جستجوی مقالات مرتبط با کلیدواژه « explosion » در نشریات گروه « پدافند غیرعامل »

Dams are one of the vital components of human societies and one of the strategically important assets of any society with a significant role in the sustainable development of the country. In this research, the damage caused by the blast of a double curvature arch concrete dam has been evaluated according to the mean velocity and frequency caused by the blast in the near-field. The model of the material used is the numerical simulation include the explosives, air, water, and concrete, which has been modeled. The problem-solving method used to apply the blast in modeling is Load Blast Enhanced. Using this method, the propagation of the pressure wave caused by the blast and finding the critical points of the dam body against the blast have been investigated. Then, the structural responses and the dam damage characteristics in different blast scenarios have been investigated according to the change in the blast depth, the distance from the concrete dam body, and the blast load. Also, by using vibration parameters such as peak velocity summation (PVS) and mean frequency (MF), the combined spectrum has been evaluated and proposed as a way to design a blast-resistant dam and find a safe standoff distance in case of emergency. Finally, two PVS-MF spectra have been suggested according to the charge weight and their distance for optimal and useful classification of dam damage according to three modes: slight, moderate, and severe, for initial and critical evaluation.

Due to the emergence of terrorist threats in recent years, in the form of air attacks, sudden explosions of ammunition and suicide bombers around special and strategically important structures such as arched concrete dams that have a very high capacity for storing surface water, the performance and design of this The threatened structures are mandatory and their possible failure can cause a huge flood, which can cause huge financial and human losses downstream. Therefore, the purpose of this research is to identify the nature of the explosion along with investigating the vulnerability of concrete dams. arching and investigating the parameters affecting the non-linear response of the structure by comparing the location change of the dam crest and the amount of compressive and tensile damage for dam-piling and dam-piling-reservoir systems due to explosion. The results of the sensitivity analysis for the linear and non-linear behavior of concrete showed that it is necessary to model the non-linear behavior of concrete in order to investigate the behavior of arched concrete dams against dynamic loads, especially loads of an impact nature such as explosion. In the linear mode, the changes in the amount of the explosive material in the time history of the location change are not noticeable and the permanent location change of the crown is very close to each other for all the explosive loading conditions and finally returns to the final value of the static condition. Also, comparing the outputs of linear and non-linear analysis showed that the difference between the answers from the explosion of 500 kg of TNT at a distance of 8 meters to 1500 kg of TNT at a distance of 2 meters has an increasing trend, so that the difference between the response of the change of location The background values for the linear and non-linear states are 18.7% and 25.2%, respectively, which emphasized the necessity of considering the non-linear behavior of concrete, especially for explosion in the near field. By comparing the maximum displacement responses of the full tank state, it was concluded that the presence of the tank reduces the influence of the reference point position and the amount of explosive charge on the crown response, compared to the empty tank state. Also, the results showed that in the full tank state The extent of pressure vulnerability is greater for the downstream, which indicates the application of hydrodynamic pressure of reservoir water to the downstream elements of the dam, and this happened due to the shape of the arch, but in the case of an empty reservoir, due to the absence of hydrodynamic pressure, the extent of this The damage was less.

The issue of explosion is one of the new issues that cause different events or intentional events and the behavior of structural members under the load of explosion has been the subject of many research projects in recent years. Since it is not possible to perform experimental experiments on a real dam and it is not a reasonable practice, and considering that today a reliable solution by computer and the development of finite element method has made it possible to model these problems, so the problem of underwater explosion and Its effect on the arched concrete dam can be modeled with this method, which leads to reliable results. The study also showed an arched dam with a height of 141.73 meters and a width of 184 meters and a central angle of 133 degrees and a thickness of about 3.66 meters in the crown. And creates an explosion wave. After performing the accuracy and reliability of the explosion by SPH method, the weight of TNT was analyzed for 500 and 1000 kg in the tank and outside the tank. The effect of explosive amount on the horizontal displacement of the dam crown is significant and with increasing the weight of TNT From 100 to 500 and 1000 kg, 20 and 100% increase in displacement were observed, respectively. The results also showed that with increasing the amount of explosive, the amount of energy consumed by the fluid also increases. Explosion inside the tank due to creating a wave in the fluid and propagation in the direction of hydrostatic pressure causes absolute pressure and more displacement.

