Safety Significance of a Type of Seismic Input Motions and Consequences on Nuclear Industry Practice

Abstract eng:
The fact that, in nuclear industry, usual practices of earthquake engineering widely overestimate the damaging effects of near-field input motions generated by low–medium magnitude earthquakes was identified in 1997 by the OECD. This issue was addressed by the IAEA in a Coordinated Research Project (2002-2005). The project included a large benchmark, based on experimental data provided by France (relating to a concrete wall subjected to different seismic input motions on a shaking table) and seismic input motions provided by Japan. A major conclusion is that the root cause of the identified issue is relating to the fact that seismic input motions are conventionally regarded as force controlled loads, while, due to their high frequency content, input motions under consideration should be regarded as displacement-controlled loads, so as to take benefit of the fact that structural margins are much larger under displacement controlled loads than under force controlled loads. However such margins are accessible only when modelling the non-linear behaviour of structures. Therefore the IAEA recommends that nuclear industry practices evolve so that the dynamic modelling techniques take into account at least small nonlinearities in the models.

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