The Canadian Standard CAN/CSA-S37-M86 “Antennas, towers and antenna supporting structures” follows a quasi-limit states approach in which the member forces determined for specified loads are multiplied by a unified factor and compared with factored resistances given in CAN3-S16.1-M84. This results in designs basically the same as those resulting from a working stress design with a factor of safety of 5/3. Such structures exhibit a non-linear structural behaviour even under service loads. Thus the effect of ice accretion and direct interaction between wind and ice does not permit the load factors specified in CAN/CSA-S16.1-M89 “Limit states design of steel structures” to be directly applied to antenna supporting structures.In this study, 41 different towers (representing various heights and designed for different ice classes and wind pressures) were analyzed under specified loads and then under a set of factored loads. From the comparison of the design forces in the towers with those calculated according to the existing standard, a set of partial load factors was derived. The new load factors to be used in the 1993 edition of S37 are presented and justified. Key words: antenna towers, guyed towers, ice and wind loads, limit states design, self-supporting towers, working stress design.
The present study contains an analysis of the recorded and predicted values of ice accretion for the meteorological stations in Canada; also, the value of the wind pressure associated with the maximum ice accretion is studied. The values were compared with those specified in CAN/CSA S37-M86. Changes to the ice map of Canada are proposed based on the climatic data analyzed, and this map is compared with the one specified in the 1991 edition of the Ontario Highway Bridge Design Code. Also, some modifications to the method of calculating radial ice thickness are recommended to include the size of the member. Key words: antenna towers, environmental loads, guyed towers, ice loads, self-supporting towers.
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