• Title/Summary/Keyword: equivalent SDOF system

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Responses of Equivalent SDOF System for System Ductility Demands Evaluation of Multistory Building Structures (건축구조물의 시스템 연성요구도 평가를 위한 대표응답의 활용)

  • 최원호;이동근
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2001.04a
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    • pp.446-453
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    • 2001
  • System-level ductility is an essential parameter for seismic performance evaluation of multistory building structures. The ductility demands for single degree of freedom structures or individual structural members can be determined easily. However, there is no clearly established method to determine the ductility demands for structural systems. The system ductility demands are estimated in this study by the equivalent SDOF system methods and proposed method which used the representative responses obtained from the MDOF systems directly. And seismic performance of building structures is evaluated by the modified Capacity Spectrum Method using the representative responses, and the result was compared with those of the inelastic time history analysis.

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An equivalent linearization method for nonlinear systems under nonstationary random excitations using orthogonal functions

  • Younespour, Amir;Cheng, Shaohong;Ghaffarzadeh, Hosein
    • Structural Engineering and Mechanics
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    • v.66 no.1
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    • pp.139-149
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    • 2018
  • Many practical engineering problems are associated with nonlinear systems subjected to nonstationary random excitations. Equivalent linearization methods are commonly used to seek for approximate solutions to this kind of problems. Compared to various approaches developed in the frequency and mixed time-frequency domains, though directly solving the system equation of motion in the time domain would improve computation efficiency, only limited studies are available. Considering the fact that the orthogonal functions have been widely used to effectively improve the accuracy of the approximated responses and reduce the computational cost in various engineering applications, an orthogonal-function-based equivalent linearization method in the time domain has been proposed in the current paper for nonlinear systems subjected to nonstationary random excitations. In the numerical examples, the proposed approach is applied to a SDOF system with a set-up spring and a SDOF Duffing oscillator subjected to stationary and nonstationary excitations. In addition, its applicability to nonlinear MDOF systems is examined by a 3DOF Duffing system subjected to nonstationary excitation. Results show that the proposed method can accurately predict the nonlinear system response and the formulation of the proposed approach allows it to be capable of handling any general type of nonstationary random excitations, such as the seismic load.

Evaluation of Inelastic Earthquake Response of MDOF System by Equivalent SDOF System (등가 1자유도계에 의한 다자유도 비선형 지진응답 산정)

  • Kim, Bu-Sik;Noh, Phil-Sung;Jun, Dae-Han;Song, Ho-San
    • Journal of Korean Association for Spatial Structures
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    • v.2 no.2 s.4
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    • pp.45-49
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    • 2002
  • Current seismic design codes for building structures are based on the methods which can provide enough capacity to satisfy objected performance level and exactly evaluate the seismic performance of buildings. This paper is to suggest the method of inference of inelastic earthquake response obtained from MDOF system by equivalent SDOF system, and to prove the validity. The analysis results form simple model shows a good application possibility.

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Ductility and ductility reduction factor for MDOF systems

