final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 59
does not indicate the need for it; this may be especially important in the partially erected condition.
Safe working loads on proprietary equipment should
take into account all relevant boundary conditions,
i.e, loads on expanding floor centres should not be so
high that the timber supports crush. The designer
must consider and cater in his design for every use
to which the equipment may be put so that those on
site are not, through absence of relevant data, themselves tempted to design details for which they may
not have the requisite skills.
The designer should bear in mind that the falsework
will not be erected perfectly vertically and without
eccentricities .and that the design should cater for
normal site tolerances. Such tolerances and limits
should be clearly indicated on the drawings in order
that the operatives and supervisors, having been
made aware of these, can take suitable remedial
measures should they be exceeded.
Use of proprietary equipment
All proprietary equipment as well as other falsework
should be erected strictly in accordance with properly
prepared drawings and with the manufacturer's
instructions. Evidence submitted to the committee
has indicated that where problems have arisen they
are often the result of lack of attention to seemingly
small details. Instances of these are inadequate end
bearing of expanding floor centres which had not
been opened out sufficiently, use of incorrect pins
and wedges, etc, eccentricity of loadings and lack of
verticality of props. CIRIA report No 27 investigates
this last aspect and calls attention to the resulting loss
of capacity.
Both operatives and supervisors should be made
aware of the importance of attention to detail in the
use of proprietary falsework equipment.
Operatives involved in erection of proprietary equipment should be experienced in the use of the type
being erected. If they are not experienced they should
be given training by a suitable instructor. Even if the
training session is brief, it will save time and money in
the. long run and lead to safer practice.
Appendix H of the report of the Joint Committee of
the Institution of Structural Engineers and the Concrete Society lists defects commonly found in the use
of proprietary equipment.
Damaged equipment should not be used until it has
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been thoroughly inspected and where necessary reconditioned to meet the original load specification.
Testing
Proprietary equipment requires to be tested when
first supplied and at various stages throughout its
production life in order to ensure its fitness for use.
Standard test methods should be devised for the more
usual types of proprietary equipment so that the data
produced are more reliable and more uniform. Such
tests should simulate typical site usage, to reduce the
risk of mis-application of test data.
At present no such tests have been agreed. BS 4074,
Metal Props and Struts, has a test method appended
to it: but as this bears no relation to site practice, it
cannot be used as an example. BS Committee PEB/1
has a brief to standardise test methods and the first
for telescopic floor centres, has been circulated to industry for comment.
The specification of test conditions should aim to
reproduce site conditions as far as practicable. Such
specification needs to be definitive in order to avoid
variation between test houses.
Such particulars as the end fixing conditions, the
materials to be used at support points and the method
and rate of loading should be rigorously specified. In
order to give repeatable results, natural materials such
as timber should as far as possible be eliminated from
test procedures.
The test programme laid down should establish the
effect of variations in usage which occur on sites.
New proprietary equipment should be tested (a) prior
to its introduction to users and (b) during its life on
site. The latter could be achieved by sample testing
of randomly selected units. This will enable a check
to be made that the characteristics do not significantly
differ from the original model tested. These procedures apply equally to major modifications of existing
types of equipment.
For initial assessment, several samples of a new piece
of equipment should be tested to destruction and the
results assessed. Using appropriate factors of safetysee page 62 - safe working characteristics can be
calculated. The test should be conducted by an independent test authority and the test certificate should
be available to those actually using the equipment.
The certificate should give all relative data of the test,
including a full description of the test method, failure
modes and yield and collapse values.
