Reliability of double-wall containment against the impact of hard projectiles

Abstract Effectiveness of single or double-wall containment structures against a possible strike of projectiles, missiles or airplanes is well researched. However, how the uncertainties involved in the various design parameters influence the reliability of the containment is not very well known. In a double-wall containment structure, as name implies, there are two walls – an outer thick reinforced concrete (RC) wall and an inner thin steel shell/wall. In the present study, a simple probabilistic procedure based on Monte Carlo simulation technique is presented to study the reliability of double-wall containment structures against the impact of external hard projectiles on outer RC wall for varying impact velocities. In order to illustrate the proposed methodology, an idealized double-wall containment structure and a hard projectile were chosen. The probability of failure and the reliability indices of the selected double-wall containment structure were obtained for different striking velocities of the projectile and safety of the containment was correlated with the ballistic limit of the outer RC wall. The results of the study show that the double-wall containment is “safe enough” against the impact of the selected projectile if the projectile nominal velocity is less than 65% of the containment outer wall's nominal ballistic limit ( V BL ). Results also show that under the given uncertainties, if the nominal impact velocity is less than 65% of the nominal ballistic limit of the outer RC wall (i.e. 0.65 V BL ), failure probability of the containment is almost zero. However, when impact velocity is more than 0.90 V BL , failure probability of the double-wall containment is quite high. It was also observed that a little change in the impact velocity over 0.90 V BL may cause a phenomenal change in the containment reliability due to substantial change in the residual kinetic energy of the projectile. A number of sensitivity studies have also been carried out to obtain the results of practical interest.