Pine Bluff daily graphic., 1902-07-10

FASCINATING DANGER.
The Perils That Beset the Builders
of Big Bridges.

of Big Bridges.
The design of long bridge span IS
one of the most elaborate mathemat-
1cal 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 hattcned 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 lii.
loaded bridge is determined, and com
pletc dra wings arc made of every mem
Der of it. The bars of steel are tested
in machines which will pun in two
horSehair or a steel bar strong enough
to lift half a score of the heaviest 10
comotiycS at once and which will
crush an cSgshcll or a steel column.
and accurately measure the stress in
each case. The different kinds of mem
bers are forged, riveted, bored, or
planed in perhaps half q 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
OF 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 OH a thousand ton
structure, high above savage chasm.
er an impossible current or roaring
ldc, 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,
hosting engines, dcrricks and 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 a
great span is skeleton with many
accurate joints and thousands of stee!
sineWS and bones, each of which must
go in exactly The right place in exact
~ the right order. The builder must |
weave into the trusses pieces larger,
heavier and far more ildeXible than
whole tree trunks, swiftly hoist and |
swing them to place hundreds of feet I
high, fit together he massive girtlers |
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
hberately, but in dangerous omercen-
cieS, at utmost speed, putting forth his
whole strength oa narrow, Sprin@ing
plankS in q furious tempest, in bitter
cold or in blazing heat. He may be
In the heart of an African desert. men,
accd 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-
chatting and difficult of engineering
problems and requires a different So
lutiUn for almost every case-Erank
w. Skinner in Century.