• Title/Summary/Keyword: 설계활하중

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Determination of Resistance Factors of Load and Resistance Factor Design for Drilled Shaft Based on Load Test (LRFD 설계를 위한 현장타설말뚝의 주면지지력 저항계수 산정)

  • Kim, Seok-Jung;Kwon, Oh-Sung;Jung, Sung-Jun;Han, Jin-Tae;Kim, Myoung-Mo
    • Journal of the Korean Geotechnical Society
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    • v.26 no.7
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    • pp.17-24
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    • 2010
  • Load Resistance Factor Design method is used increasingly in geotechnical design world widely and resistance factors for drilled shafts are suggested by AASHTO. However, these resistance factors are determined for intact rock conditions; by comparison, most of bedrocks in Korea have weathered condition, so that applying the AASHTO resistance factors is not reasonable. Thus, this study suggests the proper resistance factors for design of drilled shaft in Korea. The 22 cases of pile load test data from 8 sites were chosen and reliability-based approach is used to analyze the data. Reliability analysis was performed by First Order Second Moment Method (FOSM) applying 4 bearing capacity equations. As a result, when the Factor of Safety (FOS) was selected as 3.0, the target reliability indexes (${\beta}_c$) were evaluated as 2.01~2.30. Resistance factors and load factors are determined from optimization based on above results. The resistance factors ranged between 0.48 and 0.56 and load factors for dead load and live load are evaluated as approximately 1.25 and 1.75 respectively. However, when the target reliabilities are considered as 3.0, the resistance factors are evaluated as approximately 50% of the results when the target reliability index was 2.0.

Critical Strengthening Ratio of CFRP Plate Using Probability and Reliability Analysis for Concrete Railroad Bridge Strengthened by NSM (확률.신뢰도 기법을 적용한 CFRP 플레이트 표면매립보강 콘크리트 철도교의 임계보강비 산정)

  • Oh, Hong-Seob;Sun, Jong-Wan;Oh, Kwang-Chin;Sim, Jong-Sung;Ju, Min-Kwan
    • Journal of the Korea Concrete Institute
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    • v.21 no.6
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    • pp.681-688
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    • 2009
  • The railroad bridges have been usually experienced by vibration and impact in service state. With this reason, it is important that the effective strengthening capacity should be considered to resist the kind of service loading. In this study, NSM strengthening technique is recommended for the concrete railroad bridge because of its better effective resistance for dynamic loading condition and strengthening cost than the conventional externally bonded strengthening using fiber sheet. However, to widely apply NSM method for the concrete railroad bridge, it needs that the strengthening ratio has to be reasonably evaluated with geometrical and material uncertainties, especially for the concrete bridge under long-term service state without the apparent design history and detail information such as concrete compressive strength, reinforcing ratio, railroad characteristics. The purpose of this study is to propose the critical strengthening ratio of CFRP plate for the targeted concrete railroad bridge with uncertainties of deterioration of the structures. To do this, Monte Carlo Simulation (MCS) for geometrical and material uncertainties have been applied so that this approach may bring the reasonable strengthening ratio of CFRP plate considering probabilistic uncertainties for the targeted concrete railroad bridge. Finally, the critical strengthening ratio of NSM strengthened by CFRP plate is calculated by using the limit state function based on the target reliability index of 3.5.

Life-Cycle Cost-Effective Optimum Design of Steel Bridges Considering Environmental Stressors (환경영향인자를 고려한 강교의 생애주기비용 최적설계)

  • Lee, Kwang Min;Cho, Hyo Nam;Cha, Cheol Jun
    • Journal of Korean Society of Steel Construction
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    • v.17 no.2 s.75
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    • pp.227-241
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    • 2005
  • This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology for steel bridges considering the long-term effect of environmental stressors such as corrosion and heavy truck traffics on bridge reliability. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost, and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure, which depends upon the prior and updated load and resistance histories, should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model, which takes into consideration corrosion initiation, corrosion rate, and repainting effect, are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40m+50m+40m=130m). Various sensitivity analyses are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the volume of truck traffic significantly influence the LCC-effective optimum design of steel bridges. Thus, these conditions should be considered as crucial parameters for the optimum LCC-effective design.

