Fort Worth gazette. [volume] (Fort Worth, Tex.) 1891-1898, 1891-11-07
load from the smaller cables will be thrown

SIGN bridges are agreed that where two or
! more cables are used in the design, the
load will be distributed to each OF them in
proportion to their strength, 1T simply re-
sultlng that where We have two cables to
| carry load, and one IS seven times as
large as the other, then it is seven times as
strong or rigid, and will consequently carry
seven-eighths of the load, and the smaller
one one-eighth of the load. This is prin-
| ciple in the application of mechanics Of alb
| solute application. In as flexible system as
suspension bridge the accuracy Of the adj
justment of the various members is only OF
| minor importance, and no absolute nicely
is essential in the distribution of the sus-
| penders.
IA. Nearly all suspension bridges have
| two or more cables, one above the other
In such case it is necessary that the sus-
pender from the upper cable should come in
contact with the lower cable. TO prevent in
jury to either cable or suspender; it IS pro-
| yiGed in our specifications that each is to be
wrapped at the points of contact. Should
there be chafing, as MIR. G. fears, the wrap
ping would bear the injury, and could be
| renewed when necessary, but we do not
| think this would ever be found necessary,
as no such experience has ever been known.
| Is. The attachment of the suspenderS to
| the lower auxiliary cables may be novel
| and unusual, but that is no ground for con-
| demnation. That an iron rod of the same
weight of metal would be stronger is de-
| MED, and l challenge authority for the
statement. That it would be cheaper cuts
no figure in this case. The auxiliary cables
| perform various and sundry offices besides
! being used to attach suspenderS to, among
which may be mentioned their adaptation
TO assisting in staying the bridge against
| vibrations from traffic, also in staying it
| from under pressure from wind or flood, all
of which seems to have entirely escaped the
notice of Mr.. c.
16. Any movement of the diagonals at
| the point of attachment to the main cables
| is impossible, without also moving out of
place the adjoining diagonal which a refer
ence to the drawing will show is strained in
| the opposite direction, and also the main
| suspender as well, all being joined in at
! tachment at the same point. The manner
of fastening specified has been employed by
Mr.. Roebling in all his bridges, and none of
| them have ever slipped.
IL The long stays referred to are to
| stiffen the bridge against distortion. As
MIR. c. fails to say whether any one has
sufficient strength or not, it must be pre-
sumed that any one is equal to the greatest
strain, and if, however, this is important,
the number of wires in those next to the
| towers can be reduced.
If the strain can be calculated On any sus-
| pension bridge, they can be on this bridge,
| as the design in no essential feature differs
! from that Of ordinary suspension bridges,
| the only changes introduced being such as
are intended to stiffen the structure and
| prevent undue distortion to the floor, and
as stay against wind and flood.
! do not understand that Mr.. G. was
asked to comment on this form of bridge as
compared to that of a truss bridge, and il is
significant of his position that he takes oc-
| casion to indirectly recommend an iron
truss in the place of 4 bridge of the design
submitted.
Further, he says that an iron truss would
be less expensive. Either he is mistaken
on this point or the representatives of the
iron bridge companies in Texas have at
tempted to get vastly greater sum than
their bridges are worth, as they all had an
opportunity to bid on this bridge, and
failed by large amount to submit figures
anywhere near the sum asked for 4 bridge
of the size of the design in controversy.
1t will be noticed that Mr.. c. fails to
make any comment whatever on the
strength of the cablef the sufticiency of the
towers, foundationsy anchorage, or floor
all of which are the vital features of the
structure.
AS it is perfectly evident, from the gen.
eral tone, and from the attempt to argue
for an iron bridge in Mr.. C's effusion, the
plans submitted were mauifestly tired
condemned solely in the attempted inter
est of the iron bridge companies, in ad-
vance, perhaps, even of their arrival in
New York, and that the plans and speci-
cations were examined with the single OBJ
Jet of finding ground on which to condemn,
it can fairly be presumed that the floor,
towers, cables, foundations and anchorage
could not be successfully assailed. If they
could have been, it would not have been
found necessary to resort to criticisms of
the specifications for ''paint" and 'bond in
masonry" etc, for ground on which to base
his condemnation.
1t will be noticed that there is wide diff
ference between Mr.. kerr's report of three
or four weeks ago and Mr.. Collingwood's
report.
Mr. Kerr said that the cables were not
sufficient. Mr.. Collingwood, by his silence
on that point, says they are, and condemns
only on account of the specifications for
wrapping. Mr.. Kerr said the towers were
not strong enough. Mr.. C. has nothing to
say about the towers, but wants ribs in the
bed plates.
Mr. Kerr said that "the anchorage is
reckless" Mr. c. avoids making any COM
ment on that point by saying that he does
not know what the strain on the back
stays is.
Mr. Kerr condemned the floor system.
Mr.. c. did not feel like commenting on the
floor system, but says 1.-The adjustment for
the wind brace cables is crude DEVICE
and so on. / will add that if Mr.. G. is I'M
able to calculate the strains in our bridge
as he states, how can he consistently offer
an opinion at ala
The iron bridge companies are fighting
the wire bridges with all the weapons they
can obtain, because it is manifestly to their
interest to do so. That Is all right, and fair
enough for them, but would suggest that
a photograph of the King iron truss bridge
that fell into the Colorado river at Austin,
or that of another bridge by the same COM
pany that recently fell from its own weight
into the Canadian river in the Panhandle,
or of the North Side bridge when propped
UP, would be as ornamental to the city engi-
the alleged failure eff a wire bridge in Cali
fornia. Respectfully yours,
l. c. TERRY, C. F..
FORT WORTH, TEX. Oct. 6, 1891.
To the Honorable Mayor and City Council
GENTLEMEN-Inclosed please find
printed copy of the communication of F.
Collingwood, to whom MIR. Kerr, on your
order at his request. submitted the plans
of the proposed Trinity river bridge for an
opinion on their suficiency, and in connec-
ton and attached to it a review of the
same by our engineer, which will speak for
itself We have joined the two together
for convenience of the council in referring
to both.
We beg to call your attention to the fact
that Mr.. c. IS communication does not even
approach the dignity of an opinion, mas
much as he disquallfies his entire state
ment at the outset with the announcement
that without going over the entire compu
tation, it is impossible to tell whether the
sizes given are correct" This refers to
the sizes of the constituent members of