Second-order analysis of lattice booms considering restraint from the web members

Lattice booms, used in mobile cranes, are welded using slender high-strength steel tubes, and their carrying capacity is determined through the local stability of the chords. However, of the two methods for calculating it, the overall stability formula of axially compressed members is too conservative, and geometrically nonlinear analysis with imperfections is too complicated to apply. To achieve a more accurate and simple calculation of the local chord stability, a second-order analysis considering restraint from web members and initial geometric imperfections is proposed. This study demonstrates that web members not only reduce the maximum chord deflection but also supply a restraint moment for the chords, thereby reducing the maximum stress of the chords, which was ignored or partially ignored in the past. A numerical example is presented to verify the effectiveness and correctness of the second-order analysis of the maximum stress on the chords presented in this paper. This method can be extended to the design and analysis of other similar lattice structures.