thesis fulfill an intensive research regarding the analysis and simulation for collapse of cable-strut tensile structures.Not only fine analysis of beam and cable element,but also fracture and contact during the process of progressive collapse are taken into considerations in this reseach.The baisc conceptions of the VFIFE are introduced in this thesis.The formulas of strain and internal force of bar element,cable element and beam element are derived on the basis of the VFIFE,which is the basic method used in this paper.Considering coupled effects of multifactor,such as pull and press,bend,shear,torsion,the formulas of strain and internal force of the fine beam model,applying to VFIFE analysis,are derived.And corresponding programs are developed by Fortran language to prove the accuracy of the method on structural elastic analysis.The element cross-section does not keep plane as the increase of the strainwithin the plastic range,and the error caused by the plane-remains-plane assumption cannot be ignored.Applying to VFIFE analysis,the formula of strain and internal force of the fine beam model are derived.The plane cross-section assumption is also modified when the material is at plastic stage.Using the proposed model,computer programs are developed by Fortran.Comparison between the computational results by present method and numerical or experimental results in literature show that the present fine beam model of VFIFE is more efficient and accurate when the analyzed beam has a large depth-span ratio and material is at plastic stage.The static tension model of steel strand is established in this article based on the theory of curved bar theory.The expression of the axial force,torque and bending moment can be obtained under the external load through the equilibrium equation of the helical wire.Besides,the elastic modulus and the bending stiffness of the helical wire can be derived based on the static model.The relations of helical angle,the elastic modulus and the bending stiffness with the external forces are expressed by using Fortran language.By using differential geometrical theory,the geometrical model is established.The wire rope strand,steel strands and Semi-Parallel Wire Cables are analyzed by ANSYS to study the distribution of steel strand section stress.The cross section is divided into several layers along radial direction,and the correction coefficient of equivalent stress of the rope section is proposed.According to the ANSYS analysis results,the distribution of the correction coefficientis obtained.Considering the influence of friction on the steel strand section stress,steel strands are analyzed by ANSYS with penalty algorithm.The failure criterion and modeling of bar element,cable element and beam element are proposed,respectively.And the calculation algorithm of the nodalparameterssuch as mass,cross sectional moment of inertia and internal force etc,during the collapse process isdeveloped.The collapse process of bar structures and beam structures are simulated by the numerical method.And the fracture algorithm is certified according to the energy conservation.The contact algorithm during the progressive collapse process is proposed according tospatial relative positioncriterion,and the formulas of contact force and velocity considering contact between structural members are developed.The energy dissipationalgorithm during the contact process of structural members is proposed on the basis of physicsimpact test research.The criterion for judging failure of cable-strut tensile structures is proposed based on existing researches.The maximum nodal displacement and the number of strutural members that slack or rupturedare used as failure criterion.Taking Levy domes and suspen-domes as examples,thestructural behaviors and mechanisms after local component failure or are investigated.This study discuses the fine analysis of cable element and beam element,and the results are used in the simulation of progressive collapse of cable-strut tensile structures.It enriches the element models of the VFIFE,and also provides a new effective method for the research of local component failure and progressive collapse of cable-strut tensile structures.