The citizen., 1902-06-20
FASCINATING DANGER,
The PeriIs That Reset the Builders
of Big Bridges

The design of a long bridge span is
one of the most elaborate mathemat.
ical problems that arise in constructive
work. The stresses produced by its
own weight by the weight of traffic,
by locomotive drivers, by the hammer
ing Of fiattened wheels, by the action
OF brakes on an express train, by the
high speed on curved track, by the
wind and by the expansion and con-
traction of the steel in summer and
winter are all accurately calculated.
The DETECTION of the loaded and un-
loaded bridge is determined, and COM
plete drawings are made of every men,
Der of 1t. The bars of steel are tested
in machines which will pull in two
horsehair or steel bar strong enough
to lift half score of the heaviest 10.
comottves at once, and which will
crush an eggshell or a steel column,
and accurately measure the stress in
each case. The different kinds of men,
bers are forged. riveted. bored, or
planed in perhaps half a dozen remote
shops, and, although usually not fitted
together there, are examined and meas
ured by specialists to see that they are
correct, and are then shipped by scores
or carloads to the site of the proposed
structure, where steam derricks unload
them and pile them many feet high in
stacks covering acres of ground.
The bridge piers may rise above the
water hundreds of feet apart. 1t re-
mains to place them on thousand ton
structure, high above savage chasm.
over an impossible. current or roaring
tide, where the water is deep, the bot
tom of Jagged rocks or treacherous
quicksand, or where an old bridge must
be removed and the new one built in
its place without interrupting traffic
on the bridge. To accomplish this the
engineer has timber, bolts and ropes,
holsting engines. derricks and a band
of intrepid builders who have perhaps
followed him for years through more
hardship and danger than fall to the
lot of almost any other calling.
The complicated framework of
great span is skeleton with many
accurate joints and thousands of steel
sinews and bones, each of which must
go in exactly the right place in exact
ly the right order The builder must
weave into the trusses pieces larger,
heavier and far more inflexible than
whole tree trunks swiftly hoist and
swing them to place hundreds of feet
high, fit together the massive girders
and huge forged bars with watchmak-
er's accuracy, support the unwieldy
masses until they are keyed together
and self sustaining. and under mil
lions of pounds of stress must adjust
them at dizzy heights to mathematical
lines. This he may need to do not de-
liberately, but in dangerous emergen-
cies, at utmost speed, putting forth his
whole strength on narrow, springing
planks in a furious tempest, in bitter
cold or in blazing heat He may be
in the heart of an African desert, men,
aced by bloodthirsty fanatics, or in a
gorge of the Andes, hundreds of miles
from tools or supplies, where there Is
absolutely no supplement to his own
resources. Under such conditions
bridge building is one of the most fas-
cinatlng and difficult of engineering
problems and requires a different So
luton for almost every case.-Frank
w. Skinner In Century.