The Savannah morning news., 1901-05-08
QUEER BRIDGES THESE.
THEY SPLIT IN THE MIDDLE AND
EACH HALF REARs ITSELF
UPRIGHT.

fective Than Amy other Type of
Movable Bridge-They Act Swiftly
and Arc Very Inexpensive to Run,
Requiring Only One Man to Each
Structure and Expenditure OF
About $50 Per Month for Electric
ity-System of COunterweightinE
Renders Their Operation Easy.
Engineers Claim That Rolling
Lift Bigger Than the Brooklyn
and Operated.
Copyright, 1901, by Walden Fawcett.
Chicago, May BIN medieval times the
| feudal lord, besieged in his batlemented
castle, shut off communication with the
! outside world by simply drawing up the
| bridge spanning the moat surrounding the
fortress, very much as hinged trap door
might be raised. The dawn of the new
century finds this same principle, with
notifications and improvements utilized
in Americas busiest inland city in order
that the flow of its traffic by land and
water might be less seriously interrupted
| than by the cumbersome drawbridges of
the old type, slowly swinging on pivot.
Some time ago an elevated railroad
found its entrance to the business center
of Chicago blocked by the necessity of
providing a form of bridge which would
permit the heavy traffic over its four
tracks to cross the Chicago river without
seriously interfering with the commerce
of this crowded stream, up and down
which thousands of vessels pass every
month in the season of navigation The
! perplexing problem was submitted to
number of prominent engineers, and final
ly one of them, Mr.. William Scherzer, hit
upon the idea of the rolling lift" bridge
the introduction of which has marked a
new era in the progress of movable
| bridges.
n man interested in the invention has
| compared one of these new bridges to
a pair of giraffes standing on opposite
! banks of a stream, their heads meeting
in the center of the brook as they drink
which, when startled, suddenly rear their
necks perpendicularly either side of
the waterway. The smile aptly Illus
| trates the workings of these remarka-
BILE aids to commerce In appearance a
! rolling lift bridge is very similar to any
other steel suspension structure of the
same class, broad and low and of COM
! paratively short span. The roller bridge,
however is cut in two squarely in the
center. and when boat desires to pass.
instead of drawing aside or swinging
| around in the middle of the stream af-
ter the fashion of the ordinary draw
| bridge, each half of the structure is
| quickly drawn by an invisible force to
an upright position on the bank of the
! river. In order to facilitate the sudden
! IL, To-.
/ of iron and steel, the ends of the bridge
resting on the river banks are rounded
off much after the fashion of the rockers
| of a rocking horse. Electrical power is
| utilized, but a surprisingly small amount
! of the magic current is used, the NOV
ing spans being so perfectly counterbal-
anced that they rock or roll virtually
without friction in opening and closing.
The time-saving element is one of the
chief advantages of this new invention.
The movable spans even of the largest
rolling lift bridges respond and acquire
momentum so rapidly that the current
is usually turned into the motors for
less than twenty seconds for a complete
operation of opening and closing the
bridge.
One man can operate this type of bridge
A majority of the rolling lift-bridges in
! Chicago have movable spans ranging from
wide enough for several teams abreast
There are also now in use rolling lift
bridges crossed by two, four and even six
railroad tracks. Oyer some of these more
than thousand trains pass every day in
the year. The Rush street bridge is
probably the most active bridge in the
world. record recently kept for 259
consecutive days showed that in that time
the bridge was opened 10, 100 times, giving
passage to 12S61 vessels. In other words
the structure was opened and closed on
an average of about twice an hour. day
and night. Despite the activity of the
highway across the river the city rec
ords show that the electricity for operat-
ing this bridge costs not more than 500
per month. or less than many a merchant
expends on the electrical display before
his place of business.
One of the annoying features of navi-
cation on the Great Lakes is found in
the seeming inevitability of frequent col
lisions by vessels with bridges and docks
owing to the narrowness of the naviga-
BILE channels at many of the ports Chi
cago river was formerly the bugbear of
the lake mariner in this respect. but con-
dition have somewhat improved since the
introduction of what the fresh water sail
ors were at first wont to call freak
bridges" The giant rocking structures
can roll up out of the way of the ap-
preaching vessel on such short notice that
in very many cases the lodging is sue
cessful, and either an adjacent dock has
to stand the brunt of the blow or else
the additional margin offered allows the
vessel to pass on unscathed.
A majority of the large steel vessels
now carrying the bulk of the commerce
of the Great Lakes are prevented from
entering the harbor of Chicago because
the river is obstructed by about thirty
swing bridges, the center piers and pier
projections of which absolutely block
the passage of the modern lake carrier-a
vessel large as any of the steamers
to be found on the Atlantic a few years
ago. Lately there has been inaugurated
a policy which contemplates the earliest
possible removal of all the swing bridges
now obstructing the Chicago river and the
substitution of rolling lift structures IN
one form or another. When 1t is explain
ed that many of these bridges will cost
upward Of a third of million of dollars
each the magnitude of the undertaking
may be appreciated.
Prophecies have recently been made of
some surprising developments in rolling
lift bridges in the future. The investors
and engineers who have superintended
the construction OF the larger structures
at Chicago are now confident that such
bridges may be greatly increased in length
of span without passing the limits of safe