To study the **seismic** **soil** **structure** **interaction**, building frames of 4, 6 and 8 storey was modeled in Ansys software. 3D models of square frame with 3 bays in both X and Y directions are modelled. The storey height and length of each bay of all building frames were chosen as 3m and 5m respectively which is reasonable for a residential building. The thickness of floor slab and roof were taken as 100mm. beam and column dimensions were as given in table 1. The grid dimensions and pile dimensions were calculated according to the axial load they have to carry. Square Pile of 550mm side dimension and 20m length, and grid beam with 1m width and 500mm depth were considered for the analysis (fig 2). The materials considered for design were M30 and Fe 415 steel.

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The nuclear power plant structures, systems, and components (SSCs) important to safety must be designed to withstand the effects of the Safe Shutdown Earthquake ground motion. The design evaluation of these SSCs should take into account **seismic** **soil**-**structure** **interaction** (SSI) effects. The established SSI analysis methodologies are used primarily for the current generation of large LWRs whose structures are founded on or near the ground surface. Influenced by benefits such as enhanced protection from missiles and aircraft impact and potential reduction in **seismic** demands, several SMR designs propose to bury or deeply embed major plant structures below grade, which presents new technical challenges with respect to the **seismic** design and analysis of these structures. Figure 1 illustrates typical embedment depths for large LWRs and SMRs. In this paper, some key technical issues pertaining to the **seismic** SSI analysis of deeply embedded nuclear structures are addressed and related guidance provided in the recent DSRS for an SMR design is illustrated.

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This paper presents the computation of response spectra for a nuclear building, including **seismic** **soil**- **structure** **interaction** (SSI), using two different methods. To do so, established computer programs like the SASSI computer code and ABAQUS with Infinite Elements are used. The SASSI computer code is based on the Thin Layer Method developed by Lysmer et al. (1981) as a method for computations in the fre- quency domain. The calculations here are realized with the enhanced efficient SASSI 2010 by Ostadan et al. (2012). Another method, known as the Lysmer damper and also developed by Lysmer and Kuhlemeyer in 1969, is implemented in ABAQUS and called Infinite Elements. These elements contain values for the boundary damping effect. Considering linear elastic material behavior close to the bounda- ry, both methods transmitted and absorbed all normally incoming plane body waves.

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The boundary element method has been used to model the far-field soil which has been shown to be very effective for a surface foundation or an embedded foundation in a linearly elastic h[r]

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The main aim of the present study is to investigate the effect of **soil** **structure** **interaction** on RC bridges with pile foundation located in soft and medium **soil** during earthquake. To investigate this a 4 span continues bridge having span length 30m was modelled using finite element software SAP2000. Total 6 bridge configuration was selected with same span length. The set of 11 ground motions recorded on soft and medium **soil** where selected from PEER data base. **Seismic** analysis was performed for the 6 model bridges as described in previous sections.

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[13] Gazetas, G. and Mylonakis, G. (1998). “**Seismic** **soil**- **structure** **interaction**: New evidence and emerging issues”, State of the Art Paper, Geotechnical Earthquake Engineering and **Soil** Dynamics Gee-Institute ASCE Conference, Seattle, August 3- 6, 1998, Vol. II, pp. 1116-l 174.

During the last quarter of the 20th century, the importance of dynamic **soil**-**structure** **interaction** for several structures founded on soft soils was well recognized. If not accounted for in analysis, the accuracy in assessing structural safety in the face of earthquakes cannot be accounted for adequately. For this reason, **seismic** **soil**-**structure** **interaction** analysis has become a major topic in earthquake engineering. In Earthquake Engineering when the **soil** medium is relatively soft, the dynamic **interaction** between the superstructure, its foundation, and the **soil** medium may become important. During the shaking of an Earthquake, **seismic** waves are transmitted through the **soil** from fault rupture to a **structure** of interest. The wave motion of the **soil** excites the **structure** which in turn modifies the input motion by its movement relative to the ground. These **interaction** phenomena will be called "so il fo undatio n -sup er **structure** interactio n" or simp ly "so il **structure** **interaction**". Depending upon the material properties of the **soil** medium, the source of dynamic excitation and the particular type of foundation considered, the response of the structural system can be quite different from the case where the supporting system