The purpose of this study is to investigate the effect of blast wave trap on reducing the detonation effect in tunnels and its effect on reducing the load on the explosion-proof door end of the tunnels and to analyze the types of doors in order to determine which type has the best performance against detonation. To this end, the propagation of the waves induced by the explosion of TNT-type beams with different weights is simulated in the tunnel span with a blast wave trap. The AUTODYN hydrocode is used for numerical simulations. The simulation and numerical modeling are compared and validated with analytical and empirical relationships of previous studies. Considering the maximum pressure applied to the tunnel intersection, the proper location of the blast wave trap, the optimal blast wave trap length and its effect on the maximum value of the tunnel end pressure are investigated. The output of the load applied to the end of the tunnel (location of the explosion-proof door) resulting from this time-dependent explosive load modeling is transferred to ABAQUS software to analyze and compare the types of explosion-proof doors. From the point of the load exerted on explosion-proof doors, hinged doors with different flat and arched geometries are analyzed using ABAQUS software and the maximum displacement and von-Mises stress of the doors are compared. The results show that the arch door performs better than the flat door.

This study has been conducted to investigate the ability of prestressed concrete slabs against explosion with passive defense objectives by the structural method. In this research, one-way and two-way concrete slabs have been modeled with Abaqus finite element software.  The dynamic analysis has been performed by the explicit step-by-step time history method. The non-linear plastic failure model has been used for the concrete behavior, whilst a linear model has been used for the steel and prestressed tendons. Explosive loading has been applied to the slab samples experimentally using the CONWEP model and free boundary conditions have been defined for the edges of the studied slabs. The results of the finite element model shows that the maximum stress in prestressed concrete reaches three times the stress experienced in the reinforced concrete. Also, prestressing the slab reduces the maximum deformation by about 3 cm compared to the reinforced concrete slab. The results show that the behavior of concrete against explosion is remarkably improved by prestressing. However, the optimal amount of prestressing and the distance of the tendons required to improve the slab behavior against explosion, can be calculated through more modeling. It can be said with certainty that prestressing is a good way to improve the behavior of slabs against explosion in explosion-proof defensive fortifications. The results show that the effect of slab geometry, whether it is one-way or two-way and the location of the explosion, affect the values of stress and deflection due to the explosive load.

Concrete retaining walls gratitude to their significant-high mass are considered a protective barrier and explosion resistance. The fabricated walls generally made of reinforced or fiber-reinforced concrete. This study deals with investigating the destructive effects of the explosion on retaining walls made of reinforced and fiber-reinforced concrete. For this purpose, the intended wall simulated by Abaqus software with various blast loads at different distances. Then, to investigate the damage caused by the explosion, the explosives were modeled in three positions attached to the wall, at a distance of one meter and at a distance of ten meters from the wall, perpendicular to the highest midpoint of the structure and the junction of wall and ground.The modeling results showed that the explosion at the connection of the wall to the ground has more destructive effects than the detonation at the highest point of the wall. The failure load of the reinforced concrete wall and fiber-reinforced concrete at the junction of the wall to the ground equals 5 kg C4 and 10 kg TNT and 15 kg C4 and 15 kg TNT at attached and distance of one meter from the wall respectively. The failure load was equal to 60 kg C4 and 70 kg TNT and 90 kg C4 and 100 kg TNT for reinforced concrete and fiber-reinforced concrete wall respectively at a distance of 10 meters from the wall and at the junction of the wall to the ground. Also, the explosion at the position attached to the wall and one meter from the wall showed local effects on the wall and occasion local damage. However, the explosion at a distance of ten meters did not act locally due to the large distance of the explosion from the wall, and more explosives are needed to destroy the wall at this distance.

