• Title/Summary/Keyword: LRFD규정

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Reliability Analysis of Single and Continuous Span Composite Plate and Box Girder Designed by LRFD Method under Flexure (LRFD법으로 설계된 단경간 및 연속경간 강합성 플레이트 거더 및 박스 거더의 휨에 대한 신뢰도해석)

  • Shin, Dong Ku;Roh, Joon Sik;Cho, Eun Young
    • Journal of Korean Society of Steel Construction
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    • v.20 no.1
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    • pp.183-193
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    • 2008
  • The reliability analysis of simply-supported and continuous composite plate girder and box girder bridges under flexure was performed to provide a basic data for the development of LRFD c ode. The bridges were designed based on LRFD specification with newly proposed design live load which was developed by analyzing traffic statistics from highways and local roads. A performance function for flexural failure was expressed as a function of the flexural resistance of composite section and the design moments due to permanent load and live load. For the flexural resistance, the statistical parameters obtained by analyzing over 16,000 domestic structural steel samples were used. Several different values of bias factors for the live load moment from 1.0 to 1.2 were used. Due to the lack of available domestic measured data on the moment by permanent loads, the same statistical properties used in the calibration of ASHTO-LRFD were ap plied. The reliability indices for the composite girder bridges with various span lengths, different live load factors, and bias fact or for the live load were obtained by applying the Rackwitz-Fiessler technique.

Design Comparison of Composite Girder Bridges Designed by ASD and LRFD Methods (허용응력설계법 및 하중저항계수설계법에 의한 강합성 거더교 설계결과 비교)

  • Cho, Eun-Young;Shin, Dong-Ku
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.5A
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    • pp.447-456
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    • 2009
  • The design comparison and flexural reliability analysis of continuous span composite plate girder bridges are performed. The girders are designed by the methods of allowable stress design (ASD) and load and resistance factor design (LRFD). For the LRFD design, the design specification under development mainly by KBRC, based on AASHTO-LRFD specification in case of steel structures, is applied with the newly proposed design live load which has been developed by analyzing domestic traffic statistics from highways and local roads. For the ASD based design, the current KHBDC code with DB-24 and DL-24 live loads is used. The longest span length for the 3-span continuous bridges with span arrangement ratio of 4:5:4 is assumed to be from 30 m to 80 m. The amount of steel, performance ratios, and governing design factors for the sections designed by the ASD and LRFD methods are compared. In the reliability analysis for the flexural failure of the sections designed by two methods, the statistical properties on flexural resistance based on the yield strength statistics for over 16,000 domestic structural steel samples are applied.

Inelastic Design of Continuous-Span Composite Plate Girder Bridges by LRFD Method (비탄성 설계법에 의한 플레이트 거더 연속교의 LRFD 설계)

  • Cho, Eun Young;Shin, Dong Ku
    • Journal of Korean Society of Steel Construction
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    • v.20 no.4
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    • pp.469-481
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    • 2008
  • The inelastic design of the three-span continuous composite plate girder with consideration of moment redistribution over the interior pier is performed using the LRFD method. The design of the girder section, based on the inelastic method, is compared with that by the conventional elastic design. The length of the center span for the three-span continuous bridge ranges from 40m to 70m and the relative ratio of the span length is assumed to be 4:5:4. Although the AASHTO- LRFD specifications are applied in the design of the composite girder, the recently proposed new design live load is used. After determining the maximum positive and negative sections by the elastic design for various limit states, the amount of moment redistributed to the maximum positive moment section is calculated. With the increased design moment due to moment redistribution from the interior pier, the maximum positive section designed by the elastic method is checked for the strength limit state and the service limit state. The maximum negative moment section is redesigned by reducing the size of the steel girder relative to the section designed by the elastic method and the new section is checked for the service limit state. Based on the design results for the five bridges considered in this study, it is estimated that about 23% of steel can be saved in the interior pier section if it is designed by the inelastic method compared with that designed by the elastic method.

