Soil-structure interaction analysis of NPP containments: substructure and frequency domain methods

M&D Professional Services, Inc. (M&D) is under subcontract to Pacific Northwest National Laboratories (PNNL) to perform seismic analysis of the Hanford Site Double-Shell Tanks (DSTs) in support of a project entitled Double-Shell Tank (DST) Integrity Project - DST Thermal and Seismic Analyses. The original scope of the project was to complete an up-to-date comprehensive analysis of record of the DST System at Hanford in support of Tri-Party Agreement Milestone M-48-14. The work described herein was performed in support of the seismic analysis of the DSTs. The thermal and operating loads analysis of the DSTs is documented in Rinker et al. (2004). Although Milestone M-48-14 has been met, Revision I is being issued to address external review comments with emphasis on changes in the modeling of anchor bolts connecting the concrete dome and the steel primary tank. The work statement provided to M&D (PNNL 2003) required that a nonlinear soil structure interaction (SSI) analysis be performed on the DSTs. The analysis is required to include the effects of sliding interfaces and fluid sloshing (fluid-structure interaction). SSI analysis has traditionally been treated by frequency domain computer codes such as SHAKE (Schnabel, et al. 1972) and SASSI (Lysmer et al. 1999a). Such frequency domain programs are limited to the analysis of linear systems. Because of the contact surfaces, the response of the DSTs to a seismic event is inherently nonlinear and consequently outside the range of applicability of the linear frequency domain programs. That is, the nonlinear response of the DSTs to seismic excitation requires the use of a time domain code. The capabilities and limitations of the commercial time domain codes ANSYS{reg_sign} and MSC Dytran{reg_sign} for performing seismic SSI analysis of the DSTs and the methodology required to perform the detailed seismic analysis of the DSTs has been addressed in Rinker et al (2006a). On the basis of the results reported in Rinker et al. (2006a), it is concluded that time-domain SSI analysis using ANSYS{reg_sign} is justified for predicting the global response of the DSTs. The most significant difference between the current revision (Revision 1) of this report and the original issue (Revision 0) is the treatment of the anchor bolts that tie the steel dome of the primary tank to the concrete tank dome.

Nonlinear seismic soil-structure interaction analysis of nuclear reactor building considering the effect of earthquake frequency content

Time-domain soil-structure interaction analysis of nuclear facilities

Boundary reaction method for nonlinear analysis of soil–structure interaction under earthquake loads

This paper investigates the seismic behavior of a wind turbine, including soil–structure interaction (SSI). A full-system finite-element model is introduced for dynamic analysis, including SSI. The model is based on the NREL 5 MW reference wind turbine that consists of a rotor blade system with three rotating blades, nacelle, and tower connected to a soil–foundation system. The proposed model is validated using the full-system natural frequencies of the reference wind turbine. In the soil foundation system, the foundation is modeled as a rigid gravity-based foundation with two DOFs and the SSI effect is considered using a cone model. Dynamic analyses are developed in frequency and time domains, and the model is subjected to earthquake excitation and wind loading for different soil types for parked and operational conditions. Transfer functions are obtained, and the modal frequencies of the soil foundation structure system are estimated. Results show that SSI plays an important role in the response of the wind turbine. We can conclude that for a parked wind turbine, the effect of SSI is beneficial while considering that SSI has a detrimental effect in the operational conditions of wind turbine. The participation of different input loads in total response of an operational wind turbine is also presented.

Real-time dynamic hybrid testing for soil–structure interaction analysis

The influence of soil-structure interaction in the Natural Frequency of a parabolic reflector antenna is investigated. The main free vibration characteristic of an antenna is natural frequency. The analysis model simulated with fixed base condition and soil structure interaction. A parametric study is conducted to understand the antenna structure soil behavior (soil structure interaction (SSI)) by changing the antenna orientation, soil properties with impedance functions (spring constants) as per ASCE 4-16 and 3D (three dimensional modeling of founding medium) model methods. To address this problem, Finite Element Method is used to model soil structure interaction analysis of antenna structure with foundation by MSC PATRAN & NASTRAN using direct method and impedance method. The soil considered as homogeneous and analyzed for shear wave velocity (Vs) 100 m/s, 180 m/s, 250 m/s, 450 m/s, 760 m/s for antenna with 90° elevation. To study the embedment effect, soil around the footing and pedestal is considered. The frequency results are compared for antenna with four orientations with Vs 100 m/s soil properties. Considerable reduction in frequency observed with soil structure interaction in higher modes. Soil structure interaction study in antennas helps in finding what extent the natural frequency falls when the soil interaction is incorporated in the model.

