عنوان مقاله [English]
Terrible environmental effects maybe consequence of aircraft crash into protective concrete structures. Dynamic loading of aircraft crash are defined as pressure-time curves based on analytical methods in related references such as International Atomic Energy Agency (IAEA). It is obvious that impact loading is a function of many variables such as rigidity, mass and impact angle of projectile, and also rigidity and ductility of target which are mostly ignored in simplified analytical solutions. By developing numerical techniques it is a topic of interest to evaluate the effect of aircraft impact to structures more accurate. Because of its high performance in complex problem analysis such as high velocity impact loading, including interaction and large deformations, numerical approach is an appropriate tool for analyzing crash problems. In the numerical simulation method, details of projectiles and target structures, namely geometry, boundary conditions and interaction between the constituents can be considered to obtain the results with an acceptable accuracy. In crash cases, it is expected to have large variations in results due to huge material and geometric nonlinearities, therefor adjusting the accuracy and stability parameters to control elements erosion and zero energy modes removal is an important problem. In this paper RF-4 aircraft crash to concrete protective shell is investigated using nonlinear finite element analyses applying nonlinear material models for concrete and metals including strain rate for high velocity effects and erosion of elements in large strains to capture penetration and spalling occurrence by ANSYS AUTODYN software. Effect of concrete shell thickness and amount of flexural reinforcement on failure modes have been investigated. It is concluded that concrete shell thickness increasing, causes to reduction of scabbing and penetration depth. Optimum concrete thickness is obtained about 1.5 m, in which failure has significant reduction. In addition thickness increasing more than 1.5 m has not considerable effect on damage intensity and failure mode. Another result was that variation of flexural reinforcement between minimum and maximum amount has more protective effect in thinner thickness and penetration depth in thicker shells has less dependency on flexural reinforcement amount. Sensitivity analyses performed to determine week location, show that bottom cylindrical wall is more vulnerable than upper dome shaped roof.