The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1877-01-03
IRON BRIDGES.

VIII you allow one who has had over twenty-five
years. experience in bridge building, and who has tor
tho last years been engaged In designing and con-
structng bridges, TO say few words sug-
gested by your editorial comments the terrible
catastrophe ut Ashtabula? The questions OF immedi-
ate and vital interest the pubic follows:-
Fst-Can bridges be constructed TO be abso
lutety safer
Accidents to bridges are Of two classes-one when
the the rails and dashes violently against
bridge and destroys IT, such are really accidents
and are difficult 10 guard against; but better precau
ons Oud DO taken than now done. by placing the
IN osSer woras making Icck bridge Of IT, bv tho
heavy stone parapcs ON the abutments TO break
the force OF the Shock and by the use OF very heavy
and rong wooden ties under the rails provided WIKI
GUARD rails whose Office Is to conhnc tho passage Ut
the tram the centre OF the bridge, # off the
track This requires strong fl. or ana very strong
bridge altogether yet there numbers OF instances
record where trains have crossed bridges IN safety
running on tho ties.
bridge scs down." as the phrase is, under the dead
weight oil the tram without any shock or blow upon H.
THIS to have been the case AT Ashtabua and IL
falsely called accident but II Is not IL 10 the in
eyitablc result later, OF bad design, bad ma
teriai and bad Workmanship ny looking a. what are
the requisites OF safety wo shall see that this must be
First-Good design. This implies scicntac knowl-
edge proportion the sizes oi the parts that the
weight the structure Itself and that OF the greatest
load that can possibly como upon IL shall not
strain iron greater by dead loads than onciourth
Its ultimate strength by i've loads than oneegnth
and by loads alternately OF tension and compress
SION not more than onc.tweth OF It's tmate
Besides this mechanical skill is wanted 10 combine all
the parts into whole, so as 10 make tho wnolc bridge
strong as the parts OF which II IS composed Tho
old tdcacon's shay" immortallzed by Er. Holmes, Is
an example OF what perfect bridge should be- II
should break, If overloaded, In all parts ut once
made o, a Uniform quality IL wrought iron, having
great toughness and ductiity ne well us strength
have condemned IRON urnisned for bridges that would
sustain 700 pounds 1000 pounds per square
inch OF weight and yet be brittle and snap like
glass under bow. Uniformity Of quality IL OF the
highest portahce nnd cannot be got except by
rerolling arrd this high priced The use Of
cast IRON should Sc confined To washers JOINT boxes
and bed plates all Of compact and massive proportions
aud subject 10 compression only, never as posts or
chords.
The third requisite, without which tho others are
useless, Is honest and accurate workinanshp IL an
iron bridge meets all these requirements II Is abso-
luely safe, long the tram docs not leave tho
bridge, high embankmcnt or sido cutting over .
deep ravIue This answers the first question.
The second question is, Giren q brtdge, so CON
struct,d chdt is tts probable ye and c be dyectd
injariousiy by extreme coidy
Careful experiments made for the Prussian govern
ment, and extending over space Of twelve years,
have good ron subjected ~ strains
greater than those above described, Will las N:
definitely. but II the strains are much Increased u VIII
lose its strength and break IN "A tme, shortened IN
proportion To the increase OF strains.
The HE of iron bridge becomes question OF the
proportion Of the IRON 10 The load CARRIED III strained
WITHIN asccrt.ncd limit and kept free from rust II
will last long "a stone bridge, provided dftodys that
the connections arc As strong AS tho bars ncmscVcs
II slightly ovcrstraincd II will wear out because loose
in its JOINTS and jingle under passing trains IT, much
ovcrsrancd IL Will break down at last suddenly and
| without warning, AS the Ashtabula .rdge did
The effect OF severe cold on wrought iron il, wnIlo
not affecting It's capacity TO support dead weight, 10
make brittle and liable 10 break suddenly under
] blow Common iron IL more inurousy affected by
cold IN this way than refined iron or Bessemer steel.
has oiien been known to break IN very cold
weather without any apparent cause. The reason Is
that cast iron, IRON unequal cooling, often conceals
enormous internal bursting strains, and, when the
cold contracts the outside something has 10 give way
Hence, cast IRON should DO used very sparinRly Ia
bridges, aud not IN intricate shapes so much for
theoretical reasoning. The longest experience we
have this country that OF the ron bridges tho
Grand Trunk Railway of Canada, some sixty OF
seventy OF which have been Ia constant use since
1850, exposed to severe cold. They are In
| us good CONDITION now ms when built.
We have tried TO show that an iron bridge can be
| made sale and durable.
The third question Is, Are they so mddey They are
and they are not IL depends the skill and honesty
OF the makers. As you well say 'tbcy cin DO maut
for any price, ana IN the long the cheaper they
are made the worse they Will be.
The earlier iron bridges built in this country, will
some cxccptiohs show bad design, bad material AM
are altogether 100 weak. Cast iron is used in post
and chords where II Is liable to come under tension
The workmanship W. not w to the standard oil ordi
| narly good workmanship OF The present day, an'
much below that OF the best where the parls ~ lik
| those Of locomotive. II these assertions be tru
there many iron bridges now In daily and nourl
use as dangerous rs that AT Ashtabula.
Now thut bridge builders have learned TO avoid thcs
detects OF earlier practice, new danger presents
scf As YOU sny bridges arc sometimes contracted 10
at prices barely Sufficient to pay ior good iron. Tn
pro any. ~ only 10 DC had by using iniorior iror