Today, increasing the flexibility and strength of structures against explosions and impacts is one of the main concerns of governmental organizations across the world. The consideration of progressive destruction has added to the importance of structural strength against explosions and impacts in recent years. In this regard, most of the existing structures do not have adequate resistance and flexibility against explosions and impacts. The present study investigates the behavior of a one-sided concrete slab in four cases, including the reinforced and non-reinforced concrete, using glass-fiber-reinforced plastic (GFRP) plates in a gravity bearing building system on and under the slab explosive-loaded as a one-story structure with a span against direct explosive pressure. A TNT explosion model in the form of a 0.5-kg cube was applied to evaluate the deflection of the slabs in the ANSYS software which is capable of analyzing the explosion-load behavior of the structure. The loading parameters obtained from geometric modeling and other parameters required by the structure were modeled as 3D objects. The results indicated that the use of GFRP and carbon fiber reinforced polymer (CFRP) reinforcement plates were effective in reducing the displacement of the slabs due to the explosion load. They prevented the spalling and collapse of slabs and reduced slab displacement by 62%. In addition, an increase in the thickness of slabs, the diameter of GFRP bars, the number of CFRP layers, and their slab coverage percentage dramatically reduced the deflection of the samples.

Explosions at the entrance of tunnels and underground spaces can lead to losses. To decrease side effects of such explosions, some approaches like dead_end, bends, geometric barriers and anti-explosion doors are available. Using geometric barriers, especially the waveguides, is the most commonly used and economical way. The purpose of this paper is to investigate the effect of the angle of rotation of the longitudinal axis (bend) and the local variation of the tunnel area on reducing the impact of explosions. Appropriate angle of rotation of the longitudinal axis and suitable location for local variation of the tunnel cross section in line with the tunnel are calculated, by numerical analysis, using Abaqus software.  Finally, proper characteristics are used to propose a method, requiring the least drilling in construction (the most economical method), and generating the highest reduction in the effects of the explosion (the highest vulnerability reduction) in explosions near and away from the span. The results show that the localized change in the tunnel cross-section at the end of the direct path and the change in the angle of rotation of the long axis from 135 ° to 90 ° (90 °) will lead to the greatest reduction in pressure.

In passive defense projects, retrofitting of masonry walls has especial importance. One of the commonly used methods for seismic retrofitting of the walls is the implementation of a reinforced shotcrete layer. The behavior of walls strengthened with shotcrete against earthquakes have been studied by many researchers. However, the behavior of the walls against the explosion has received less attention and the effect of the mesh specification and the thickness of the shotcrete against this type of loading has not been investigated. In this research, the damage index is investigated for 700kg TNT explosion located at distances of 3,9 and 15 m from a masonry wall. In steel mesh, when the distance between the bars is 10 and 15 cm, and shotcrete layer thickness of 5, 10 and 15 cm damage index investigation is performed. Finally, 18 different models of steel mesh and thickness of shotcrete are introduced. With shotcrete strengthening, the wall failure index and the maximum displacement of the wall center is decreased. In all models, due to the closeness of the explosion to the wall, the wall was eventually destroyed and the effect of the reinforcement spacings on reducing the wall fracture was negligible. In contrast, the thickness of the wall has a greater role in reducing the tensile damage index of the wall.

Nowadays, one of the most common methods for water transmission is through underground tunnels. Tunnels are in line with the fundamental principle of the passive defense for protection of water resources and are able to prevent any potential risks to water transmission lines. In this research, a numerical study has been employed to investigate the effects of surface explosion on the water transmission tunnels. Herein, by changing the distance of explosive materials as well as the thickness of concrete segments, response displacements and explosion effects on the concrete segments have been calculated. For this purpose, three concrete segments with the thicknesses of 0.2, 0.3 and 0.4 m were selected and subjected to the explosive materials located 0.5, 1 and 2 m away from them. The obtained results showed that the concrete segments with the thicknesses of 0.2 and 0.3 m experienced significant damage when subjected to 20 lb. explosive material at the distance of 0.5 m. It was found that burying the structures or embankments of the structures were among the best methods for damping the blast waves.

