Seismic Response of an NPP on Linear and Nonlinear Soil and Contact Boris Jeremi´ c et al. This example is based on Sinha et al. (2017). 1 Introduction Seismic simulations to structures are often done by 1-D input excitations defined from a family of damped response spectra. These input motions are applied uniformly to the entire base of the structure regardless of its dimension and dynamic characteristics of the soil, foundation and motion itself. This not only ignores the foundation and its contact with soil, soil-structure interaction (SSI) but also the 3D nature and variability of seismic waves. Interest to study SSI effects has grown significantly in recent years. However Tyapin (2007) and Lou et al. (2011) note that even after four decades of extensive SSI research, there still exists a large gap. Lou et al. (2011) notes that spatial analysis of full model in 3D is hardly done. To reduce the amount of calculations, many existing publications simplify extremely the super-structure to spring mass damper model or consider only limited interaction. Elgamal et al Elgamal et al. (2008) performed a 3D analysis of a full soilbridge system, focusing on interaction of liquefied soil in foundation and bridge structure. Jeremi´ c et al. (2009) showed a full 3D soil-structure interaction of a prototype bridge, devised as a part of grand challenge, pre- NEESR project. Investigations of SSI have shown that the dynamic response of a structure supported on elastic-plastic soil may differ significantly from the response of the same structure when supported on a rigid base Chopra & Gutierrez (1974), Bielak (1978). The difference comes because of the dissipation of part of the vibrational energy (seismic energy) by hysteresis action of the soil or structure itself. This results in damping of high frequency components, which could potentially prove quite useful for equipment that are prone to damage from high frequencies. On the other hand Jeremi´ c et al. (2004) found that SSI can have detrimental effects on structural behavior as well and is dependent on the dynamic characteristics of the earthquake motion, the foundation soil and the structure. Dissipation of energy during seismic events is another important factor to consider in design for its safety and economy. Dissipating energy in structure can lead to material degradation and damage. It is desired to dissipate most of the energy in soil with acceptable level of deformations in structure. A common neglect of plastic free energy has been observed in many publications, which results in clear violation of the second law of thermodynamics. A thermomechanical framework that can correctly evaluate energy transformation and dissipation in dynamic SSI simulation was presented by Yang et al. (2017), Yang & Jeremi´ c (2017) based on works of Rosakis et al. (2000), Dafalias et al. (2002). This framework is applied to the prototype NPP model that is being analyzed in this paper. Locations with high possibility of damage are identified and insights on design improvement are discussed. Only a few full 3D SSI interactions have been studied that too mainly focusing on bridges or small soil-foundation system. However, as per authors knowledge a full 3D non-linear analysis for a structure with soil-foundation-structure and contact effects have not been investigated. Purpose of this paper here is to present a methodology for high fidelity modeling of seismic soilfoundation-structure (SFSI) interaction for a prototype of Nuclear Power Plant (NPP) with surface (shallow) foundation. Presented methodology employs the currently best available models and simulation procedures. In addition to presenting such 1