118 BELL SYSTEM TECHNICAL JOURNAL 



convenience in engineering studies and in the design of the pole and 

 wire plant the country has been divided into areas according to three 

 intensities of storm loading, designated as heavy, medium and light. 

 Although not denned by the same limits, these classifications for all 

 practical purposes agree with the relative severities indicated by the 

 sleet storm map. 



The heavy storm loading as used in engineering studies is defined 

 as the load caused by a 1 /2" radial deposit of sleet on the wires, 

 strand, etc., combined with a horizontal wind exerting a pressure of 

 8 pounds per square foot upon the projected areas of cylindrical 

 surfaces. The medium storm loading is defined as 2/3 of the heavy 

 loading. The light storm loading is defined as 2/3 of the medium 

 or 4 /9 of the heavy and is in general considered as applying to those 

 areas in which no appreciable sleet storm damage has been recorded. 

 This so-called light loading is, however, in the case of small wires 

 such as those used in telephone plants, considerably in excess of the 

 load created by high wind velocities with no sleet deposit. 



The effective wind pressures used in defining these storm loadings 

 are considered as being produced by steady winds of uniform velocity. 

 The dynamic forces and cumulative loads which might be developed 

 by sudden gusts of wind and vibration of the line are not considered 

 because experience has indicated that aerial plant designed to with- 

 stand the more readily determined static forces is satisfactory. 



A brief discussion of the effect of various sleet and wind loads 

 upon the tension in telephone wires will emphasize the value of in- 

 formation as to probable storm loads, in the design of the aerial wire 

 and pole plant. 



Design of the Wire Plant 



In the design of the wire plant the horizontal component and the 

 vertical component of the storm load must be considered. The weight 

 of the ice covered wire represents the vertical component. The wind 

 pressure upon the projected area of the ice covered wire represents 

 the horizontal component. 



The curves in Fig. 3, show the relative magnitude of the loads 

 upon the wires caused by (a) winds of various velocities with no 

 sleet on the wires, (b) various ice coatings with no wind, and (c) 

 the combination of an 8-pound (73.6 miles per hour indicated velocity) 

 wind with the same ice coatings as in (b). These curves indicate 

 that the wind exerts a relatively small load upon the wire plant even 

 at high velocities and that the load caused by ice accumulation in- 

 creases very rapidly as the radial coating of the ice increases. 



