Structural assessment of current steel design models for transmission and telecommunication towers

The usual methods of structural analysis involved in the design of steel telecommunication and transmission towers tend to assume a simple truss behaviour where all the steel element connections are considered hinged. Despite this fact, the most commonly used tower geometries possess structural mechanisms that could compromise the assumed structural behaviour. A possible explanation for the structure stability is related to the actual behaviour being close to semi-rigid connections instead of the assumed hinged connections. This paper proposes an alternative structural analysis modelling strategy for the steel tower design considering all the actual structural forces and moments combining three-dimensional beam and truss finite elements. Comparisons of the two above-mentioned design methods with a third method based on the use of spatial beam finite elements to model the main structure and the bracing system on two actually built steel telecommunication towers (40 and 75 m high steel towers) are described. The comparison is based on an extensive parametric study of the tower geometry in order to access the structural tower ultimate and serviceability limit states.