New-York tribune., 1908-12-08
CRITICISE OUR BRIDGES
MISTAKES IN AMERICA.
Sharp English Comment on Methods
of Engineers Here.

the safety Of the structure on the demand made
| by The Tribune.
| In It's issue of November p, Engineering, the
| well known English authority on technical engi-
| neering subjects devotes long leading editorial
10 the safety of the Blackweils Island Bridge, in
! which very drastic comments are made on
| what is called the American system of bridge
! manufacture and the custom which, IL states
is in vogue this country of calling for comped-
! tive plans and tenders for the erection OF large
| bridge structures.
The astounding failure of the Quebec bridge. a
| structure for the plans OF which the recognized
/ head Of the ultra-American school of bridge de-
sign responsible. and the construction of which
undertaken by the leading bridge building hrIn
in the States says Engineering" raised in an
acute form the question as to whether the AHerl-
! system of bridge manufa ctIre, highly ingenious
as it is in many respects. is well adapted to the
satisfactory building OF structures of exceptional
! dimensions This doubt gains unexpected force
from the reports just published of two independent
inquiries into the suffciency for its designed load
/ of the Blackwells Island Bridge the East
River az New York, now on the point OF COM
pletion."
After describing in technical language the re-
quirements Of the Blackwell's Island Bridge under
the contract specifications and the extent to which
| the bridge erected is shown by the reports OF
the engineering experts appointed to examine INTO
its safety to fall short of those requirements,
Engineering" remarks:
While American and British engineers hold widely
g6 s G as se 9 %af if is eIreg sPG e s
markable that both here Ba ckwels Island Bridget
on the very points to Which, they attach. in Eng
lish opinion exaggerated importance. II there
thing more than another which Amerl-
engineers agreed in emphasizing, il was the
Sag members Of bPdge % ' In fact the dfeuy Of
doing this with exactitude has been the sole point
they have been able against the superior
practical efficiency of double intersection trusses
both at BiackweIi's Island and at Quebec
errors ot t1e hrst magnitIde nave Peen IN mace aI IN
stresses would have exceeded the designed stresses
at BIackwes island the overstress is even larger.
70 no biI Ie5 .h I % 90 per cG' i aceee5 m 9e in
This excess is particularly serious m view of the
extremely high working stresses provided for, no
fatigue formula. At BlackwelPs Island. II viii ap
pear. this range was by no means inconsiderable
in the main to the fact that they are for the most
part civil engineers professors and technical
engineers They certainly appeaT to have much @
resistance Of materials than is usual here in Eng
lated stresses may safely approach the so-calied
elastic limit and. on the other hand; not few |
limit is ruined. This latter statement is disproved
by daily exPerefce in every shipyard in the coun-
try and The former requires much auabacatio1n
be taken as entirely adequate guide che /
proporuonng Of scantings In his report Pro |
81 tbe slsstjr 6it f tere are " certeinv msaS
cases where even this would prove unsafe. there
ar Others IN which the limit t. may be e.ceed,9d
for ]udgment has not yet been eliminated in con-
Engineering" says that many structural details .
of the BlackwelIs Island Bridge inadequate
to English eyes, the design OF the main compress
sion members being certainly less rigid and sub
stantial than It might be. They resemble in gen
eral arrangement those of the Quebec bridge. but
with heavier latticing. The type in spite Of It's
cheapness seems weak. and the paper is strongly
of the opinion that Well stifened box section,
having only the amount OF material in IT, /
would have higher ultimate strength. American
2 In haVa atTa led rph
Importance TO the elastic limit consider any /
margin OF strength beyond this unnecessary.
good design. however. Will have a in
plastic strength of the material even after the
elastic limit has been locally exceeded from
accidental cause other The paper adds:
The inadequacy Of American designs for struts
las probably originated IN the system there in
II designs Of all kinds II Is necessary to arrange
cheapest possible. Where the designer is not ths
enderer The compromse is not unlikely to lean
prepares his own designs on a competitive basis
en- OF construction that Will pass muster. This
onsideraton %ii go faF to account T9T the Gn-
'ers now being used in some large American
Another noteworthy and Objectionable feature Is
he Of extra soft metal for struts which appears
i've process Of punching plates instead Of drilling
c excellent for furnace plates Of boiler, but
teel having a tensile strength nearer forty than T
1irty tons per square inch. In fact, the, upper ,
he harder metal than by any doubt the n ,
erent stability of such material. in place, !
-hich must be capable Of w-thstandng considerable
Lloyds permit the use Of thirty-one-ton
In the same issue of Engineering" there is a ?
stter written by Philip P. Brown, a well known '
,nglish engineer, commenting the official n
OF the engineering experts appointed to in r
estigate the safety OF the BlackwelI's Island :,
ridge published in full in ''The Engineering .
ews." or this city, and stating that these re- =
orts contain information astonishing TO the last
eeree and Of the greatest interest to all en- y
neers who are connected with large bridge a
ruction. In his letter Mr.. Brown summarizes y
le findings OF the engineering experts as follows:
The specifications call for a bridge 70 sustain
e geaIes md m one e2eI an snd fo fnr fo
evated railway tracks and two side paths on the
one report shows that the bridge as built will
relieved OF thousand pounds foot dead
dc paths. and that the four elevated railway
acks cannot be used at all The other report
la5 pa and regrlsted fTs4c on the trolley racks
nd trains a thousand feet apaTt of the
eyated railway tracks It also shows that. al
lough the specified maximum stress is be % 600
1unds a square inch twithOUI allowing for wind
low and secondary stresses recognized TO be
many Of the members of the structure II they
ere Loaded as as called for IN the sPecifcati9rs
,me Of the eve-bars would be stressed beyond
leir elastic limit
This causes The Engineering News" says the
tier ito rightly call for investigation to show
w II was that the Department OF Bridges of New
ork came make such errors. whereby thou
nds OF people might have been killed should this
1dge ever have been loaded the extent called
T in the specifications"
A. BAKER NEW DEPUTY COLLECTOR.
Announcement was made at the Custom House
COLI rFs-s Tagr