  • Reyes-Salazar, Alfredo
    • Structural Engineering and Mechanics
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    • v.13 no.4
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    • pp.369-385
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    • 2002
  • Ductility capacity is comprehensively studied for steel moment-resisting frames. Local, story and global ductility are being considered. An appropriate measure of global ductility is suggested. A time domain nonlinear seismic response algorithm is used to evaluate several definitions of ductility. It is observed that for one-story structures, resembling a single degree of freedom (SDOF) system, all definitions of global ductility seem to give reasonable values. However, for complex structures it may give unreasonable values. It indicates that using SDOF systems to estimate the ductility capacity may be a very crude approximation. For multi degree of freedom (MDOF) systems some definitions may not be appropriate, even though they are used in the profession. Results also indicate that the structural global ductility of 4, commonly used for moment-resisting steel frames, cannot be justified based on this study. The ductility of MDOF structural systems and the corresponding equivalent SDOF systems is studied. The global ductility values are very different for the two representations. The ductility reduction factor $F_{\mu}$ is also estimated. For a given frame, the values of the $F_{\mu}$ parameter significantly vary from one earthquake to another, even though the maximum deformation in terms of the interstory displacement is roughly the same for all earthquakes. This is because the $F_{\mu}$ values depend on the amount of dissipated energy, which in turn depends on the plastic mechanism, formed in the frames as well as on the loading, unloading and reloading process at plastic hinges. Based on the results of this study, the Newmark and Hall procedure to relate the ductility reduction factor and the ductility parameter cannot be justified. The reason for this is that SDOF systems were used to model real frames in these studies. Higher mode effects were neglected and energy dissipation was not explicitly considered. In addition, it is not possible to observe the formation of a collapse mechanism in the equivalent SDOF systems. Therefore, the ductility parameter and the force reduction factor should be estimated by using the MDOF representation.

Capacity Spectrum Analysis using Equivalent SDOF Method and Equivalent Damping Method for RC Wall Structure (철근콘크리트 벽체구조물에 대한 등가단자유도 방법 및 등가 감쇠비 산정방법에 따른 역량스펙트럼해석)

  • Song, Jong-Keol;Jang, Dong-Hui;Kim, Hark-Soo;Chung, Yeong-Hwa
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.21 no.2
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    • pp.169-187
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    • 2008
  • Performance-based approaches as an alternative method of the existing force-based approach have gradually become recognized tools for the seismic design and evaluation. The maximum inelastic displacement response using capacity spectrum method (CSM) with elastic response spectrum is estimated from seismic response of equivalent linear system converted from nonlinear system. The purpose of this paper is to evaluate accuracy of capacity spectrum method using the equivalent SDOF methods of 4 types and the equivalent damping methods of 5 types for RC wall structure. In order to evaluate accuracy of capacity spectrum analysis, the shaking table test results for RC wall structures are compared with those by the capacity spectrum analysis. Also, the effect of bilinear capacity curves by two bilinear approximation methods for capacity spectrum analysis is compared.

Soil interaction effects on the performance of compliant liquid column damper for seismic vibration control of short period structures

  • Ghosh, Ratan Kumar;Ghosh, Aparna Dey
    • Structural Engineering and Mechanics
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    • v.28 no.1
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    • pp.89-105
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    • 2008
  • The paper presents a study on the effects of soil-structure-interaction (SSI) on the performance of the compliant liquid column damper (CLCD) for the seismic vibration control of short period structures. The frequency-domain formulation for the input-output relation of a flexible-base structure with CLCD has been derived. The superstructure has been modeled as a linear, single degreeof-freedom (SDOF) system. The foundation has been considered to be attached to the underlying soil medium through linear springs and viscous dashpots, the properties of which have been represented by complex valued impedance functions. By using a standard equivalent linearization technique, the nonlinear orifice damping of the CLCD has been replaced by equivalent linear viscous damping. A numerical stochastic study has been carried out to study the functioning of the CLCD for varying degrees of SSI. Comparison of the damper performance when it is tuned to the fixed-base structural frequency and when tuned to the flexible-base structural frequency has been made. The effects of SSI on the optimal value of the orifice damping coefficient of the damper has also been studied. A more convenient approach for designing the damper while considering SSI, by using an established model of a replacement oscillator for the structure-soil system has also been presented. Finally, a simulation study, using a recorded accelerogram, has been carried out on the CLCD performance for the flexible-base structure.

