The Yakima herald. [volume] (North Yakima, W.T. [Wash.]) 1889-1914, 1902-10-07
A PERILOUS CALLING
Difficulties and Dangers Met With
IN bodybuilding.
Mammoth Steel Sinews Must he
Woven IatO the Di.sy Structures
with Math ematicaI Accur-
racy ut All Tines.

The design of a long bridge span is
one of the most elaborate mathemat-
zeal problems that arises in construc-
tive work. The stresses produced by
its own weight, by the weight of traf-
fic, by locomotive drivers, by the ham
mering of fiattened wheels, by the
action of brakes on an express train,
by the high speed of a curved track,
by the wind and by the expansion and
contraction of the steel in summer
and winter, are all accurately calcu-
lated. The definition of the loaded
and unloaded bridge is determined,
and complete drawings are made Of
every member of il. The bars of steel
are tested in machines which will pull
in two a horsehair or a steel bar
strong enough to lift half score of
the heaviest locomotives at once, and
which will crush an egg-shell or
steel column. and accurately measure
the stress in each case. The differ
ent kinds of members are forged riv-
eted. bored or planed in PERHAPS half
a dozen remote shops. and although
usually not fitted together there. are
examined and measured by special
lists to see that they are correct,
and are then shipped by scores of
car loads to the site of the proposed
structure, where steam derricks I'M
load them and pile them many feet
high in stacks covering acres Of
ground.
The huge piers may rise above the
water. hundreds of feet apart. 1t re-
mains to place on them a 1,OOO-ton
structure. high above savage chasm,
ing tide, where the water is deep. the
bottom of jagged rocks or treacher-
Gus quicksand. or where an old bridge
must be removed and the new one
built in its place without interrupting
navigation or obstructing continuous
traffic on the bridge. To accomplish
this the engineer has timber, bolts
and ropes, hosting engines. derricks.
and band of intrepid builders, who
have perhaps folio ved him for years
through more hardship and danger
than fall to the lot of almost any
other calling. writes Frank W. Skin
ner. in Century.
The complicated framework of a
great span is a skeleton with many
accurate joints and thousands of steel
sinews and bones, each of which must
go in exactly the right place in ex-
actly the right order. The builder
must weave into the trusses pieces
larger, heavier and far more inflex-
ible than whole tree-trunks: swiftly
hoist and swing them to place hun
dreds of feet high; fit together the
massive girders and huge forged bars
with watchmaker's accuracy; support
the unwieldv masses until they are
KEYED together and self-sustaining;
and under millions of pounds of stress
must adjust them. at dizzy heights,
To mathematical lines. This he may
need to do, not deliberately in a com
Portable shop or on solid platform,
but in dangerous emergencies. at ut
most speed. putting forth his whole
strength on narrow. springing planks
in furious tempest. in bitter cold OF
in blazing heat. He may be in the
by blood-thirsty fanatics, or in
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
fascinating and difficult of engineer
ing problems, and requires a differ