• Title, Summary, Keyword: 강도감소계수

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Evaluation of Strength Reduction Factors using Smooth Hysteretic Behavior (완만한 곡선형 이력거동을 이용한 강도감소계수의 평가)

  • Song, Jong-Keol
    • Journal of the Earthquake Engineering Society of Korea
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    • v.14 no.4
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    • pp.49-60
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    • 2010
  • The actual hysteretic behavior of structural elements and systems is smooth. Smooth hysteretic behavior is more representative of actual behavior than bi-linear or piece-wise linear stiffness degrading models. The strength reduction factor in seismic design is used to reduce the elastic strength demand to design levels. In this study, the effect of smoothness on the strength reduction factor is evaluated for several smooth hysteretic systems subjected to near-fault and far-fault earthquakes. For design purposes, a simple expression of the strength reduction factor considering hysteretic smoothness and earthquake characteristics, represented as near-fault and far-fault earthquakes, is proposed. The strength reduction factors calculated by the proposed simple formulation are more similar to the factors directly obtained from inelastic response spectrum analyses than those calculated by several existing formulas.

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
    • Journal of The Korean Society of Civil Engineers
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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.

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Analysis of Long-Term Performance of Geogrids by Considering Interaction among Reduction Factors (감소계수 상호영향을 고려한 지오그리드의 장기성능 해석)

  • Jeon, Han-Yong;Kim, Yuan-Chun;Jang, Yeon-Soo
    • Journal of the Korean Geotechnical Society
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    • v.28 no.7
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    • pp.55-65
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    • 2012
  • Total reduction factor that is used when calculating allowable tensile strength of geogrids is made by multiplying the installation damage reduction factor ($RF_{ID}$), chemical degradation reduction factor ($RF_D$), and creep reduction factor ($RF_{CR}$) etc. In case of a model estimating allowable tensile strength considering reduction factor over the short-term tensile strength of geogrids, it has a limit of not considering interaction force between reduction factors. Junction strength comes to be reduced by installation damages or chemical degradation in the same way as tensile strength. Single junction test method cannot properly test damaged samples and shows large deviations as it does not consider scale effect. Besides, regarding calculating shear strength, no reasonable study on reduction factors was conducted yet. Therefore, in this study, reduction factors that may affect the long-term performance of geogrids were revaluated considering various conditions and accurate long-term allowable tensile strength was calculated considering interrelation between reduction factors. Creep results after installation damage and chemical resistance test showed lower value than calculated value according to GRI GG-4. After the installation damage test and the chemical resistance test, the reduction factor of junction strength was less than that of tensile strength. Shear strength before and after installation damage showed no change or increase.

Comparative Evaluation of Formulas of Strength Reduction Factors for the Generation of an Inelastic Demand Spectrum (비탄성요구스펙트럼의 작성을 위한 강도감소계수 공식의 비교 평가)

  • Cho, Sung-Gook;Park, Woong-Ki;Joe, Yang-Hee
    • Journal of the Earthquake Engineering Society of Korea
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    • v.15 no.6
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    • pp.33-44
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    • 2011
  • The shape of an inelastic demand spectrum may have a major impact on the seismic evaluation results of a structure. The inelastic demand spectrum could be obtained by scaling down from the elastic response spectrum by applying the strength reduction factor (SRF). This study has investigated formulas for SRFs that were suggested by numerous previous studies. This paper compares their characteristics, including the shapes of the curves of the SRFs and the inelastic demand spectra that were produced by applying the various formulas for SRFs. The mean curve was computed from the SRF curves generated by the various formulas. This study derives a new formula for the SRF curve through regression analysis. From the comparative study, it is shown that the proposed formula for the SRF can generate the mean curve of the inelastic demand spectra which have been previously suggested by others.

Evaluation of Nominal Flexural Strength in RC Beams Strengthend with CFRP Plate and Failed by Intermediate Crack Debonding (중간부 부착파괴된 CFRP 판 보강 RC 보의 휨강도 평가)

  • Hong, Sung Nam;Park, Jong In;Kim, Tae Wan;Park, Sun Kyu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.5
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    • pp.101-112
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    • 2011
  • This paper shows a study carried out on the estimation of nominal flexural strength for CFRP-plated RC beams failed by intermediate crack debonding. A strength reduction factor is proposed to consider the effect of the intermediate crack debonding for the determination of nominal flexural strength. The proposed factor is derived from experimental data and utilizes the ratio of effective stress(or strain) in the CFRP plate to its ultimate strength(or strain) which is called effective strain model. An analytical equation for the estimation of the nominal flexural strength is formulated as a function of strength reduction factor. The validity, accuracy and efficiency of the proposed factor are established by comparing the analytical results with the experimental data, and the major design codes, as well as a number of factors given by researchers. The analytical results presented in this paper indicate that the proposed factor can effectively estimate the flexural nominal strength of CFRP-plated reinforced concrete beams failed by intermediate crack debonding.

