Bridge Progressive Collapse Research

Nowadays, some architectures and bridges suffer widespread failures of structural components that are disproportionate to the initial local failure under accidental circumstances. This process is named progressive collapse, and structural design against progressive collapse has become the focus of research. Most of the researches on progressive collapse are based on architectures; however, researches on bridge progressive collapse are rare. Several typical progressive collapse events are introduced in order to analysis the characteristics of bridge, bridge design methods against progressive collapse are proposed, and the progressive collapse of Zhuzhou City Red Flag road viaduct is simulated by finite element program. The main research outcomes are presented as following:Based on the former researches and relevant design codes, progressive collapse characteristics of bridges and disadvantages of current bridge design methods are analyzed. Bridges are exposed to some accidental loads with strong uncertainty in operation, and the ways of progressive collapse are different by the types of bridge. Current bridge design methods use limit state method based on reliability theory, are applied on the local level but the whole structural system, and take no account of those potential accidental events. However, reliability theory does not apply to the design against progressive collapse.Design system against progressive collapse is brought forward. Design against progressive collapse is divided into three steps of goal. General conception design guarantee reasonable whole arrangement; key element design or non-structural protective measure avoids initial local failure; and alternative load path method or isolation method by segmentation prevents structural progressive collapse after initial local failure. Particular design methods are proposed respectively for beam bridge, beam bridge, suspended bridge and arch bridge.The implementation process of the numerical simulation by LS-DYNA dynamic finite element method is illustrated, involving Nonlinear finite element control equation, Explicit central difference method, Contact and collision, time-step control, computational stability and so on. Commonly-used concrete constitutive relation includes Concrete-Damage Model, Holmquist-Johnson-Cook Model and Kinematic Hardening Cap Model. And Concrete-Damage Model is adopted after comprehensive comparison. Besides, the effect of mesh size and stain rate effect of materials should be taken into consideration in simulation.The progressive collapse process of Zhuzhou City Red Flag road viaduct is introduced in detail. And its nonlinear dynamic finite element model is established to numerical simulation. The result shows that the road viaduct undergoes domino-type progressive collapse. The pier suffers strong collision force when upper hollow slabs fall after initial failure, and then damaged pier leads to fall of adjacent hollow slabs and failure of other piers. Damage degree of the pier is simulated after fall of a certain hollow slab. The result shows that fall of a certain hollow slab could cause local damage, migration and torsion of the pier but collapse, let alone the progressive collapse. Based on these results, key element design and isolation method by segmentation are proposed to the design against progressive collapse for multi-span simply-supported and voided slab beam bridge.