The Anaconda standard. [volume] (Anaconda, Mont.) 1889-1970, 1896-05-21
PERMA'S NEW BRIDGE
Trains Are Now Running Over the
New Steel Structure.
IT'S THE FINEST ON THE N. P
The General Supervision of the
Work Has Reen I'm the Hands of
J. a. Weed-A Description of
the Magnificent Span.

Missoula, May 20.-It is six months
since the work on the new railroad
bridge at Perma was begun. The last
of the four spans has been connected
and swung clear of the false work and
trains are now running over the new
structure. The bridge is one of the
finest on the whole line of the Northern
Pacific and has been constructed with
out accident, except for the fire That
started at one time in the false work.
This did but little damage and the rec
ord for quick work has been an excel
lent one. The four spans of the bridge
are each $50 feet long, making the
bridge, aside from the approaches, 40
feet in length. 1t is all steel and is as
strong as IL is possible to make
bridge. 1t has been given the hardest
tests and has stood them all. The To-
cation of the bridge at the first cross
ing of the Clark's Fork. has always
been considered a dangerous place, but
there will be no fears for the present
structure.
The reconstruction of a long bridge
is an exceedingly difficult problem for
the bridge engineer to handle on ac-
count of the necessity of disposing of
the old structure to clear space for
the new and at the same time to avoid
Stocking the stream and delaying the
traffic of the road that must be handled
whenever a train arrives at the end of
the bridge. II is process of which the
average man knows but little and Its
various stages are Interesting to one
who follows them. From the time the
work of building the false work is be-
gun to the time when the painters are
put to work on the structure there are
many things that must be done and all
of them are hindered by the two condi-
lions that are mentioned above. The
l4xt1 luVa hnG "a Fd IA al N q
construction of some of his work, but
he has a place to stand on and he does
not have to keep a right OF way clear
at all times for traffic where he Is at
work. Both of these conditions render
the work of the bridge builder che of
the most difficult problems tn 1t the en-
gineer is required to solve.
The first step is to construct the false
work, as II is called. for the support of
the new work and for passage for the
trains while the work is in progress.
This false work is in reality pile and
trestle bridge. having pile foundation
that supports the frame bents that in
turn are capped with long, heavy tim
bers, extending clear across the old
spans. After the false work is &C M
pleted the floor system, which X that
part of the bridge on which che 4 acK
is directly supported. is put In place by
putting in stringers on the bents of the
port of the track from the old structure
to the false work.
After the track has been provided
for, the old spans are blocked up on
the ends of the caps on the top of the
butts of the false work, so that the
trusses are supported at number of
intermediate points, making Ii possible
for the bridge men to disconnect the
timbers and separate them and the
rods that are used with them in the
bridge. These are taken piece by piece
to the material yard at the end of the
bridge. In this manner comparative
ly clear space is afforded for the con-
struction of the new bridge. Care Is
always taken to so locate the false
work that II will clear the sites on
which the new piers are to be built.
The process of building the piers has
already been described in the Standard.
In the construction of the Perma
bridge 5000 barrels of imported Port
land cement were used. with 400 cars
of stone used in rip-rapping the piers
and banks. to say nothing OF the rock
used In the concrete and the cut stone
on the abutments. Now that the con-
crete forms and molds have been re-
moved, the piers present a very hand
some appearance, resembling solid
rock and being as strong. When the
piers are completed the abutments re-
ceive their finishing touches and then
comes the work of putting into place
the superstructure. by which is meant
the steel spans, the carrying part of
the bridge. The previous work has
been essential and is the most labor
ious and exacting portion of the build
ing of the structure. Much of II is
hidden but If IL were not well done, no
matter how perfect the subsequent
work the bridge would be weak. The
span work of the bridge is the show
work and is the most attractive OF all
the structures of modern engineering.
The spans of a steel bridge are design
ed to carry a train of locomotives. COW
ering the entire length of the bridge.
These spans are built from carefully
prepared plans, by contract, by one of
the large bridge companies that have
shops equipped with heavy machinery.
designed for this purpose. The spans
of the Perma bridge were built by the
Milwaukee Bridge company at it's shops
in Milwaukee. At the shops the parts
of the bridge, made of long plates,
heavy angles. channels and other rolled
sections OF the best quality OF soft
steel. are riveted up into sections as
long and as heavy as can be handled
and transported. Many OF these pieces
in the Perma bridge weighed from five
TO 10 tons. These heavy pieces consist
of the stringers, posts and braces and
sections of the top and bottom chord.
Some of them We're so large sEst but
few of them could be put on a car.
From the ends of the different Sec
lions plates project. which are studded
with rivet holes so that. when the
members of the bridge are assembled
in place they come together so nicely
that the bridge men have no difficulty
in inserting the large number of rivets
that are required TO hold the different
sections together making the bridge a
solid structure. All of these pieces are
designed and constructed with such ac-
curacy that they fit perfectly and
there are no changes that have 10 be
made. The PeFma bridge has what Is
known as a Pratt truss with single
intersection and seven panels with
stiff T1veted connections. In the struc-
ture there are 80 carloads OF steel
The process OF erecting the super
ssfr1tcftI--a Is one of the most interest