final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 102
(c)
(d)
(e)
(f)
(g)
to and that the falsework design underwent considerable modification
in the process of obtaining approval.
the tenders and acceptances for both the foundations and bridge structure
the materials, methods, workmanship, supervision and inspection related
to the permanent bridge structure
the subsoil, most of the foundations, bearing loads and settlements
the formwork, the steel beams imm ediately under the formwork and the
hardwood caps supporting the steel beams.
wind and earthquakes; there was no appreciable wind and no earthquake
activity in the vicinity of the site at the time of the collapse.
Recommendations
As a result of these investigations, a number of recommendations were made.
One was that the specification of the Department of Highways of Ontario be
revised to provide for:
(a) Mandatory design live loads including a horizontal live load of 2 per cent
of all dead and live loads acting at the level of the falsework at which the
vertical loads are applied.
(b) A requirement that approved design and construction drawings for
falsework carry the stamp of a Registered Professional Engineer (Civil).
Summary of a report of the fallure of falsework at the Birling
Road Overbridge, Kent 1971
General
At approximately 1500 hours on Monday 22 March 1971 the falsework to the
Birling Road Overbridge collapsed as the deck concrete was being poured. The
bridge was part of a contract to provide a by-pass around Ditton on the A20 in
Kent.
One man was killed, five men were seriously injured and twelve others slightly
injured.
Description of the project
The Birling Road Overbridge was a post-tensioned concrete bridge, consisting
of three spans. The approach spans were of about 46 ft and the main span of
138 ft, all lying in a roughly north-south direction. The bridge was curved
on plan and had a crossfall of one in fifteen. The underside of the deck was
approximately 18 ft above ground level. The deck was 4 ft 6 in deep and contained void formers. A sketch of the bridge is on page 104.
Foundations
Preparations for the construction of the bridge started early in 1970 with the
replacement of peaty ground which lay above firm gravel. This entailed excavation to a depth of about 9 ft and replacement with compacted Folkestone sand.
Piling for abutments and piers took place in June 1970 and the construction of
the abutments and piers was completed during November.
Falsework and formwork
A 'birdcage' type of falsework employing conventional 2 in diameter scaffold
tubes and couplers, was erected· on sleeper foundations. A gap was left to enable
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