SMART 2013: Lessons learned from the international benchmark about the seismic margin assessment of nuclear RC buildings

In this paper, the main findings and conclusions drawn from the second international benchmark named SMART 2013 and jointly organized by the French Sustainable Energies and Atomic Energy Commission (CEA) and Electricité De France (EDF) within the framework of a wide research program entitled “Seismic design and best-estimate Methods Assessment for Reinforced concrete buildings subjected to Torsion and nonlinear effects” (SMART) are presented. A 1:4-scaled reinforced concrete (RC) specimen, representing a part of a nuclear auxiliary building and designed according to French guidelines for a PGA level equal to 0.2 g, was subjected to shaking table tests; results of this experimental campaign are used as reference data for this benchmark. The input ground motions considered in the seismic loading sequence are mainly natural bi-axial signals (main shock and aftershock) recorded during the Northridge earthquake that took place in California, USA in 1994 and have a PGA (Peak Ground Acceleration) about 1.8 g. These high-intensity seismic loadings allow assessing the relevancy of nonlinear numerical models when they have to deal with strong nonlinearities due to concrete cracking. The results produced by the 42 teams which participated in the international benchmark show that (i) the dynamic behavior of the specimen is well captured when dealing with the design level, (ii) the displacement are underestimated when dealing with the beyond design behavior, (iii) the peak frequency shifts are well captured and (iv) the damaging effect of the Northridge aftershock is almost null. Last, seismic safety margins of the specimen are quantified by two mechanical indicators; the results confirm the fact that the RC specimen which was designed according to the codes applicable in the French nuclear industry, exhibits noticeable good performance level regarding collapse prevention.