Impact of Aircraft Engines Into Reinforced Concrete Walls

Major components of storage facilities and nuclear power plants are designed using reinforced concrete walls. Accidental or intentional impact of these structures by aircraft is a concern. The potential for penetration of these facilities by the aircraft or its components and the subsequent damage to the contents and release of toxic substances is a major concern. This paper focuses on analyzing the impact of jet engines into heavily reinforced concrete walls. These engines are among the stiffest and most massive components of an aircraft and the most likely to seriously damage and penetrate the reinforced concrete. We model both the engine and the reinforced concrete deformations using failure models for reinforced concrete and metals. Unlike many projectile impact problems, the impacting engine cannot be considered to be rigid. A large amount of energy is consumed in the plastic deformation and fracture of the engine components. The reinforced concrete is modeled using hexahedral elements for the concrete and beam elements for the rebar reinforcement. An advanced three invariant viscoplastic softening cap constitutive model describes the ductile and brittle rate-dependent characteristics of concrete. The rebar is modeled using a rate dependent, strain hardening von Mises formulation with failure controlled by fracture energy dissipation. A similar constitutive model is employed for the shell elements used to represent the engine components. These failure models are included in the FLEX large deformation finite element code which uses an explicit, central difference solution procedure with subcycling to solve the equations of motion. Element erosion using different criteria for concrete and metals is used to remove severely distorted and failed elements. Procedures used to mitigate the deleterious and unrealistic effects of hourglass control and viscoplasticity in the softening and failure regimes are discussed. The results from the computations are compared with experimental data generated by impacting a TF-30 engine into a two foot thick concrete wall.