Lateral Stability of Welded Light Trusses

An analysis based on the work energy principle is presented for the elastic lateral stability of light continuous chord trusses supported laterally at equidistant points along both chords. Tests on steel joists, which are representative of light trusses, show good agreement with the analysis. An approximate method, similar to that used for rolled beams, is on the conservative side of test results and is adequate for continuous chords of open cross-section. The more exact analysis of this paper is recommended for continuous chords of closed cross-section of large torsional stiffness compared to the stiffness of the web members. Additional tests on steel joists show that removal of lateral support on the bottom chord reduces the Critical load by about 10%. An analytical study of several selected joists shows that the spacing of bridging during construction depends on the physical properties of the chords, and the spacing at acceptable stress levels is significantly different than that presently used.