The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1885-1921, 1888-02-13
IRON GENERALIZATION.
How it Produces Changes in the Fibers OF
the Metals and Weakens it.

=
cry living soul upon it to certain death,
there has been no railroad bridge dis
aster that has excited so much public
attention as that which occurred on the
Boston & Providence railroad at the
Bussey bridge near Boston. In both the
cause appears to have been a structural
defect. This may also be said of the
Ashtabula accident. whose horrors. how
ever, were increased by the fierce work
of flames and the inclemencies of Bit
terly cold winter night.
Bridge accidents are considered by
all railroad men as incOmparably the
worst to which travel by rail is exposed,
and as among the most difficult to
guard against absolutely. One source
of danger was shown when the peculiar
effects of a locomotives hammer blows
upon a track were explained The
theory was advanced that a girder of
the bridge had broken beneath the en-
gine's drivers, whose pounding upon
the effectively constructed bridge was
thus primarily the cause of the acct
dent. This brings up phase of rail
road and bridge accidents which is at
present receiving a great deal of atten-
ton. Capitalization in the material of
iron bridges is an element of danger
now SO well recognized that the Penn
sylvania Railroad Company has adopted
the definite policy of substituting stone
for iron bridges, and the same plan is
being followed by other railroad COM
panies.
The lifetime of an iron bridge is from
twenty to twenty-five years, and con-
slant care is necessary to insure its
safety. The Ashtabula bridge was
thirteen years old, and at the time it
fell beneath the weight of two engines
and heavy express train the theory
was commonly advanced that crystal
ization had impaired its original
strength. The two great moving causes
of capitalization are vibration and the
hammer blows of the locomotive, which
gradually, by repeated impact, turn the
fiber of iron or steel into a mass of
crystals, needing only some unusual
pressure or blow to cause them to
break apart. Add to this the oscillation
caused by the passage of trains at a
high rate of speed, and it will be seen
that an iron bridge is exposed to pecu-
liar perils, which can only be guarded
against by rigid inspection and con-
slant renewals.
Capitalization was one of several
theories advanced by Park Benjamin, a
New York engineer, to account for the
Tay bridge accident. He said:
General indications 90 to show that
the cause must be sought in an abnormal
condition of the structure, orrather one
which did not enter into the calculations
of the builders. Such condition would |
be the deterioration of the metal by its |
change from a fbrous % a crystalline |
state under repeated vibration. That |
this occurs in railway bridges has been
disputed by many we'll
known engineers. On the other hand, |
many examples are quoted by different
to support the theory. APP
Dropos to this particular accident, a
French engineer and iron
founder now in this country informs US
hat he has known bars of iron made by
himself from Scotch pig to change from
l tough fibrous to brittle crystalline
structure in travelling by rail only from
he north of France to Paris. This is, OF
course. an extreme instance
Again, recent research has dem
'nstrated that because Il structure
large quiescent load that
act is little proof of stability under re.
'eated shocks and vibrations. Metals
ire believed to have life. A bar. for
may stand million vibra-
ions and break down at the million
nd first, and yet the last shock may be
lighter than preceding ones. Attempts,
owever, to reduce this law to
PRACTICAL application have elected
n abundance of conflicting evidence;
ut, nevertheless, it is well settled that
4 no department of mechanics is an
course of actual experiment.
1g more urgently needed or of graver
ublic Importance"
The strength of the Tay bridge at the
me of its building was such that it
'as pronounced perhaps the most
structure in the world"
a British magazine, speak
lg of its test, when five engines,
eighing $50 tons, were placed on a
ngle span, said: ''The result is the
omplete establishment of this fact $50
npOrtant to the public, that the
ridge is strong out of all proportion to
5 possible necessities. The load which
lie structure is calculated to carry is
X times greater than that to which it
as subjected"
And yet this great bridge. which cost
100000, collapsed within a few
onths after it was finished, the acct
INT being the only one in all railroad !
story in which no survivor lived to tell {
e tale. s
The theory of crvstaIIization mt for {