final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 69
Inspection
The inspection of a falsework under construction
should be a continuing process. The inspectors who
form part of a contractor's team should have received
copies of the detailed erection drawings and should
have familiarised themselves with them at the earliest
opportunity. The inspectors should observe the manner
in which the falsework is constructed from its inception and, throughout its construction, up to the
time it is loaded. They should adopt a standard procedure for correcting errors or omissions - for example
by affixing a particular coloured tape to indicate a
defect and another colour, or the same colour twice,
for an omission such as a missing coupler or crossbracing member.
Different contractors adopt different methods for
indicating that the work has been attended to. Whereas
the removal of warning tapes or chalk marks seems
to have worked well on many projects, we have heard
instances of the obliteration or unauthorised removal
of the indicator without the appropriate rectification
having been made. Some firms believe that the replacement of the warning tape by an "action taken"
tape is required. It is essential that the system adopted
should be understood by everyone concerned. In view
of the mobility of the work force there is considerable
advantage in a standardised system and we commend
this to the Falsework Committee of the British
Standards Institution.
We suggest that the use of numbered and lettered
ยท grids on the falsework drawings would make it easier
to record the position of faults and to check that action
has been taken, and indeed, it would facilitate accurate
setting out in the first place.
It is important that faults should be discovered and
rectified as soon as possible. Often apparently minor
but important features are overlooked, for example
failure to mount a base plate centrally on a load
spreading sleeper, or failure to extend a diagonal
bracing tube to meet a longitudinal ledger as required
by the design, or incorrect use of couplers. Inadequate
tightness of components, forgetting to fix headplates
to wooden bearers by spikes or nails, excessive
cantilevering of beams beyond their end supports,
and the over-extension of fork-head screws, are all
features which need correcting before the erection
has advanced to a stage where remedial work becomes
difficult.
A proper inspection of load-spreading bearers, such
as sleepers, is important to detect subsidence, indentation, over-turning and possible splitting. Inspections should be made frequently and not only just
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prior to loading. Proper setting out is vital, especially
on sloping ground where creep may occur. The
inspection of foundations should be continued during
and, indeed, after a concrete pouring operation and
precautions should be taken to ensure that curing
water applied to the concrete is diverted in purposemade channels away from the area of the bearers.
On completion of the construction an inspection of
the falsework must be made to ensure that all faults
have been corrected. In the case of inspection on
behalf of sub-contractors, a handing-over certificate
should be given to the main contractor. Such a
certificate may follow the scheme outlined in Appendix
3 of the Report published by the Department of
Employment on "Safety of Scaffolding".
Near the sea, on-shore winds may cause brine to be
deposited on steel members and protection against
saline corrosion is needed: members should be inspected at frequent intervals if the falsework remains
standing for any length of time. Diurnal variations in
temperature produce successive tightening and expansion of members and joints: regular inspection is
needed to ensure that stressed members such as
threaded bolts have not sheared or become loosened
in this process.
Loading of falsework
The response of the falsework when it is first loaded
is an indication of its soundness. Lookouts should
therefore be stationed at vantage points to observe any
undue deflection or the escape of concrete through the
soffit or the side formwork. Skill and judgment is
needed to make sure that the placing of concrete or
pre-cast beams does not impose high impact loads on
the supporting members and that loads are distributed
evenly over areas where this is critical.
Where concrete is to deposited from skips, crane
drivers should either be in a position where they have
a full view of the landing area or should be aided by
a properly trained banksman. The driver should be
made aware of the importance of avoiding impact and
shock due to the dropping of the skip load. In the
United States the representatives of the Iron Workers'
Trade Union propose that one of their men is present
as a banksman during all pouring operations.
Tell-tale devices or strain gauges are of value. The
observers must check that snap ties do not yield and
that the ends of timber bearers do not crush.
