final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 125
Case 17
A multi-storey concrete building 316 ft high was under construction. Falsework
was erected around the services tower to support formwork for the cantilevered
floor 18 in thick, of the boiler room.
The falsework was in the form of a conventional heavy duty scaffold, 40 ft
wide, with double standards for the bottom 80 ft. The timber formwork to
support the 18 in thick slab consisted of 4 in x 3 in joists at 15 in centres,
carried on 8 in x 3 in joists at 4 in centres, which in turn were supported on
the adjustable forkheads to the scaffold. Ladder beam sections were also used
in this area because of the heavy loading and bending effects. This falsework
had originally been designed for a 12 in thick floor slab. To accommodate
the thicker slab, standards were doubled up and a raking system introduced
whereby it was hoped that some of the load could be carried on the shell of the
building.
After the boiler room floor slab had been cast, the standards in the upper
section of the scaffold buck.led but were held in position by the ties. Thus the
scaffold did not fall to the ground.
It was difficult to arrive at a firm conclusion regarding the cause of the collapse.
Access to the damaged falsework was difficult. Clearly the standards had failed
though buckling and the form they took suggested that the effective length was
at least two lifts, i.e., 13 ft O in. This could have been the result of inadequate
tying and/or bracing on one of the corners of the structure. There was also doubt
about the effectiveness of the raking system mentioned above.
Case 18
The third floor of a reinforced concrete hospital was under construction at the
time of the accident.
The soffit of the floor slab was supported by falsework. This was a proprietory
system consisting essentially of plywood panels set in steel frames which fitted
between fabricated beams. The beams were located on lugs on drop-head units
which were carried on adjustable steel props. The drop-head units permitted the
soffit shuttering to be struck leaving the props in position until the concrete
had cured sufficiently to achieve its required strength. Single horizontal tubes
were fixed to the steel props in the direction of the steel beams and these were
occasionally tied together with tubes at right angles.
It was during the laying of the panels between the beams that the accident
occurred. Some of the panels would not fit between the beams and when force
was applied by kicking the panel, the whole assembly collapsed,
This collapse resulted from the instability of the falsework when subjected to
horizontal loading. The provision of temporary diagonal bracing with horizontal tie tubes in two directions would have stabilized the structure. Alternatively the falsework could have been tied back to the existing building.
Case 19
The roof, 52 ft O in long x 9 ft 8 in wide x 8 in thick of a reinforced concrete
building was under construction at the time of the accident.
The falsework consisted of adjustable centres 12 in apart supporting the plywood lining, which rested on 5 in X 3 in timber bearers. These were carried in
adjustable wall brackets spaced at 4 ft. centres. These brackets were suspended
from the in situ concrete roof beams which had been cast three weeks previously.
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