Lifetime Reliability Based Life-Cycle Cost-Effective Optimum Design of Steel Bridges (생애 신뢰성에 기초한 강교의 LCC최적설계)

  • Lee, Kwang Min;Cho, Hyo Nam;Cha, CheolJun;Kim, Seong Hun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.1A
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    • pp.75-89
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    • 2006
  • This paper presents a practical and realistic Life-Cycle Cost (LCC) optimum design methodology of steel bridges considering time effect of bridge reliability under environmental stressors such as corrosion and heavy truck traffics. The LCC functions considered in the LCC optimization consist of initial cost, expected life-cycle maintenance cost and expected life-cycle rehabilitation costs including repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socio-economic losses. For the assessment of the life-cycle rehabilitation costs, the annual probability of failure which depends upon the prior and updated load and resistance histories should be accounted for. For the purpose, Nowak live load model and a modified corrosion propagation model considering corrosion initiation, corrosion rate, and repainting effect are adopted in this study. The proposed methodology is applied to the LCC optimum design problem of an actual steel box girder bridge with 3 continuous spans (40 m+50 m+40 m=130 m), and various sensitivity analyses of types of steel, local corrosion environments, average daily traffic volume, and discount rates are performed to investigate the effects of various design parameters and conditions on the LCC-effectiveness. From the numerical investigation, it has been observed that local corrosion environments and the number of truck traffics significantly influence the LCC-effective optimum design of steel bridges, and thus realized that these conditions should be considered as crucial parameters for the optimum LCC-effective design.

A Ultimate Shear Performance of Elastomeric Bearings (탄성받침의 극한전단성능)

  • Yoon, Hye-Jin;Kwahk, Im-Jong;Kim, Young-Jin
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.11a
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    • pp.117-120
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    • 2008
  • The bridge bearings are devices absorbing the displacements of the superstructure. KS F 4420 relative to the design of elastomeric bearings in Korea allows shear deformation up to 70% of total rubber height. For the elastomeric bearings to fulfill their shear function required in the design, the stability of allowable shear strain of elastomeric bearings relative to the shear failure should be guaranteed. Moreover considering the possibility that elastomeric bearings are applied to the seismic design together with isolation devices, elastomeric bearings is supposed to display higher shear performance. In this paper ultimate shear performance tests were performed. The measured ultimate shear strains were over 200%. Therefore an allowable shear strain provision becomes safe. But elastomeric bearings expected to show their performance in one united body reveled the separation of components near 200% shear strain. These separation in elastomeric bearing can cause unexpected impact or concentrated stress to bridge system considering to application of seismic design. Therefore provision relevant to separation problem is necessary.

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Characteristics of Heavy Vehicles Using Expressway Networks Based on Weigh-in-motion Data (WIM 데이터를 이용한 고속도로 중차량 특성 분석)

  • Gil, Heungbae;Kang, Sang Gyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.5
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    • pp.1731-1740
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    • 2013
  • The design life and durability of the bridges are strongly affected by the Gross Vehicle Weight(GVW) of heavyweight trucks. The Weigh-In-Motion(WIM) systems are typically used to collect information on truck total weight and speed. The statistical analysis of the GVW measured using High Speed WIM systems showed that most of heavy vehicles were from Vehicle Type 7, 10, and 12. The analysis was also carried out to determine goodness of fit with theoretical probability distributions. The normal distribution was shown to best describe the overall distribution of GVW. The top 10% of the GVW appeared to best fit by the Weibull 3 probability distribution.

Strengthening Design by External Pre-tensioning and Post-tensioning Methods for Steel-concrete Composite Girders using Rating Factor (내하율을 이용한 강합성보의 외부 프리텐션과 포스트텐션 보강 설계)

  • Choi, Dong-Ho;Yoo, Dong-Min;Jeong, Gu-Sang;Park, Kyung-Boo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.11 no.5
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    • pp.123-134
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    • 2007
  • A method to determine the initial force of external tendon is proposed to improve the load carrying capacity in existing steel-concrete composite bridges. This method is applied to tensioning external tendons prior to and after concrete replacement for strengthening composite girders. A procedure to determine the number of tendon and initial tendon force is described with the proposed rating factor, which considers the increment of tendon force due to live loads. The method is applied to the improvement of rating factor in an existing composite bridge and its validity is confirmed.

Analysis of Buckling Causes and Establishment of Reinforcement Method for Support of Plate Girder Bridge (플레이트 거더교 지점부의 좌굴발생 원인분석 및 보강방안 수립)

  • Ok, Jae-Ho;Yhim, Sung-Soon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.20 no.11
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    • pp.520-526
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    • 2019
  • I-type girders are widely applied as very economical sections in plate girder bridges. There has been research on developing composite laminated panels, curved plates reinforced with closed-end ribs, and new forms of ribs and compression flanges for steel box girders. However, there is a limitation in analyzing the exact cause of local buckling caused by an I-type girder's webs. Therefore, an I-type girder's web was modeled using the finite element analysis program LUSAS 17.0 before and after reinforcement. We checked for the minimum thickness criteria presented in the Korea highway bridge design code, and the cause of buckling after performing a linear elastic buckling analysis of dead and live loads was analyzed. Before reinforcement, an eigenvalue (λ1) at the 1st mode was 0.7025, the critical buckling load was smaller than the applied load, and there is a buckling. After reinforcement, when applying vertical and horizontal stiffeners to the web part of the girder at support, a Nodal line was formed, the eigenvalue was 1.5272, and buckling stability was secured. To improve buckling trace of the girder at the support, an additional plate was applied to the web at the support to ensure visual and structural safety, but buckling occurs at center of web. The eigenvalue (λ1) was 3.5299, and this method is efficient for reinforcing the web of the support.

