اثرات نسبت تقویت و چیدمان در رفتار سازه یک ساختمان هسته ای تحت تاثیر هواپیما

This study presents the effectiveness of the rebar ratio and the arrangement of reinforced concrete (RC) structures on the structural behavior of nuclear buildings under aircraft impact using a finite element (FE) approach. A simplified model of a fictitious nuclear building using RC structures was fully modeled. The aircraft model of a Boeing 767-400 was used for impact simulation and was developed and verified with a conventional impact force–time history curve. The IRIS Punching test was used to validate the damage prediction capabilities of the RC wall under impact loading. With regard to the different rebar ratios and rebar arrangements of a nuclear RC building, the structural behavior of a building under aircraft impact was investigated. The structural behavior investigated included plastic deformation, displacement, energy dissipation, perforation/penetration depth and scabbing area. The results showed that the rebar ratio has a significant effect on withstanding aircraft impact and reducing local damage. With four layers of rebar, the RC wall absorbed and dissipated the impact energy more than once with only two layers of rebar for the same rebar ratio.

An aircraft crashing into a structure is considered to be extremely hazardous and could almost certainly cause extensive damage to a building. The evaluation of airplanes crashing into a fictitious auxiliary nuclear building has become necessary since the U.S. Nuclear Regulatory Commission (U.S. NRC) has determined that the impact of a large, commercial aircraft is a beyond-design-basis event. To provide a calculation method for the equivalent impact force, Riera (1968) proposed a formula to evaluate the reaction–time relationship in the case of an accidental impact of a large commercial aircraft against a rigid wall. According to Riera's proposal, the total reaction P(t) is the function of crushing force Pc(x), mass per unit length μ(x), and velocity of uncrushed portion: P(t) = Pc(x) + μ(x)v2(t). Subsequently, Wolf et al. (1978) checked the validity of Riera's approach on calculating the impact force of an aircraft crash using Boeing 707 impacting into a rigid target. Bahar (1978) and Kar (1979) modified Riera's equation by introducing the coefficient α into the second term of Riera's equation. Based on the experimental results of the full-scale aircraft impact test of an F-4 Phantom on a massive target, Sugano et al. (1993a) determined the values of α as from 0.7 to 1.0. Another work of Sugano et al. (1993b) was a series of engine model impact tests on a reinforced concrete panel. Riedel et al. (2010) also conducted a series of scaled aircraft engine impact tests on reinforced UHPC panels. Local damage of reinforced concrete and reinforced UHPC panels was determined and classified into four to five major modes. The study of Zerna et al. (1976) dealt with the optimization of reinforcements for resisting impact forces resulting from an aircraft crash. Dundulis et al. (2007) studied nonlinear behavior of an INPP ALS building subjected to a Phantom RF-43E crash. Jin et al. (2011) developed an FE model of a large aircraft engine and evaluated the localized damage of a concrete wall. The behavior of nuclear power plant containment subjected to an aircraft crash was also carried out by Abbas et al. (1996). Arros and Doumbalski (2007) performed an analysis of a Boeing 747-400 aircraft impact on a concrete building using LS-DYNA. In Arros’ works, the comparison of shock loading obtained from the Riera force history analysis with that from the missile-target interaction analysis was carried out, and sensitivity studies were also conducted. In the preliminary evaluation of aircraft impact on a nuclear containment of Frano and Forasassi (2012), the effects of different wall thicknesses and reinforced/prestressed concrete was carried out as a sensitive analysis. Although the mentioned studies focused on a wide range of aircraft impact investigation, the evaluation of the influence of the rebar ratio and arrangement on structural behavior of an auxiliary nuclear building has still not been carried out. In this study, the effect of the rebar (horizontal rebar and vertical rebar is called “rebar”) ratio and the number of rebar layers on local and global damage of the auxiliary nuclear building was investigated while the wall thickness was assumed to be constant. A three-dimensional numerical impact simulation of a Boeing 767-400 into the nuclear building was modeled using the LS-DYNA program. The fictitious auxiliary nuclear building model, adopted and modified from the work of Arros and Doumbalski (2007), was used. The numerical analysis focused on the following issues: • Impact force–time history was verified by comparing with that of the Riera approach. • The damage prediction capabilities of the RC wall under impact loading were validated using the IRIS Punching test. • The structural behavior of the building with different rebar ratio was investigated. • The analyses of RC walls with two, three, and four layers of rebar were performed respectively to investigate the influence of the rebar arrangement in regard to the punching resistance of RC walls. The numerical results for the structural behavior, including plastic deformation, displacement, energy dissipation, perforation/penetration depth and scabbing area were discussed. An efficient design of RC wall was recommended.

A reliable nonlinear finite element model of a nuclear power plant building under aircraft impact was developed, and the structural components and their contacts were fully modeled. The aircraft impact force-time history was verified by comparing with that obtained using the Riera function. The validation of the damage prediction capabilities of the RC wall under impact loading was assessed by verifying using IRIS impact tests. A parametric study was performed to investigate the influences of the horizontal and vertical rebar ratio and rebar arrangement to the behavior of nuclear power plant structure. The following conclusions were obtained: (1) The rebar ratio had a significant effect on reducing the local damage and increasing the energy absorption ability of the overall building, which may lead to a higher displacement of the building. However, the displacement of the building did not increase significantly when the rebar ratio was increased from 0.39% to a higher value. (2) The rebar arrangement also has an important effect on the local damage and energy absorption ability of the RC wall. As the number of rebar layers increased, the perforation depth, scabbing area of the RC wall, and the dissipated energy decreased. The RC wall with four layers of rebar (RCW-C) showed a good capacity to absorb the impact energy that leads to a smallest local damage among the three. (3) The proposed RC wall with a thickness of 1.2 m, having a rebar ratio of 1.54% (each direction) arranged with 4 layers was determined as the efficient design of the RC wall being capable to withstand an aircraft impact.