Comparison of frequency- and time-domain analyses for guyed masts in turbulent winds

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Authors: B.F. Sparling and L.D. Wegner
Date: Feb. 2006
From: Canadian Journal of Civil Engineering(Vol. 33, Issue 2)
Publisher: NRC Research Press
Document Type: Article
Length: 6,746 words
Lexile Measure: 1820L

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Abstract: Both frequency- and time-domain methods have been employed in the dynamic analysis of guyed telecommunication masts subjected to turbulent winds. Although the probabilistic frequency-domain approach offers some advantages in terms of its relative ease of implementation and in the statistical reliability of wind load descriptions, the deterministic time-domain method permits a more realistic treatment of system nonlinearities. In this study, a numerical investigation was undertaken to compare frequency- and time-domain dynamic response predictions for a selected guyed mast in gusty winds. Two different analysis techniques were employed, with the frequency-domain calculations performed using response influence lines and the time-domain analyses carried out using a stiffness-based finite element model. Good agreement was observed in root-mean-square and peak dynamic response estimates after compensation was included for differences in turbulence intensity levels assumed in the two models. In general, natural frequencies and mode shapes were also similar.

Key words: guyed mast, dynamic analysis, wind, turbulence, nonlinear behaviour, finite element analysis, cables, frequency domain, time domain.

Resume : Les methodes de domaine frequence et domaine temps ont ete employees lors de l'analyse dynamique des pylones de telecommunication a hauban soumis a des vents turbulents. Alors que l'approche probabiliste du domaine frequence offre certains avantages en termes de facilite d'implantation et de fiabilite statistique des descriptions des charges de vent, la methode deterministe du domaine temps permet un traitement plus realiste des non-linearites du systeme. Cette etude presente une analyse numerique entreprise pour comparer les previsions en reponse dynamique du domaine frequence et du domaine temps pour un pylone a hauban donne dans des vents soufflant par rafales. Deux techniques d'analyse differentes ont ete utilisees dans lesquelles les calculs du domaine frequence etaient effectues en utilisant les lignes d'influence de reponse et les analyses du domaine temps ont ete effectuees en utilisant un modele d'element finis base sur la rigidite. Une bonne correlation a ete observee dans la valeur quadratique et dans les estimations de reponse dynamique de pointe apres avoir inclus la compensation, qui tenait compte des differences dans les niveaux d'intensite de turbulence hypothetiques des deux modeles. Regle generale, les frequences naturelles et les formes des modes etaient tres similaires.

Mots cles : pylone a hauban, analyse dynamique, vent, turbulence, comportement non lineaire, analyse par elements finis, cables, domaine frequence, domaine temps.

[Traduit par la Redaction]

1. Introduction

Guyed telecommunication masts are exceptionally tall, slender structures used to support and elevate various types of broadcast and communication equipment. Because of their inherent flexibility, guyed masts are prone to large-amplitude dynamic motion when excited by the turbulence in gusty winds. Consequently, the dynamic portion of the wind-induced response is typically more severe in both magnitude and distribution than the static response to the steady component of the wind (Vellozzi 1975; Davenport and Sparling 1992). Inadequate recognition of the dynamic behaviour of guyed masts in design standards has contributed to their high failure rate relative to conventional civil engineering structures, as reported by Magued et al. (1989).

Dynamic response calculations for guyed masts are complicated...

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Gale Document Number: GALE|A148277504