Confining Stress of Internally Confined Hollow CFT Member Under Compression (압축을 받는 내부 구속 중공 CFT부재의 구속력 평가)

  • Yoon, Na Ri;Won, Deok Hee;Park, Jong Gun;Kang, Young Jong
    • 한국방재학회:학술대회논문집
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    • 2011.02a
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    • pp.37-37
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    • 2011
  • 최근 세계적인 지진의 발생과 함께 구조물의 내진성능 평가 및 증진 방법에 대하여 많은 연구가 진행 되고 있다. 특히 교량 구조물의 교각의 경우에는 상부구조의 고정하중 및 활하중을 지반에 전달하여 주는 역할을 하기 때문에, 역으로 지진이 발생하였을 경우 교각의 내진성능에 따라서 교량의 안전도에 많은 영향을 미칠 수 있다. 또한 산악지역이 국토의 70%이상을 차지하는 우리나라의 지형적인 특성상 고교각을 이용한 장대교량의 건설이 필요하며 도시지역의 교통량 증가로 인한 도시고속도로의 건설 등 고가교의 필요성이 점차 증가하고 있다. 그러나 CFT(Concrete Filled Tube)부재의 경우에는 콘크리트가 3축 구속 상태로 존재하지만 자중이 크며 내진 성능이 떨어지는 단점을 가지고 있다. 이러한 단점을 보완하기 위하여 CFT부재의 단면을 중공으로 만듦으로써 부재를 경량화하고 내부 튜브를 삽입하여 내부를 구속 시킨 내부 구속 중공 CFT 부재(Internally Confined Hollow CFT Member, ICH CFT)가 개발되었다. 이는 콘크리트가 내 외부 튜브에 의하여 구속되어 3축 구속 상태로 존재함으로써 콘크리트 중공부로의 취성파괴를 방지하여 연성도 및 강도를 향상시켜주며, 단면의 감소로 인해 재료비를 절감 할 뿐 아니라 자중 감소로 인해 내진 설계에도 유리하다. 현재 내부 구속 중공 CFT 부재에 대한 연구가 많이 진행되고 있지만, 튜브를 삽입함으로써 부재의 중공부로 발생하는 구속력의 특성을 해석적으로 정립한 연구는 미비한 실정이다. 본 연구에서는 압축을 받는 중공 CFT 부재에 내부 튜브를 삽입함으로써 발생하는 콘크리트의 구속력을 해석적 연구를 통하여 수행하였으며, 구속력을 파악하기 위한 평가 방법으로는 구속 콘크리트의 중공비와 직경, 외부튜브의 두께, 내부튜브의 두께 등으로 평가하였다. 해석적 연구 결과, 내부 튜브를 삽입함으로써 발생되는 외부 구속력은 이론적 수식에 의한 구속 응력값과 비슷한 값을 가지지만 내부로 발생하는 구속력은 이론적 수식에 의한 구속 응력값에 도달하지 못하는 것을 확인할 수 있었다.

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Application of Proposed Rating Equations using LRFD Beam-Column Interaction Equations for Girders and Towers in Steel Cable-Stayed Bridges (강사장교 거더와 주탑에 하중저항계수설계법의 보-기둥 상관식을 사용한 내하율 산정식 적용)

  • Choi, Dong Ho;Yoo, Hoon;Lee, Beom Soo;Cho, Sun Kyu
    • Journal of Korean Society of Steel Construction
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    • v.19 no.1
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    • pp.1-13
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    • 2007
  • As girders and towers in cable-stayed bridges are subject to bending moments as well as axial forces, the conventional load rating equation, which considers only the single force effect, cannot be used to evaluate the rating factors of cable-stayed bridges. The load rating equation for components in cable-stayed bridges is not currently established yet. In this paper, we propose load rating equations for girders and towers in cable-stayed bridges using the interaction equations for beam-column members. Moving load analyses were performed for the cases of a maximum axial compressive force, maximum positive moment and maximum negative moment for each component in cable-stayed bridges and detailed procedures to apply proposed equations were presented. The Dolsan Grand Bridge was used to verify the validity of proposed equations. The conventional load rating equation overestimates rating factors of girders and towers in the Dolsan Grand Bridge, whereas proposed equations properly reflect the axial-flexural interaction behaviour of girders and towers in cable-stayed bridges.