New-York tribune., 1874-06-11

will probably tend TO withdraw the one svoe VI ,S .
o,her from fhe abutments, extreme neat OF coiu
oscs the rib At the suggestion Of chief assistant
Col Fad TO give greater resistance 70 cnangs o. lor
of the rib nnder unequal loading, the skewDacKs 10
which the tubes fastened are tigldy neid TO tne @
b. anchor bolts Thus AZ times tune as Ine
abfmens may not only be relieved OF all oOmpression
but may bear and pull upon its oy
which additional compressiye strain may be trahs ,hs,
contingency additional sections had to be provided IN
depih Of the rib would have increased all these strains
temperature, and would thus have involved larger
sections at the cram d ana 1a snsa but
more flexible rib under equal loading would have re-
suited. Between these evils on either hand aiter var
Gus calculations the most economic and Satisfactorily
results were obtained with IL feet depth OF IT'D.
DIFFERENCE BETWEEN THE SYSTEMS.
No one will think, deny that the cheapest possible
form In which DO used to span an open
ing and support an equally distributed load is the
catenary suspended arch 1t is equally evident that
II an upright arch the span weight and curve
of any given catenary the strains In the one form would
be intense than In the other In the upriens
arch they would be compressive strains ana Ia Tue s
pended form the section OF metal may DO sod In the
upright must be hollow, tubular or OF some construc
II must NOT necessarily he More weighy. II either form
have equally distributed load placed ON 1t no Dracns
will be requisite TO preserve its normal curvature Inc
same load II within the elastic limit OF the metal can De
borne by either with the amount material Hence
the only difference IN material required or tue W1 s
TENS for auy gwen span and load must be In the diner
ence of bracing them to resist M M. h eu @
the supporting towers in the aud tue abqt-
mens in the other Between ssess Of asob NAV be- the
same under equal loads. In TINS OF course assuh1
that tue iron or sseS S In ta6a
lar other sections are quite capaDie OF SUSTAINING III
b eneS Of the compessve members do not
exceed eight or ten diameters In te o LOUIS M %
GeweyeI they ars II. M asbns the span It Is evident
that long span in the suspension cable involves tne
sectional area also in the shore Spans or
hatvy he
when the stream Is Spannou socior I'm 'ths ths
s5S s sean nofa does OF not s"ca EXIST
almost always be short spans Peter W. Barlow z. b.,
sion Bridge In 1860 in which he gives clear expana
tion OF that all known systems OF grdefs our
times as much metal is required to obtain the same rg
dy as ia needed with the arch the cable The chci
causes which have conspred to lessen tne evuuve ,
form of the arch when unequal loaded 2 the enecss
of temperature; 90 the necessity OF heavier ~ the ycS
The economy OF continuous eirder resting on central
support depends upon the several supporting points
one or Inc Elevation Of another creates strains in
the grder which destroy all the advantages OF con
tinuity. TIE great economy OF glrderp0ye theoret
cay shown by Mr. Barlow. is not attained In any sus-
pension bridge OF which have knowledge because inc
effects OF temperature have not been avoided ln tner
construction The extension and contraction OF tue ca
bes caused the center part OF the grde to a ana rg
This is avoided even when the towers are Oh rou
also.
STRAINS IN THE GIRDER.
which increased sections required These strains
can be avoided however by joining tho cables at the
center span aud cutting the grder In two at the
point BY this means each half length OF the
grder the half length OF cable to which It is at
tached III the end each half girder be securely fas
tened to the central joint the economy OF continuous
grder may be attained because the effect OF the load In
bending the One-haf girder down Is resisted by the
other lust Ii would be II the two were continuous
The loaded one cannot defect without distorting the
cable above it, and the cable cannot defect there
"
could only occur by bending up the unloaded hali-
wise the each half of its length Is
rendered rigid by its connection with tho nall girdcr
contract at the towers. II column OF metal be
suspended by its upper end, Its weisht VIII VIII @ resist
blow II standing its base IL must be remen-
bered however that If suspended the resistance OF the
weight only effected after the center OF gravity OF Tue
column has been moved. The bridge should be braced
against all movement by wind as far as possioe, ana
the stability Of the cables due to their weight
will not Investigation, be found 10 possess as nucn
Importance as has been claimed for IT. Tne plan OF
spreading the arch at ITS bases as proposed oy l19ru
in his 6oofeet span for the Thames has been applied ~
its reverse form to the suspension ogdge as Oh
Either application of this feature suspended or up
cable arch as the supporting power OF either or Is
essened the plane of the curve ncnes from tne yer yer
means of securing stability should DO charged ih the
The SaIfgrder system Of stifenng the arch will be
found economical than any method OF p spanaIel
bracng. because vertical members only arc REQUISITE %
tionate depth is practicable without Involving such
long compression members. But greater economy and
greater rapdty be attained by 1t than by spande
braciug, for another important reason .
am confident that 1t is entirely prdctcaDle 10 brace
the upright arch efectuay and with equal II not
greater economy than possible by any known method
of stifening suspension bridges. BY any method OF
oder construction hitherto known IT Is Impossible 10
swan clear opening OF 800 feet with less than three
times the dead weight OF the arch In the proposed sys
TEN with equal strength of grder and with the same
material and allowable strain. -. -, -, - , l.,
The objection to the combination OF wood and iron IN
bridge construction owing to the difficulty OF repairing
the BRIDGE does not exist in this method La all others
the wood is either under tension or compression and
therefore difficult TO be removed In this the enre cords
of any one could be removed without endangerng
the stability OF that arch OF any other one OF the
series; is plain that IL temporary weight were
placed on the floor which would equal the weight OF the
cords to be removed, the equilibrium OF the whole
series would undsurDed by their removal 30 long
the whole bridge remained unlOaded In repairing 1t
would never necessary. however to remove any one
cord entire at once only replace such piecos
were found defective.
ANCHORAGE OF THE EAST RIVER BRIDGE.
BY FRANCIS CoLLINGwoOD OF NEwYORK.
The front face of the Brooklyn anchorage of
the East River Bridge $50 feet back from the center Of
the tower The the 'front.' and for IS feet and
% faat inoha a