El Paso herald. (El Paso, Tex.) 1901-1931, 1913-10-20

means are used. a bridge crossing
the Iowa river at Columbus Junction
has been one of the recent notable re-
constructions. Sometimes 1t becomes
necessary to have a double track IN
place of a single one. A bridge near
Montreal has recently been changed
from a single to a double track with
out interfering with the traffic An
other track was built next to the old
one. The old bridge was then re-
moved span by span so carefully that
parts of it could be used elsewhere.
Then a second new track was built
onto the first, thereby making a COM
plete double track bridge.
Three Types of Bridges
The iron girder bridge. TIE eanti-
lever bridge and the suspension bridge
are the three types now most popular.
Many noteworthy examples of each
have been erected in this country in
the past quarter of a century. The
bridge crossing. the. Kentucky river
upon the Cincinnati Southern Rail-
road is one of the best long span
iron girder bridges. The frame is
1,13S feet long and consists of three
spans. The piers are of stone for six
ty feet with iron above
Is japanese Design.
The cantiIever design IS adapted
from the old Japanese method of
bracketing logs together in bridge
building. The modern cantilever bridge
is a succession of iron brackets, each
arm being composed of rigid semi
arch The Forth Bridge of Scotland,
considered until recently the finest
bridge in the world, is a cantilever
bridge having a span of LOO feet be-
tween its piers. Until the erection OF
the Quebec Bridge this was the long
est in the world. The Greensboro
bridge of New York is a continuous
cantilever having several spans of
different sizes and total length OF
7,750 feet It's construction cost SIS
100000, exclusive of the land. The
Memphis bridge across the Missis-
sippi River from Tennessee to Arkan-
SITS is also of this type.
The modern suspension bridge de-
velOped in steel cables and girders is
an evolution of one of the earliest de-
signs for crossing a stream. The ear
~ Peruvians constructed their bridges
by stretching SIX cables across a
stream. Four of them were used to
carry the platform made by laying
sticks across the cables. The others
were stretched considerably higher
than the platform and served as
rails to guard the passengers. The
upon this principle 1t has a single
span of nearly 1900 feet and two
spans The weight of the structure
Is suspended between two towers. The
cables each 16 inches in diameter and
composed of 5000 steel wires.
Stronger Foundations Required.
The increased strain upon bridges
over them calls for deeper foundations |
than. formerly. This requires larger /
excavation. These can only be &C
complished by the sinking of caissOns !
into the ground, frequently far under |
Ihe' level of the river bed. The water !
IS pumped out of these caissons and /
the men make the excavations being
supplied with air by tubes going down |
from the surface Working under !
such conditions is extremely hazardous
as well as detrimental to the health,
and IL is claimed that thousands of men
have died from it Caisson disease |
may be fatal and il frequently brings |
about partial or total paralysis
Caisson workers are usually sent down
IN two hour shifts, few men being I
able to stand the pressure for a
longer period, although improved me-
thOds are continually lesSeniue the
difficulties of this work. Most of the |
great modern bridges are upon caisson |
foundations. Those have been made
of timber, iron and steel and lately |
reinforced concrete has been used !
river at Black Rock. concrete !
caissons were sent through so feet OF /
tough red clay to rock bottom.
The Key West railway extension is /
one of the most remarkable bridge
building feats of the day. It con- l
meets the islands between the main /
land of Florida and Kew. West by a !
chain of bridges making possible a !
continuous track for a distance of 12S |
miles, a noteworthy example of the /
speed with which modern bridge |
building operations are carried on was 4
given at Oak Island, New Jersey, last I
summer when two and a half miles 1
Of trestle bridge which had been des-
troyed by fire were replaced in u !
days This operation employed a |
force of 1900 men; 1000 of whom /
worked upon the day shift and 500 at |
night.
Tomorrow - The Congregational |
Church.