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塔吊臂架或塔身等常为格构式受压构件,在研究其整体稳定时,除考虑弯曲变形的影响外,还要考虑剪切变形;用静力平衡方法可推导出在弯曲和剪切变形影响下的临界应力为σ=π～2E/λ_h～2,其中折算长细比λ_h=(λ～2+π～2EAγ_(?))～(1/2)为剪切角。各种双肢、三肢或四肢的缀条式受压构件λ_h值是不同的,见《钢结构设计规范》TJ17-74的表15,和《起重机设计规范》的表J5。这些λ_h计算公式的表下都注明斜缀条
Tower crane booms or towers are often latticed compression members. When studying the overall stability, in addition to taking into account the effects of bending deformation, shear deformations must also be considered; static and balanced methods can be used to derive bending and shear forces. The critical stress under the effect of shear deformation is σ=π~2E/λ_h~2, in which the slenderness ratio λ_h=(λ~2+π~2EAγ_(?))~(1/2) is the shear angle. The value of λ_h for various types of compression members of the double limbs, three limbs or four limbs is different, see Table 15 of the “Steel Structure Design Specification” TJ17-74, and Table J5 of the “Crane Design Code”. These λ_h calculation formulas are marked with slashes