DEM simulations of the progressive collapse of framed structures

Progressive collapse of framed structures is a complex topic going beyond the usual tools of structural mechanics. The analogy with the propagation of damage in the framework of fracture mechanics has already brought some theoretical results, especially when the energy fluxes are analyzed. Nevertheless, the difficulty to get representative experimental data avoids proposing and eventually proving the effectiveness of new theories modeling collapsing frames with equivalent homogeneous cracking continua (or foams). Therefore, reliable computer simulations based on widely accepted methods are necessary. Since traditional FEM are inapplicable when a structure looses rigidity, DEM have been used to run the simulations shown throughout this paper. The advantages, the limits and the problems of this approach are discussed and particular attention is paid to the effects of impacts between falling elements and the structural members

Finite Element Simulation of Dense Wire Packings

A finite element program is presented to simulate the process of packing and coiling elastic wires in two- and three-dimensional confining cavities. The wire is represented by third order beam elements and embedded into a corotational formulation to capture the geometric nonlinearity resulting from large rotations and deformations. The hyperbolic equations of motion are integrated in time using two different integration methods from the Newmark family: an implicit iterative Newton-Raphson line search solver, and an explicit predictor-corrector scheme, both with adaptive time stepping. These two approaches reveal fundamentally different suitability for the problem of strongly self-interacting bodies found in densely packed cavities. Generalizing the spherical confinement symmetry investigated in recent studies, the packing of a wire in hard ellipsoidal cavities is simulated in the frictionless elastic limit. Evidence is given that packings in oblate spheroids and scalene ellipsoids are energetically preferred to spheres.Comment: 17 pages, 7 figures, 1 tabl