208 BELL SYSTEM TECHNICAL JOURNAL 



only a moderate degree of success was obtained. From an examination 

 of the data in Table I, it appears for the condition "Equal Sag" that 

 threshold velocities increase with the spacing between the wires and 

 the span length and decrease with an increase in the sag. Because 

 large sags usually accompany long spans it may be somewhat difficult 

 to appreciate the fact that the threshold velocities increase with 

 span length. This is a fact, however, when sag and wire spacing 

 remain constant. Using this basic relation an empirical equation (5) 

 has been developed from the data obtained and is given in Appendix 

 II. A nomogram was constructed for this equation (5) and is given 

 in Fig. 8. 



Results of Natural Wind Tests 



In Fig. 9 are given two curves of the wind velocities recorded at 

 Chester, New Jersey, during the first seven of the eight years the test 

 was in progress. One of the curves (marked, "Maximum") gives the 

 average annual frequency of occurrence in terms of five-minute periods 

 of maximum wind velocities grouped in cells of five miles per hour. 

 The other curve gives the corresponding data for the five-minute 

 average wind velocities. The maximum velocity reached 60 miles 

 per hour on several occasions each year and exceeded 70 miles per 

 hour on at least one occasion. The velocities occurring during the 

 test are considered to be as great as or greater than those to which 

 the structural plant is usually subjected. 



Regarding the data obtained during the presence of glaze, wires 

 with the spacings and sags tested contacted at velocities as low as 10 

 to 15 miles per hour. To some extent the number of contacts increased 

 with the amount of glaze and the velocity of the wind. Also, generally, 

 a greater number of contacts occurred on the more closely spaced 

 wires than on those with greater spacings. In cases of wires spaced 

 3 and 4 inches apart there were occasions when they contacted and 

 froze together for periods of several hours. Due to the erratic action 

 of the wires during the presence of glaze not all of these data were 

 classified in detail as were the results obtained when glaze was absent. 



The classified data obtained during the absence of glaze in terms 

 of normal threshold wind velocities (maximum) are given in Table I 

 for all the arrangements tested, approximately eighty-five. The data 

 given in this table were collected over a period of approximately eight 

 years. While none of the arrangements were under test over the 

 whole period, all were under test for at least one winter season during 

 these eight years. Since the higher velocities occurred more frequently 

 in the winter than in the summer most of the threshold velocity data 