Evaluation of N2 method for damage estimation of MDOF systems

  • Yaghmaei-Sabegh, Saman;Zafarvand, Sadaf;Makaremi, Sahar
    • Earthquakes and Structures
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    • v.14 no.2
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    • pp.155-165
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    • 2018
  • Methods based on nonlinear static analysis as simple tools could be used for the seismic analysis and assessment of structures. In the present study, capability of the N2 method as a well-known nonlinear analysis procedure examines for the estimation of the damage index of multi-storey reinforced concrete frames. In the implemented framework, equivalent single-degree-of-freedom (SDOF) models are utilized for the global damage estimation of multi-degree-of-freedom (MDOF) systems. This method does not require high computational analysis and subsequently decreases the required time of seismic design and assessment process. To develop the methodology, RC frames with period range from 0.4 to 2.0 s under 40 records are studied. The effectiveness of proposed technique is evaluated through numerical study under near- and far-field earthquake ground motions. Finally, the results of developed models are compared with two other simplified schemes along with nonlinear time history analysis results of multi-storey frames. To improve the accuracy of damage estimation, a modified relation is presented based on the N2 method results for near- and far-field earthquakes.

An Evolution of Nonlinear Dynamic Response of an Unreinforced Masonry Structure (비보강 조적조의 비선형 동적 거동의 전개)

  • Kim, Nam-Hee
    • Journal of the Earthquake Engineering Society of Korea
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    • v.10 no.3 s.49
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    • pp.77-84
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    • 2006
  • Unlike homogeneous material structure, the behavior of masonry structure is not perfectly elastic even in the range of small deformations because it is a non-homogeneous and anisotropic composite structural material, consisting of masonry units, mortar, and grout. This paper proposes a simplified way of investigating the evolution of the deformation and damage of the structure subjected to a series of successive ground motions with varying shaking. Especially, the most simple but useful algorithm of Fast Fourier Transformation (FFT) has been adopted to investigate the evolution of the deformation and damage of the structure tested on the shaking table. Moreover, the development of a hi-linear curve for an equivalent SDOF system which is obtained by exploiting the frequency and stiffness relationship was discussed. Finally, some important findings related to inelastic properties of the URM are summarized.

A Study on the Resilience-Based Performance Evaluation Method of Structures and Their Application Plan (구조물의 회복탄력성 기반 성능평가법에 대한 고찰 및 적용 방안에 관한 연구)

  • Kim, Yu-Seong;Kang, Joo-Won;Lee, Joon-Ho
    • Journal of Korean Association for Spatial Structures
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    • v.20 no.4
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    • pp.159-167
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    • 2020
  • The resilience performance evaluation method of a structure can evaluate the ability to recover after an earthquake disaster, and this study deals with the consideration and introduction of the resilience performance evaluation method. The resilience evaluation method can be expressed as a quantified number by constructing a loss estimation model and a recovery evaluation model. The recovery evaluation model should consider downtime in addition to the repair time, and the loss estimation model should consider not only direct loss to structures and non-structures, but also indirect loss due to functional loss of the building. In addition, to build a loss estimation model, the structure should be simplified to perform an efficient analysis. Therefore, in this study, the equivalent terminal induction system proposed cantilever-type and rahmen-type SDOF, and it is evaluated somewhat conservatively compared to the example structure, and it is judged that there is a need to improve the hysteresis characteristics by applying the stiffness reduction factor of the SDOF model.

Experimental Study on Equivalent Linear System for Rotational friction Damper (회전마찰감쇠기의 등가선형시스템에 관한 실험적 연구)

  • 김형섭;박지훈;민경원;이상현;이명규
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2004.10a
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    • pp.296-303
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    • 2004
  • In this study, equivalent linear damping and stiffness of a single-degree-of-freedom (SDOF) structure with a rotational friction damper are estimated using the result of experiments and compared with those obtained from non-linear time history analyses. First, the transfer function of the test model is constructed and then the equivalent stiffness and damping are calculated, using the half-power bandwidth (HPB) method. For comparative study, those properties are estimated based on stochastic theory in the time domain. Both equivalent linear systems identified from experiments and numerical analyses correspond well. Further, it is observed that there exists an optimal clamping force on the rotational friction damper from estimated equivalent damping.

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