RESEARCH ON THE OVERTURNING MECHANISM OF HIGH RISE BUILDINGS UNDER NUCLEAR BLAST LOADING

A large number of civil air defense basements in China are constructed under high rise buildings which have large stiffness and strength. High rise buildings may be deformed, damaged and destroyed extensively under blast loading. During this process, severe overturning action may be imposed to the basement shelter attached to the building and make it overturned, resulting in the lost of defense function of the basement. This paper focuses on the overturning mechanism of basement attached to high rise buildings under nuclear blast loading, which not only relates to the interaction between the upper structure, the base and the foundation, but also depends on nonlinear material properties, nonlinear contact, rate dependent straining and compression hardening of soil. This paper presents some recent works on this topic made by authors, including: (1) concrete masonry walls subjected to blast loadings were analyzed with the explicit dynamic finite element program LS-DYNA; (2) the overturning mechanism of the basement attached to high rise buildings under nuclear blast loading was investigated with the finite element program MSC.Marc with incorporated subroutines for modified D-P soil model, Thufiber model of reinforced concrete component, and spring model for soil-pile interface. The numerical model was established considering the interactions between the super structure, the basement, the pile foundation and the soil. The numerical results show the basement attached to high rise reinforced concrete shear wall structures may incline more than 3°―5° or even collapse completely, resulting in the lost of its protective functions. The pile foundation can strengthen considerably the vertical and rotational constraints on the basement and reduce the overturning effects on the basement significantly, thus, it can be used for resisting the overturning of basements attached to high rise buildings. On the basis of rational design demand, the variation of length, spacing and diameter of piles will not affect the overturning of the basement considerably.