The St. Louis Republic. [volume] (St. Louis, Mo.) 1888-1919, 1901-03-17

De Salu. me TeuuCllOu III COSl VI Opcidliht
our railways, and the consequent fall II
freight rates, have been potent factors II
| enabling the United States to send abroa'
last year N,45S. 000.0 90 worth Of exports an
food the world with our food and manufac
tured products.
Picturesqueness in Bridges Has
Given Place to Cheapness
And Ugliness.
In early days the building Of a bridge wal
a matter Of great ceremony, and 1t wal
consecrated to protect 1t from evil spirits
Its construction was controlled by priests.
as the title Of the Pope Of Rome. "Ponti-
feN MaXimus.' indicates.
Railways changed all this. Instead Of tbs
picturesque stone bridge. whose long line
Of low arches harmonized with the land
scape. there came the straight girder or
high truss. ugly indeed. but quickly built,
and costing much less.
Bridge construction has made greater
progress in the United States than abroad.
The heavy trains that We have described
called for stronger bridges. TIL large
American rolling-stock is not used in Eng
land, and but little on the Continent of
Europe. as the width of tunnels and other
obstacles will not allow of it. 1t Is said
that there is an average of one bridge for
every three miles OF railway in the United
States. making 1000 bridges. most of which
have been replaced by new and stronger
ones during the last twenty years.
This demand has brought into existence
many bridge-building companies, some Of
whom make the whole bridge, from the ore
to the finished product.
Before the advent of railways. highway
bridges in America We're made of wood, and
| called trusses. Few of them existed before
railways. The large rivers and estuaries
were crossed in horse boats, Il trip more
dangerous than an Atlantic voyage now is.
A few smaller rivers had wooden truss
bridges. Although originally invented by
Leonardo da Ninci. in the Sixteenth Cen
fury, they We're reinvented by American
carpenters. Some of Burr's bridges are
still standing after more than one hundred
years use. This shows what wood can do
when not overstrained and protected from
weather and fire.
The coming Of railways required u strong
er type of bridge to carry concentrates
loads. and the Howe truss, with vertical
iron rods, was invented, capable of 15O-foot
spans.
ABOUT 1865 iron bridges began to take the
place OF wooden bridges. Die-forged eye
bars and pin connections allowed of long
er panels and longer spans. The first long
span bridge was a single-track railway
bridge of 4O0-foot span over the Ohio at
't'Nh was ~ " u
great achievement in 1870.
The kinzua viaduct. $40 feet high and
over half i mile long, belongs to this era.
1t Is the type of the numerous high via
ducts now SO common
About 1855 a new material was given to
engineers, having greater strength and ten
acity than iron, and commercially available
from its low cost. This is basic steel. After
many experiments, the proper proportions
OF carbon, phosphorus. sulphur. and man.
ganese were ascertained, and uniformity re-
suited. The open-hearth process is now gen.
orally used. This new chemical metal, for
such II is. is 30 per cent stronger than iron.
and can be tied in n knot when cold.
The effect of improved devices and the
use of steel is shown by the weights OF the
4oe-foot Ohio River iron bridge, built in
1879. and a bridge at the same place, built
in 1886.
The bridge of 1870 was Of iron, had panels
twelve feet long, and its height was forty
five feet. and span 400 feet.
The bridge of 1856 was Of steel, had pam
els thirty feet long. and its height was
eighty feet. Its span was go feet. The
weights of the two were nearly alike.
The cantilever design, which is a revival
OF a very ancient type. came into use. The
great Forth bridge. in Scotland. 1.60G-foot
span, is of this style, as are the O1-foot
spans at Poughkeepsie. and now a new one
is being designed to cross the st. Lawrence
near Quebec. of 1.sOO-foot span.
This is probably near the economic limit
OF cantilever construction, but the s,lspen-
sion bridge can be extended much farther.
as 1t carries no dead weight of compress
sion members.
The Niagara Suspension Bridge, Of slO-foot
span. built by Roebling in 1852. and the
Brooklyn bridge. of LOO feet. built by Roeb-
ling and his son. twenty years after. marked
a wonderful advance in bridge design.
Thirty years later, when a new bridge of
l,6U feet was wanted to cross another part
of the East River at New York, the same
lines Of construction were followed, and thew
Will be followed in the 2. 1GO-foot span. de-
signed to cross the North River, some time
In the Twentieth Century. The only radical
advance IS the use of a better steel than
could be had in earlier days.
Steel-arched bridges now are scientifically
designed. Such are the new Niagara bridge.
of S4O-foot span. and the Alexandra bridge.
at Paris.
1t Is curious to see how little is said about |
these beautiful bridges, which the public
takes as a matter of course. II they had
been built fifty years ago their engineers |
would have received the same praise as |
Robert Stephenson or Roebling, and Justly |
so. as they would have been men of excep. |
tional genius. When these bridges were |
built, in 1898. the path had been made so |
clear by Investigation and the |
OF a better steel. that the task
easy.