Using the value for W corresponding to a temperature of freezing,
or 32" F., and a barometric height of 30 inches, which is 0.08071
pounds per cubic foot, and changing the wind velocity from feet per
second to miles per hour, the formula for normal pressure per square
foot on a flat surface of rectangular outline becomes :

P = 183 X 2 x 32.2 X 60x16 X 6OT0O X V
or P = 0.0049335 V

WIND PRESSURE ON WIRES

In the case of cylindrical wires the pressure per square foot of pro-
jected area is less than on flat surfaces. The coefficient by which the
pressure on flat surfaces must be multiplied to obtain the pressure on



a Dy Google



Transmission Towers 9

the projected surface of a smooth cylinder, varies, according to different
authorities, from 45% to 79%. Almost all Engineers in this country
assume this coefficient to be one-half, and, on this assumption our
formula becomes

P - 0.00246675 V>
for the pressure per square foot on the projected area of the wire, with
any coating it may have on it.
Mr. H. W. Buck has given the results of a series of wind pressure
experiments made at Niagara on a 950 ft. span of .58 inch stranded
cable, erected so as to be normal to the usual wind. From the data
obtained, the following formula was derived:

P = 0.0025 V
in which

P — Pressure in pounds per sq. ft. of projected area
V — Wind velocity in miles per hour.
