The united opinion. [volume] (Bradford, Vt.) 1881-1970, 1907-04-05
THE WIND ALOFT.
Towering Skyscrapers Have to Stand a
Lot Of Blowing.

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Lot of Blowing.
The wind velocity in the vicinity of
New York is not, on the average the
year round, extraordinary, but at times
it blows at the rate of fifty and sixty
miles an hour. Then signs go scurry-
ing up Broadway, umbrellas turn in
side out and the wearers of skirts
struggle frantically to hold together
their various articles of clothing. The
man on the top of a skyscraper is like
a sailor sent aloft in a storm to furl
sails. He clings by tooth and nail to
whatever support he can find and gets
down again, if he can, with more alac-
rity than he went up This wind We
locity-not in its average, but at it's
maXimum-is an important mathemat-
ical problem with the engineer when
he runs a building twenty to forty
stories high. The wind pressure on a
tall building must be reckoned very
carefully. A structure five or six hun
dred feet in the air must be braced to
withstand a wind pressure of some
thing like thirty pounds to the square
foot. With a tower siXty-fve feet
the top of the main building there is
a wind pressure at certain seasons of
the ear sufficient to drive a dozen
ocea steamers half across the ocean
if it could be harnessed and converted
into available horsepower. The re-
sistance to this wind pressure must be
secured by angle braces every second
or third story and the whole calculated
out by mathematical formulas.
If there is any doubt in the mind Of
the skeptical about the force of the
wind at great attitudes, he should
drop a plumb line from the top of the
structure to the bottom of some in
closed court on a windy day. The line
would then be found to vibrate and
swing very much like the pendulum of
a clock A recent test of the vibration
of tall building in a heavy wind was
thus made, and it was found that the
line swung back and forth through an
arc of nearly two degrees. Nature has
supplied us with something that CORE
spends to a plumb line. Our brains
appear to float in liquid when stand
ing on a vibrating tower, and the dizzy
sensation communicated to US is not
all fancy. The rocking of tower five
or six hundred feet in the air is not
very different from that of a ship In
sea. There are cases Of "seasick-
ness" among the cliff dwellers of Man
haitian, and they have to get accus-
toned to their high attitudes before
they are immune.
If the wind pressure should at any
time reach the maximum stress al
lower for the Singer building, it would
represent over its whole surface
force equal to 12S,0OO foot tons. AS the
total weight of the tower is only $4,000
tons, 1t would be possible to overturn
this portion of the building, or, rather,
lift it up from its foundations, should
the wind blow at such a velocity as to
exert an even pressure of thirty pounds
per square foot. To avoid any such
contingency each heavy iron column is
anchored to the foundation caissonS
some sixty feet below the surface of
the ground. The margin of safety thus
obtained is sufficient to Withstand any
of the summer wind squalls or tail
ends of West Indian hurricanes which
sweep across Manhattan. - Harper's
Weekly.