A review study on seismic behavior of individual and adjacent structures considering the soil – Structure interaction

The soil surrounding and underlying the below grade portion of the structure affects the response of buildings to earthquakes. A common seismic design approach is to neglect the soil and analyze the entire free-standing structure for its response to earthquake ground motion applied at the foundation. Concerns have been expressed whether this simpler approach is acceptable, particularly when the below grade parkade is comparatively tall. This study evaluates the response of shear wall buildings with towers of varying heights, but all with a five-level below-grade parkade. The buildings are assumed to be located in Vancouver and subjected to earthquake loads prescribed by the National Building Code of Canada [6]. Two finite element models, both with soil surrounding the parkade, are analyzed. In the first case the tower and the parkade are supported by foundations placed directly on bedrock, and in the second model the tower and the parkade are supported on a rigid mat foundation resting on a soil deposit overlying the bedrock. A number of ground motions that are compatible with the uniform hazard spectrum for Vancouver are used to assess the response of each building model for a range of subsoil conditions. The results show that soil-structure interaction (SSI) can significantly increase the seismic forces in the structure. This effect is less pronounced for models in which kinematic interaction is present. Overall, the present study shows that for the type of buildings studied SSI magnifies the forces in the structure and needs to be considered in design.

Evidence of past earthquakes highlighted the seismic vulnerability to buildings due to soil liquefaction and lateral spreading phenomena. Damage to buildings on a liquefiable site, especially on a gently sloping site, can be severe. The liquefied soil can undergo permanent lateral ground displacements as large as several meters in some cases, which can be severely disastrous to buildings. Recent physical tests and effective stress analyses of nonlinear dynamic soil-structure interaction (SSI) proved that simplified empirical processes are often improper for evaluating liquefaction-induced building settlements. A better understanding of the SSI effects is also essential in cases where the underlying soil is susceptible to liquefaction. In this respect, the interaction of the earthquake excitation and ground failure (i.e. soil liquefaction and lateral spreading) for buildings considering SSI is investigated herein. Typical low-code reinforced concrete (RC) frame buildings of different heights with shallow spread footings on liquefiable level-ground or sloping soils subjected to ground shaking are considered. The direct SSI approach is implemented. Predictive relationships are established between the maximum normalized differential displacements (horizontal or settlement) and the permanent ground displacement (PGD) vector at the level of foundation for low-code RC frame buildings with shallow spread footings on soils with high liquefaction potential subjected to ground shaking. Finally, vulnerability is expressed in terms of fragility and vulnerability curves as well as in terms of fragility surfaces as a function of two intensity measures.

"Seismic Response of RC Frame Buildings: Theoretical Formulation and Modeling with Soil- Structure Interaction Analysis," offers a comprehensive exploration of the seismic response of reinforced concrete (RC) framed structures, with particular emphasis on soil flexibility. Through a meticulous response spectrum analysis, the study delves into the influence of soil flexibility on buildings of varying heights, ranging from five to nine storeys, considering both fixed and flexible support conditions across diverse soil types. The research draws the following significant conclusions: Significance of Soil-Structure Interaction (SSI): Incorporating soil-structure interaction (SSI) into the analysis leads to a noteworthy extension of the natural time period of the structure. This parameter stands as a linchpin in grasping the lateral response of framed structures, underlining its pivotal role in the precision of seismic design calculations. Soil Flexibility and Amplified Base Shear: Enhanced soil flexibility is found to correlate with a proportional increase in base shear. This phenomenon is most pronounced in soft soil conditions, where base shear experiences substantial escalation, particularly in taller buildings. Roof Displacement as a Performance Indicator: Roof displacement, a crucial indicator of structural performance, exhibits an upward trajectory owing to the cumulative effects of SSI. Notably, soft soils manifest higher roof displacements, with these variations becoming more pronounced as the building's height increases. The insights garnered from this analysis underscore the profound influence of SSI on a building's seismic response. Furthermore, the study highlights that advancements in finite element methods (FEM) and computer technology have significantly facilitated the integration of SSI into structural analysis. Therefore, it is imperative to harness these advancements fully to enhance our comprehension of structural behavior and to promote the adoption of secure construction practices in seismic-prone regions.

