Evening star., 1909-06-23

even of S25 feet In substantially within
the limits of approved construction The
upper Niagara bridge, $40 feet is the
largest existing steel arch. The design
| for the He'll Gate bridge contemplates a
| / .OOO-foot arch. But in concrete there is
nothing even remotely approaching In
| magnitude the proposed span The Grun-
Gd nrdss over f the snan lsaT is the srses
completed concrete arch. The walnut
Lane concrete arch bridge. now being
built. has a slightly longer span. 233 feet,
between faces of abutments. These spans
become insignificant, even trivial. when
compared with that now proposed for the
Hudson Memorial bridge.
"A better idea of the bo1dness OF the
proposal is had from comparison with
the general field of masonry arch con-
struction. since the problems of design
and erection for arches of stone and con-
crete are in measure the same. The
Cabin John arch at the Washington aque.
duct. 22G feet In span, built about half
ed upon as an exceptional achievement.
being the largest stone arch in the world.
Only In the last eight years. has 1t been
exceeded. and there are now three larger
spans in stone, besides the 2sO-foot concrete
arch at Grunwald; at AIDA, 230 feet:
Luxembourg. 27s feet. and Plauen, 295
feet. In fifty years designers have
ventured only one-third beyond the limits
by the Cabin John arch, and only in three
cases have they found it necessary. Now.
in one leap, the present limit is to be
multiplied by two and one-half.
1.-The deck of the roadway consists of
plain concrete arches sprung between the
stringers. The sidewalk floor is made Of
reinforced concrete slabs separately mold
ed and bolted on the top fanges of the
stringers. The roadway is paved.
1.-The approaches to the great arch
are formed Of succession Of 100
l g.
lures calling for special remark. The
roadway on the approaches has q grade
of ~ per cent from either side up toward
the center: over the main span vertical
curve unites the slopes BY adopting
height of arch was secured as compared
with the first design, and the arch
stresses correspondingly reduced The
1OO-foot arches are of concrete, properly
reinforced. The piers between them, de-
tailed to harmonize with the treatment
Of the two main piers. are faced with
stone in rusticated coursing. All other
surfaces of the structure are concrete.
This is expected to give a marked relief
between the pier faces and the arch and
spandrel faces"
The New Greensboro Bridge.
There are several splendid new bridges
i'm New York. What is known as the
Greensboro bridge. so named because 1t
connects New York at Canal street with
the borough of Queens. was opened to
traffic in the presence Of Secretary Dick
inson and Gov. Hughes recently. 1t
crosses East river by way of Blackwelis 8
Island, where the reformatory and hos
pitfalls are. The Manhattan bridge. which
also crosses the East river. will be opened
this fall Both rank among the greatest
half dozen great bridges of the world.
Only three with longer spans than that
of the greensboro bridge exist The
greatest is that over the Firth of Forth,
near Edinburgh, which Is Ito feet: next
IS the new Williamsburg bridge. with
span of 1900 feet: then the Brooklyn
bridge, with a span of l l.13a feet. and then
comes the greensboro bridge, with span
of 1,1s2 feet. The Scotland bridge. the
| Oueensboro bridge and that which is now
being constructed over the st. Lawrence
river at Quebec are the greatest exam
| ples of the cantilever type in the world.
The Williamsburg and Brooklyn bridges
are both Of the suspension type.
The total length of the new Queens
boro bridge. with its approaches is S.231
feet; the length Of the bridge proper is
S.724 feet; the length, Of the span east
rests, is 9S4 feet and that west OF Black
! wells Island is 1.1S2 feet. The center Of
| the arch is 135 feet above the water.
| Ground was broken for the bridge In
| 1903, and ii was finished March 81, 1909.
| There are approximately $4,000 cubic
feet of masonry in the arch and piers.
and the steel superstructure weighs a.-
600 tons 1t can accommodate 215,OOO
persons at one time. Its maximum load.
| including track material and paving. is
| estimated at 12OOOO.O0O pounds. There
are two floors; the top one carries four
elevated tracks and two promenades elev
| en- feet wide: the lower floor has four
| trolley tracks, a driveway thirty-fAve
feet wide and two promenades each
eleven feet wide.
Proposed Bridge Over the Hudson.
For many years there have >been peri
| odical agitations to bridge the Hudson