The explosion occurrence is the most likely events that may occur during a fire incident. This paper studies on nonlinear response of steel column against an explosion during fire event by using dynamic explicit finite element scheme. In this study, the effect of temperature of steel surface at the moment of explosion and scaled distance parameter are investigated. The results show that increasing temperature to more than 400 °C may cause large displacements and ultimately led to collapse the column. It is shown that increasing the temperature of the instant explosion for more intense explosions is less effective than explosions with larger scaled distance (Z).

The specification of underground structures, and investigation of earth-penetrating weapons, and ultimately the major and minor impacts resulted from an invasion on these structures is one of the significant issues that each country may encounter. In other word, understanding the materials and applicable methods in the construction of buried components, to defend against the potential threats, has an important role in terms of the management construction’s principals, like time management, expenditure, and quality. Moreover, according to questionnaires and the experts’ opinions, utilization of the quantitative methods such as AHP, and the EXPERT CHIOCE software provide the opportunity to identify such indexes and alternatives. This study shows that the fiber concrete materials, reinforced concrete, nano materials, and FRP, introduce the best efficiency and function compare to other alternatives. As such, these materials are highly applicable not only in the construction of reinforced or fiber concrete, and Lattice Panel, but also in the process of retrofitting.

According to the importance of windows in the building at the time of the explosion, their proper designing in compliance with all technical and security standards, particularly the standard of passive defense in designing building is crucial. In this regard, the glass of windows has had almost less resistance against explosions confusion and at the time of explosion they collapse and debris are thrown around, that is almost the major cause of casualties of bombings. In this paper, the impact of resistance of the proportions of the windows are evaluated against explosions and then by examining different models, one perfect model has been designed. To this end, the proposed method has designed four types of window with the same area and different proportions that has been tested with ABAQUS. Results showed that the stretched proportions of the windows have better performance against explosion. This can help engineers to select the most effective method of constructing, retrofitting and upgrading for better performance of proportion of windows in an explosion in the future.

An accurate and safer analysis for structure is possible if we can identify factors in the analysis more accurately. One of the important factors in the analysis is the identification the kind and intensity of structural loading. Among the types of loading, especially dynamic loads and impact loads resulting from the explosion, is far more complicated and difficult to determine. According to lab explosion modeling problems, using numerical modeling to analyze these phenomena can be reasonable. Uses grid methods like Finite element method caused a numerical error due to intense deformation and high velocity of blast. In this paper, underwater explosion was modeled and programmed with numerical mesh-less method, Smooth Particle Hydrodynamics (SPH), using Fortran programming language and explosion pressure and water level changes in the blast were studied. Finally the solving problem is compared with empirical relation. The results of this model are very similar to empirical relationship. This program can be used for underwater explosions modeling and the results can be used to determine pressures and impacts on marine structures.

Underground tunnels, play an important role in protecting important installations from various forces including explosions. Surface and penetrating blasts could deteriorate tunnel surcharge, enveloping space and exerting a lot of load on the tunnel lining. Therefore, to withstand the blast, blast load should be taken into account in tunnel design, in such a way that the tunnel could bear the loading caused by devastation of surrounding soil and rock. One of the widely used criteria for assessing failure of tunnel and underground structures due to blast loads is “Peak Particle Velocity”. In the present paper, this criterion is employed in order to investigate the behavior of underground tunnels under blast load using of explicit dynamic nonlinear finite element software LSDYNA. Then, the effect of cross-section on tunnel under blast load is investigated by comparing the peak participle velocity parameter, displacement of center of roof and Von-Mises stress on the rectangular and horseshoe cross-section. It has been shown that, with equal dimension, the environment enveloping the rectangular cross-section possesses higher resistance than horseshoe cross section.

