The Caucasian. (Shreveport, La.) 1900-192?, 1907-03-17
THE WIND AL0FT.
Towering Skyserapers Have to Stand a
of of EIoNyino

Towering Skyserapers Have to Stand a
Lot of Blowing.
The wind velocity in the vicinity o.
New York is not. on the average t..
year round. extraordinary. but at time ;
1t blows at the rate of fifty and six:
miles an hour. Then signs 20 scu3ay-
ing up Broadway, umbrellas turn i'll
side out, and the welrers of skirt;
struggle frantically TO hold togethe.
their various articles of clothing FL.'
man on the top of skyscraper is like
sailor sent aloft in storm to fur
sails. He clings Gy tooth and nail to
whatever support he can find and gets
down again, if lie can. with more alac-
rity than he went up This wind We
locity-not in. its average. but at its
maximum-is an important mathemat-
zeal problem with the engineer when
he runs building twenty to forty
stories high. The wind pressure on Il
tall building must be reckoned very
carefully. A structure five or six hun
dred feet in the air must be braced to
withstand wind pressure of some
thing like thirty pounds to the square
foot, With tower siXty-fiye feet
square and several hundred feet above
the top of the main building there IS
wind pressure at certain seasons of
ocean steamers half across the ocean
il it could be harnessed and converted
into available horsepower The re-
sistance to this wind pressure must he
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 III
closed court on windy day. The line
would then he found to vibrate and
swing very much like the pendulum Of
clock. A recent test of the vibra tio.;
of a tall building in a heavy wind wa
thus made. and it was found that til.
line swung back and forth through II
arc of nearly two degrees. Nature he's
supplied us with something that ro""e.
spends to a plumb line. Our brains
appear to float In a liquid when stand
ing on vibrating tower. and the dizZr
sensation communicated to us Is not
all fancy The rocking Of tower fire
or six hundred feet in the air Is not
very different from that Of shin in a
sea. There are cases of "seasick
ness" among the cliff dwellers Of Man.
haitian. and they have to get accns-
toned to their high attitudes before
they are immune
II the wind pressure should at any
time reach the maximum stress al
lower for the Singer building. il wc,,'
represent over It's whole surface a
force equal to $4,000 foot tons. AS t''e
total weight of the tower is only 230c0
tons. 1t would he possible to overturn
this portion OF the building. or. rather
lift 1t up from its foundation should
the wind blow at such velocity as to
exert an even pressure of thirty pounds
per square foot. To avoid any such
contingency each heavy iron column i;
anchored to the foundation caissons
some sixty feet below the surface of
the ground. The margin of safety THIS
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