The Tucson citizen., 1902-06-27
FASCINATING DANGER.
The PeriSa That Besct the Builders
of Big Bridges.

of Dig bridges.
The design OF long bridge span Is
one of the most elaborate mathemat-
zeal 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 Hattened wheels, by the action
OF brakes on an express train, by the
high speed on a 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 ii. The bars of steel are tested
in machines which will pull in two
horsehair or a steel bar strong enough
to lift half score of the heaviest To-
comoUves at once, and which will
crush an eggshell or steel column,
and accurately measure the stress In
each case. The different kinds Of men,
bers are forged, riveted, bored, or
plancd in perhaps half 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 jse 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 trea Cherous
| Quicksand or where an old bridge must
be removed and the new one built IN
its place without iDterruptinG ira tfic
| on the bridge. TO accomplish this the
engineer has timber, bolts and ropes.
| hosting engines, derrlcks 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 In 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 infexible than
whole tree trunks. swiftly hoist and
swing them to place hundreds OF feet
high. nt together the massive girders
and huge forged bars with watchmak-
| <r's accuracy. support the unwieldy
masses until they are keyed together
| and self sustaining. and under mil.
ions 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 eIpergen-
cies. at utmost speed, putting forth his
| whole strength on narrow, springing
plaDks 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 milea
from tools or supplies. where there is
absolutely no supplement to his own
resources. Under such conditions
bridge building is one Of the meet fas.
cinating and difficult Of engineering
problems and requires q different go
luton for almost every case.-Frank
w. Skinner in Century. .~-