Techno Press

Steel and Composite Structures   Volume 3, Number 4, August 2003, pages 261-275
Out-of-plane buckling and bracing requirement in double-angle trusses
Shaofan Chen and Mingzhou Su

Abstract     [Full Text]
    Truss members built-up with double angles back-to-back have monosymmetric cross-section and twisting always accompanies flexion upon the onset of buckling about the axis of symmetry. Approximate formulae for calculating the buckling capacity are presented in this paper for routine design purpose. For a member susceptible only to flexural buckling, its optimal cross-section should consist ofrnslender plate elements so as to get larger radius of gyration. But, occurrence of twisting changes the situation owing to the weakness of thin plates in resisting torsion. Criteria for limiting the leg slenderness are discussed herein. Truss web members in compression are usually considered as hinged at both ends for out-of-plane buckling. In case one (or both) end of member is not supported laterally by bracing member, its adjoining members have to provide an elastic support of adequate stiffness in order not to underdesign the member. Thernstiffness provided by either compression or tension chords in different cases is analyzed, and the effect of initial crookedness of compression chord is taken into account. Formulae are presented to compute the required stiffness of chord member and to determine the effective length factor for inadequately constrainedrncompressive diagonals.
Key Words
    truss; double-angle section; flexural-torsional buckling; width-thickness ratio; elastic support; lateral stiffness; bracing; effective length.
School of Civil Engineering, Xi

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