The Tucson citizen., 1902-07-07
FASCINATING DANGER.
The PerIis That BeAet the Builders
of Big Bridges.

The design of a long bridge span Is
one Of the most elaborate mathemat'
lcal problems that arise in constructive
work. The stresses produced by its
own weight, by the weight of traffic.
by locomotive drivers, by the hammer
ins Of tlattcncd wheels. by the action
Of LrakrS 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 ana
winter are all accurately calculated.
The detection Of the loaded and un-
loaded bridge : determined, and COM
plctc dra awnings are made of every mem
Der OF IT, The bars of steel are tested
IN machines which viii pull in two a
horSc,:air or 4 steel bar strong enough
to lift half Il score of the heaviest To-
comOtiycS at once, and which vii!
crush m cGLShell or a steel column.
and accurately measur the stress III
each case The different kinds Qf MEM
bers are forged. riyeted, bored, or
plancd in perhaps half a dozen remots
shops, aud. although usually not fitted
together there. 1v" examined and meas
ured by Specia ~ts 10 500 that they are
correct, and are then ehipped by scores
Of carloads 20 he site Of the proposed
structure where steam darricks unload
them anl pile EhHu, many feet high in
stacks covering acres Of ground.
The bridge p.'r~ may rise above the
water hundreds of feet apart. II re-
mains to place hem on thousand ton
structure hiEl above . savage chaSm.
over an impaS>abie current or roaring
tide. where the water : deep, the bot
tom OF jagged rocks or trc1cherouS
Quicksaud. or whore m OIL bridge must
he removed and the new one built il
its place without interruptinG tratfic
on the bridge. 10 accomplish this the
engineer has timber. bolts and ropes,
hoisting engines. derrick4 and 4 band
OF intrepid builders who have perhaps
followed him for years through more
hardship and danger than fail 10 the
lot of almost any other calling.
The complicated framework OF q
great span is skeleton with many
accurate joints and thousands Of steel
snews and bones, each OF which must
so in exactly the. right place in exact
ly the right order. The builder must
weave into the truss.s pieces larger.
heavier and far more iudnxibe than
whole tree trunks. swiftly hoist and
swing them TO place hundreds OF feet
high. fit together the massive cirderS
and huge forged bars with watchm0k-
et's accuracy, support the unwjedy
masses until they are keyed together
and self sustaining, and undcr mil
lions OF pounds OF stress aust adjust
them at dizzy heights to mathematical
lines. This he may need TO do not de-
liberately. but In dangerous cneFgen-
cies. at utmost speed, putting forth his
whole strength on narrow. sprinSins
planks In furions tempest, IN bitter
cold or In blazing heat. lie 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
". Skinner In Century.