Delaware gazette and state journal. (Wilmington, Del.) 1883-1902, 1902-06-19
pERILs or nnIDGE-nrIEDING.

Tho design of long bridge-span is
one of the most elaborate mathematical |
problems that arises in constructive |
work, The stresses produced by its |
own weight, by the weight Of traffic,
bv locomotive drivers, by the hammer
ing Of hattencd wheels, by the action
of brakes on an express train, by the
high speed on q 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 I'M
loaded bridge is determined, and COM
plete drawings are made of every mem.
Der OF it, The bars of steel are tested
| in machines which will pull in two
horsehair or steel bar strong enough to
| lift half q score of the heaviest locomo-
! tives at once, and which will crush an
egg shell or steel column. and accu-
rately measure the stress in each case.
The different kinds OF members are
forged, rivctcd, bored, or planned in
perhaps half dozen remote shops,
and, although usually not fitted to-
gether there, are examined and meas
| ured by specialists to see that they are
correct, and arc then shipped by
scores of carloads to the site of the
proposed structure, where steam der
ricks unload them and pile them many
feet high in stacks covering acres OF
ground.
The bridge piers may rise above tho
water, hundreds of feet apart. 1t re-
mains to place ca them l,0O0-ton
structure, high above savage chasm,
over an impossible current or roaring
tide, where the water is deep, the
bottom of Jagged rocks or treacherous
auicksand or where an old bridge must
be removed, and the new one built in its
place without interrupting navigation
or obstructing continuous tratic on the
bridge. To accomplish this the engl-
ncer has timber, bolts and ropes, hoist.
ing engines, derricks, and band of in
trepid builders, who have perhaps fol
, lowed him Tor years through more
: hardship and danger than fall to tht
lot of almost any other calling.
The complicated framework of {
great span is Il skeleton with many ac
curate joints and thousands of stee
r sinews and bones, each of which mus
90 in exactly the right place in exactl,
n lhn right order The builder mus
a weave into the trussns pieces larger
, heavier, and far more intieXible thai
4 whole tree trunks; swiftly hoist AM
+ swing them to place hundreds of lee
4 high; fit together the massive girder
+ and huge forged bars with watch
!, makers accuracy; support the IN
= wieldly masses until they are keye
10 together and self sustaining; and unde
& millions of pounds OF stress must ad
+ Just them. at dizzy heights, to mathe
" NAUTICAL lines. This he may need to dc
h not deliberately in comfortable sho
,r or on solid platform, but in danger
Gus emergencies, at utmost speed, put
nj ting forth his whole strength on MAJ
of row, springing panks, in a furiot
al tempest, in bitter cold or in blazin
is heat He may be in the heart of a
a African desert, menaced by blooi
L. thirsty fanatics, or in II gorge OF Il
If Andes, hundreds of miles from too
No or supplies, where there is absolute
nv no supplement to his own resource
Ia Under such conditions bridge bull
se ing is ono of the most fascinating al
av difficult of engineering problems, al
az requires different solution for almu
;es every case Frank w. Skinner, in t.
he Century.