Fort Worth gazette. [volume] (Fort Worth, Tex.) 1891-1898, 1891-11-07
stem. ACROSS these timhers the floor i

| shall be OF good ordinary pine lum Der, free
from injurious knots AMI windshakes. three
| inches thick and of sufficient length TO lay
| on the bias as shown on plans, to be well
| nailed to the fioor-beamS. The flooring for
| sidewalks shall be the same except that it
| shall be two inches thick. and shall be laid
down as shown on plans. The girders,
| fioor-beams, chords and posts of the hand
| rail shall be of hrst-claSs long leaf pine
free from injurious knots, windshakes and
| other defects.
All lumber and timbers shall be well fitted
together 50 as to present finished and
workmanlike appearance when the struct-
| ure is completed.
| The hand rail is composed of top and
| lower chord of a Aka piece each with
wooden post 4x4x3jj4, placed every five feet
! with plank ks nailed between as shown
| on plans. The diagonal round iron rods be-
| tween the panels will be g inch in diameter
and will have cast fittings at the top joints.
| The flooring will extend out eighteen inchs
| at each panel to support Is inch brace rod
| to stiffen said hand rail.
Foundations-Ihey will rest upon bed
of concrete as shown on plans. The ma
sonry must be laid i'll courses as shown with
cemented joints and battered sides as
shown. in neat manner, except that the
portion below the surface may present
rough outer faces. The retaining
walls will be constructed Us shown, of
dry masonry and pointed well between out
er joints with cement mortar. The outer
surface TO be battered, as shown on plans.
Towers-The towers are made of rolled
steel, Tapped and well riveted y inch in
| thickness and of the length and dimensions
shown on plans. When in place they are
to be filed with concrete to prevent sweat
ing and rust inside. The towers will rest
on circular caSt-lron Oed-plateS, the center
one three and one-half feet and the outer
ones three feet in diameter. The thickness
at the certer will be two inches, tapering to
one-half inch at the edge and being pro-
vided with stiffening ribs extending from
the center to the SIDES. The towers will be
well braced at the top with portal as indi-
Gated on plans except, perhaps, the lower
angle irons will need to be placed foot
higher up so as to give more space for high
loads to pass under.
Lateral brace cables of thirty No gal
vanized steel wires will be placed as exhib-
tied on the plans, except that they are to
pass in Il continuous cable around the tow
erS in a figure Of eight styles, instead of be-
ing fastened to collars at the bases of the
towers as shown, crossing on the bridge as
shown on the plans. This will secure them
to the bases of the towers with certainty.
These lateral wind cables are laid in slots
at the top surface of the girders. prevent
ing side motion of all parts OF the bridge.
The cables rest at the top of the towers
in grooved cast fitting SO as to hold them
in position and transmit the strains evenly
upon the shell of each tower.
The cement mortar for the piers shall be
made as follows: One measure of Portland
cement TO two measures OF clean sharp sand
mixed dry, and on y water enough added to
form thick paste. All mortar must be
made fresh when used.
Concrete-The concrete for archorages
and foundations is to be made from Louis
vile cement and shall be made as follows:
To one measure of cement add two meas
ures of sand well mixed dry. To this add
four parts of coarse gravel or broken rock,
or if rock shall be placed in the interstices
between the piling; grouting composed of
the same proportion of cement and sand,
may be made to fiji between the rock and
around the piling. Louisville cement is
preferable to Portland ABOUT the anchor
ages, as it does not set so rapidly
as the former. Too rapid set
ting is Objectionable on account
of the liability to crack on ac-
count of vibrations in cables during con-
structiou.
All iron work and the hand rail is to be
well painted with two coats of good paint,
also the cables if desired.
All work herein specified for to be exc
cuted in neat, Thorough and workmanlike
manner, and the bridge when completed
shall present finished appearance.
These specifications are to govern where
there exist any differences between them
and the accompanying plans, provided such
differences shall not work to the detriment
of the structure.
The specifications arc so extended as to
include the attached report of the engineer
ing firm of Johnson s. F'lad of St. Louis
made on the plans of the proposed bridge
for Neil 2. Anderson & Co who are inter
ested in this undertaking, and are made
part hereof.
ST. LOUIS, Oct. 90, 1891.
Mcssrs. Neil P. Anderson s. Co, Fort Worth,
Tex.
GENTLEMEN-In accordance with your in
strUctions of the 18th inst. we have eX-
amined the plans and specifications of the
proposed suspension bridge over Trinity
river at your city, and beg leave to submit
the following report:
l. Assumed loads-The live loads which
have been assumed for this bridge are ex-
cessive. 1t is practically impossible to get
live load of 100 pounds per square foot on
any bridge. The greatest load which can
be put upon a bridge is crowd of people,
solidly iammed together, and then about
eighty pounds per square foot is all that
can be put on. In northern countries
snow load of some thirty to forty pounds
per square foot is allowed for, but this is
not necessary in your latitude. To require
factor of safety of five, therefore. with
this excessive load is making the structure
unnecessarily expensive. A factor of four
with these loads would be ample.
The cables-Taking the loads and dimen-
sions specified we find that the cen
ter cables carry a total load of
1000 pounds, and each pair of
side cables 81 900 pounds. Now there are
two cables to carry each OF these loads,
main cable with a sag of twenty feet
and an auxiliary cable with sag of twenty
five feet. Furthermore, the main cables
are designed to be aoout five and one-half
times as large as the auxiliaries. In such
a case the load will divide itself between
the cables in proportion to their size and to
the squares of their Says. Thus the load on
the main is to the load on
the auxiliary as 51%x2Ox2O is to 1x25x25, or
as 22O0 is to 625. That is to say, seven
ninths of the load will go on the main and
two-ninths on the auxiliary cables. Hence
We Will have the following loads, stresses
and sizes, allowing working stress of 49,
600 pounds per square inch in the wires, and
taking fifty-eight No. wires to the square
inch of solid metal:
e.... = I'LL :