Out-of-Plane Stability of Circular Steel Tubular Vierendeel Truss Arches Incorporating Torsional Effects of Chords

Torsional stiffnesses of chords contribute considerably to the sectional torsional stiffness of steel tubular Vierendeel truss arches and hence determine their out-of-plane buckling. To obtain a more accurate stability design for the Vierendeel truss arches, torsional effects of chords on their out-of-plane stability and failure mechanisms were investigated theoretically and numerically. This paper firstly derives the theoretical formulas of the sectional torsional stiffness and the out-of-plane elastic buckling loads for the pin-ended circular steel tubular Vierendeel truss arches. It is found that incorporating the torsional stiffness of chords can remarkably enhance the sectional torsional stiffness of the Vierendeel truss arches and their out-of-plane elastic buckling loads by similar to 41%. Then, the out-of-plane elastic buckling loads are calculated for the pin-ended arches by the equilibrium theorem and for the fix-ended arches by the numerical fitting. In both cases, the sectional torsional stiffness and elastic buckling loads are closely dependent on the transverse-to-chord member stiffness ratio (i(t)/i(c)). Furthermore, the out-of-plane inelastic buckling behaviors are investigated numerically in the end-fixed Vierendeel truss arches with large i(t)/i(c), where the ultimate bearing load in full-span radially uniform manner can be significantly enhanced by similar to 43% by incorporating the torsional stiffness of chords. The calculated reduction factors confirm the design curve b from GB50017-2017 or Eurocode 3 and can provide a conservative design for the out-of-plane stability of the circular steel tubular Vierendeel truss arches.