Prediction of Penetration Depth for Reinforced Concrete Panels by Projectile Impact

Abstract

Since impact of large commercial aircraft became a serious issue for safety after 9.11 terror, it has been required that nuclear power plant(NPP) structures should be designed considering aircraft impact because failure of NPP structure lead to severe disaster by radiation leakage. When the object considered as projectile like aircraft collides with structure, the impact load that have large in a very short time is generated in the structure. This impact force generates not only global behavior that means conventional behavior of deflection but also local effects that means premature damage occurring in proximal area of impact. The local effects mainly consist of penetration, spalling, scabbing, perforation. Penetration means tunneling into structure by the projectile, scabbing means ejection of fragments of structural material from distal face of the structure, and perforation means complete passage of the projectile through thickness of the structure. Generally, the local effects dont lead to overall collapse of structure, but design for the local effects is necessary because fragments of the structure by scabbing and projectile entering inside of structure by perforation can damage internal facility like reactor of NPP structure.

Penetration of the local effects is the primary behavior occurring immediately after projectile impact, so scabbing and perforation are affected by penetration because scabbing and perforation occur after penetration. Therefore, to evaluate and predict the local effects accurately when NPP structure is designed for the local effects, accurate evaluation and prediction of penetration behavior is required preferentially. In 1997, Forrestal & Tzou suggested penetration mechanism model for concrete target by using dynamic cavity expansion theory. Then, Forrestal et al. (2003) conducted experimental verification of the penetration mechanism model by performing impact test, and suggested semi-analytical prediction formula of penetration depth. However, the semi-analytical formula has limitations to apply to prediction of penetration depth for actual structure size because the previous research performed impact test for not structural member specimen simulating the actual structure but only non-structural specimen of cylinder shape having very large diameter and thick thickness. In addition, the previous research performed the impact test for not several nose shapes of projectile but only ogive nose shape, so there is limitation for lack of experimental evaluation for effect of nose shape on penetration.

In this study, impact tests for Reinforced concrete(RC) panels simulating actual containment wall of NPP and several nose shapes of projectile were performed to predict penetration depth accurately for structural RC member. Then, by utilizing the form of semi-analytical prediction formula of penetration depth widely used by several researchers, undetermined coefficients of the semi-analytical formula were modified by experimental verification and evaluation from the test results. Therefore, penetration depth for structural RC member simulating the actual structure is well predicted by using the modified undetermined coefficients.

In addition, it is expected that the result of this study can be used as basic research to predict penetration depth of several structures difficult to test and to predict scabbing and perforation affected by penetration behavior.