final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 70
It is recommended that a diagram shewing the loading
sequence should be produced by the falsework designer and supplied with the falsework drawings to the
contractor for transmission to those in charge of
loading operations. It is necessary to specify the
sequence for loading of pre-cast beams as well as for
concrete cast in situ. If the pre-cast beams are of
different sizes they should be clearly marked to
correspond with similar markings on the loading
diagram. If concrete is to be cast for longitudinal
beams or cross members in which the location of reinforcing bars or wire mattresses is critical, the loading
diagram should indicate the order of in-fill so that no
displacement occurs.
Temporary Works Co-ordinator
One school of thought recommends pouring concrete
at the centre of a bridge first so that the maximum
deflections occur early and thereafter pouring outwards to the two abutments of the bridge. This is
thought to produce less movement of the falsework
under the setting concrete. Other experts prefer to
start pouring close to the abutments. In some countries,
e.g. Canada, the United States and Germany this
procedure is recommended in conjunction with the
use of a plasticiser to retard setting. But in every case
the procedure must be agreed by the falsework
designer and specified in the loading diagrams. An
agreed plan of action should be worked out for all
operatives, and those operating spreaders, vibrators
etc. should be made fully aware of the proper sequence
of their particular operation.
Following publication of the Interim Report we
received many encouraging comments on our proposal. Several organisations have told us that they
have appointed Temporary Works Co-ordinators. In
what follows we discuss the role in more detail.
A final check must always be made within 24 hours of
loading falsework.
General site procedures
We have already discussed the need for the falsework
designer to specify his assumptions about how the
falsework is to be loaded having liaised with the
designer of the permanent works in this respect.
Any major change in the planned sequence of loading,
due for example to materials arriving on site either
late or early, must be referred back to the designer and
the engineer.
It is important that no-one should be allowed underneath or adjacent to falsework which is being loaded
unless he has a specific duty to perform, such as
monitoring leaks. Indeed the whole construction site
should be planned to ensure that no-one is exposed to
unnecessary risk at any time. This moral is pointed
by the collapse of the Westgate Bridge over the River
Yarra in Australia which killed a number of persons
who had no need to be beneath it.
The procedures that we have outlined require that at
each stage of the design and construction of falsework
a check or inspection should be made by a competent
person. A senior designer must countersign the plans:
an inspector must sign off the construction. Many
independent organisations are involved and the
correction of faults often requires co-operation
between more than one of them. We therefore believe
that it is essential that one individual in the construction organisation be given the duty of ensuring
that all the procedures and checks have been carried
out. In our Interim Report we described this person as
the Temporary Works Co-ordinator, or TWC ..
It would be impossible to find a person who was so
expert in every specialist field involved that he could
himself check the work of all the individual specialists.
Nor should it be necessary to check the checkers. The
duty of the TWC is simply to satisfy himself that the
appropriate checking has indeed been done.
The TWC must also ensure that where faults have
been revealed they have been corrected to the satisfaction of the checker: and that where there are
differences from the construction, loading and striking
procedures specified in the design, they have been
sanctioned by the appropriate authority.
In order to give the TWC sufficient authority to be
able to control the falsework we recommend that no
loading should take place until he has signed an
official permit to load. This permit would last for 24
hours after which it would need re-authorisation. A
copy would be lodged with the site agent and another
with the resident engineer.
Similarly the TWC should be required to sign the
permit to strike the various units of the falsework.
This he will do after other interests have been satisfied,
e.g. the Engineer or Architect will have laid down
certain requirements such as the minimum time for
curing the concrete, and may have indicated that he
wants to inspect the permanent works before the
falsework is struck.
Among his duties the TWC must pay particular
attention to the following questions:
Is the design brief adequate and does it accord with
actual conditions on site?
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