Evening star. [volume] (Washington, D.C.) 1854-1972, 1900-04-09
M MORAL BRIDGE
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cars. With this in view the width of road
way proposed by the boardl and upon which
the tracks are to be laid. is not less than
sixty feet, the sidewalks, bordering the
roadway, to be each not less than twelve
feet wide making the tot al width, between
ratings. not less than eighty-four feet.
In the opinion of the board a steel bas-
Guile draw for this bridge is preferable to
swing or an ordinary vertical lift draw.
and the substitution of a curve. instead of
right line. for the lowest part of the draw
is regarded desirable. The bascule form
is provided for in design No, 2.
Referring to the use of steel and concrete
combined in construction, the board does
not favor the use of concealed iron or steel
work that requires painting or other similar
application for its preservation. 1t is
claimed, however, especially by advocates
of the Melan system, that steel we'll i'm
bedded in hydraulic cement concrete or
properly coated with the same is practi-
cally imperishable and advocates of that
and other similar methods Of combining
iron or steel and concrete in construction
have adduced. as arguments, many observa-
steel that had been imbedded in or coated
with concrete for long term of years. A
large number of bridges has been built
within the past few years on the Melan or
bined), though the longest arch span in this
country of which the board has definite in
formation that is built on that system Is
one of 125 feet. Professor Burr's plan No.
2. which is here placed No. l in the order of
merit to be constructed on the Melan sys-
TEN, proposes spans as great as 1872 feet.
AS to the grade for the roadway. the
board Is Of opinion that it should rise
slightly toward the crown of the bridge. and
that the initial point of the approach at the
intersection Of 23d street and New York
-ho k1
ence) Of about ffty-five referred to the
United States engineer datum (mean low
water of the Potomac). Also that while the
design No. 2 of Mr.: Burr is regarded as the
most suitable and the best, the general
treatment of the towers. especially at the
as preferable to that Of his No. 2.
The board is of the opinion that the gen.
eral design Of Mr.. Burr, designated as the
first in the order of merit, meets the con-
ditions Of the problem, and should be
adopted subject to the recommended lions
and notifications herein set forth as to
width. slope of roadway curve of under
side of draw. towers. provision for tram
cars elevation of initial point. &c, and
rience may suggest. upon the undertaking
of the work or during its progress
The notifications recommended will, It Is
estimated, add about 80 per cent to the
of Mr. Burr. bringing it up to about
$4,S6 600.
Prof. Burr's Design.
Prof. Burrs design No. 2. which is des-
ignated by the board as first in the order
of merit, Is described in the report as fol-
lows:
This is design for a single-deck bridge,
60 feet In width between railings providing
Tor two sidewalks. each 10 feet wide and
a roadway. 40 feet wide. This design makes
no provision for street railway tracks The
total length Of the open work Of the bridge
proper and approaches Is about 3, 400 feet.
The bridge proper is to consist of three
19-foot span masonry arches, one steel
draw span having clear width of 159 feet.
and three more 192-foot span masonry
arches.
The 192-foot masonry arches are circular
lsegmentaD, the springing line being "a
feet above mean low water, the rise above
the spring 90 feet, and the radius of the in
trados 1898 feet.
The clear head room under the crown of
the arch Is 81 feet. A clear head room of
about 81 feet at low water is provided I'M
der three arches for a width Of 80 feet at
the center. and of about As feet inches for
a width OF 100 feet. The face of the arch
ring Is of granite, but the construction of
the main part Of the ring is on the Melan
system. there being five main concrete steel
ribs. The granite arch ring is 5 feet G
inches deep at the crown and 3 feet q
inches deep at the spring. while the con-
crete steel ribs are 80 inches deep at the
crown and feet inches at the spring A
solid masonry spandrel wall. partly of
granite and partly of concrete, rests upon
the granite arch ring. The asphalt road
way and granolithic sidewalks are sup
ported by concrete floor arches between
l-Deams The weight of this floor system is
carried down to the arch ring by framed
steel posts. between the above masonry
Spandrel walls
The draw span has two bascule arms GIN
frlnninnS hal INV,
tensions and CONFERENCE.-The The clear
opening fs about 1876 feet, the clear span at
low water level 159 feet. and the span.
from center to center of trunnions, 10
rect. Inc bascule arms are composed of
hve steel trusses Of the lattice girder TYNE
with parallel cords twelve feet six inches
deep between centers. The clear head room
Is about fifty-one feet when the draw ia
closed. The floor is to be of asphalt cork
plccks. nodded to fit the buckle plates
winch are supported by the floor beams
and strfngers carried by the trusses 1t Is
proposed to operate the draw by four fiftv
horsepower electric motors
The Washington approach is to consist
OF Twelve sixty foot span masonry arches,
DUCK oi Whlch Is an earthen embankment
about $50 feet long.
Ihe sixty-foot span masonry arches are
Iuii semi -ctrcular, the springing line being
tWenty-four feet above low water the rise
ABOVE tne spring thirty feet. and the radius
Of the intrados thirty feet. The arch is
constructed of the same materials and in
the same manner the 192-foot masonry
arch above described. The granite arch
ring Is four feet deep throughout, while
the concrete and steel ribs are sixteen
inches deep at the crown and forty-eight
inches deep at the spring.
Inc Arlington approach will consist of
fifteen sixty-foot masonry arches, Identical
with those composing the Washington ap-
proach, back of which Is about 1850 linear
feet Of earth embankment
The piers and their foundations are SINH
lar to those OF design No. 1. the six ma