Elasto-plastic progressive collapse analysis based on the integration of the equations of motion

Structural mechanics

This paper considers the progressive collapse analysis of reinforced concrete structures based on the sudden removal of a load-bearing structural element and simulation of the dynamic structural behavior, taking into account the elasto-plastic properties of the material and the degradation of concrete during cracking. A specially developed finite element library is used, which includes triangular and quadrilateral shell finite elements of medium thickness, and a two-node finite element of a spatial frame, which take into account the discrete arrangement of reinforcement and various elasto-plastic material models for concrete and reinforcement. The novelty of the proposed approach lies in the formulation of both: the spatial frame and shell finite elements as a three-dimensional solid body with sequential application of the conventional hypothesis of the for Mindlin-Reissner shells of medium thickness, Timoshenko beams, and the elasto-plastic constitutive models. This makes it possible to achieve sufficiently high reliability of the results for engineering analysis, and on the other hand, a relatively simple implementation, which makes it possible to perform an elasto-plastic dynamic analysis of the entire design model of the structure, and not a separate fragment, in real time from the point of view of practical design. This approach is free from assumptions related to the introduction of a dynamic amplification factor into the quasi-static analysis, which is widely used to solve such problems. The paper provides a numerical example illustrating the effectiveness of using a special structure – an outrigger storey, to prevent progressive collapse, and a comparison of the nonlinear dynamic analysis and the linear one.