Current Methodologies for Incorporating Ground Motion Incoherency in Ssi Analysis Using Sassi (original) (raw)
Related papers
Comparative Studies on Seismic Incoherent Ssi Analysis Methodologies
2013
The paper discusses the effects of the 3D seismic random wave propagation (incoherent motion) vs. the 1D seismic deterministic wave propagation (coherent motion) on SSI response. Both theoretical and practical aspects are presented. The presented incoherent SSI analyses were performed using deterministic and stochastic incoherent SSI approaches with and without complex response phase adjustment as implemented in the ACS SASSI code (Ghiocel, 2013). The incoherent SSI approaches with phase adjustment were validated by EPRI (Short, Hardy, Merz and Johnson, 2007) and accepted by US NRC (2008) for their application to the seismic SSI analysis of the new nuclear power plant structures in United States. The paper investigates the effects of complex response phasing on the incoherent instructure response spectra (ISRS) for different nuclear island SSI models. It is shown that EPRI validated incoherent SSI approaches are always conservative, but sometimes they could be overly conservative fo...
SSSI Analysis and Uncertainties in Foundation Design for Nuclear Power Project
The nuclear power plant (NPP) structures impose heavy loads on foundation and subsurface materials. Hence, it becomes essential to study and evaluate the properties of the underlying and supporting soil / rock material up to sufficient depth, beyond which the properties does not affect the foundations and safety of the plant. The nature and properties of foundation materials are of utmost importance, as they can affect the safety of the structures by transmitting vibratory ground motion, which may result in stress levels exceeding the design limits, in the plant structures. The design bases for nuclear power plants include a requirement that the plant and systems must withstand seismic loads up to a predefined intensity of ground motion, without jeopardizing safety. Thus, for any NPP structure, Geo-technical investigations form an important design basis for site selection and evaluating the parameters for suitable foundation design.
2013
The paper presents the selected results of the validation study for the application of the Modified Subtraction Method (MSM) to the seismic soil-structure interaction (SSI) analysis of the MHI US-APWR Reactor Building complex. The MSM method is based on the SASSI Flexible Volume substructuring approach in the complex frequency domain. The MSM is much faster than the reference Flexible Volume (FV) method that could be impractical due the large computational resources needed for large-size SSI models. However, the recent drafts of the ASCE 04-2013 Standard and USNRC SRP 3.7.2-2013 recommend that MSM is checked against the reference FV method before is applied to SSI production runs for seismic design-basis analyses of nuclear structures. The focus of this paper is on the MSM validation when applied to SSI analyses of large-size embedded NI complex SSI models. The comparisons of the SSI results of the MSM and FV methods obtained for the investigated case studies indicated that MSM is a...
Seismic SSI Response of Reactor Building Structures
2010
This paper presents a case study that illustrates the soil-structure interaction (SSI) effects on the seismic response of reactor building (RB) structures at a rock site in the Eastern US with input ground motion that is characterized with high frequency content and high peak ground acceleration (PGA). The study includes the site-specific SSI effects of 40 ft thick embedment backfill soil and the effects of seismic motion incoherency on the structural response at high frequencies. The responses obtained from these site-specific analyses are compared with results of a set of site-independent analyses that envelope the response of the R/B structures at a wide range of sites characterized with seismic ground motion with frequency content similar to the US NRC RG 1.60 and PGA of 0.3 g and serve as basis for standard design of these structures. The focus of the study is on the results of the SSI analyses that define the sitespecific demands for seismic design of the building structural m...
Component Mode Synthesis Based SSI Analysis of Complex Structural Systems Using SASSI
Volume 8: Seismic Engineering, 2009
Three-dimensional seismic soil-structure interaction (SSI) analysis of nuclear power plants (NPP) is often performed in frequency domain using the computer program SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using de-convolution method and/or spatially variable ground motions. For large, complex structural systems with multi-million degrees of freedom (DOF) and large foundation impedance matrices associated with deeply embedded foundations, the conventional sub-structuring analysis approach employed in SASSI often results in a coefficient matrix that is too large to solve with currently available computer resources. To address this problem, the method of component mode synthesis (CMS) is employed in the SSI analysis. This involves partitioning the structure into several interconnected compone...