final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 33
the contribution made by sub-standard or wrongly
chosen materials; corroded and damaged steel cornponents; inadequately repaired materials; cracked,
knotted and rotten timber.
Most of the falsework components are used over
and over again. Without an efficient inspection system
there is always the likelihood of defective pieces
finding their way into a structure.
There is also a danger that designers may be misled
by claims made on behalf of proprietary materials.
Working loads may be quoted which are not applicable
under the conditions of practical construction. Special
recommendations are made on this point in a later
section.
Finally, there are the cases of unauthorised changes
in materials. The design of a structure clearly involves
stipulation of the materials to be used. It is therefore
of fundarr:ental importance for erectors of falsework
to appreciate that the capacity of the falsework to
support the anticipated load rests upon a preconceived understanding of the load-bearing properties of
the specified components. To alter one of these components and to substitue another could endanger the
concept upon which the design was based.
Oversize forkhead and incorrect use of folding wedges will
produce eccentric loading
Faulty setting-out
With the methods and organisation which exist on
civil engineering and building sites it is unlikely that
all the materials necessary for the falsework arrive
ready for the start of the job. Erection often begins
as soon as the first load of essential materials arrives.
Unless this load is quickly supplemented by further
deliveries there will be a temptation to improvise in
order to avoid delays in construction and unprofitable
waiting time. It is at such a stage that unauthorised
substitutions of material can easily occur though the
blame rests more on managerial failures than the
positive acts of the erection team.
It is an undeniable pre-requisite of satisfactory false-
work construction that the ground plan for the falsework supports should be in accordance with the
drawings. We have even been informed of an extreme
case where the pegging out for a falsework had been
carried out in entirely the wrong place. Other examples
of inaccurate planning have been given to us, particularly on skewed structures where elements of the
falsework have been placed significantly away from
the intended position. It is, therefore most important
for the contractor to arrange for surveyors to be
involved in the initial setting-out, and for a check to
be made of the pegged-out location marks upon
completion of the setting-out.
Defective or inadequate materials
A review of the major technical causes of falsework
collapse would not be complete without reference to
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Dismantling
The specification of the order in which falsework
should be dismantled is of considerable importance
both in ensuring that stresses are safely relieved and
that the permanent structure takes up the support of
its own self weight without imposing extra stresses on
the falsework. It is essential to follow the specified
order to ensure that there is no member under stress
which could produce springing or dislodgment and
put at risk other parts of the structure or those working
on it. We have received evidence of the partial collapse
of falsework being dismantled due to instability of
separate sections.
We have also heard of cases of inadequate re-shoring
or re-propping of parts of the permanent structure
