The Washington herald., 1922-02-08

wall over the stage practically
formed an expansion joint.
Successive expansions and con-
fractions of the roof and structure
extending over a period OF i've
years undoubtedly resulted in some
outward set of the top OF the Co.
lumbia road wall, and this de-
creased the wall bearing of beam
B-21. Just previous to the failure
the beam probably rested with only
one corner of the f1ange bearing on
the wall plate. Below this wall
plate is a lighter colored and prob
ably softer tile than was used else
where in the wall construction.
The corner of the flange of this
beam Is bent up, the light colored
tile was crushed and considerably
pulverized. indicating that tie wall
plate rotated out and down under
this eccentric concentration of load.
There was no concrete filling in tile
at this or other beam bearings
Evidence OF the action described
above can be seen by examining
the end Of the beam and what Is
left of the wall bearing.
Steel Trusses Detected.
The decrease in bearing area of
beamB-21 on the wall was also af-
fected by the detection of the steel
trusses and the entire roof. includ-
ing the general detection Of roof
slab and beams: the horizontal
movement as a result of the defiec-
ton being in addition to the move
ment resulting from contraction
from falling temperature.
The general DETECTION of the ma
roof was increased by the heavy
cinder concrete fill and by the loads
from ventilating equipment on the
main roof, all in addition to the
snow load. The creeping and move
ment of the steel on the wall bef-
inGs would also be affected by the
vibration of the motor and fan
equipment. The outward move
ment of the top of the Columbia
road wan. the contraction on ac-
count of temperature. and the hori-
zontal movement resulting from de-
Election. all added increments tend
ing to decrease the eXteut of the
bearing of the steel beams on the
wall plates.
Roof Rested on Tile.
In general, the reinforced con-
crete roof slab spanning the roof
beams had two and three-Quarter
inch thickness and was reinforced
with Clinton wire mesh No. wires
on three-inch center. with effective
depth from the top of the roof slab
to the center Of reinforcing steel of
two and a fourth inches. The roof
beams were imbedded in the bot
tom of the slab above the depth Of
the edge of the flange. At the cor
ner where the Columbia road wall
met the stage wall. it is possible
that the roof Slab had a depth Of
from three to three and a half
inches and was reinforced with
three-eighths inch deformed round
bars on siX-inch centers. Fragments
of slSb. corresponding to the last
mentioned dimensions, were found
under this location.
The roof slab extended over and
rested also on tile in the Columbia
road wall. and where the roof slab
met the stage wall it rested on a
ledge about two inches in width.
which ledge was built up with
broken brick and wide mortar
joints. from an offset in the tile
below.
Beam Pulled from Socket.
When the bearing failed under the
wall end of beam B-21 II is possible
that this beam hung for some time
with the bent up corner of the bot
tom fiange pressing against the
partly rotated wall plate over the
crushed tile. The roof slab in such
a case would have passed more OF
its load to the Columbia road wall
to the two-inch ledge on the stage
wall and to beam B-22. There Is
evidence that this condition may
have existed. as the outer edge o.:
bottom fianges where II slid from
the bearing Is somewhat compressed
ard scratched The effect of this
movement would be to increase the
detection Of the light roof slab de-
prived of its support on B-21, and to
greatly increase the lateral pull on
the end of beam B-22 in a direction
toward Columbia road.
The angle Of the roof slab at this
location is such that there could be
only partial restraint in the slab it.
self to resist such lateral force, ana
as the ledge along the stage wall
was insecure. and with further con-
traction of the roof and deection
of the slab as a result of the load
from the snow. a condition was
reached where the lateral pull on
the end Of beam B-22 was sufficient.
to move this sideways from its
socket. as is evidenced by the
sheared brick and tile which can
now be seen at this bearing.
Portions of the roof slab examined
show that the reinforcing steel In
the slab was not'raised to near the