Amplification of seismic input due to 1D, 2D and 3D effects, and their importance for nuclear power plant structures

Abstract of the technical paper presented at:
21st International Conference on Structural Mechanics in Reactor Technology (SMiRT-21)
New Delhi, India
November 6–11, 2011

Prepared by:
B. Jeremic, N. Tafazzoli. University of California, Davis, U.S.A.
N. Orbovic and  A. Blahoianu  Canadian Nuclear Safety Commission, Ottawa, Ontario, Canada

Abstract

Presented here is an investigation of the amplification of seismic input for massive NPP structures due to 1D, 2D, and 3D effects. Of particular interest is the difference in nuclear power plant (NPP) motions resulting form a full three dimensional, realistic ground motions (including proper modeling of seismic body and surface waves) and those motions resulting from reduced dimensional (1D and 2D) inputs to NPPs. The main differences that lower dimensional inputs (might) have when compared with realistic 3D motions is the possible lack of rocking and torsional modes. Realistic modeling of ground motions for massive structures such as NPPs is very important as combination of translational, rocking and torsional modes can (significantly) affect the response. Rocking, torsional and translational seismic motions can have beneficial or detrimental effects on the NPP seismic response, particularly if they are able to excite rocking, torsional and translational modes for the containment and internal structures.

Numerical results will be used to illustrate a number amplification effects resulting from the 3D realistic motions, as well as the changes to NPP response due to using 2D and/or 1D seismic inputs. Of particular interest are the choices that need to be made when full 3D motion inputs are reduced to 2D and 1D. In addition to that, discussed will be the development of a full 3D, realistic ground motions (that include a full set of body P and S waves, as well as surface Love and Rayleigh waves, representing inclined waves that lack correlation) from recorded/available 3D motions that record only three translational motions at a point. Variations in the influence rock/soil profiles (from hard rock to soil) have on the response of the NPP system (rock/soil, foundation and the structure) will be analyzed and conclusions drawn. Results will also be used to illustrate beneficial and detrimental effects that combining rocking, torsional and translational seismic inputs can have on the seismic response of the NPP system.

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