The times dispatch. [volume] (Richmond, Va.) 1903-1914, 1907-06-23

came problem of the designing en-
gineer how best to span this street.
1t was found that with Orders sixty
inches deep, the depth allowed here,
that the beam would not contain
enough concrete to take the compress
sion stresses. A T-shaped beam was
finally decided on.
The spans vary in length from TWEEN
ty-three feet six inches to sixty seven
feet five inches centre to centre OF
bents, the long spans being used at
Railway and streets which had to be
crossed with clear span. Expansion
in the structure Is taken care OF by ex-
pansion joints placed at intervals of
about 200 feet, consisting of q grooved
steel plate on top of the bent, on which
planed steel plate on the bottom OF
the girder slides, while a sliding toggle
near top of girder prevents any ten
dency to turn the glrder. The accom-
panying general elevation shows the
entire arrangement of spans. On &C.
count of unavoidable circumstances.
1t was necessary to put two seven
degree curves In the viaduct, both in
the same direction. The grade Is up
ward from the north end of the viaduct
to about 200 feet from the terminal. al
grade on the tangent is plus 10 per
cent. and on curves plus 0.7763 per
cent, there being a total difference In
elevation of twenty-five feet between
the two ends of the structure.
The concrete OF 1:2:4 mixture. was
figured for compressive stress Of soc
pounds per square inch and shear OF
fifty pounds. while the steel used was
given tensile stress of 10000 pounds
compression. 10000 pounds. and shear
of 10000 pounds per square inch OF
cross section. The modulus OF
elasticity OF concrete to steel was
taken as 1919. and the percentage OF
steel to be less than 1.45 per cent
Wilson Commenced Work.
Work on the viaduct was begun by
Contractor Wilson in the latter part OF
May, 906 and was quite slow until the
contractor got system of operations
fully established. Work was started
at two points. the northern end and
about the middle, and both forces
worked southwark The footings for
| the columns were first put in. having
four three-quarter-inch rods project
ing four feet, around which the column
was built, and also a pocket left for
the bottom of the column. The foun-
dations We're either hard clay or COM
pact gravel and were calculated for I:
pressure not to exceed 5000 pounds
! per square foot AS the structure was
designed so that 1t could be readily
double-tracked when necessary, the
footings We're made twice as large as
they would have been If designed sim
liply for single track. and a four-foot
stump of column was left on which
the future double-track column will
rest. When traffic justifies double
tracking the viaduct it will be easy to
construct an additional Eirder with
proper supports, on one side Of the viat-
duct. shift the track so that 1t will be
supported by the new girder and one
of the original Orders and carry the
traffic on this track during the con
struction OF the additional girder and
new track on the other side. Cored
holes We're provided to take care OF
fastening new work to the old when
Notwithstanding is begun. The foot
ings were carried down uniform
depth of four feet, unless extra depth
was required to get suitable founda-
tions.
The viaduct proper was completed in
the early part of the year, and experts
from various parts of the country have
been here to look upon tho work Al.
pronounce 1t great.