The Columbian. [volume] (Bloomsburg, Pa.) 1866-1910, 1905-12-07
FINE AMERICAN BRIDGES
lead the World in Size and
Method of Construction
PART TAKEN BY ROADS
new Inventions to Suit Conditions
Longest Bridge at Cairo, ILL.,
Brooklyn Most Expensive Struct-
ure In World-Changes Most No
ticeable I'm Smaller Construction.

ticeable I'm Smaller Construction.
To the railroad must be given the
credit for furnishing the impetus
hat has resulted IN the marked ad-
rances of the past half century. Es-
>ecially Is this true in the United
States, whose unprecedented growth
would have been impossible without
he aid of its transportation lines.
The railroads, In their constant
ndeavor to improve, their unceas-
ng effort to give the American peo-
lie a service unexcelled in the whole
world for comfort, speed and cheap
iess, have so Increased the weight Of
heir rolling stock and train loads
hat the light structures which did
service when the first transconti-
rental road penetrated to the Pacific
)oast have become obsolete and ut
erly incapable Of meeting the de-
nands of standard modern carriers.
Thus stronger and better bridges
lad to be built.
Co-extensive with the develop
nsnt of railroading has been that of
he iron and steel industry. The two
lave co-operated in a transforma-
ion that is one OF the marvels OF the
nineteenth and twentieth centuries.
America, the land Of big things,
Possesses more striking examples Of
dvanced bridge construction prob
sbly than any other country It has
be longest metallic structure across
my river in the world-that over
he Ohio River at Cairo, ILL.,, exceed
ng in length the renowned Tay
Bridge in Scotland by SS feet.
The Cairo bridge was finished in
1883. 1t is 10,560 feet-precisely
wo miles-in length, though origi-
ally, with the timber trestle ap-
roaches, which have since been
nled In and replaced by solid en-
ankments, there was almost four
niles Of continuous bridge work.
A bridge with the longest single
pan ever built is one by an American
irm across the st. Lawrence River
TX miles above Quebec. 1t is de-
igned for both railway and wagon
rafilc and contains a central span
300 feet in length and $50 feet
bove the water, permitting the un-
Instructed passage of the largest
sssels afoat.
In drawbridges, too, America leads
he world. There was opened at
)maha recently a center pier dou-
lie drawbridge each swing span Of
rhich Is 525 feet long.
This excessive length was neces-
ary on account Of the shifting chan
,el Of the Missouri River, which Is
onstantly undergoing changes in its
curse, and the new bridge was de-
.gned to provide as much as posi-
lie for the future vagaries OF the
sream.
In the common types of steel
rfdges--the truss, the cantilever,
10 suspension, etc.-it cannot be
aid that there have been any ex-
-aordinary changes since these
ypes were first introduced. Beyond
eing successfully strengthened and
improved in minor details so as to
AXE care Of the greater loads they
re called upon to bear, these struct-
res remain practically unaltered in
heir general outlines.
Bridge engineers to-day confine
themselves chiefly to the study OF
.resses and strains, the provision Of
laximum strength with the mini
ium use of material, and conse-
.uent minimum cost. Every pin or
olt that can be dispensed with Is
much saved.
1t is in the smaller bridges that the
reatest changes have occurred in
scent years. In movable structures
yer navigable waterways the devel-
pment has been revolutionary in its
.ature.
The old style swing or draw
ridge is being rapidly superseded;
t least where the channels are not
excessively wide, by the roller lift
ridge, an improvement on the pivot
ascule type which had its origin In
ne feudal days when the spans over
astle moats were raised up on end
o shut of communication with the
outside world.
The original design of the roller
1T consisted of two movable leaves
hat met In the center OF the stream
md were rolled up and down from
piers on either shore. Single-leaf
5raws, however, are now being built
n many instances where this form
Of construction is best adapted to To-
2al conditions.
Its advantages over the center
pier bridge are overwhelming, In
that 1t leaves unobstructed the full
width of the river or canal. Vehi-
cles or cars cannot fall into the wa
ter when the lift Is open to vessels.
1t Is more rapid and economical
of operation, saving delay and ex-
pense.
Concrete, reinforced by steel, Is
becoming more and more a popular
material for the construction of per-
manent bridges over small streams
and ravines. Their advantage over
Iron structures lies In their greater