final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 66
It is obviously essential that good communications
are established as quickly as possible between the
designers of the permanent works and those designing
the temporary works. This will ensure that time is not
wasted in devising a method of construction that is
subsequently found unacceptable. It may also make
possible slight modifications to the permanent works
which will, without affecting their performance, ease
the falsework design and construction.
Similarly it is essential that the falsework designer
knows about the actual methods of working on site
so that he can make reasonable allowances for live
loads, can choose realistic tolerances and so on.
It is unfortunate that many designs must be done
twice, once in a preliminary way for estimating purposes and then in final detail. Once the contract has
been awarded it is essential that the design brief is
updated to take account of the latest available
information.
It is convenient for design offices to maintain a simple
check list of all the information required. This would
include:
foundations and soil conditions
local restrictions
restrictions on methodof construction
philosophy of permanent works design
dead loading
available materials
available equipment
special live loads
accepted tolerances
The designer could then check immediately what information was not available. This would allow
estimates to be appropriately factored or would set in
train a request for the information.
Checking of designs
Any major falsework design may involve the assembly
of several parts which were designed independently.
Not all the designers will be equally experienced;
indeed some may still be under training. It is therefore
essential to institute checks to ensure first that the
overall structure is integrated and that different
assumptions about cross loading or mutual support
have not been made by the designers working on different parts; second that there are not basic errors in
arithmetic, or unwarranted assumptions about capaity of materials; and finally that all foreseeable contingencies have been allowed for. These checks are
particularly important if any of the components, or any
of the design principles, are novel. Particular care must
paid to the interface and inter-relationships between
different sections of falsework structures.
In some countries a well recognised standard has been
set and only those who possess the necessary qualifications are allowed to design or approve falseworks.
For example the enquiry into the Heron Road falsework collapse in Canada gave rise to a system of
procedures and checks which, with certain refinements,
has been shown to be practical. One of the Canadian
requirements is that the falsework drawings should
be stamped by a properly authorised professional
engineer. Such a man is examined and licensed by a
provincial authority, and no design drawings may be
acted upon unless he has signed them. It must, however, be remembered that in a continent as large as
Canada some such form of standardised authorisation
is essential because of the difficulty of establishing
nationwide reputations for competence and integrity.
In the UK such rigid systems may not be required and
would have the added disadvantage that they do not
allow for the enormous variation of technical difficulty
and complexity in falsework: nor do they make
adequate allowance for the man with design experience
but no paper qualifications. We would therefore only
insist that all designs should be checked by a competent designer within the design office and that he
should sign them off after examination: all major
designs should be signed off by a chartered engineer.
It is the contractor's duty to ensure that this checking
is done. However, the checker need not necessarily
be within the contractor's own organisation. In the
case where the design is unfamiliar or untried, or
where new materials or new methods of assembly are
introduced, and where clearance cannot properly be
given by the head of the design organisation, then
the whole scheme should be passed to an independent
design engineer, qualified and well versed in falsework
technology, for his opinion. This optional procedure
is a parallel to the design check which the Merrison
Committee required for all steel box girder bridges.
We have reviewed the practice of having a 'proof
engineer on the German model and, while it would be
acceptable on many counts, we think that his function
is covered by the design checking scheme which we
propose. Remembering that the number of qualified
engineers is limited, we do not wish to multiply the
checks required beyond those which are absolutely
necessary.
In referring to experience in the foregoing discussion
we must again emphasise that it is experience of the
special problems of falsework design, construction
and dismantling that is needed. It is the contractor's
duty to ensure that the man authorised to sign off a
falsework design has this experience and competence.
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