Non-linear behaviour of lattice panel of angle towers

Abstract

Lattice microwave towers and transmission towers are frequently made of angles bolted together directly or through gussets. Such towers are normally analysed to obtain design forces using the linear static methods, assuming the members to be subjected to only axial loads and the deformations to be small. The effects of the end restraints, eccentricity of connections and secondary bracings (redundants) on the strength of the compression members are usually accounted for in the codal recommendations by modifying the effective length of the members and thus the design compressive strength. Hence, forces in the redundants are not known from the analysis and their design is empirical. In this study, non-linear analysis of angle compression members and the single panel of angle planar as well as three-dimensional lattice frames, as in typical lattice towers, are carried out using MSC-NASTRAN software. Account is taken of member eccentricity, local deformation as well as rotational rigidity of joints, beam-column effects and material non-linearity. The analytical models are calibrated with test results. Using this calibrated model, parametric studies are carried out to evaluate the forces in the redundants. The results are compared with codal provisions and recommendations for the design of redundants are presented.