جستجوی مقالات مرتبط با کلیدواژه « انفجار سطحی » در نشریات گروه « عمران »

The importance of developing passive defense systems requires the study and analysis of structures in this area due to surface explosions. Due to the localization of the explosion phenomenon and the effects and environmental characteristics and existing obstacles, this phenomenon has special complexities. In this research, using the finite element method and with LS-Dyna, the nonlinear behavior of the walls of concrete structures reinforced with GFRP in a war shelter against The charge due to the impact of the surface blast wave is simulated and investigated in a more precise three-dimensional space. In this study, the explosive load, abutment conditions, wall dimensions, fiber material, and characteristics of the materials used are considered the same, and the effect of different reinforcement modes with GFRP sheet and their thickness in these modes is investigated. First, the stress distribution in the walls of the reference concrete structure was calculated and the critical areas of the structure were identified. Then, the response of the walls of the reinforcement structure in the critical area with different thicknesses is compared with each other and with the reference structure and the effect of using this reinforcement method for the walls of the structure against surface explosion loading is determined. Finally, the amount of displacement and stress distribution for different geometric locations of GFRP sheets is calculated and due to the extraction of the optimal state of reinforcement against full coverage of the walls of the structure, the use of this method in this method is considered appropriate.

The increasing number of worldwide terrorist attacks in recent years and danger of enemy air attacks highlights the significance of the secure design of urban structures and explosion mechanics as the passive defense. Iran is no exception from these external threats considering its position in the Middle East. Subway stations are considered as the safe and strategic structures during terrorist operations since they provide a safe route for the transfer of power and equipment. Tunnel structures can be exposed to internal or external explosions. The internal explosions are less likely to occur because it is hard to get an explosive material inside a tunnel due to modern security and control systems inside subway tunnels. However, external blasts are more likely to occur due to the difficulty of detecting and preventing their threat. The present study was carried out in the finite element software LS-DYNA using the ALE (Arbitrary_Lagrangian _Eulerian) technique to simulate and monitor the propagation of the blast pressure waves into the soil. Furthermore, the performance of Tehran metro stations in response to a surface explosion of 11ton TNT, equivalent to the explosive power of the most potent non-nuclear missile, was evaluated. The results from validation model analysis indicated that the pressure waves propagated into the soil as the hemispherical waves as well as the peak pressure values closely matched the predicted values of the technical design manual TM5-855-1. The results also showed that the depths of the crater created by the detonation of 3, 7, and, 11 tons of TNT were 6.5, 9, and 12 m, respectively, for the surface detonation of 11 tons of TNT charge. The affected region of the soil was about 18 m beneath the ground surface, and the duration was almost 0.4 seconds. In addition, although the safety of stations with depths of less than 19 m against the 11-ton explosive charge was not guaranteed, that of the stations deeper than 19 m could be quite ensured.

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.

This paper, using hydro code -LS-DYNA, investigates and observes the dynamic response of cemented bridge under the effect of a number of TNT explosives placed around the columns. Damage quantities will be reported accordingly. To ensure the efficacy of the finite-element method, a comparison is made between numerical and experimental results derived from army explosive ordinance America TM5-855-1. The results indicate that no damage whatsoever occur on the deck under the effect of 500 kilogram TNT explosives at one-meter distance from the bridge base while the has base undergone 2 meters of damage along X direction and 3.5 meters along Y direction. Moreover, the area of damage is at the pile as high as 4 meters, and under 1000 kilogram TNT explosive's blast, the length of the base damage is 3 meters at X direction and 6 meters along Y direction.