Evening public ledger. [volume] (Philadelphia [Pa.]) 1914-1942, 1916-05-31
SUBWAY TRACK WALLS
TO BEMADE STRONGER
TO HELP SUSTAIN HALL
Transit Department Agrees on
Selid 4-Foot Steel and Con-
crete Construction of Rows
of Pillars
WILL INCREASE SAFETY

Ar important change in the design of the
Broad street subway structure under city
Hall has just been agreed upon by the De.
partment of City Transit to solve some Of
the engineering problems encountered thus
far in the work The change is the sub
stitutIon of solid concrete walls between the
tracks and supporting the roof OF the tube
for rows Of castiron, concrete-fi filled columns.
Under the new design each of the four
tracks when completed will appear like a
single track subway, and only at few
points, where there will be arched openings
IN the masonry wallis will the trains on the
paralel tracks be visible from the adjoining
tracks. The change will bring greater
strength and safety at the expense of ar
tistic beauty of construction.
Under the original plan the two outside
walls of the tube were to be of rod-rein-
forced concrete feet in thickness Each
of the three inside walls, however, which
eeparate the four tracks and support the
roof of the subway, and consequently the
weight of a considerable section of CITY
Hall was to be row of cast Iron com
crete-filled, cylindrical columns, feet
inches in thick and placed about 12 feet
apart.
The roof of the tube, consisting of longI-
tudinal and transverse steel-plate girders
was TO De supported on the three rows of
columns. In working out the structure of
the tube, however, II was found that girders.
on account of their size and weight, could
be placed In position only with the utmost
difficulty. This was found particularly true
slnc6 the stress and weight must be care
fully distributed among the pillars.
As the tube will run diagonally under
the City Hall the girders will not be
parallel to the foundations of the building
and will have to be placed on top of the
Eirders. To support this complex structure
upon pillars almost IL feet apart IL was
found would be to court danger. The
change In design was therefore worked out
by the department engineers.
Under the new plan the two outside walls
of the tube will not be changed. The three
inside walls, however, instead of being rows
of cylindrical columns, will be three solid
rodreinforced concrete walls four feet in
thickness At few places the walls will
be arched to facilitate ventilation and to
apermt communication between the tracks
The heavy girders which will be placed
across the walls, will be Z feet In depth
and 20 feet in length. The span from one
wall to the next will be approximately 81
feet. The girders and the beams above
will be filled in between and covered with
concrete, SO that the roof will be one solid
piece of masonry. The Importance of
strong construction Is apparent when II Is
understood that the new City Hall founda-
tions are to be constructed down only to
the top level of the subway roof and the
weight of the building will, therefore, be
supported directly by the roof of the tube
Engineers working on the new founda-
tions estimate that 1t will be almost a
month before they will have carried their
work forward to point where work on the
subway proper can be begun.