Verification of Lateral Live Load Distribution Factors for Continuous Steel Girder Bridges Based on Diagnostic Testing Results (현장계측결과를 이용한 강거더연속교의 횡방향 활하중 분배계수에 대한 연구)

  • Eom, Jun-sik
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.13 no.4 s.56
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    • pp.180-187
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    • 2009
  • The objective of this research is to verify the code-specified girder distribution factors (GDF) for continuous steel girder bridges by field testing. Previous analytical study revealed that current GDF's specified in AASHTO Standard and AASHTO LRFD, developed for the simple span bridges are conservative even for the continuous bridges. In this study, field tests were performed for three continuous steel girder bridges to validate the GDF's specified in the AASHTO codes. The results show that the code values are conservative when compared with field tests, and in some cases, too conservative. Also, strains measured from the field test are, in most cases, smaller than those expected from the analytical results. However, when the GDF's from measured strains are compared with GDF's from analysis, it is found that the analysis results are not conservative, and in some instance, the analytical results underestimate the actual GDF's, which can lead to a groundless notion of safety. In one case, test results showed that the code GDF's specified in AASHTO LRFD is too permissive. As a result, it is found that GDF's specified in AASHTO LRFD should be used with careful reservation.

Design Comparison of Totally Prefabricated Bridge Substructure Systems Designed by Present Design and LRFD Methods (현행설계법 및 하중저항계수설계법에 의한 완전 조립식 교량 하부구조의 설계결과 비교)

  • Kim, Tae-Hoon;Kim, Young-Jin;Shin, Hyun-Mock
    • Journal of the Earthquake Engineering Society of Korea
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    • v.15 no.2
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    • pp.11-22
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    • 2011
  • The design comparison and nonlinear analysis of totally prefabricated bridge substructure systems are performed. The prefabricated bridge substructures are designed by the methods of present design and load and resistance factor design (LRFD). For the design, the current Korea Highway Bridge Code (KHBD), with DB-24 and DL-24 live loads, is used. This study evaluates the present design method of KHBD (2005) and AASHTO-LRFD (2007) for totally prefabricated bridge substructure systems. A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of reinforced concrete structures, was used.

LRFD Design and Reliability Level Estimation of a Steel Closed-Box Girder Bridge (폐단면 강박스거더교의 LRFD 설계와 신뢰성수준 평가)

  • Huh, Jung-Won;Yun, Dong-Geon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.23 no.2
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    • pp.217-225
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    • 2010
  • Most of the steel bridges in Korea are being currently designed by the allowable stress design method that uses the conventional deterministic factors of safety. However the limit state design based on the concept of probability, statistics and reliability engineering is becoming very popular as a global standard deign method, leading the rational and economic bridge design. As part of the fundamental research to establish the load and resistance factor design(LRFD) of steel bridges considering domestic environmental conditions and regional characteristics, an experimental design is conducted by applying AASHTO-LRFD specification especially to a steel closed-box girder, which occupies relatively a large portion of steel bridges in Korea. Throughout the experimental design according to various sectional changes, some of the issues to be considered in the LRFD design of a composite steel closed-box girder bridge are examined. In this process, an Excel-based design verification program is developed for easy computation and prevention of errors. Quantitative reliability levels of the bridge sections designed by LRFD are also estimated using a reliability analysis method, and compared with the target reliability indexes applied in the LRFD design to verify the validity of the procedure and methodology used in this study.

