The daily Gate City. [volume] (Keokuk, Iowa) 1855-1916, 1911-11-10

The new structure carries double
track electric car line and high
way and has two 9-foot cantilevered
I sidewalks. 1t consists of middle
segmental span of PSI feet, two 100
foot semicircular spans, 100-foot
semicircular span, a retaining wall SO
| feet in length with maximum height
of SO feet. The main arches are not
reinforced, but others are either of
wire mesh or OF structural steel en-
cased in concrete.
The main arch has an intrados on
q 14123-foot radius and 115-foot rise.
1t is of twin-rib construction, each
being CTS feet in depth and 16 feet
in width at the crown and 1875 feet
deep and 20 feet wide at the spring,
with a 36-foot spacing between cen
ter of ribs. The arches are sur
mounted with solid spandrel walls,
spanned by semicircular arches of 20
feet 5lls inches u. to the four middle
pannels, which are sub-divided by
smaller walls.
The spandrel walls are spanned
t transversely all the way across the
structure by fioor-beams made up OF
concrete encased I-beams, 21-incf
built-up beams across the two center
spandrels for the street railway sup
port and Pinch I-beams for the road
way. The fioor-beams are longitudin
ally connected by similarly constitut
ed stringers, making regular rec
tangular fioor-supporting system, upon
which the reinforced concrete foo
slab rests.
; The south abutment, which forms
the most unusual feature OF the de
sign, is 40 feet in height 1t wa!
made necessary by the fact there i:
no natural supporting ground on tina
side of the river On account of thi
peculiar condition the springing lin'
of the 120-foot arch is about IS fee
above the rock foundation to provid
Ian abutment to carry the sloped lin
of stress from the first named line t
the rock. Thus, each of the fou
Earch ribs is carried separately cow
to the base of the abutment. in sue
q shane that the center line from tn
Y thrust will always keep within tn
middle third. All the arches wer
analyzed on the elastic theory
n The north retaining wall consists c
n high and thin reinforced concret
., face slab, counterforted on the insid
u, with riangular-shaped buttre sse
3 which are anchored with rods int
Il the solid rock. Bed rock, compose
exclusively of the basalt common
s. the lava fields of the northwest, is e,
n posed the entire length betwee
n abutments.
- When the new bridge was first di
70 eussed by the city council. in 1908,
II. was intended TO erect structure (
b. 800 feet. costing $4,000 A yes
er ago, however, it was decided to buil
~ IT. the near future A-track steam "a
~ way with fanking electric car lint
he and streets crossing the line of II
in bridge at a high level, taking
space nearly 700 feet of the old SOU
"a abutment. This projected constru
wv ton necessitated starting the ne
he bridge a distance north of the o
ed span and also required that amp
re- clearance be allowed for railw;
~ tracks. AS a consequence, som
he what extraordinary layout and d
err sign. already briefly described, we
rs. adopted.
IN The result was saving of $500
to the taxpayers, as against the str,
We ture of greater length, and, in adj
ge ton, it has resulted in the creation
or some highly desirable real estate. .
90 timated to be worth more than :
,ly 100000. which has accrued to the eli
or Every dollars worth of work "
done by day labor, the city paying