Calculation for of Strength Reduction Factor for Concrete Beam reinforced with GFRP rebars (GFRP rebar로 보강된 콘크리트보의 휨 강도감소계수 보정식 제안)

  • Sim, Jong-Sung;Park, Cheol-Woo;Park, Sung-Jae;Kang, Tae-Sung;Kwon, Dong-Wook;Lee, Yong-Taek
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.137-140
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    • 2008
  • If the flexural member of concrete is designed using the FRP rebar, suddenly brittleness destruction resulted from the fracture of FRP rebar is generated in the extreme situation because of brittleness characteristics of FRP rebar and concrete when designed to be less than balanced reinforcement ratio, so it is recommended to design the flexural member of concrete to be more than balanced reinforcement ratio. In ACI 440.1R-06 proposes the different bending strength decrease coefficient according to destructive form of concrete flexural member using the FRP rebar. However, ACI 440.1R-06 applies the same strength decrease coeffient to all FRP rebars made of diverse materials. If the same strength decrease coefficient is applied to all FRP rebars, effect of increasing the reinforcement ratio and selection of FRP rebar will be considerably limited. In this regard, we are to propose the formula to calculate the bending strength decrease coefficient in consideration of change in characteristics of FRP rebar and L/D through the reliability analysis in this paper.

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Bending Properties of Multifilament Yarns (연속필라멘트사의 휨특성에 관한 연구)

  • 김상용
    • Textile Science and Engineering
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    • v.9 no.2
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    • pp.7-30
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    • 1972
  • 연속필라멘트사가 탄성 및 탄성-소성 휨을 받을 때 실의 휨성질을 섬유의 인장 및 구조에 의하여 표시할 수 있는 방법이 이론적으로 고찰되었으며 그 결과 다음과 같은 결론을 얻었다. 필라멘트간의 마찰이 영과 무한대의 중간치를 갖는 경우에는 마찰계수가 증가할수록 실의 휨강도는 증가한다. 표면라여각이 증가함에 따라서 실의 휨강도는 처음에는 증가하며 최대치에 이른 다음 감소한다. 휨 회복도도 같은 현상을 나타낸다. 실의 잔류모멘트는 실의 저라여각에 있어서는 필라멘트의 마찰 계수가 증가함에 따라서 증가하고 고라여각에 있어서는 감소한다. 탄성 휨에 있어서는 마찰계수가 0.1~0.6인 경우의 실의 휨 강도는 마찰계수가 영인 경우의 실의 휨 강도의 4~20 배가 된다.

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Effects of Inelastic Demand Spectrum on Seismic Capacity Evaluation of Curved Bridge by Capacity Spectrum Method (역량스펙트럼을 이용한 곡선교의 내진성능평가에 대한 비탄성요구스펙트럼의 영향)

  • Cho, Sung Gook;Park, Woong Ki;Joe, Yang Hee
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.3
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    • pp.195-206
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    • 2011
  • The capacity spectrum method(CSM) has been more frequently used as a tool to evaluate the seismic capacity of the structure. Many formulas of strength reduction factors(SRF) have been proposed and adopted to generate the inelastic demand spectrum for the CSM. This study evaluates the impacts of the type of the SRF on the inelastic demand spectrum and finally on the seismic response displacement of curved bridge. For the purpose, the several existing formulas of SRFs were comparatively investigated through the case study. Curved bridges with different subtended angles were selected and the displacements of the bridge piers were estimated by using the different formulas of SRFs. Nonlinear time history analyses were also performed for the validation purpose of the CSM results. According to study results, the CSM may generate the larger displacement responses than the actual behaviors for the curved bridge with larger subtended angles. Though many methods have been suggested to generate the inelastic demand spectrum for CSM, they might not give noticeable differences in inelastic displacement of the bridge pier.

A Study on the Estimation and Application of Failure Coefficients of Rock (암석의 파괴조건계수 평가 및 적용성에 관한 연구)

  • 장명환;양형식
    • Geotechnical Engineering
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    • v.14 no.4
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    • pp.103-116
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    • 1998
  • To estimate pure shear strength, 150 sets of triaxial test data were analyzed. The proportional coefficient of shear strength($I_c$) at zero normal stress was nonlinearly decreased as failure coefficient m increases, while the internal friction $\phi_0$ at zero normal stress was nonlinearly increased. The ratio of shear strength $(c/\phi_0)$was inversely proportional to the ratio of the internal friction angles$(\phi/phi_0)$ The shear strength decreased as m increased, while internal friction angle increased. And uniaxial strength was proportional to $c,\phi$ Regression analysis showed that shear strength strongly affects m and $\sigma_c$ The proportional coefficient of shear strength was nonlinearly increased with RMR, while the internal friction angle $(\phi}$was linearly decreased.

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