Analysis of mechanical characteristics of double flat arm derrick based on three-moment equation with elastic supports

ZHOU Xingyin; CHANG Fengxi; WANG Meng

doi:10.16579/j.issn.1001.9669.2026.08.017

Abstract：[Objective]Conventional force analysis methods for the horizontal arm of double flat-arm derricks fail to consider the influence of tensile elongation of tie rods on mechanical performance and neglect the additional bending moments induced by axial eccentric loads,resulting in insufficient calculation accuracy.To address these issues,an improved analytical method based on the three-moment equation with elastic supports was proposed.[Methods]Firstly,the two-suspension-point horizontal arm of a double flat-arm derrick was taken as the research object,and the tensile elongation effect of tie rods was equivalently treated as elastic supports,from which the three-moment equation applicable to axially eccentric two-suspension-point structures was derived.Secondly,a mechanical model of the axially eccentric two-suspension-point horizontal arm was established,and the axial forces of the two tie rods under both elastic and rigid supports were calculated separately.Then,a finite element model was established using ANSYS software for simulation verification.Finally,the theoretically calculated results were compared with the finite element results.[Results]The results show that the axial forces of tie rods calculated by the three-moment equation with elastic supports are in better agreement with finite element simulation data compared with those obtained using rigid supports,with the maximum relative error reduced from 89.52％under rigid supports to 8.05％under elastic supports.The correction effect of elastic supports becomes more significant with larger lifting loads and smaller tie rod cross-sectional areas,and the influence of tie rod elongation on axial force calculation results cannot be neglected.The proposed method can effectively improve the calculation accuracy and safety of horizontal arm design,and provides a reference for structural analysis of horizontal arms in similar lifting equipment.