The selection of representative ground motions (GMs) for dynamic analysis of soil and structural systems considering soil–structure interaction (SSI) is critical for accurately predicting their performance under seismic loads. Site-specific GMs are typically generated first by selecting a set of seed time histories and then modifying them by matching to the target spectrum using either Time-Domain (TD) or Frequency-Domain (FD) techniques. While previous studies have recommended TD over FD techniques based on 1D site response analysis and engineering judgment, their effects on predicting soil and structural performance, considering SSI, are poorly understood in a 3D nonlinear domain. In this study, a set of seed ground motions corresponding to 3% and 50% in 75 years hazard conditions specific to Charleston, SC, was selected and modified using TD and FD techniques. Then, sixteen dynamic nonlinear 3D finite element simulations of a bridge bent supported by a 2 × 2 pile group were performed using the general-purpose finite element software ABAQUS by applying the motions generated using the FD and TD techniques. The geotechnical properties specific to Charleston were obtained from published documents, and the stress–strain behavior of the soil was represented by the Drucker-Prager model. The soil domain was spatially discretized with 3D brick elements. The structural components were represented by linear elastic beam elements. Results indicate that FD matching tends to distort nonstationary waveform components, particularly in displacement time histories. In contrast, TD matching preserves waveform features, including phase and frequency content, more effectively. Despite this, these distortions in FD-matched motions did not lead to substantial differences in structural response in most cases. However, noticeable response variations were observed in the 1 to 2.5-s period range. Overall, TD matching exhibited greater consistency and reliability in preserving input motion characteristics and is recommended for use in nonlinear SSI analyses.

：Numerical simulation is an important approach to conduct soil-structure dynamic interaction analysis, while the realization of the seismic wave input determines the accuracy of the simulation. Wave method is one of the most commonly used methods for seismic wave input, which converts the input wave into the equivalent loads on the artificial boundaries. Comparing with other methods, the wave method has high precision, but the implementation is relatively complicated. Based on another form of equivalent input seismic loads in the finite element model, a new seismic wave input method was proposed. In the new method, by imposing the free-field displacements on the nodes of the substructure composed of the elements containing the artificial boundary nodes, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Afterwards, the equivalent input seismic loads are applied to the nodes of the artificial boundaries to complete the seismic wave input and the seismic analysis of the soil-structure dynamic interaction model are performed. In comparison with the original wave method, the new method avoids the complex processes of calculating the free field stress on the artificial boundaries and the additional forces caused by the artificial boundaries, and determining the directions of the loads on different artificial boundaries. Therefore, it is simple to calculate the equivalent input seismic loads and easy to implement the seismic wave input process in the new method. The validity of the new method is verified by the numerical examples of the seismic analysis of the elastic half-space and layered half-space under vertical and oblique incident seismic waves.

Shaking table tests on a dynamic interaction system of hard layered soil, pile foundation and frame structure were carried out. The earthquake damage of the superstructure and foundation was reproduced. Based on these tests, several key issues about the seismic response of the dynamic soil-structure interaction (SSI) system were studied. The natural frequency of the system was less than that of the structure on rigid foundation if the SSI is not taken into account, while its damping ratio was larger than that of the structure. The mode shape of the system was different from that of the structure on the fixed base in that there were rocking and swinging at the foundation. Magnification or reduction of vibration transferred by soil was related to soil characteristic, excitation magnitude, and so on. Generally, sand magnifies vibration, while viscous powder soil dampens vibration. The components of the acceleration response at the top of the superstructure were based on the relative magnitude of the rocking stiffness, the swing stiffness of the foundation and the stiffness of the super-structure. The multi-direction excitations have little effect on the key issues of the horizontal SSI.

Purpose – Analytical determination of harmonic components of current in electric circuits containing semiconductor converters with the use of a small parameter method (SPM) in frequency domain. The paper aims to discuss these issues. Design/methodology/approach – A SPM realized in frequency domain was used in the analytical analysis of electric circuits with semiconductor converters. An automated method of formation of orthogonal harmonic components of electrical values on the basis of discrete convolution algorithm was used to provide the possibility of realization of calculation in frequency domain. A nonlinear characteristic of a semiconductor converter was presented by the method of numerical approximation. A numerical structured simulation method was applied to determination of the reference values of current in the analyzed circuit. Laws of theoretical electrical engineering were used for formation of the equations of voltage balance in the circuit with a nonlinear element. Findings – It is shown th...