On the performance of lumped parameter models with gyro‐mass elements for the impedance function of a pile‐group supporting a single‐degree‐of‐freedom system

Ghaemmaghami

2015

Summary A number of methods have been proposed that utilize the time‐domain transformations of frequency‐dependent dynamic impedance functions to perform a time‐history analysis. Though these methods have been available in literature for a number of years, the methods exhibit stability issues depending on how the model parameters are calibrated. In this study, a novel method is proposed with which the stability of a numerical integration scheme combined with time‐domain representation of a frequency‐dependent dynamic impedance function can be evaluated. The method is verified with three independent recursive parameter models. The proposed method is expected to be a useful tool in evaluating the potential stability issue of a time‐domain analysis before running a full‐fledged nonlinear time‐domain analysis of a soil–structure system in which the dynamic impedance of a soil–foundation system is represented with a recursive parameter model. Copyright © 2015 John Wiley & Sons, Ltd.

Section: Review Of Time‐domain Analysis Methods With a Frequency‐depementioning

confidence: 99%

Section: Inverse Fourier Methodsmentioning

confidence: 99%

Section: Lumped Parameter Modelsmentioning

confidence: 99%

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Stability of the time‐domain analysis method including a frequency‐dependent soil–foundation system

Laudon

Ghaemmaghami

2015

“…PROPOSED MODEL ASSEMBLYBecause the inelastic dynamic behavior of the condensed soil foundation segment can now be extracted in the form of a preselected number of (reduced) complex matrix pairs RF and S reduced , it is possible to develop a modified LP model assembly capable of emulating such behavior. The predefined type 3 LP design, proposed by Saitoh, is selected as the basis of the newly developed inelastic LP model. The resulting LP model for the scenario of a single interface DOF is illustrated in Figure .…”

Section: Inelastic Ssi System Order Reductionmentioning

confidence: 99%

A frequency‐dependent and intensity‐dependent macroelement for reduced order seismic analysis of soil‐structure interacting systems

Lesgidis

Sextos

2018

Summary The computational demand of the soil‐structure interaction analysis for the design and assessment of structures, as well as for the evaluation of their life‐cycle cost and risk exposure, has led the civil engineering community to the development of a variety of methods toward the model order reduction of the coupled soil‐structure dynamic system in earthquake regions. Different approaches have been proposed in the past as computationally efficient alternatives to the conventional finite element model simulation of the complete soil‐structure domain, such as the nonlinear lumped spring, the macroelement method, and the substructure partition method. Yet no approach was capable of capturing simultaneously the frequency‐dependent dynamic properties along with the nonlinear behavior of the condensed segment of the overall soil‐structure system under strong earthquake ground motion, thus generating an imbalance between the modeling refinement achieved for the soil and the structure. To this end, a dual frequency‐dependent and intensity‐dependent expansion of the lumped parameter modeling method is proposed in the current paper, materialized through a multiobjective algorithm, capable of closely approximating the behavior of the nonlinear dynamic system of the condensed segment. This is essentially the extension of an established methodology, also developed by the authors, in the inelastic domain. The efficiency of the proposed methodology is validated for the case of a bridge foundation system, wherein the seismic response is comparatively assessed for both the proposed method and the detailed finite element model. The above expansion is deemed a computationally efficient and reliable method for simultaneously considering the frequency and amplitude dependence of soil‐foundation systems in the framework of nonlinear seismic analysis of soil‐structure interaction systems.

“…where C i are the Fourier amplitude coefficients, f i are the discrete fast Fourier transform frequencies between 0.25 Hz ≤ f i ≤ 20 Hz, and Δf ≤ 0.05 Hz is the frequency interval used in the fast Fourier transform. It is noted herein that the mean frequency of excitation f m is used for the parameterization of the frequency-independent K-V model as opposed to the fundamental frequency f SSI of or the pseudonatural frequency (f pSSI ) of the coupled system, the latter defined as the frequency where the ratio of the horizontal displacement of the superstructure us is maximized with respect to the foundation motion up [42] for three main reasons: (i) being a key parameter of the dynamic stiffness of the system, (ii) it has been parametrically found as the most efficient alternative in defining frequencyindependent K-V models [21], and (iii) given that the site response analysis of the five soil profiles studied is equivalent linear, the fundamental frequency f SSI or f pSSI of each coupled system is effectively intensity-dependent, thus calibrating that the K-V model to the frequency of the system would hinder the identification of clear trends. In regard to the LP dynamic spring formulation, the three-core LP model illustrated in Figure 10(d) is selected for the particular study because of the accurate representation and computational efficiency that it has to offer.…”

Section: Extracted Dynamic Stiffness Integration Into the Bridge Fem mentioning

confidence: 99%

Influence of frequency‐dependent soil–structure interaction on the fragility of R/C bridges

Lesgidis

Sextos

2016

Summary Bridge performance under earthquake loading can be significantly influenced by the interaction between the structure and the supporting soil. Even though the frequency dependence of the interaction mentioned in this study has long been documented, the simplifying assumption that the dynamic stiffness is dominated by the mean or predominant excitation frequency is still commonly made, primarily as a result of the associated numerical difficulties when the analysis has to be performed in the time domain. This study makes use of the advanced lumped parameter models recently developed in order to quantify the impact of the assumption on the predicted fragility of bridges mentioned in this study. This is achieved by comparing the predicted vulnerability for the case of a reference, well studied, actual bridge using both conventional, frequency‐independent, Kelvin–Voigt models and the aforementioned lumped parameter formulation. Analysis results demonstrate that the more refined consideration of frequency dependence of soil–structure interaction at the piers and the abutments of a bridge not only leads to different probabilities of failure for given intensity measures but also leads to different hierarchy and distribution of damage within the structure for the same set of earthquake ground motions even if the overall probability of exceeding a given damage state is the same. The paper concludes with the comparative assessment of the effect for different soil conditions, foundation configurations, and ground motion characteristics mentioned in this study along with the relevant analysis and design recommendations. Copyright © 2016 John Wiley & Sons, Ltd.