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장대 강사장교의 극한거동 분석 및 내하력 산정방법 (Ultimate Behavior and Load Carrying Capacity of Long Span Steel Cable-stayed Bridges
Researcher who has been awarded a research grant by Humanities and Social Studies Support Program of NRF has to submit an end product within 6 months(* depend on the form of business)
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  • Researchers have entered the information directly to the NRF of Korea research support system
Project Number D00071
Year(selected) 2005 Year
the present condition of Project 종료
State of proposition 재단승인
Completion Date 2007년 10월 29일
Year type 결과보고
Year(final report) 2007년
Research result report
  • Abstract
  • Cable-stayed bridges exhibit nonlinear behaviors under the normal design loads due to the beam-column effect, cable sags and large displacement. In addition, these bridges are highly redundant structure, so that the inelastic redistribution of the internal forces at a certain load configuration is more diverse and complex than that of other typical highway bridges. Since the buckling behavior and the ultimate strength of the bridges are affected considerably by these inelastic material effects, it is needed to account for both geometric nonlinearities and material inelastic behavior of the structural members in the design of steel cable-stayed bridges.
    There are two main streams for assessing the stability and the ultimate strength of steel cable-stayed bridges: the stability of main structural members and the ultimate strength of the overall bridge. The purpose of this thesis is to propose a new method for evaluating the stability and the ultimate strength of long-span steel cable-stayed bridges based on the concepts of these two main streams.
    For the stability evaluation of steel cable-stayed bridges, an emphasis is focused on the stability of main structural members such as the girder and tower in the bridge based on the element-based stability concept. The interaction equation of AASHTO-LRFD is adopted in order to evaluate the stability of main members of the bridge. Determination of the effective length is an important procedure in that the effective length of main structural members is used not only for determining the nominal strength of members, but also for evaluating the secondary moment effects. Conventional elastic buckling analysis has the inherent absurdity of calculating unduly large effective length for the members that have a small axial force. In this thesis, a methodology for determining the effective length of girder and tower is proposed considering the concept of a fictitious axial force in order to amend the absurdity of elastic buckling analysis. Verification examples of several frame structures demonstrate that the proposed method provides acceptable outcomes.
    For the evaluation of the ultimate strength of cable-stayed bridges, the ultimate behavior and the ultimate strength of the bridges are studied based on the concept of the structure-based stability concept. New criteria, which are derived from the beam-column interaction equation, are proposed in order to consider the effect of primary bending moment as well as axial force in beam-column members. Based on this criterion, iterative eigenvalue analysis is employed to obtain the ultimate strength of the structures. Simple columns with geometric imperfections and several frames are analyzed as benchmark problems. The results show that the proposed inelastic buckling analysis suitably evaluates the critical load and failure modes of steel structures.
    In order to examine the applicability of the proposed methods to bridge structures, example bridges, which have the center span of 600 m, 900 m and 1200 m with various girder depths, and the Incheon Grand Bridge are analyzed by using the proposed inelastic buckling analysis alongside currently established methods. The new methodology of determining the effective length of members proposed in this thesis is proven to be reasonable as well as theoretically valid for the design of a cable-stayed bridge. The proposed criteria for inelastic buckling analysis well describe the distribution of plastic hinges and failure modes of the bridge predicted by the nonlinear elasto-plastic analysis. Consequently, the proposed inelastic buckling analysis is certified to be a competitive alternative of a sophisticated nonlinear elasto-plastic analysis for evaluation of the ultimate strength of steel cable-stayed bridges.
  • Research result and Utilization method
  • (1) The proposed inelastic buckling analysis leads to more economical outcomes than conventional elastic buckling analysis for the design of the girders and towers in steel cable-stayed bridges. In the element-based stability concept, since the proposed inelastic buckling analysis yields smaller effective length of girders and towers than elastic buckling analysis, the peak values of interaction equations by the proposed inelastic buckling analysis are smaller than those by elastic buckling analysis. Consequently, more economical design can be feasible by using the proposed inelastic buckling analysis.

    (2) The proposed inelastic buckling analysis with the concept of a fictitious axial force provides reasonable effective length of the girders and towers in cable-stayed bridges. The system buckling approach, which is generally used to obtain the effective length of the members in the bridges, suffers from the anomaly that unduly large effective length may be obtained for the members having small axial force. Based on iterative eigenvalue analysis, this anomaly can be removed in the proposed inelastic buckling analysis by adding a fictitious axial force for each member.

    (3) The proposed inelastic buckling analysis is a competitive alternative of the sophisticated nonlinear elasto-plastic analysis for evaluation of the ultimate strength of steel cable-stayed bridges in the structure-based stability concept. The proposed inelastic buckling analysis can predict not only the ultimate strength but also the failure modes of the bridges. Because there are no repetitions of solving algebraic equations in the procedure of the proposed inelastic buckling analysis, completion time of the proposed method is not a burden even for some outdated computers. The error between the proposed inelastic buckling analysis and rigorous nonlinear elasto-plastic analysis is small enough to be generally accepted.

    (4) Developed computer program is an integrated solution for performing nonlinear elasto-plastic analysis, elastic buckling analysis and the proposed inelastic buckling analysis. Numerical results of the developed computer programs were in good agreement with the previous published results by other researchers and the results by proprietary software.

    (5) The massive section of girders with no particular aims has no advantages for improving the stability of main structural members and the ultimate strength of the cable-stayed bridges. According to the results of parametric studies, the effective girder depth of the example cable-stayed bridges ranged from 2 m to 3 m and higher girder depth than this range was of no use to improve the stability and ultimate strength of the bridges. In real design situation, some parametric studies should be performed to determine the effective girder depth of the bridge.

    (6) Nonlinear analysis with the proposed inelastic buckling analysis is recommended as the most economical method for design of the cable-stayed bridges in that this combination provides the smallest peak value of the interaction equation for stability evaluation. However, linear analysis is also adequate in that the difference between linear and nonlinear analysis is small enough to compromise.
  • Index terms
  • Cable-Stayed Bridge, Stability, Inelastic Buckling Analysis, Ultimate Strength, Nonlinear Analysis
  • List of digital content of this reports
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