مهندسی عمران شریف (Feb 2021)
DAMAGE REDUCTION DUE TO AIRCRAFT CRASH TO CONCRETE PROTECTIVE STRUCTURES
Abstract
Terrible environmental effects may be the consequence of aircraft crash into protective concrete structures. Dynamic loading of aircraft crash is 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 that are mostly ignored in simplified analytical solutions. By developing numerical techniques, it is a topic of interest to evaluate the effect of aircraft impact against structures more accurately. 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 acceptable accuracy. In the crash cases, it is expected to have large variations in results due to huge material and geometric nonlinearities, thus adjusting the accuracy and stability parameters to control element erosion and zero energy mode removal is an important problem. In this paper, RF-4E aircraft crash to concrete protective shell is investigated using nonlinear finite element analyses by 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. Effects of concrete shell thickness and amount of flexural reinforcement on failure modes were investigated. It was concluded that increasing the concrete shell thickness caused a reduction in scabbing and penetration depth. Optimum concrete thickness is obtained about 1.5 m, in which failure has a significant reduction. In addition, thickness increasing more than 1.5 m has no considerable effect on damage intensity and failure mode. Another result was that variation of flexural reinforcement between minimum and maximum amounts had more protective effect on thinner thickness and penetration depth in thicker shells had lower dependency on flexural reinforcement amount. Sensitivity analyses performed to determine week location showed that the bottom cylindrical wall was more vulnerable than the upper dome shaped roof.
Keywords
