final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 117
The collapse
The collapse of this building occurred at about 14.30 on Friday 2 March
1973, killing 14 men and injuring 34.
The collapse extended between shear wall H and column 33 on the south face,
a distance of about 65 ft and on the north face extended between columns 12
and 17, a distance of about 104 ft. The collapsed portion of the building was
located approximately under the slab being cast and extended vertically for the
full height of the building, 23 storeys plus 4 basement storeys.
The collapse progressed vertically, the debris from one slab overloading the
floor below and collapsing that, so that it fell onto the one below, which in
turn became overloaded. It also caused failure of the entire adjacent garage
area (approximately 300 ft x 340 ft on plan) for which one entire floor and
part of the next had been cast.
Investigations
Investigations were conducted by officials from various US Departments and
covered such items as concrete and steel strengths, stress analysis of floor slabs
and of falsework systems. The effects of the tower cranes on the building were
also considered. Although some of the factors relating to tower crane installation and usage deviated from the prescribed regulations there was no suggestion
that the cranes had initiated the failure. There was a complete lack of field-cured
concrete specimens but it has not been suggested that the concrete mix and
control were inadequate in any way.
Findings of investigations
Cause of collapse
The premature removal of the propping system initiated the failure.
Mode of failure
On the basis of evidence as well as analysis, it appears that the collapse was
initiated at the 23rd floor level.
t
3 8 6' approx
Ar~a which cottcpsed
I .
'
,
µ
. I
'
'1
~
J ~
I
Building A- 4
118
i
'
I
-
·1
'
I _
i
ih
®
