The Ottawa free trader. [volume] (Ottawa, Ill.) 1843-1916, 1880-01-31
4 Comparison.
fst Louis Republican.

things they have done IN tbs direction, the
fact still remains tha, the Tay bridge Is in It's
way, perhaps, the most remarkable structure
IN the world
If we compare the Fay bridge with The one
over the Mississippi at ST. LOUIS, It, Claims as
~ masterpiece OF cu-Iucu.uy' fade away into
utter iusigniicaGCc,
According to the published accounts, the
Tay bridge consist OF 20 spans The thirteen
spans which were blown away were each 2ij
feet long. As these were the longest spans
and were located over the deepest water, they
must have taxed in the highest degree the
abilities Of the engineer in Their construction.
We are told the huge girders for the 2i5.
foot spans, although weighing 200 tons each,
were put together on shore, ilOated into the
swift stream on pCntoors and lifted bodily into
place by the rising OF The tide and by new ar.
rangcments Of hydraulic rams" In 1913 the
40Oloot spans Of the Conway tubular bridge,
each weighing $50 tons, nearly six times as
heavy As the Tay tru-seS, We're raised in thus
manner by Robert Stephenson. The immense
tubes for the Britannia bridge at the Menai
straits, each 4GOlpol span, and weighing 1,5SI
tons, were raised by Stephenson u year or two
later
The central arch OF the st. LOUIS bridge Is
j2O feet in clear span between the masonry
piers, and is Tie longest fixed span in the
world. 1t is SIXTY feet longer than the Menai
straits spans, and nearly two and a half times
as long as the longest spans OF the Tay bridge.
1t is made Of ca,t-stcel, and the immense sruc-
ture was hung up in two halves by enormous
chains or guys, depending from temporary
wooden towers erected on the masonry piers,
The navigation beneath these two halt arches
was uninterrupted and the arch was completed
by the joining of the two parts at the middle
A. L.. g Al ...,1. 4
is another one Of caststeel, having a clear span
of SOP feet, All three of three immense arches
were erected in this manner.
We do not mean 10 say that such length Of
spans and magnitude Of piers as constitute
the -. Louis bridge were needed at the river
Tay, but we wish to show the absurdity of
claiming that that bridge was wonderful
piece OF engineering. The facts prove ii to be
very defective one, The largest piers of the
Tay bridge are formed Of single tubes, 81 feet
in diameter. They therefore rest on an area
of less than 500 square feet The piers Of the
st. LOUIS bridge are solid hcXugonal masses of
masonry, each placed on the bedrock, and
each one rests upon an area five or SIX times
as large as those of the Tay--onc of them
covers an area Of 5000 square feet; about the
size of the largest public diningroom in New
York city.
None of the piers Of the Tay bridge were
sunk over 70 feet deep. Some Of those Of the
St Louis bridge rest 1876 feet below the high
water mark of the Mississippi The weight
of the largest piers Of the Tay bridge will not
exceed four thousand five hundred tons. One
pier Of the st. Louis bridge IS therefore equal
to ten such piers The piers Of both bridges
were sunk down to their resting places by the
same methods The engineer of the Tay
bridge had the full benefit Of the improved
devices designed by Mr. Eads for sinking and
controlling The monster piers i'll the hlississlp-
pi. At ST. Louis provision had to be made
against acres of floating driftwood during the
floods, and against fields of ice in winter yet
so complete were the plans for meeting these
difficulties that scarcely any interruption DC
CURED from them. The workmen on the bed
rock Of the river under the piers, although
working in an atmosphere 80 pounds per
square inch greater than the normal pressure
were in constant Geographic communication
with the Office Of the chief engineer and that
Of the superintendent Of construction, and the
work was actually carried on during several
days at one Of the piers III the river when the
floating ice prevented all communication with
the shore except by the electric wire, stores Of
materials, bedding and food for the worbmen
and engineers having been previously prov-
ded at the pier for such contingency.
At the official test Of the Tay bridge five 10
comotives and Their tenders were put upon the
largest spans At tie official test here four
teen locomotives and their tenders were cOu-
pied together and run back and forth over each
track of the bridge. Then they were arranged
in two separate trains of seven each and these
were run side by side back and forth over each
span, and this was made while the upper road
way (or wagon road and fOopaths were coy
cred with passengers and traffic.
The usual wind pressure assumed as posi-
bic by English engineers is 40 pounds per
square foot of exposed surface. We do not
know what pressure per square foot was as
sumed us possible for the Tay bridge, The
fact that thirteen girdcrs were blown away is
ample proof that the possible pressure was I'M
dercstimated. On the bridge at ST. Louis 1t
was believed possible that the wind pressure
of tornado might reach 100 pounds per
square foot, and the wind braclng OF the struc-
turc was made to meet such contingency.
Enormous bolts of iron extend from the ends
of the spans of the upper roadway down into
the body of the massive piers, and are there
securely, while the size of these bolts
is so great that this enormous wind pressure, |
if ever eXertcd, would not tax them beyond
of their ultimate strength. Besides
these massive bolts each arch has a complete
system of wlnd-bracing from end to end, |
formed of cast-stcel rods carefully tested to
nearly twice as great Il strain as the wind-pres-
sure Of 100 pounds per square foot could pro
duce.
There Is no doubt the error IN the Tay
bridge was in Understanding the force of the
wind. Experiments 10 measure this force are
invariably made near the esrth's surface, and
the velocity of currents there is assumed to be
the same rs at greater heights. 1t by no
means follows, however, that because an in.
strumcnt on the top of a fourstory house indi-
Gates a velocity of 90 miles an hour that the
wind 100 feet higher is not moving at a much
greater velocity. We might as well expect to
find an equal. velocity of current at the bottom
Of river, of that the velocity Of the Cuff
stream Is rs great near the bed Of the ocean as
It Is near its surface, rs 90 suppose that the !,
winds arc not retarded 10y the irctional resist