Dynamic Progressive Collapse Simulation Analysis Of 3-D Steel Frame Structures

At present, the design of the structural system under the normal loads has been prefect. However, abnormal loads may be lead to structures with deficient inherent resistance to progressive collapse, and this usually causes disastrous casualty and enormous loss of economy. The text takes into account dynamic progressive collapse simulation analysis of 3-D Steel Frame Structures with ANSYS/LS-DYNA finite element software to research collapsing mechanisms of structures and design structures that have sufficient resistance to progressive collapse.For one thing, in order to validate the correctness of ANSYS/LS-DYNA software using progressive collapse simulation analysis, it is necessary to analyze and compare the results of the computational model of a 2-story and 2-bay planar steel frame structures with the example. Because the progressive collapse process is dynamic and nonlinear, and static analysis can't account for dynamic response of structures in collopsing, the ratio of the maximum response for dynamic case versus the static case (Dynamic Increase Factor) to show the extent of dynamic effects for 3-D steel frame structures in research; Structures is at rest with deformation due to the long effects of gravity loads before columns failure, so the responsor of initial deformation against steel frame structures is considered for according with practice in computing. Basing on this case, comparing results of abnormal loads with different locations against structures, situations of loads redistribution against different locations elements, and transferable results of dynamic loads along stories or bays as the number of stories or bays increasing, collapsing mechanisms of 3-D steel frame structures can be studied, and the effects of progressive collapse that a variety of factors act on steel frame structures can be more understand. When one or two columns are failure in the first floor, the whole process of the progressive collapse is simulated, types of the progressive collapse are ascertained, and structures collapsing influences caused by asymmetric distribution of mass are researched. Adopting 3-story and 4-bay steel frame structures producing progressive collapse under various cases to be studying objects, and then chosing tying intension method to withstand collapse. Analytical results from this research demonstrate that dynamic effects strongly influence the extent to which plasticity spreads from the site of the original member failure; Aiming for vertical displacements at node F and dynamic increase factors of plastic rotation angles, results of abnormal loads with different locations give rise to some distinctions; As for loads redistribution against different locations elements for the first floor, axial forces of interior columns are stronger than exterior ones, but moments of exterior columns and beams are stronger than interior ones; While effects of lateral loads redistribution by initial deformation are obvious, ones of vertical loads redistribution are little; Increasing storiers participate in dynamic loads redistribution, and loads doesn't spread to the additional bay as the number of bays increasing. As far as collapsing forms, two adjacent enterior or interior columns failures in the first floor cause Mixed-type collapse and Pancake-type collapse respectively; In the case of collapsing properties, both of them are attributed to Instability-type collapse. When the remains of structures can't accept increasing loads redistribution causing by asymmetric distribution of mass, it will accelerate collapsing destruction. Tying intension method for steel frame structures is effective to resist progressive collapse; By this method, steel frame structures with large vertical displacements are reconstructed and ones with progressive collapse can avoid collapsing destruction; Structural integrity and continuity is intensified as the tying interval diminishing, and the effects of resisting progressive collapse are noticeable.At last, some suggestions can be expounded according to correlative conclusions, and the relative contents of the article can provide some referenced values about progressive collapse of steel frame structures.