• Title, Summary, Keyword: strength reduction factor

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Modal strength reduction factors for seismic design of plane steel frames

  • Papagiannopoulos, George A.;Beskos, Dimitri E.
    • Earthquakes and Structures
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    • v.2 no.1
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    • pp.65-88
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    • 2011
  • A new method for the seismic design of plane steel moment resisting frames is developed. This method determines the design base shear of a plane steel frame through modal synthesis and spectrum analysis utilizing different values of the strength reduction (behavior) factor for the modes considered instead of a single common value of that factor for all these modes as it is the case with current seismic codes. The values of these modal strength reduction factors are derived with the aid of a) design equations that provide equivalent linear modal damping ratios for steel moment resisting frames as functions of period, allowable interstorey drift and damage levels and b) the damping reduction factor that modifies elastic acceleration spectra for high levels of damping. Thus, a new performance-based design method is established. The direct dependence of the modal strength reduction factor on desired interstorey drift and damage levels permits the control of deformations without their determination and secures that deformations will not exceed these levels. By means of certain seismic design examples presented herein, it is demonstrated that the use of different values for the strength reduction factor per mode instead of a single common value for all modes, leads to more accurate results in a more rational way than the code-based ones.

Strength reduction factor for multistory building-soil systems

  • Nik, Farhad Abedi;Khoshnoudian, Faramarz
    • Earthquakes and Structures
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    • v.6 no.3
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    • pp.301-316
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    • 2014
  • This paper is devoted to investigate the effects of SSI on strength reduction factor of multistory buildings. A new formula is proposed to estimate strength reduction factors for MDOF structure-soil systems. It is concluded that SSI reduces the strength reduction factor of MDOF systems. The amount of this reduction is relevant to the fundamental period of structure, soil flexibility, aspect ratio and ductility of structure, and could be significantly different from corresponding fixed-base value. Using this formula, measuring the amount of this error could be done with acceptable accuracy. For some practical cases, the error attains up to 50%.

Design parameter dependent force reduction, strength and response modification factors for the special steel moment-resisting frames

  • Kang, Cheol Kyu;Choi, Byong Jeong
    • Steel and Composite Structures
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    • v.11 no.4
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    • pp.273-290
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    • 2011
  • In current ductility-based earthquake-resistant design, the estimation of design forces continues to be carried out with the application of response modification factors on elastic design spectra. It is well-known that the response modification factor (R) takes into account the force reduction, strength, redundancy, and damping of structural systems. The key components of the response modification factor (R) are force reduction ($R_{\mu}$) and strength ($R_S$) factors. However, the response modification and strength factors for structural systems presented in design codes were based on professional judgment and experiences. A numerical study has been accomplished to evaluate force reduction, strength, and response modification factors for special steel moment resisting frames. A total of 72 prototype steel frames were designed based on the recommendations given in the AISC Seismic Provisions and UBC Codes. Number of stories, soil profiles, seismic zone factors, framing systems, and failure mechanisms were considered as the design parameters that influence the response. The effects of the design parameters on force reduction ($R_{\mu}$), strength ($R_S$), and response modification (R) factors were studied. Based on the analysis results, these factors for special steel moment resisting frames are evaluated.

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.

Material Resistance Factors for Reinforced Concrete Flexural and Compression Members (철근콘크리트 휨부재 및 압축부재의 재료조항계수 적용에 관한 연구)

  • 김재홍;이재훈
    • Journal of the Korea Concrete Institute
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    • v.12 no.2
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    • pp.21-30
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    • 2000
  • In the Ultimate Strength Design, the design strength of a member is determined by multiplying the strength reduction factor to the nominal strength. This concept may be a reasonable approach, however it can not consider failure modes appropriately. Moreover, column design strength diagram show an abrupt change at a low level of axial load, which does not seem to be reasonable. This research compares the design strength determined by the strength resistance factors. As the material resistance factors for flexure and compression, 0.65 and 0.90 are proposed for concrete and steel, respectively. The design strength calculation process by applying material resistance factors addresses failure modes more effectively than by applying member strength reduction factor, and provides more resnable design strength for reinforced concrete flexural and compression members.

