final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 103
. construction traffic to pass through the structure. The original intention was
for this gap to be bridged by steel beams but it was finally decided to fill the
gap with shoring frames. Some jacking was done to provide the correct soffit
profile.
Formwork consisted basically of¾ in plywood on 6 in x 3 in bearers at approximately 1 ft centres. These in turn were carried by double 9 in x 3 in timbers
supported in the forkheads. The walkway areas of the bridge were cantilevered
from the main deck and the shuttering for these was somewhat different.
The collapse
The concreting operation began at 0100 hours on the morning of 22 March
· at the .south end and shortly afterwards work started at the north end. Both
operations continued until 1500 hours when the collapse occurred. At this
stage there remained a gap of about 37 ft between the two advancing faces of
concrete. The south face was more advanced than the north and had reached
the centre of the main span. Concrete was deposited by two pumps, one at each
end of the bridge.
Witnesses both on and off the bridge described the collapse as starting with a
sharp noise. All suggested the collapse started at the north end close to the
pier and progressed in a wave across the span to the south end.
The main span collapsed entirely but the side spans remained more or less
intact.
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69'-0"
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104
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Section B-B
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