The Analysis Of Internal Forces In Members And Progressive Collapse Analysis Based On CVGM Model For Sigle-layer Reticulated Shells Under Severe Earthquakes

The refined numerical simulation of catastrophic process of large-span space structures should be based on systematic and refined modeling theory and numerical algorithm, in which the damage of material and members should be considered to conduct the dynamic failure and collapse study in a multi-layered and multiscale method. However, there lack accurate and quantitative loading law of axial force and bending moment in current research aiming at numerical simulations and experiment studies on hysteretic characteristics of circular steel tube and spherical joint. And nonlinear constitution of material considering cumulative damage is seldom used in failure and damage analysis of reticulated shells under earthquakes. Therefore, it is necessary to analyze the response of interal force in terms of structural members and develop the refined analysis method which can consider damage and fracture of materials in order to achieve thoroughly studies of dynamic failure and collapse mechanism.In terms of members and the whole structure, the analysis of internal force response and progressive collapse analysis base on refined numerical simulation are put forward in this paper. The specific works are as follows:(1) Since the reticular shells can be classified according to gaussian curvature, single-layer spherical lattice shell (positive gaussian curvature) and single-layer sandle shaped shell (negitive gaussian curvature) are selected as study subjects. Considering the influence of geometric parameters, the value range of initial axial compression ratio and change of amplitude and the relationship of frequencies of axial force and bending moment are confirmed. The result of interal force analysis shows that there is obvious variation of axial force amplitude and the relationship of interal force frequencies, which should be taken into account in hysteretic analysis.of members in shells under earthquakes.(2) Compared with the traditional analysis of beam element widely used in single-layer reticulated shell, the refined analysis of shell element has advantages in considering local deformation of members and joint stiffness, which can enable a refined nonlinear dynamic time-history analysis based on geometrical model. The result shows that the vibration characteristics and elastic response of two types of analysis method are nearly the same, while the response of refined model of shell element under severe earthquakes is significantly greater than traditional model of beam element. Therefore, the refined model can accurately simulate the plastic property of member and structure.(3) Based on combined hardening constitutive, the Cycling Void Growth Model micromechanical fracture criteria can be adopted in refined model. With the help of element deletion technique, the VUSDFLD subroutine according to CVGM was written in FORTRAN language that can simulate the process of member fracture and structural progressive collapse in refined analysis model based on material constitutive. The VUSDFLD subroutine in this paper has been verified by an authenticated subroutine, indicating that the CVGM micromechanical fracture criteria can be applied to analyze the progressive collapse of reticulated shells.(4) The simulation of structural progressive collapse of two types of single-layer sandle shaped shells under severe earthquakes is carried out with refined analysis method.