Manufacturing and Assessment of High Performance Geosynthetic Composites for Reinforcement (보강용 고성능 토목건설 복합 보강재의 제조 및 평가)

  • ;George R. Koerner
    • Textile Science and Engineering
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    • v.40 no.3
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    • pp.272-280
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    • 2003
  • The composite type geogrid having 8 ton/m design strength was manufactured to develop the junction and creep properties. Three different types of geogrids(membrane type, textile type(warp/ knitted, woven type) and junction bonded type geogrids) are used to compare the long-term performance by total factor of safety with reduction factors during service periods. To evaluate the reduction factors, wide-width tensile and junction strength, installation damage, creep deformation, chemical and biological degradation were performed. Total factors of safety for these different type geogrids were interpreted through the results of these reduction factors. The long-term performance was evaluated by the long-term design strength of these geogrids to be calculated the constitutive equations of GRI standard Test Method GG4. Reduction factor of creep deformation mainly influenced on the long-term performance and composite type geogrid showed the most excellent long-term performance among these geogrids.

Estimation of response reduction factor of RC frame staging in elevated water tanks using nonlinear static procedure

  • Lakhade, Suraj O.;Kumar, Ratnesh;Jaiswal, Omprakash R.
    • Structural Engineering and Mechanics
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    • v.62 no.2
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    • pp.209-224
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    • 2017
  • Elevated water tanks are considered as important structures due to its post-earthquake requirements. Elevated water tank on reinforced concrete frame staging is widely used in India. Different response reduction factors depending on ductility of frame members are used in seismic design of frame staging. The study on appropriateness of response reduction factor for reinforced concrete tank staging is sparse in literature. In the present paper a systematic study on estimation of key components of response reduction factors is presented. By considering the various combinations of tank capacity, height of staging, seismic design level and design response reduction factors, forty-eight analytical models are developed and designed using relevant Indian codes. The minimum specified design cross section of column as per Indian code is found to be sufficient to accommodate the design steel. The strength factor and ductility factor are estimated using results of nonlinear static pushover analysis. It was observed that for seismic design category 'high' the strength factor has lesser contribution than ductility factor, whereas, opposite trend is observed for seismic design category 'low'. Further, the effects of staging height and tank capacity on strength and ductility factors for two different seismic design categories are studied. For both seismic design categories, the response reduction factors obtained from the nonlinear static analysis is higher than the code specified response reduction factors. The minimum dimension restriction of column is observed as key parameter in achieving the desired performance of the elevated water tank on frame staging.

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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An Application of Strength Reduction Factors to Reinforced Concrete Columns considering Ductility (연성을 고려한 철근콘크리트 기둥의 강도감소계수 적용에 관한 연구)

  • 손혁수;이재훈
    • Journal of the Korea Concrete Institute
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    • v.11 no.4
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    • pp.147-156
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    • 1999
  • Current design code states that the strength reduction factor shall be permitted to be increased linearly from that for axial compression to that for flexure as the design axial load strength $\Phi$cPn decrease from 0.1fckAg to zero. Since this empirically adopted axial load level of $\Phi$cPn=0.1fckAg considers only sectional area and concrete strength, the other variables such as steel ratio, steel yielding strength, and steel arrangement can not be considered. This research is performed to investigate the consistency and the rationality of the code requirement for determination of column design strength. A nonlinear axial force-moment-curvature analysis was conducted in order to investigate the ductility of reinforced concrete column sections. As the result of ductility analysis, it was found that the ductility at the axial force of $\Phi$cPn=0.1fckAg represented a lock of consistency for the various variable contained sections. Therefore, a more reasonable application method of strength reduction factor is proposed, that is based on the strain ductility index.

Slope Stability Analysis Considering Seepage Conditions by FEM Using Strength Reduction Technique (강도 감소법에 의한 지하수위를 고려한 FEM 사면안정해석)

  • 김영민
    • Journal of the Korean Geotechnical Society
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    • v.20 no.8
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    • pp.97-102
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    • 2004
  • In this paper, a finite element based method far determining factor of safety of slopes which has certain advantages over conventional limit equilibrium methods is described. Particularly, the slope failure behaviour considering different seepage conditions is produced by finite element method using strength reduction technique. It is shown that both the failure mechanism and the safety factor that are analyzed by the FEM using strength reduction technique are an effective means of slope stability analysis. And the stability of a slope with rising water table and rapid drawdown are analyzed and the results are compared with the simplified Bishop Method of the Limit Equilibrium Methods.