Abstract Support for antennas placed as high as 40‐50m demands traditional trussed steel or pole towers, the former with much larger base area than the later and the consequences for the costs of the ground occupancy. This aspect is of upmost importance for both urban and rural areas and the reason for the development of higher steel poles with polygonal cross‐section, searching for slender thin‐walled structures. The present research focus is cold‐formed steel conic twenty‐sided polygon solution allowing 40‐50m high antenna support, for which one must deal with the following challenges: (i) wind‐induced dynamic behavior, (ii) buckling analysis, (iii) localized stress concentration close to the openings along the pole, (iv) connection solution that strongly affects the erection procedure and (v) the fatigue effect. Beyond these aspects, results of the dynamic behavior, elastic buckling, nonlinear structural behavior until the collapse and design procedures for the computation of the structural strength of the steel pole are presented and commented, revealing the importance of structural analysis by combining tailored numerical tools as the finite strip and the finite element methods, as well as frequency domain methods for smooth and turbulent wind actions. Additional CFD and experimental wind tunnel results should be considered for advanced structural design, as well as experimental structural analysis to confirm the set of numerical results and the design procedures adopted for the steel polygonal poles.
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.
modos de falha e o caminho crítico.
Construções leves em aço são frequentemente utilizadas como uma solução estrutural apropriada permitindo redução do custo da supra e infraestrutura. Nesse contexto, empregam-se Perfis Formados a Frio (PFF) e que, sendo elementos estruturais esbeltos, tornam-se propícios a condições de flambagem. Assim, este estudo desenvolve uma solução de telha autoportante em PFF do tipo viga-calha que apresente o melhor rendimento tanto à flexão (provocada pela ação do vento) quanto à cobertura obtida. Para a análise de estabilidade, utilizou-se o software CUFSM (Constrained and Unconstrained Finite Strip Method) baseado no Método das Faixas Finitas. Além disso, usou-se o Método da Resistência Direta para a determinação da resistência à flexão de projeto. Logo, este artigo apresenta seis análises numéricas a fim de propor um modelo que apresente a melhor relação entre Momento Resistente Efetivo e taxa de cobertura. Finalmente, sugere-se uma solução de telha do tipo viga-calha autoportante que se mostre eficiente na flexão sob vento de sucção e apresente uma taxa de cobertura satisfatória.
Buckling mode interaction in cold-formed steel (CFS) members must be considered for the structural design, which may lead to a significant reduction of the structural strength, usually recognized as erosion of the limit load. So far, the distortional-global (DG) buckling interaction is not covered by codes, e.g. Brazilian code NBR 14762:2010. The present investigation is aimed at the DG interaction of CFS lipped channel (LC) columns, which is the most usual section. The methodology evolves a parametric analysis, over a single LC column under DG buckling interaction. First, a study of initial geometric imperfection (IGI) sensibility is performed, with the purpose of understanding the influence of the IGI on the column’s behavior. Moreover, the parametric analysis is extended to a set of yielding stress and column lengths, to understand the ultimate load under different types of DG buckling interaction natures. Conclusions on this research have been shown that the actual global buckling equation from the Direct Strength Method is already suitable to cover the DG buckling interaction for the case of lipped channel columns.
This research was financially supported by CNPq (Proc. 131199/2018-8) and FAPERJ grant E-26/200.825/2019 (242580).
The Direct Strength Method (DSM) is a well-known formulation presented in the Brazilian standard ABNT NBR 14762:2010, that estimates the strength capacity of cold-formed steel (CFS) members. However, this formulation requires the elastic critical buckling loads as point of departure, regarding local (L), distortional (D) and global (G) modes, which can be obtained by (i) elastic buckling analysis or (ii) available direct equations. The present study is dedicated to the development of a computer program, FStr Computer Application, with graphical user interface (GUI), in order to make the buckling analysis easier and approachable for both research activities and engineering design of thin-walled structures with arbitrary cross-sections (sections combining closed cells with open branches). The proposed application uses the Finite Strip Method (FSM), mainly focused on a simple and accessible GUI, which was implemented in the MATLAB App Designer. Validation of the FStr was performed with the help of examples of open and closed cross-sections and comparison with the results of acknowledged computer programs, such as CUFSM and GBTul, based respectively on FSM and GBT (Generalized Beam Theory), as well as analytical procedures for the case of the global buckling modes. Both, the critical buckling loads expressed by the computed signature curve and the correspondent critical buckling modes are compared, confirming the adequate performance of the proposed computational tool. As future research, the authors plan updates for the FStr Computer Application, including the computation of the buckling modal participation and the automatic strength predictions, based on the DSM-based design prescriptions.
