SAFE, an experimental evidence of the frequency dependence of shear wall seismic design margins

The SAFE experimental programme consists of a series of 10 specimens of shear walls, with different reinforcement ratios, tested until their ultimate capacity under seismic input motion by the pseudo dynamic method. A unique input signal is used, calibrated for controlling the seismic demand. Its input central frequency is selected so that for some specimens it is lower than their eignenfrequency, while for other ones it is the opposite. In conclusion there is clear experimental evidence that design margins are much larger in the second case (input central frequency larger than structure eignenfrequency) than in the first one. PURPOSE OF THE SAFE PROGRAMME Because the vast majority of nuclear buildings are made of shear walls, the Kashiwasaki-Kariwa (2007) and the Fukushima (2011) seismic events, have renewed the interest for realistic estimates of shear wall actual capacities, or in other words of their design margins. Although it was launched in the nineties, the SAFE research programme intended actually to provide data on such margins, and more precisely to provide experimental evidences that the frequency content of the seismic input motion plays a crucial role when estimating the actual seismic capacity of shear wall buildings. The SAFE programme was cofunded by Electricité de France (EDF), the Compagnie Générale des Matières Nucléaires (COGEMA, now part of AREVA) and the European Commission Joint Research Centre (JRC), Ispra, Italy. The testing campaign, designed by Gallois (1994), was performed by the European Laboratory for Structural Assessment (ELSA) of the JRC (Pégon 1999). The JRC uses the pseudo-dynamic test method, which consists of applying displacements on the structure through actuators attached on a reaction wall. The method combines numerical integration of the dynamic equilibrium equation of the system (to compute the displacement to be applied) with measurement of reaction forces corresponding to the prescribed displacement. The measured restoring forces are used to feed the said equation of motion back. The dynamic equilibrium equation does not include a damping matrix (Molina et al., 2011). Several authors published theoretical research covering a reduced part of the SAFE programme (Mazars et al., 2002; Kotronis et al., 2003; Brun et al., 2003 and 2011; Gallitre, 2008). A recent paper by Labbé et al. (2015), summarized here, presents the full set of SAFE experimental inputs and outputs. Test of nuclear type shear walls were also carried out from 1994 to 2003, by the Japan Nuclear Energy Safety Organisation (Kitada et al. 2006). The main conclusion was that methodologies presented in JEAG-4601 (NRC 1994) were validated, including an analytical methodology applicable in the range equal to or less than 2 × 10–3 rad. An equivalent viscous damping was identified. Series of tests of shear walls were also performed in USA, in particular at Los Alamos National Laboratory, summarized by the IAEA (2011). A database of more than 400 walls was processed by by Gulec & Whittaker (2009) to obtain a performance based assessment of squat shear walls. In Europe, a database of more than 600 walls, a minority of them being squat, has been gathered by the Patras University (Grammatikou et al. 2014). 23 Conference on Structural Mechanics in Reactor Technology Manchester, United Kingdom August 10-14, 2015 Division V