Iowa state bystander. [volume] (Des Moines, Iowa) 1894-1916, 1913-10-31
HIGH ONES SAFEST.
Facts About Tall Buildings That
Shake.
Delicate instruments Record Lateral
and Vertical NEUTRALITY-SUSPICIOUS.
Of selsmograph and Trepadoms-
ter Used t,. Suits for Damages.

and Vertical observation-disclosures
Of ssIsmosraph and Trepadome-
ter Used h,, Suits for Damages.
The towering skyscrapers. despite
their massive appearance, are rarely
absolutely at rest. An almost contin-
uous series Of vibrations passes over
New York's massive skyline, says the
Sun OF that city. The rush Of street
trafac, the action of engines and ele-
vators. the tricks Of wind pressure are
constantly setting up wave motions
throughout the great structure of
steel and masonry. The fact that
these buildings are, within certain
limits, elastic, is OF course an assur-
ance Of their safety. Accidents from
too much vibration are practically un-
heard Of.
The problem Of the vibrations is Per
haps nowhere so complicated as in
downtown New York. Here are group
ed. of course, the greatest collection
of sykscrapers to be found anywhere
in the world. The constant passing Of
subway trains at the very base OF
these buildings tends to set up vibra-
tons in every direction. The ele-
waited railroads and the surface cars
cause still other vibrations. In every
ONCE building again will be found con-
siderable machinery for running the
elevators and performing other work.
This is usually located in the low
erlbasements at the roots Of the foun-
dations and the waves thus set in mo-
tion travel to the extreme height OF
the structure. The wind pressure is
another important factor.
In order to know exactly how a
building is affected by these vibra-
tions several extremely delicate instru-
ments have been invented. They are
adaptations of the familiar seismo-
graph used to record earthquakes, al
though less complicated and sensitive.
The commoner form, the seismograph,
is used to measure lateral vibrations.
Another machine, the trepadometer;
measures the vertical vibrations.
The general principle Of the apparat-
US in both cases is very simple. The
seismograph consists Of metal table
supported by screws so contrived
that the surface may be placed in an
absolutely horizontal position. On
this table rests a sheet of heavy
glass on four steel balls, which are
perfectly spherical. Above the glass
plate is an adjustable: needle which
passes back and forth along sliding
bar
A piece OF smoked paper is laid on
the glass and the needle adjusted to
touch the surface. And vibration of
the building is taken up by the steel
balls so that the glass on them re-
mains absolutely stationary. The
needle, however, vibrates exactly like
the floor beneath it and scratches a
fine, ragged line along the surface OF
the smoked paper. This line records
the vibration of the building with SCI
entific accuracy.
In the trepadometer heavy weight
Is suspended by long vertical string
so delicate that it responds to the
slightest vibration. A long arm car
rying a pen is attached to the lower
section OF the spring. A very slight
vibration is magnified by the apparat-
US, and the pen at the end of the arr,
traces an irregular line as the spring
moves ever SO slightly up or down.
The pen is set above sheet Of pa
T.. hx,o Ia lx Tho
paper is placed about drum which
revclves once in "a hours. The irreg-
ular line traced by the pen thus re-
cords the vibrations of the building
for one day.
The records of these instruments
are used at times in court to decide
damage cases in which the vibration
Of buildings figures. There may be
great difference Of opinion as to the
damage done by the vibration, but the
records of the seismograph and trep-
adometer are accepted as accurate. In
q recent case suit was brought to re-
cover damages alleged to have been
caused by the vibration set up by ma.
chinery In operation. A number Of
printing presses, it was said, had
caused such vibration that the walls
were finally cracked. Several Wit
nesses visited the building. but their
testimony was contradictory. The
readings Of the apparatus told the
true story, however, and the damages
were awarded on this evidence.
The most violent vibrations are
not found in the highest buildings. as
might be imagined, but often n struc-
lures three or four stories high Of old
construction. Such buildings are Of
solid masonry, and therefore have lit
tie elasticity, and cannot take up the
wave motion. When heavy machinery,
such as printing presses, for instance,
10 set in such building, the jar will
be very perceptible on every floor.
The structure Of the modern sky
scraper Ia entirely different and far
safer. In it the brick or stone 10 mere
ly q shell hung upon a great steel
structure The steel riveted together
ID more or less elastic. A building Of
say 40 stories could vibrate like . g.
ant tuning fork, could even crack and
loosen the brisk and masonry, and yet
not be in danger Of being injured.
The vibrations In q building may be
shown with spoonful Of water in
q small dish. A glass dish 10 better
for the purpose, a watch crystal is
just the thing. Let this be set In any
building in the busy, crowded parts al
the city and you will lind a frequent
vibration. The test may be made more