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Steel and Composite Structures
  Volume 36, Number 3, August10 2020 , pages 307-319
DOI: https://doi.org/10.12989/scs.2020.36.3.307
 


Nonlinear stability of the upper chords in half-through truss bridges
Wen Qingjie, Yue Zixiang and Liu Zhijun

 
Abstract
    The upper chords in half-through truss bridges are prone to buckling due to a lack of the upper transverse connections. Taking into account geometric and material nonlinearity, nonlinear finite-element analysis of a simple supported truss bridge was carried out to exhibit effects of different types of initial imperfections. A half-wave of initial imperfection was proved to be effective in the nonlinear buckling analysis. And a parameter analysis of initial imperfections was also conducted to reveal that the upper chords have the greatest impact on the buckling, followed by the bottom chords, vertical and diagonal web members. Yet initial imperfections of transverse beams have almost no effect on the buckling. Moreover, using influence surface method, the combinatorial effects of initial imperfections were compared to demonstrate that initial imperfections of the upper chords play a leading role. Furthermore, the equivalent effective length coefficients of the upper chord were derived to be 0.2~ 0.28 by different methods, which implies vertical and diagonal web members still provide effective constraints for the upper chord despite a lack of the upper transverse connections between the two upper chords. Therefore, the geometrical and material nonlinear finite-element method is effective in the buckling analysis due to its higher precision. Based on nonlinear analysis and installation deviations of members, initial imperfection of l/500 is recommended in the nonlinear analysis of half-through truss bridges without initial imperfection investigation.
 
Key Words
    half-through truss bridge; aluminum alloy bridge; stability; nonlinear; influence surface
 
Address
Wen Qingjie, Yue Zixiang and Liu Zhijun: State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering,
China University of Mining & Technology, 1 Daxue Road, Xuzhou, Jiangsu province, China
 

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