Fort Worth gazette. [volume] (Fort Worth, Tex.) 1891-1898, 1891-11-07

this should be transmitted through the
steel plates, which with factor Of safety
| of six, would require one-half inch metal in
| all towers, with the diameters given, in
| place of three-eighth inch, as given on the
| plans. These should also be made Of single
| plates, rolled into cylinder, so IS to dis
| pense with horizonal abutting joints.
! The wind bracing.-The total wind pres
! sure allowed for should be about thirty
| pounds per square foot, and for the con-
/ struction shown, thirty No. . steel wires
! would stay it against this load, but we
| think they should be laid in curve, in slots
| in all floor beams, so as to pull equally on
all. instead of only. on the center beam as
| shown. We have indicated the proper az
rangement on our drawing. The towers
should also be stayed by stronger system
, of wind bracing than shown on the draw
! ings. The towers are so small that they
have not great deal of stability on their
| bases. We have shown such bracing on
| our plan.
The piers-If the piers be made of good
| masonry, laid in Portland cement mortar,
| and the steel towers rest on castiron caps
fioated to place on Portland cement n!Or
tar. the resistance to crushing Immediately
below the towers will be ample For the
maximum load, a casting of but three feet
III diameter under the center column, and
| one two and q half feet III diameter under
the side columns, would give 4 crushing
load of but 400 pounds per square inch,
which gives a factor of safety here of at
least five or six. With larger castings the
pressure would be correspondingly less.
The two or three top courses of stones,
however, should be well-titted. squared
stones of uniform depth of course, with
thin and well-ftted joints, with good cap
stone, so as TO allow of an even distribution
of pressure and of settlement over the
whole ar Of piers.
The anchorages.- system of an
chorage proposed is satisfactory. if made of
sufficient size. II concrete be used we esti-
mate that mass of concrete, made OF nat
ural or Louisville cement, eight feet high
six feet wide and forty feet long, with eight
feet of earth over its surface will have, by
It's own weight and the resistance of the
earth in front of and above it, about twice
the resistance of the maximum pull on all
the cables when the bridge is fully loaded,
which it is quite impossible for it ever to
be. If piles are used in addition as shown
on our plans, the resistance will be i'm
mensely increased. We would not fear that
these piles would decay under the concrete,
even though above the line of low water.
They would certainly last hundred years
or more in such place, if the air cannot
circulate about them. We have known of
similar instances where, after fifty years,
they seemed to be as sound as ever. But
in this case the stability of the anchorage
would not depend upon tne pies, DuI upon
the dead weight of the concrete and the
ground resistance in front.
Floor systematic floor system designed
is amply strong to carry the proposed loads,
but it would have great tieXibility, and the
only reliance against an unequal distortion
would be in the diagonal wire bracing. We
think this would probably not be satisfac-
tory, and hence we take the liberty of sug-
costing the following:
Proposed changes of plans.-In order to
obtain greater stiffness against unsym-
metrical loads, as well as to avoid undula-
tions from the wind, we think it would be
well to change the plans in the following
particulars:
l. Reduce the sag of both cables,
that of the main cable to fifteen
feet, and of the auxiliary cable to
twenty-five feet. This, in itself, would
add greatly to the stiffness of the bridge.
If the st VS. be increased in size as indi-
Gated above, and if they be estimated to
carry their due proportion of the total live
loads which they must do OF necessity,
then we find the size of the main and auXil-
larry cables to be as follows