• Title/Summary/Keyword: seismic inelastic response

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A new practical equivalent linear model for estimating seismic hysteretic energy demand of bilinear systems

  • Samimifar, Maryam;Massumi, Ali;Moghadam, Abdolreza S.
    • Structural Engineering and Mechanics
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    • v.70 no.3
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    • pp.289-301
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    • 2019
  • Hysteretic energy is defined as energy dissipated through inelastic deformations during a ground motion by the system. It includes frequency content and duration of ground motion as two remarkable parameters, while these characteristics are not seen in displacement spectrum. Since maximum displacement individually cannot be the appropriate criterion for damage assessment, hysteretic energy has been evaluated in this research as a more comprehensive seismic demand parameter. An innovative methodology has been proposed to establish a new equivalent linear model to estimate hysteretic energy spectrum for bilinear SDOF models under two different sets of earthquake excitations. Error minimization has been defined in the space of equivalent linearization concept, which resulted in equivalent damping and equivalent period as representative parameters of the linear model. Nonlinear regression analysis was carried out for predicting these equivalent parameter as a function of ductility. The results also indicate differences between seismic demand characteristics of far-field and near-field ground motions, which are not identified by most of previous equations presented for predicting seismic energy. The main advantage of the proposed model is its independency on parameters related to earthquake and response characteristics, which has led to more efficiency as well as simplicity. The capability of providing a practical energy based seismic performance evaluation is another outstanding feature of the proposed model.

Pushover Analysis of a 5-Story RC OMRF Considering Inelastic Shear Behavior of Beam-Column Joint (보-기둥 접합부 비탄성 전단거동을 고려한 5층 철근콘크리트 보통모멘트골조의 푸쉬오버해석)

  • Kang, Suk-Bong;Kim, Tae-Yong
    • Journal of the Korea Concrete Institute
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    • v.24 no.5
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    • pp.517-524
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    • 2012
  • In this study, the effects of the inelastic shear behavior of beam-column joint and the vertical distribution of lateral load are evaluated considering higher modes on the response of RC OMRF using the pushover analysis. A structure used for the analysis was a 5-story structure located at site class SB and seismic design category C, which was designed in accordance with KBC2009. Bending moment-curvature relationship for beam and column was identified using fiber model. Also, bending moment-rotation relationship for beam-column joint was calculated using simple and unified joint shear behavior model and moment equilibrium relationship for the joint. The results of pushover analysis showed that, although the rigid beam-column joint overestimated the stiffness and strength of the structure, the inelastic shear behavior of beam-column joint could be neglected in the process of structural design since the average response modification factor satisfied the criteria of KBC2009 for RC OMRF independent to inelastic behavior of joint.

Error Analysis of Nonlinear Direct Spectrum Method to Various Earthquakes (다양한 지진에 따른 비선형 직접스펙트럼법의 오차해석)

  • 강병두;박진화;전대환;김재웅
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2002.04a
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    • pp.53-60
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    • 2002
  • It has been recognized that damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the inelastic response is required. The methods available to the design engineer today are nonlinear time history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. Some codes proposed the capacity spectrum method based on the nonlinear static(pushover) analysis to determine earthquake-induced demand given the structure pushover curve. This procedure is conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method to evaluate seismic Performance of structure, without iterative computations, given the structural initial elastic period and yield strength from the pushover analysis, especially for multi degree of freedom structures. The purpose of this paper is to investigate accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters.

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A Study on the Use of Friction Dampers for the Seismic Performance Upgrade of RC Structures

  • Kim, Jin-Ho;Kim, Lee-Hyeon
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.05a
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    • pp.482-485
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    • 2004
  • A Performance Based Design procedure for retrofitting the RC frame with friction dampers is described. The Capacity Diagram Method procedure is used to estimate the inelastic response of the example model. The example models were retrofitted using SBC dampers and the retrofitted example models were computation ally modeled. The results show that the performance of the retrofitted frame satisfies the target objective.