Reliability Analysis of Composite Girder Designed by LRFD Method for Positive Flexure (하중저항계수설계법(LRFD)으로 설계된 강합성 거더의 휨에 대한 신뢰도해석)

  • Shin, Dong-Ku;Kim, Cheon-Yong;Paik, In-Yeol
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.3A
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    • pp.539-546
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    • 2006
  • The reliability analysis of simply-supported composite plate girder and box girder bridges under positive flexure is performed. The bridges are designed based on the AASHTO-LRFD specification. A performance function for flexural failure is expressed as a function of such random variables as flexural resistance of composite section and design moments due to permanent load and live load. For the flexural resistance, the statistical parameters obtained by analyzing over 16,000 samples of domestic structural steel products are used. Several different values of statistical parameters with the bias factor in the range of 0.95-1.05 and the coefficient of variation in the range of 0.15-0.25 are used for the live-load moment. Due to the lack of available domestic measured data on the dead load moment, the same values of statistical properties used in the calibration of AASHTO-LRFD are applied. The reliability indices for the composite plate girder and box girder bridges with various span lengths are calculated by applying the Rackwitz-Fiessler technique.

Calibration of Load and Resistance Factors in KCI Code Based on Domestic Data (국내 통계자료를 이용한 설계기준의 하중저항계수 검증)

  • Kim, Jee-Sang;Kim, Jong-Ho
    • Journal of the Korea Concrete Institute
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    • v.23 no.4
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    • pp.495-501
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    • 2011
  • The load combinations in current KCI Design Code are determined with reference to those in ACI 318-05, which adopts the LRFD (load and resistance factor design) format. The load and resistance factors in LRFD format should be determined to meet the required levels of reliability index or probability of failure for various predetermined failure modes, which are also based on the statistical data reflecting locality and contemporary situation. However, the current KCI Design Code has been written utilizing foreign data, because of insufficiency in accrued data in Korea. This study considered the current safety levels of KCI Code based on published domestic data to evaluate appropriateness of the current KCI regulations. Based on the calibrated reliability index of the existing Code, the new resistance factors are suggested. The results presented in this paper can be considered as a basic research for establishment of unique design format for future Korean Codes.

3-D Frame Design Using Second-Order Plastic-Hinge Analysis Accounting for Lateral Torsional Buckling (횡비틀림좌굴을 고려하는 2차 소성힌지해석을 이용한 3차원 강뼈대 구조물 설케)

  • 김승억;박주수
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.1
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    • pp.117-126
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    • 2002
  • In this paper, 3-D fame design using second-orders plastic-hinge analysis accounting for lateral torsional buckling is developed. This analysis accounts for material and geometric nonlinearities of the structural system and its component members. Moreover, the problem associated with conventional second-order plastic-hinge analyses, which do not consider the degradation of the flexural strength caused by lateral torsional buckling, is overcome. Efficient ways of assessing steel frame behavior including gradual yielding associated with residual stresses and flexure, second-order effect, and geometric imperfections are presented. In this study, a model consisting of the unbraced length and cross-section shape is used to account for lateral torsional buckling. The proposed analysis is verified by the comparison of the LRFD results. A case studs shows that lateral torsional buckling is a very crucial element to be considered in second-order plastic-hinge analysis. The proposed analysis is shown to be an efficient reliable tool ready to be implemented into design practice.

3-D Frame Analysis and Design Using Refined Plastic-Hinge Analysis Accounting for Local Buckling (국부좌굴을 고려하는 개선소성힌지해석을 이용한 3차원 강뼈대 구조물 해석 및 설계)

  • Kim, Seung Eock;Park, Joo Soo
    • Journal of Korean Society of Steel Construction
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    • v.14 no.1
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    • pp.13-21
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    • 2002
  • In this paper, 3-D frame design using refined plastic-hinge analysis accounting for local buckling is developed. This analysis accounts for material and geometric nonlinearities of the structural system and its component members. Moreover, the problem associated with conventional refined plastic-hinge analyses, which do not consider the degradation of the flexural strength caused by local buckling, is overcome. Efficient ways of assessing steel frame behavior including gradual yielding associated with residual stresses and flexure, second-order effect, and geometric imperfections are presented. In this study, a model consisting of the width-thickness ratio is used to account for local buckling. The proposed analysis is verified by the comparison of the LRFD results. A case study shows that local buckling is a very crucial element to be considered in second-order plastic-hinge analysis. The proposed analysis is shown to be an efficient, reliable tool ready to be implemented into design practice.