New-York tribune., 1908-11-11

ether portions OF the bridge would be over
stressed under the same conditions up TO
maximum Of Is per cent.
"A LACK OF FRANKNEss?"
Is this lack Of frankness. or does Professor
Rurr's strain sheet not show the main COM
rressiou members which Messrs. Boiler &
Hodge state would be subjected TO an over
strain Of II per cent over the specified strains :?
There would be Also continues Professor
BurTs report. some similar overstresses in NV
eted tension members in the same parts of the
bridge rising above 33 per cent in a single
instance
The expression rising above SO per cent"
means. according TO the Boiler & Hodge strain
sheet, rising to ~ per cent Professor Burr's
report adds
These greatest stresses running with two or
three exceptions not above a maximum OF 25
per cent OF the stresses permitted under the
xneciflcafions would not be serious II the per-
mitted working stresses were not inltlaIly hlgh-
Again, as none Of these excessive stresses per
square inch Of cross section, even when com
hined with wind load stresses, exceed some or
the elastic limits determined by experiments for
corresponding members in which they are found,
these stresses exceed but little, If any, the nm
sfs permitted for the stresses due to congested
live dead and wind loads by the commission
Of expert bridge engineers which passed upon
The plans foT the Manhattan Bridge.
WIDE DIFFERENCE IN FIGURES.
Hers again there IS a wide difference in the
figures given By Professor Burr and those which
appear upon the strain sheet prepared by
Messrs Boiler & Hodge, and the language used
by Professor Burr would seem TO indicate that
an attempt had been made TO minimize the ex-
tent ard Importance Of the overstresses which
even his Own strain sheet shows.
With two OK three exceptions, he says, the
overstresses are not above a maximum OF %
per cent Of the stresses permitted under tie
specIhcations" The Boiler & Hodge strain
sheet shows dozens of overstresses some run
ming as high as IA per cent
Again" says Professor Burr. none Of these
excessive stresses per square inch Of cross sec
ton even when combined with wind load
stresses, exceed some of the elastic limits deter
mined By experiments The expression none
of these excessive stresses exceed some Of the
elastic limits can scarcely be accepted as ac-
cu-ate IT, as the Boiler & Hodge strain sheet
shows. the elastic limit has been exceeded by as
much as 200 pounds q square inch, or % per
cent
CONDEMNS HIS OWN ARGUMENT
In his report Professor Burr says that the
commission of bridge experts which passed
upon the plans for the Manhattan Bridge al
lowed stresses up TO the elastic limit of the steel
used IN fixing standard for congested live
load II is asserted by bridge engineers that
this is an absolute -nisconstruction of the clear
meaning Of the report of that commission; but
in his report on the Blackwelrs Island bridge
Professor Burr goes the Manhattan Bridge com
mission one better, and says that he does not
agree with what he states was its findings, ana
that in MS opinion the congested load should
never produce stresses exceeding three-quaT-
ters of the elastic limit Nevertheless, he found
an apology for the Blackwelrs Island bridge on
an assumed Manhattan Bridge finding which he
himself condemns.
The Boiler & Hodge strain sheet shows mem
bers in the BIackwelrs Island bridge stressed
up TO - per cent in excess Of the elastic limit.
This is nearly twice the stress which Professor
Burr IN his offcial report states as safe.