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Efficacy of pushover analysis methodologies: A critical evaluation

  • Dutta, Sekhar Chandra;Chakroborty, Suvonkar;Raychaudhuri, Anusrita
    • Structural Engineering and Mechanics
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    • v.31 no.3
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    • pp.265-276
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    • 2009
  • Various Pushover analysis methodologies have evolved as an easy as well as designers-friendly alternative of nonlinear dynamic analysis for estimation of the inelastic demands of structures under seismic loading for performance based design. In fact, the established nonlinear dynamic analysis to assess the same, demands considerable analytical and computational background and rigor as well as intuitive insight into inelastic behavior for judging suitability of the results and its interpretation and hence may not be used in design office for frequent practice. In this context, the simple and viable alternative of Pushover analysis methodologies can be accepted if its efficacy is thoroughly judged over all possible varieties of the problems. Though this burning issue has invited some research efforts in this direction, still a complete picture evolving very clear guidelines for use of these alternate methodologies require much more detailed studies, providing idea about how the accuracy is influenced due to various combinations of basic parameters regulating inelastic dynamic response of the structures. The limited study presented in the paper aims to achieve this end to the extent possible. The study intends to identify the range of applicability of the technique and compares the efficacy of various alternative Pushover analysis schemes to general class of problems. Thus, the paper may prove useful in judicial use of Pushover analysis methodologies for performance based design with reasonable accuracy and relative ease.

Effectiveness of design procedures for linear TMD installed on inelastic structures under pulse-like ground motion

  • Quaranta, Giuseppe;Mollaioli, Fabrizio;Monti, Giorgio
    • Earthquakes and Structures
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    • v.10 no.1
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    • pp.239-260
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    • 2016
  • Tuned mass dampers (TMDs) have been frequently proposed to mitigate the detrimental effects of dynamic loadings in structural systems. The effectiveness of this protection strategy has been demonstrated for wind-induced vibrations and, to some extent, for seismic loadings. Within this framework, recent numerical studies have shown that beneficial effects can be achieved by placing a linear TMD on the roof of linear elastic structural systems subjected to pulse-like ground motions. Motivated by these positive outcomes, closed-form design formulations have been also proposed to optimize the device's parameters. For structural systems that undergo a near-fault pulse-like ground motion, however, it is unlikely that their dynamic response be linear elastic. Hence, it is very important to understand whether such strategy is effective for inelastic structural systems. In order to provide new useful insights about this issue, the paper presents statistical results obtained from a numerical study conducted for three shear-type hysteretic (softening-type) systems having 4, 8 and 16 stories equipped with a linear elastic TMD. The effectiveness of two design procedures is discussed by examining the performances of the protected systems subjected to 124 natural pulse-like earthquakes.

Probability-based prediction of residual displacement for SDOF using nonlinear static analysis

  • Feng, Zhibin;Gong, Jinxin
    • Earthquakes and Structures
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    • v.22 no.6
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    • pp.571-584
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    • 2022
  • The residual displacement ratio (RDRs) response spectra have been generally used as an important means to evaluate the post-earthquake repairability, and the ratios of residual to maximum inelastic displacement are considered to be more appropriate for development of the spectra. This methodology, however, assumes that the expected residual displacement can be computed as the product of the RDRs and maximum inelastic displacement, without considering the correlation between these two variables, which inevitably introduces potential systematic error. For providing an adequately accurate estimate of residual displacement, while accounting for the collapse resistance performance prior to the repairability evaluation, a probability-based procedure to estimate the residual displacement demands using the nonlinear static analysis (NSA) is developed for single-degree-of-freedom (SDOF) systems. To this end, the energy-based equivalent damping ratio used for NSA is revised to obtain the maximum displacement coincident with the nonlinear time history analysis (NTHA) results in the mean sense. Then, the possible systematic error resulted from RDRs spectra methodology is examined based on the NTHA results of SDOF systems. Finally, the statistical relation between the residual displacement and the NSA-based maximum displacement is established. The results indicate that the energy-based equivalent damping ratio will underestimate the damping for short period ranges, and overestimate the damping for longer period ranges. The RDRs spectra methodology generally leads to the results being non-conservative, depending on post-yield stiffness. The proposed approach emphasizes that the repairability evaluation should be based on the premise of no collapse, which matches with the current performance-based seismic assessment procedure.

