PSI - Issue 6

R.V. Fedorenko et al. / Procedia Structural Integrity 6 (2017) 244–251 Fedorenko R. et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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4.3. Aircraft impact calculation It was assumed that NPP structures foundation is fixed. The initial velocity of the aircraft is 110 m/s. In aircraft principal axes elevation angle equals 15 ° , yaw and bank angles equals 0 ° . The variable parameter is the thickness T of outer containment. Figure 8 shows the stiffness degradation (a) and equivalent von Mises (b) distributions using CDP concrete model (T=1,5 m).

a

b

Fig. 7.(a) stiffness degradationdistribution; (b) equivalent von Mises distribution.

During the simulation the acceleration was recorded as function of time (accelerogram) in three directions at target points at different height levels. In accordance with the calculation approach of the NPP secondary structures (equipment, pipe system etc.), computation under dynamic loads is performed with response spectrum method. Input data about dynamic loads on the construction is the deformation, velocity and acceleration floor response spectrums in accordance to the response spectrum theory. For the base response the most often used model is the acceleration floor response spectrum. Figure 8 shows the example of acceleration response spectrum for one of the target points of the NPP structure with two different damping ratios.

Fig. 8.Acceleration response spectrum in OX direction.

4.4. Structures strength criterion under aircraft impact For the purpose of the strength and failure survival of the reinforced concrete structures based on the finite element numerical computations, it is necessary to set up rules of numerical computation results interpretation in accordance with regulatory documents. The following criterions of the strength and failure survival of the NPP reinforced concrete structures were formulated:

 Concrete smeared cracking on the backside of the outer containment  Main crack initiation in the longitudinal direction of the outer containment  Main crack initiation in the circular direction of the outer containment  Cracking and damage initiation in the concrete inner containment  Invalid plastic strain in concrete  Reinforcement transition in the plasticity