Assessment of reinforcements for enhancing structural performance of cold-formed steel polygonal conical poles for antennas support

Abstract The objective of this research is to present practical solutions for improving structural performance of thin-walled conic polygonal monopoles. The analysis encompasses computational simulations, analytical evaluation, and structural verification of reinforcements for openings and longitudinal folded stiffeners of flat walls. A benchmarked solution is derived from a design involving a 20-sided cold-formed steel polygonal section employed to support telecommunication antennas at a height of 40 meters. The structural verification is performed under the influence of wind loads, with particular attention to the commonly reported basic gust wind speed in Brazil. The conducted analysis encompasses: (i) wind-induced static equivalent dynamic behavior, (ii) parametric elastic buckling analysis, (iii) non-linear finite element analysis of reinforced openings, and (iv) direct strength method (DSM) performance evaluation of stiffened polygonal cross-sections. The importance of combining tailored numerical tools such as the finite strip and finite element methods, as well as wind-induced behavior, is demonstrated through the structural analysis results. In essence, the study's findings reveal the previously overlooked local-distortional buckling interaction in current design guidelines. Moreover, the research demonstrates that incorporating reinforcements and longitudinal stiffeners significantly enhances the flexural capacity of slender structures. Notably, the adoption of a single 4-fold (trapezoid) stiffener shape, per polygonal wall, emerges as a promising effective solution for enhancing the overall flexural capacity. Further full scale experimental structural tests and computational fluid dynamics should be considered for advanced structural analysis and improved design.