Effects of Strength Reduction Factors for Capacity Spectrum Analysis of Bridge Structures using Inelastic Demand Spectrum (비탄성 요구도 스펙트럼을 이용한 교량구조물의 역량스펙트럼 해석에 대한 강도감소계수의 영향)

  • Song, Jong-Keol;Jin, He-Shou;Jang, Dong-Hui
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.1A
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    • pp.25-37
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    • 2008
  • The capacity spectrum method (CSM) is a simple and graphical seismic analysis procedure. Originally, it has been developed for buildings, but now its applicability has been extended to bridge structures. It is based on the capacity curve estimated by pushover analysis and demand spectrum reduced from linear elastic design spectrum by using effective damping or strength reduction factor. In this paper, the inelastic demand spectrum as the reduced demand spectrum is calculated from the linear elastic design spectrum by using the several formulas for the strength reduction factor. The effects of the strength reduction factor for the capacity spectrum analysis are evaluated for 3 types of symmetric and asymmetric bridge structures. To investigate an accuracy of the CSM which several formulas for strength reduction factor were applied, the maximum displacements estimated by the CSM are compared with the results obtained by nonlinear time history analysis for 8 artificially generated earthquakes. The maximum displacements estimated by the CSM using the SJ formula among the several strength reduction factors provide the most accurate agreement with those calculated by the inelastic time history analysis.

Application of ultrasonic energy to enhance capability of soil improving material (지반보강용 주입재의 성능향상을 위한 초음파 에너지의 활용)

  • Moon, Jun-ho;Xin, Zhenhua;Jeong, Ghang-bok;Kim, Young-uk
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.19 no.4
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    • pp.567-576
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    • 2017
  • In a performance-based design, the structural safety is estimated from pre- defined damage states and corresponding damage indices. Both damage states and damage indices are well defined for above-ground structures, but very limited studies have been performed on underground structures. In this study, we define the damage states and damage indices of a cut-and-cover box tunnel which is one of typical structures used in metro systems, under a seismic excitation from a series of inelastic frame analyses. Three damage states are defined in terms of the number of plastic hinges that develop within the structure. The damage index is defined as the ratio of the elastic moment to the yield moment. Through use of the proposed index, the inelastic behavior and failure mechanism of box tunnels can be simulated and predicted through elastic analysis. In addition, the damage indices are linked to free-field shear strains. Because the free-field shear strain can be easily calculated from a 1D site response analysis, the proposed method can be readily used in practice. Further studies are needed to determine the range of shear strains and associated uncertainties for various types of tunnels and site profiles. However, the inter-linked platform of damage state - damage index - shear wave velocity - shear strain provides a novel approach for estimating the inelastic response of tunnels, and can be widely used in practice for seismic designs.

Seismic Behavior of A 2/5-Scale Steel Structure with Added Viscoelastic Dampers (점탄성 감쇠기를 설치한 2/5 축척 강구조물의 지진하중에 의한 거동연구)

  • Oh, Soon-Taek
    • Journal of the Korean Society of Safety
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    • v.8 no.1
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    • pp.80-87
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    • 1993
  • This paper summarizes an experimental and analytical study on the application of viscoelastic dampers as energy dissipation devices in structural applications. Shaking table tests are carried out on the viscoelastically damped structure and the obtained structural responses are compared to those of the inelastic analysis results for the same test structure with no dampers added. It can be concluded the viscoelastic dampers are effective in reducing excessive vibrations of structures under strong earthquake ground motions. It is also observed that the increase in structure's stiffness by the addition of dampers can not contribute to improving the seismic response of a structure. In general. the reduction of the seismic response by adding the dampers to the structure is mostly resulted from the increased damping effect. It is found that the modal strain energy method can be used to reliably predict the equivalent structural damping. and the seismic response of a viscoelastically damped structure can be accurately estimated by conventional modal analysis techniques.

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