New-York tribune., 1903-07-25
REPLIES TO MARRIOTT.
AGAINST EYE-BARS.
Mr. Hldenbrand Quotes Figures of
T5co Bridge Plans.
Sitcr Of The Trihure

TIE tribune. plhnSned july Il. ] have stated
-.h .scts. and asserted that eye-bar cables are
,rl more costly than wire cables of the same
srrenzth. / offered TO demonstrate the truth Of
his assertion before impartial tribunal. AS
.ss-e can BE- more impartial tribunal than the
,rir I take pleasure in showing to the readers
- The Tribune in plain way. how the calcula-
-ors are made from which the results stated
ssrived
suspension bridge consists Of four distinct
parts
F7rst-The towers and anchorages. which sup
,,-t and hold the cables
second-The cables which sustain the weight OF
.bs bridge and all that comes IL.
qrird-The floor or the different platforms on
xhen pedestrians, vehicles and cars are travelling.
E-ourth-The stitfening construction, which gives
-iridtv the floor
The weight Of cables. floor and stifening con-
.,1,t5on Is called the dead weight; the weight Of
,sFons horses cars, people etc. IS called the
i've load.
.s5r stress or tension Just feels
,-rto7 ia his arm by lifting weight BY over
,stre the human arm it might either be broken
= permanently injured. The same takes place
.5,s cables or with any bar of steel 1t can be
=, as11nder al once by large weight or pull.
,sjlad tho ultimate strength or by many times
-lvire- 4 smaller weight, which is called the
elastic Limit Of the steel
= &c a.i5ent in order be safe, that the tension
a, ,be cable OF q suspension bridge must be smaller
-, me elastic limit The number Of times this
.-sfor can be- increased in order TO reach the
e+fr limit or the breaking point of the cables, Is
.are5 the factor Of safety as to elastic limit or
= 70 ultimate strength. The smaller the tension is
= the cables in proportion TO their strength, the
,ze- IS the factor Of safety and the safer Is the
bridge.
N al building material known to the engineer,
.ss, wire has the greatest ultimate strength and
- elastic limit exceeding in these qualities
f-o-, three 10 times other material or any
o-be- form OF steel. This well known fact is the
-aasor why wire cables are lighter and cheaper
than eye-bar chains
IT, tension in the cables of suspension bridge
= 4rc-, the weight sustained by the cables,
So, The length Of span and from the vertical as
.s-ce between the lowest and highest point OF me
- caued detection" The tension is not uni
form in q cable, but greatest at It's hlghest anu
smallest at its lowest point
Win these preliminary explanations. 1 will now
..l,rIate the strength OF the cables Of the VIII
,sr,,-r Bridge and that of the eye-bar chains OF
The Manhattan Bridge
The dead weight the Williams coo 49,. l,.s1 font
ne i've load is assumed 800 lbs Lneal 1901
........ q S82 lbs a lneaI foot
T sra- is co.. feet the detection OF the cable
~ The sss ss ss- Is ao5 f23nd B5 eT a g9. 2o 5dns
ssT-2a 4 r--e- e tension is l8 1904 - 600 tons
avsrzEs tension. 2o.loo tons
W. average weight Of the cables is 2991 pounds
z Iineal foot
ron the weight Of bar Of steel one foot long
the number Of square inches contained in the sec
t5,n Of the bar Is found by multiplying the weight
with and dividing by To-
Therefore. the number Of square inches of wire in
The cable is:
2ee1 $40 Ss7-
-. ultimate strength Of the wires, found by
,r-,s7 tests Of each individual wire. is IL tons
q square inch and the elastic limit Is % 'o"s q
square inch Therefore;
strength 8 s q . s o ss7 81 3 tons ms ions
r. We divide the total ultimate strength and
elastic limit by the actual tension in the cables
found to be 21.1O0 tons We have;
100 900 = 2oloo factor Of safety as to ultimate
s. 56O = 25loo "A factor Of safety as TO elastic
aTerags factor OF safety. 462.
For calculating the strength Of the chain cables
o. the Manhattan Bridge. I have taken the data
as published by AIr. Lindenthal in Engineering
News" Of June .. 1855.
TIE asa5 weight q J6e 'oEs ,no' $50 lbs neaI foot
r. Ire l-a5 assumed the same ,e
gs r1r Williamsburg Bridge 700 lbs a hneaI 1901
--r ....... Is 45O lbs. q IneaI foot
vre span Of the bridge is ], 40 feet, and the de
fecriou Of the chain cables oneeighth of the span
The ultimate strength Of the eye-bar steel as given
hy 1Ir Lla5euthal, is 42l2 tons, and It's elastic
limit = tons per square inch. From these data 81
simple formula can be derived for calculating the
weight Of an eye-b4r chain which viii have the
Williamsburg Bridge. Omittng the details Of this
calculation. 7 win only give the result and prove
that It Is correct.
The necessary weight Of the chain was found to
he $3.50 pounds Ineal foot, and, as the enlarged
ends Of The eye-hars and the pins connecting the
links oF the chain. while adding nothing t. the
strength add al least - per cent 10 the weight OF
The chain the actual weight Of ths latter Is LOO
pounds Hneal foot. This added 10 the weight
given before makes The botal weight of the Man
hzrt1r rrs q
tvo and oae-third times more than that oi ihe
Eliansaurs Bridge
- aa tension tae &c gys-6sT sso bar chain is 'oloo
~ S. -a.7l5oe1 lbs - - go tqlS a 2oo TONS
sanr 6. ssaare inches in the chains is 1soso
E strength i sa. 542t 2 Z 80 f5 10 So5s
s ,he figures by the actual tension ~ 4 lti
nae 5nsset- and l30,I7o 30 ESQ g 3S4 - factor Of
S.ey ss szzrte limit
Tas is tbe same as found for the cables Of the
Williamsburg Bridge. and proves the correctness
e ne Calculation
Il stands 70 reason that heavier bridge requires
s'ger fou-Gzrio heavier towers and more volu-
Enous archorages all Of which add 70 the cost
he bridge This increased cost is in direct
lope.tion 70 the relative weight and tension Of
es eye-bzr and wire cables, The details Of the
--eslauors were published in Engineering News"
Asrcn 2 and in The Engineering Record OF
~ 1903 The following the results:
A1oess Of weight and cost of the Manhattan
Slase over the Williamsburg Bridge;
saeaor chains. 1865 $50 ton ...- s9s.7 700
vss-saor masonry, e 600 cubic yards al 81 1000
tEsrs $40 toas 500 ton..-........... 49, ooo
h.sys-ssr oEstns q 700 pounds 29so
a. totai length q 6ridge) - 60 se4- -, ,o
~ pounds a. c=nts S5'4O-'fOo
-s s cables for the same lengths viii 1900
4S4JsvJo
Toesi IS 782 coo