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A **seismic** **soil**-**structure** **interaction** analysis evaluates the collective response of the **structure**, the foundation and the geologic media underlying and surrounding the foundation, to a specified free-field ground motion. The term free-field refers to motions that are not affected by structural vibrations or the scattering of waves at and around the foundation. SSI effects are absent for the theoretical condition of a rigid foundation supported on rigid **soil**. Accordingly, SSI accounts for the difference between the actual response of the **structure** and the response of the theoretical, rigid base condition.

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and guidelines in many countries, allows modeling of the inelastic behavior of structural systems. The frequency dependency of **soil**-**structure** impedance characteristics is usually considered in a numerical method performed in the frequency domain, whereas the nonlinearity of super structures is normally reflected in the time domain because the inelastic bilinear behavior of materials and structural members strongly depends on the stress or force-displacement path being integrated stepwise. Even the technical background is not seemed strong, a variety of methods considering the frequency-dependent impedance functions in time-history analysis have been proposed. Those procedures having the terminologies of multi-step or hybrid frequency time domain restrain the full use of frequency-dependent impedance capacity to consider inelastic behavior in the super-**structure** [1, 2, 3]. The equations of motion assumed to linear or equivalent linear system for a certain reference model is usually solved in frequency domain and nonlinear effects in the time domain are evaluated and treated as pseudo-forces. Depending on the degree of nonlinearity of the SSI system, the procedures may require large iteration works sometimes causing divergence. Another method of hybrid-time-frequency domain approach was also developed in 1998 [4]. **Soil** is represented using frequency-independent springs, dashpots, and possibly masses, and the equation of motion defined in the time domain is solved considering nonlinearity in SSI system. The feature of this method is available to analyze the non-linear SSI system with a rapid convergence

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The floor response spectra generated with the soil supported model can be used for seismic evaluation of the equipment and commodities in the Reactor Building. Seismic[r]

The earthquake ground motions for response history analyses are based on the **seismic** hazard at the site of a WUS NPP site. Panel a of Figure 2 presents the **seismic** hazard curve used for this study in terms of the horizontal peak ground acceleration (PGA) and associated mean annual frequency of exceedance (MAFE). A reference earthquake is defined for the **seismic** fragility evaluation in the SPRA process. This earthquake is defined as the uniform hazard spectrum (UHS) with a 10,000-year return period (MAFE of 1.0E-04), which corresponds to a horizontal PGA of 0.4g. Panel b of Figure 3 presents the 5% damped UHS corresponding to the horizontal and vertical directions. As a simplification for this study, the shape of the UHS is considered to be invariant within the MAFE range of interest. A suite of thirty sets of ground motion records (three components each) spectrally matched to the reference earthquake UHS are selected for this study. The horizontal ground motion records account for variability of the spectral acceleration in any arbitrary direction about the geometric mean of the two horizontal components.

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Settlements of the **soil** surface and the foundations were measured using LVDT1, LVDT2 and LVDT3 supported by cross bars and extending downward to pads placed either on the sand surface or the foundation surface. In case A (sand only) of all four tests, three LVDTs were used to measure the **soil** surface settlements, while in cases B, C, and D, LVDT2 was used to measure the settlement of the foundations. Measurements of the LVDTs were recorded during increasing the accelerations of the centrifuge “spin up” from 1g to 60g and then during the shaking. The largest settlement measured during each case occurred through the spinning from 1g to 60g, while the residual settlement measured from the displacement time history recorded during each shaking was generally small. The “spin up” settlement curves from 1g to 60g for the Free and **Structure** Fields for all tests are presented in Figures 4.1 and 4.2, as a function of the spin up time at model scale. Each relation shows a number of steps, and each step represents 10g increase in the acceleration during the spin up. A large amount of settlement data during shaking was recorded and these show typical shapes and results. Therefore, only the results for the displacement time history of shakings in Test 1, for cases A and C are shown in Figures 4.3 and 4.4 at prototype scale and the reminder are presented in Appendix (B).

