Study On Mechanism And Mode Of Progressive Collapse Of Underground Structure Subjected To Its Internal Blast Loading

Progressive collapse has become an important research area of civil engineering since the partial collapse of the Ronan Point apartment in United Kingdom in1968, and has attracted many experts and academic researchers. However, most scholars focus on the research of progressive collapse of the above-ground buildings and have obtained fruitful results in the past four decades, and few of them is committed to the progressive collapse of underground structures. With the increasing tension of the building land, more and more buildings are being built in the ground. Due to the complexity of the force of the underground structure, it will result in serious disasters if some key component of the underground structures is destroyed.Based on the explosive dynamics theory, the progressive collapse theory and the finite element method of the underground structures, building the three dimensional model of underground structure with ANSYS/LS-DYNA software, using the contact algorithm, solid-fluid interaction algorithm, the erosion algorithm and stress initialization, mechanism and mode of progressive collapse of underground structure subjected to its internal blast loading is studied in this paper. The primary work and achievements can be summarized as follows:(1) Based on the direct simulation method, a new method which is called the improved direct simulation method of analyzing the progressive collapse is proposed. Three methods which are the alternate path method,the direct simulation method and the improved direct simulation method are used to analyze the progressive collapse process of the underground structure subjected to its internal blast loading. The result shows that,the alternate path method overestimates the ability of the anti-progressive collapse of the structure. The improved direct simulation method can simulate the progressive collapse of underground structure accurately. It is more cost-efficient than the direct simulation method and facilitates practical application.(2)To study the impact of the location of the explosive on the process of progressive collapse of underground structure under its internal blast loading, models with explosives in different locations are established. The result shows that, the response of the column in the ground floor being destroyed is more severe than that of the column in the same location in the basement. At the same floor, the response of the middle column being destroyed is the most severe, followed by the side column, and finally the corner column.(3)To study the influence of the floor height and the burial depth on the process of progressive collapse of underground structure under its internal blast loading in the same location,models with different floor height and the same burial depth or different burial depths and the same floor height are established. The result shows that, the variety of the floor height has little impact on the process of progressive collapse of underground structure. The deeper the structure is buried, the faster the underground structure collapses.(4)Based on the simple slope slip theory, the formula for calculating the collapse radius of the surface casing when the progressive collapse of underground structure under its internal blast load occurs is proposed, and is proved by numerical simulation. The formula proposed provides a helpful reference for anti-declining and anti-progressive collapse design of adjacent buildings.(5)Based on the dynamic response processes of the underground structures subjected to their internal blast loading in different conditions, the modes of the progressive collapse of underground structures are proposed.The analysis results in this paper can give some reference for research and engineering applications on the progressive collapse of underground structure.