The Columbia herald. [volume] (Columbia, Tenn.) 1850-1873, 1872-04-05
The Great Bridge across the Mississip.
nj at St. Louis.

The Great Bridge across the Mississip
pi at st. Louis.
The superstructure of the Illinois
and ST. Louis bridge will be formed
by three arches, which will be thrown
over the openings, which are, one 52(
feet and two of SOP feet each, and will
be composed of four parallel ribs,
each of which will consist of two con-
centric steel chords, Joined by diagonal
braces. The distance between these
two chords will be twelve feet. To
form these chords, or members of the
rib-steel tubes, each about L feet long,
will be Joined together by sleeve
couplings. These tubes will be placed
against each other, the ends being
turned off 50 as to give the angle re-
quired by the curvature of the arch.
There will be about 1000 tubes re-
quired and they will be eighteen
inches in diameter and weigh from
{, $50 to {, 300 lbs. each.
The heaviest tubes will be required
near the abutments and the Gghtest
in the centre of each span. Each
tube will consist of six steel bars roll
ed in such manner that when placed
together, they will form hollow cyl
inder like the slaves of barrel. They
will be held together by sleeve en-
velope one fourth ofan inch thick COW
ering nearly the whole length of the
tube. The sleeve couplings will be
two equal pieces, each having the
form of half circle with flanges at
the ends. They have grooves, cores
ponding to grooves at the end of the
tubes.
Through the centre of the couplings
and through the ends of the tubes
will pass steel bars which will project
on each side of the coupling far
enough to fit into the eyes of the
diagonal braces. Between the ribs of
each arch will be strong tubular struts
and diagonal bracing to give the arch
the power of resisting the effects of
strong winds, which in such long
spans is much more considerable than
most people would suppose. In the
calculations, the effect of hurricane
has been assumed as being equal to
$40 tons for the central span. The
four ribs mentioned will form the
bearing part of the bridge. They will
spring from huge wrought iron skew
backs on the piles and abutments.
From the upper ribs will start the
supports for the railroad tracks
and the roadway. The upper road
way, which is to be used for ordinary
traffic, will be 52 feet wide, and in
clude two sidewalks. There Will be
four lines of rails laid on it, two for
street cars, and two for other vehicles.
About g feet below the upper road
way will be the railroad tracks. At
the levee the upper roadway will be
6S feet above the level of the street,
and from there to Third street will
have a fall of feet.
The tramways and tracks for street
cars will run from Third street in st.
Louis to about Fifth street in East st.
Louis, a distance of about 4, 300 feet.
HOW THE sUPERsTRUCTURE Is To BE
BUILT.
The method adopted for building
the superstructure has not been at
tempted on any but q few small
bridges, and there will be some new
features in it. The first tube will be
screwed to the skewback before the
latter is put into position, and then
the four ribs will be built out stimuli
taneously on both sides of each pier
and on the abutments by successively
placing the tubes in position and join
ing their ends by the sleeve coup
lings,'a at the same time putting in the
diagonal braces.
In this way about 125 feet of each
rib can be built out from piers and
abutments without any outside sup
port, but depending altogether on the
strength of the anchor bolts above
described. Slight suspension rods
may be beintrOduced, however, to steady
the structure and to give feeling of
greater security to the wOrkmen.
When point about 125 feet from the
las been reached, some
outside support will be required to
sustain the arches. The piers and
abutments will meanwhile have been
built up to the level of the upper
roadway, and on them will be built
timber tiestles fifty feet high, and
over the tops of these chains composed
of flat links, will he passed and fas-
tened to the ends of the two opposite
ribs on the piers. On the abutments
one end of the chain will be fastened
to the end of the rib, and the other
will be anchored on the land. Then,
by means of hydraulic rams on which
the wooden trestles will rest, such a
strain will be brought on the cables
as will bring the ends of the ribs to
their correct positions. AS tube is
added to tube the strain on the cables
will be adjusted to the increased
weight by increasing the pressure on
the rams. When near the closing of
the arches another system of posts
and tension rods will be introduced
for the purpose of lifting the ends of
the ribs into their true position, and
then the closing tubes of the inner
ribs will be introduced, and the two
inside ribs completed.
MATERIAL USED IN THE BRIDGE.
The tubes composing the ribs, the
sleeve couplings, and great many
other parts of the structure, will be
composed of steel. This material
has never before been used in the
construction of the main parts Of any
large bridge. 1t was by the most
eminent engineers, considered as
little adapted for the purpose, because
uniformity could not be obtained in
its manufacture. When Capt. Eads
conceived the idea Of using steel on
account of its great strength, and the
great reduction in the dead weight of
the structure which would thereby
be obtained, he had full investiga-
tions made into the properties and
strength of the different kinds of steel
then in the market. 1t was found
that, very uniform grade of steel
was being manufactured by several
firms in the country, and the chrome
steel, really an alloy of pure iron and
chrome, was found to give the most
favorable results. As it would have
been injudicious however, to confine
bidders for the superstructure to one
kind of steel, the specifications were
arranged without reference to the
method of manufacture, but solely
with a view to itSfpniformity and
strength. The Keystone Bridge COM
pany of Pittsburg having closed the
contract for the whole esuperstructure,
took proposals from different steel
manufacturers for the steel work of
the bridge, and finally awarded the
work to the VIM. Butcher Steel