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In the present study to account the effect of support settlement modulus of sub grade reaction(ks) is considered in modeling of buildings of height G+7 RCC structures having material properties M30 grade for concrete and Fe415 for reinforcing steel and **structure** dimensions height is 26m from the foundation or footing top, three different support conditions are considered having modulus of sub grade reaction value ks =10,000kN/m 3 , ks =20,000kN/m 3 , ks =40,000kN/m 3 and fixed base and foundation depth is considered as 2m below the ground level structures are modeled using STAAD.Pro in **seismic** zone V as per IS 1893-2002 and the plan irregular shapes considered are rectangular, L and T, It is observed that higher the modulus of sub grade reaction value (ks) lesser will be **seismic** effect on structures.

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[2] A.M.Rahman, A.J.Carr and P.J.Moss “**seismic** pounding of a case of adjacent multiple - story buildings of differing total heights considering **soil** flexibility effects” Bulletin of the New Zealand society for earthquake engineering. Vol.31,No.1 March 2001 [3] Mr. Magade S.B. and Prof. Patankar J.P. “ Effect of **Soil**

1. Fron chart 1, found that natural period of **structure** increases for building with stiffness irregularity. Rate is higher for model (2) with soft **soil**, it is increase 43.93% w.r.t regular building with fixed support condition.

• the study of the local problems where local balance is checked on each substructure, independently on the others and without taking into account the interface connections. For each subdomain, the equation of the dynamic problem under the effect of **seismic** incidental fields is solved by taking into account external forces and internal forces acting on the considered substructure;

In case of the site under consideration, the initial geo-technical investigations indicated a shear wave velocity of rock as low as 800 m/s which, on confirmatory tests, went up to 2600 m/s. Hence, a wide range of **soil** parameters is considered in the analyses. The best estimate of low strain shear modulus of the founding medium is 47500 MPa. This is the base value for the analyses (1.0K). In absence of sufficient **soil** data, the coefficient of variation is taken as 1.0. Hence, a range analysis is performed with shear modulus values of 23750 MPa (0.5K) and 95000 MPa (2.0K). Also, a lower end value of 0.15K is considered for academic purpose to study the variation of results at lower K values.

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The paper illustrates the effects of ground motion incoherency on **seismic** SSI responses of a typical axisymmetric nuclear reactor building and two industrial buildings with significant mass eccentricities. To incorporate the motion incoherency effects on SSI response we used both stochastic and deterministic approaches (Ghiocel, 2005, 2006, Ostadan, 2005, 2006, Ostadan and Ghiocel, 2007). In this study two the plane-wave coherency models are used: i) the Luco-Wong coherency model (Luco and Wong, 1986) and, ii) the Abrahamson incoherency model (Abrahamson, 2005). The motion incoherency approaches are comparatively applied for coherent and incoherent **seismic** input motions to illustrate the effects of motion incoherency on SSI response. The SSI coupling responses of structures are primarily examined to illustrate the additional rocking and torsional motion effects due to the motion incoherency. The SSI results in terms of transfer functions, acceleration response spectra and structural forces are obtained to study the motion incoherency effects. The study shows that incoherency effects are significant in the high-frequency ranges and much less significant for the low frequency responses. **SEISMIC** MOTION INCOHERENCY MODELING

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SSI are overestimated and at the upper stories have no meaningful different with the responses obtained from the situation with considering SSI. Also, it is observed that the effects of considering the SSI in low-rise structures on stiff and soft **soil**, are negligible at all stories and it is not necessary to consider (as much as 10~15% in 3 and 6-storey structures). The reduction in maximum variation is about 40% in high-rise structures (18 and 20-storey). The results indicate that about 33% increase in fundamental period in high-rise structures constructed on soft **soil** in comparison with fixed-base conditions. These case studies confirm that the SSI effects should be taken into account and it is important to consider during structural analysis and design especially in high-rise structures.

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