Out-of-Plane Effective Length Factors of Chords in a Truss-Type Spreader Beam

In the lifting operations of construction projects， the chords of a truss-type spreader beam serve as load-transferring members. These chords only contact rope-like flexible materials outside the plane of the truss and have very weak end supports. However， neither textbooks on mechanics of materials nor Standard for Design of Steel Structures （GB 50017-2017）address the stability of such a slender centrally compressed bar without end supports， nor do they provide a corresponding effective length factor. First， the static equilibrium method was used to derive the effective length factor and critical force for a slender centrally compressed bar without end supports to maintain its buckling stability. Subsequently， a compressive buckling finite element analysis was performed using the eigenvalue method in ANSYS software. The critical forces obtained by the finite element method showed strong agreement with the theoretical values. The effective length factors for the two different buckling modes （flexural and reverse flexural） were determined to be 1 and 0.5， respectively. Therefore， the chords of the truss-type spreader beam are more prone to buckling instability in the flexural mode， and using an effective length factor of 1 is feasible.