Analysis of explosive Loading on Underground Structures under Surface Explosions

Nowdays due to the increasing trend of insecurity and terrorist attacks, certainly structural engineers are aware to the importance of the proper design of secure structures against blast loading. In the field, the purpose of all designs is a structure with features which can have suitable resistance against blast loading, but for such a project with these specifications the operating costs will be very high. For solving this problem buried underground structures were considered. The reason for choosing such structures make greater use of the property to anchor the soil around of structure, reducing the structural weight, Sensible reduction of inertial forces and using the attenuation and viscoelastic property of the soil for reducing the amplitude of the shock wave from the surface and buried explosion and destructive effects of radiation. Currently the air and missile attacks on underground structures is considered one of the most important issues in studies related to this field of Civil Engineering Sciences.In the literature it has been suggested a lot of relation to obtain the shock ground parameters like peak particle velocity and wave pressure distribution in the continuous environment and free field experimentally and semi-analytical. The phenomenon of explosion is a type of high strain rate problem, which requires dynamic analysis to solve it. Also, due to the interaction between underground and soil structures, the analysis of these structures under the influence of any type of load is a nonlinear analysis. Thus, the analysis of underground explosive structures is a type of high strain rate problem, which requires a nonlinear dynamic analysis to solve it. There are two implicit and explicit solving methods for dynamic analysis, which, given the conditions of the explosion, analyze them as an explicit integral solution. Recently, numerical simulation techniques have become widely used as a new method for calculating nonlinear dynamic loads. Based on the results of the researchers, among the open source software, the AUTODYN software, due to its high power in solving problems with very high strain rates, provides good results for simulation and analysis of explosion problems. On the other hand, explosive loading of underground structures is often carried out based on theoretical and empirical research. In this research, numerical simulation method has been used for analyzing and simulating the effect of surface explosion on underground structures. Also, all simulation steps are performed using the AUTODYN hydrocode. In order to analyze the loading and response of underground structures, the effect of explosive charge weight and depth of the structure burial has been investigated and numerical results have been compared with the relationships presented in the authoritative scientific references and American guidelines. In the process of simulation conducted, to assess the dynamic response of structures and investigate shock ground parameters such as peak particle velocity, pressure and displacement, soil-structure interaction has intended. As well as the effect of changes in the factors affecting the explosion of underground structures in order to achieve a safe burial depth has been investigated. Finally, suggestions are being made to improve the loading of these structures.