Numerical Simulation Of Progressive Collapse Of Reinforced Concrete Frame Structures Under Blast Loading

Since the 9.11 terror attack event ,the progressive collapse of civilian buildings has drown the great attention of structure engineering field. The structural progressive collapse is characteristic of the short duration, massive damage and huge losses of lives and property and should be emphasized in the research of blast resistant design.Based on the theory of nonlinear static analysis and nonlinear dynamic analysis, with the help of LS-DYNA code, the collapse of planar and spatial reinforced concrete (RC) frames are modeled numerically when their different critical components are lost under blast loading. The primary work includes: (1) Planar RC frame models with the loss of middle or perimeter base column are developed and analyzed using nonlinear static and dynamic method. The complete collapse progress is realized through the development of effective plastic strain of the structure, the history of velocity and displacement of nodes versus time. The collapse mechanism of structure is analyzed. The entire building's collapse susceptibility is studied due to the loss of different columns. (2) Simple spatial frame models with the loss of middle or perimeter base column are built and studied, applying the nonlinear dynamic method. The collapse susceptibility of the whole structure is determined because of the loss of different columns. The collapse characteristics of spatial frame are compared with that of planar frame. (3) Several measures that can prevent the structural damage and progressive collapse are proposed and discussed based on the existing theories, methods and technologies. A numerical simulation is carried out to verify the validity of the measure.Some conclusions are given as: (1) When the base column of the RC frame is lost under blast loading, the damaged spans lose their direct load-distributing path and exhibit great deflection, then distribute their loads to the residual structure through the adjoin members, which cause large rotation angles and great lateral displacements of the adjacent columns. So progressive collapse occurs as a result of the increase of effects of the upper structure. (2) The collapse of the structure is more sensitive due to the loss of middle column, compared with the loss of perimeter column. It is significant to strengthen the middle column to prevent it from damage under blast loads. (3) The nonlinear static analysis can not reflect some dynamic responses of structural collapse because it neglects the load redistribution after the column is damaged.It is suitable to analyze the structures whose dynamic response can be simply identified. (4) When smear RC material is used, the catenary behavior of beams and slabs does not exhibit obviously in the progress of collapse. An attempt of using desperate RC material should be made. (5) The existing theories, methods and reinforcing technologies can be implemented in enforcement of concrete members and structures; furthermore the seismically designed RC is more effective.