The Canadian standard CANICSA-S37-94 "Antennas, towers and antenna supporting structures" (S37) has introduced as an appendix a quasi-dynamic method of analysis. This patch load method yields a more realistic pattern of forces in a guyed tower, but S37 contains no firm guidelines as to when this new method is required over the conventional static gust factor approach. This paper describes various comparative studies that were made to determine the conditions under which the normally used gust factor approach does not give sufficiently acceptable results so that patch load analyses are required. Results of the parametric studies and the analyses of a large number of actual towers showed that leg loads in the upper few spans tended to be about 15% larger on average in a patch load analysis. Face shears at the guy supports were also about 15% higher on average in the patch load method. The studies revealed no strong trends between the patch load and gust factor correlation and the tower parameters, although there were slight trends suggesting that a patch load analysis was warranted if the tower height was greater than 250 m, the aspect ratio was greater than 120, or the drag area exceeded 2.0 m2/m. The presence of a cantilever accentuated the margin between the results of the two methods.RCsumC : La norme Canadienne CANICSA-S37-94 a Antennes, tours et structures supportant des antennes ,p (S37) a introduit en appendice une mCthode d'analyse quasi-dynamique. Cette mtthode de chargement selectif aboutit h un motif plus rCaliste de forces dans les tours 8 clbles. Toutefois, S37 ne contient pas de directives fermes h propos du moment oh cette mCthode est requise plutBt que l'approche conventionnelle du souffleur statique. Ce papier dCcrit diverses Ctudes comparatives qui ont Ct C effectuCes pour determiner les conditions dans lesquelles l'approche du souffleur statique normalement utilisCe ne donne pas des rCsultats suffisamment acceptables pour que des analyses par la methode des chargements sClectifs soient requises. Des rCsultats d'Ctudes paramttriques et des analyses de plusieurs vraies tours ont montrC que les charges aux pieds des quelques travCes suptrieures avaient tendance h Etre environ 15% plus ClevCes dans l'analyse par charges ~Clectives. Les contraintes de cisaillement aux supports des cibles ont Ct C aussi environ 15 % plus ClevCes en moyenne dans la mCthode de chargement sklectif. Les mtthodes n'ont pas rtvClC de fortes tendances entre la charge selective et la corrklation du facteur de coup de vent et les paramktres de la tour, bien qu'il y avait de 1Cgeres tendances suggCrant que l'analyse par charge stlective est justifite si la hauteur de la tour d$asse 250 m, si le coefficient d'Clongation est supCrieur a 120, ou si la zone de trainte dCpasse 2.0 m2/m. La presence d'un porte-8-faux a amplifit 1'Ccart entre les rCsultats des deux mkthodes.
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