xPlanes, helicopters and other military aircrafts are one of the important features of a country's military power. Therefore, maintenance of this equipment from potential threats and vulnerabilities in the domain of passive defense appear to be necessary. Results of previous studies on aircraft hangars had been predominantly in the range of static loads and little research has been done in the field of special loads such as explosion. . Whit due attention to the spread of terrorist attacks, necessity of appropriate operation of these structures under blast loads is become clarified. Therefore in this research, behavior of semi cylindrical concrete hangar under blast loading of 1 tone TNT at near, intermediate and far from hangar has investigated. The location of explosives substance was considered in three state of perpendicular to the hangar axis in mid-length, along the axis in front of the hangar door and in front of hangar entrance with a deviation of 45 degrees. Modeling had been done with ABAQUS software. Study parameters included: the stresses created in the body of the hangar, horizontal and vertical displacement of the crown and the air pressure in the tunnel. The failure modes of the hangar also discussed in the different cases and safe scaled distance is obtained. Using the results of this study, safe distance for arbitrary values of explosives substance could be estimated. It is expected during this distance, no failure occurs in the body of hangar.

The entrance of defensive underground structures is vulnerable to blast loading. Deliberate use of prominence in the final lining of the tunnel, one of the ways of dealing with the effects of the blast wave and reduce the vulnerability to degradation. In this study, the software (AUTODYN) the explosions in the line with the distance from the mouth of the tunnel simulated and then the effects of deliberate prominence at the end of the tunnel cover Performed directly.The amount of airflow (overpressure) discussed and finally considering the size prominence of the tunnel and reducing the amount of pressure are expressed. The results show that using prominence can Reduce overpressure inside the tunnel For acceptable.

There are major differences between the behavior of explosive and another loads due to the nature of the explosive charges and the small duration of shock loads. Study on underwater explosion effects is important for evaluation of damages caused by the terrorist activities such as hydraulic structures and marine docks, dams, transmission lines in the seabed and etc. The high cost of laboratory modeling and explosion risks due to blast loads and sudden and severe deformations caused by an explosive charges in a short time, justify the use of numerical methods. In this paper the experimental results were compared with grid base numerical modeling (Eulerian and Lagrangian nature) and a meshless method (smooth particles hydrodynamics, called SPH). The numerical simulations are carried out based on the Ls-Dyna software and the maximum distance from the center of the explosion pressure, pressure time history curves at different points, and changes in water level are compared in different numerical methods. The results show that, Lagrangian approach and meshless method presents higher explosion pressure than Eulerian approach. Also, using the meshless methods, the explosion pressure can be determined in closer distance to a charge center, compared to another grid base methods.

The manner by which the shock waves, generated by an explosion, propagate in the medium surrounding an underground structure is very complex. This complexity is due to the interaction between the structure and the surrounding soil and the attenuation of the shock waves in the soil layers. In this research, by simulating the shock waves equivalent to the explosion of 900 kg of TNT, the effects of different parameters such as soil type, concrete type, and buried depth on maximum strain at the top and on the mid-length of the structure is investigated. For simulating the loading due to explosion, the finite element software, ABAQUS, has been utilized. Also, to numerically simulate the nonlinear behavior of the medium surrounding the underground structure, the Mohr-Columb model has been used. In view of the results obtained from the numerical analysis of various models, it was found that the parameter of underground structure depth has the greatest effect on the amount of maximum strain produced in the structure, followed by soil and concrete type.

One of the ways for reduction the effects of blast wave in tunnel lead to an underground structure is using from blast wave trap. In this paper discussed about the effect of angle's blast wave trap on reducing overpressure entered in main row of tunnel. In this regard, propagation's blast wave of bombs with different weights simulated in distance 1 meter from entrance tunnels with blast wave trap with angle 45,90,135 degrees. simulation of this regard have been done by numerical autodyn software. According to rate of overpressure intered in the place of the bend and overpressure have been obtained for main way ofter bend, percent of increase of preesure obtained. the result of study present that, with increasing angle's blast wave trap, percent of decrease preesure will be biger and its rate depend on overpressure intered in tunnel before bend.