The times. [volume] (Washington [D.C.]) 1897-1901, 1901-03-17

and justly So as they would have bee
men of exceptional genius. When thes
bridges were built in 1898, the path ha
been made so clear by mathematical in
vestigaticn and the command of a bette
steel that the task seemed easy.
That which marks more clearly tina
| anything else the great advance i
| American bridge building during tn
last forty years is the reconstruction o
! the famous Victoria Bridge over the ST
Lawrence. above Montreal. This bridg
was designed by Robert Stephenson. an
| the stone piers are n monument to hi
engineering skill. For forty winters the.
have resisted the great fields of ice born
by a rapid current Their dimension
We're so liberal that the new bridge wa!
put upon them, although four times 4
wide as the old one.
The superstructure was originally mad
of plate-iron tubes, REINFORCED by tee
and angles, similar to Stephenson!
Menai Straits Bridge. There are twenty
two spans of 2l0 feet each, and a centra
one of $50 feet. Perhaps these tubes wer'
the best that could he had at the time
but they had outlived their usefulness
Their interiors had become greatly cor
roded by the confined gases from the
engines and the drippings from the chem
icals used in cod-storage cars. Theii
height was insufficient for modern large
cars. and the confined smoke made then
so dark that the number of trains was
greatly limited.
1t was decided to build a new bridge OF
-
hearth steel. This was done, and the
comparison is as follows: Old bridge, II
feet wide. single track, live load of one
ton per foot; new bridge, O. feet wide
two railway tracks and two carriage-ways
live load five tons per foot.
The old iron tubes weighed 10000 tons,
cost s2,713,0o0, and took two seasons to
erect. The new truss bridge weighs %,
600 tons, has cost between $4,000 and
s., 400, 600, and the time of construction was
one year.
During his experience the writer has
seen the rolling-load of bridges increase
from 2,OG0 to 1000 pounds per iineal foot of
track, with an extra allowance for con-
centrated loads.
The modern high office building is an
interesting example of the evolution of a
high-viaduct pier. Such a pier of the re-
quired dimensions. strengthened by more
columns strong enough to carry many
floors is the skeleton frame Enclose the
sides with brick. stone. or terra-cotta. add
windows and doors and elevators, and 1t
is complete.
Fortunately for the stability Of these
high buildings, the effect of wind pres
sures had been studied in this country in
other high viaducts.
All this had been thoroughly worked
out and known to our engineers before
the fan of the Tay Bridge in Scotland.
That disastrous event led to very careful
experiments on wind pressures by Sir Ben
jamin Baker, the very eminent engineer
of the Forth Bridge. His experiments
showed that n wind gauge of 300 square
feet area showed n maximum pressure os
IS pounds per square foot, while a small
one of one and one-half square feet area
registered gusts of Il pounds per square
foot.
The modern elevated railway of cities
is simply a very long railway viaduct.
Some idea may be gained of the life of
a modern riveted-iron structure from the
en- perience of the Manhattan Elevated
Railway of New York. These roads were
built in 1853 to carry uniform loads of
600 pounds per lineal foot, except Second
Avenue. which was made to carry 200.
The stresses were below 10000 pounds per
square inch.
These viaducts have carried in twenty
two years over .. 0ooOO0 trains, Weighing
,ver 100000 tons, at a maximum speed
IF twenty-five miles an hour, and are stir
n good order.
Bridge engineers Of the present day are
Tree from the difficulties which confronted
The early designers of iron bridges. The
of bridge design was under
stood in 1870, but the proportioning of de-
tails had to be worked out individually.
Every new span was a new problem. Now
the engineer tells his craftsman to de
sign span of a given length. height. and
width. and to carry such a load. BY the
light Of experience he does this at once.
Connections have become standardized
% that the duplication of parts can be car
led TO its fullest extent.
Machine tools are used TO make every
part of a bridge, and power riveters to
asten them together Great accuracy can
low be had. and the sizes of parts have
in a remarkable degree.
We have now great bridge companies.
which are so completely equipped with
appliances for both shop drawings and
construction that the old joke becomes al
most true that they can make bridges and
ell them by the mile
All improvements of design are now pub-
ic property. All that the bridge COM
'anies do is done in the fierce light of
Mistakes mean ruin, and the
ittest only survives.
Having such powerful aids, the Ameri-
an bridge engineer of today has advan-
ages over his predecessors ard over his
european brethren, where the American
ystem has not yet been adopted.
The American system gives the greatest
ossible rapidly Of erection of the bridge |
n its piers. A span Of SIS feet. Weighing |
900 tons, was erected at Cairo on the |
in six days. The parts were |
ot assembled until they were put upon
he false works. European engineers have |
ometimes ordered a bridge to he riveted |
ogether complete in the makers yard. |
nd then taken apart
The adoption of American work in such |
ridges as the Atbara in South Africa. |
he Gokteik viaduct In Burmah 800 feet |
Ugh, and others was due to low cost. |
uick delivery and erection, as well as |
xcellence Of material and construction.
FOUNDATIONS. ETC.
Bridges must have foundations for their
iers. Up to the middle of the nineteenth
entury engineers knew no better wav of