final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 38
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The effect of impact between a road vehicle and an unprotected access opening through
falsework
incapable of supporting the main load. Similarly, we
have heard of examples where access openings for contractors' plant were introduced after the initial design
was completed, and this led to unnecessary weakness.
The particular problems of spanning roadways, rivers
and railway lines are examples of constraints which
which must be considered before design is started.
It is clearly necessary that such bodies as the river
authorities should have a primary regard for river
drainage or navigation. Similarly the Railway Board
must have the safety of the travelling public and
rolling stock as its primary concern. It was, however
suggested to us that in some cases discussions between
the authorities and the contractors might have
allowed a relaxation of arbitrary constraints and so
led to simpler and safer falsework without compromising safety elsewhere. Better communications
should ensure that such conditions as are imposed
do not make the construction of the falsework unnecessarily difficult, particularly by the imposition of
blanket rules which could well be the subject of
discussion in individual cases. For example, a rule
which prohibits the erection in midstream of falsevork supports for a bridge spanning a river may be
nsible in prohibiting a forest of falsework in the river
which could trap debris and vegetation and alter the
normal flow of the river whose discharge could
spread on to adjoining land. Similarly, as we have
heard from overseas countries that river bed props
may be prohibited because large tree trunks or blocks
of ice or rivers in spate could dislodge a vital member.
But to interpret these rules as an overall embargo preventing the placing of a central row of props under
any bridge is too authoritarian when there may be
other ways of avoiding interference with the flow.
Similarly we have been told of cases where a dialogue
between the· designer of falsework and permanent
works before the latter were finalised could have
allowed the inclusion of features that would have
considerably simplified the falsework problems. A
major problem which has been drawn to our attention
several times is that the preliminary design of falsework is undertaken at the tendering stage when only
preliminary documents are available. Instances were
given where the designer had no information on how
the falsework was to be located, no information
whatsoever on the ground conditions nor of adjacent
and even contiguous structures which could have
influenced the design. Once the contract has been
placed however, and fuller details are available, there
is tremendous pressure· to produce the final designs
at high speed. One of our enquiries revealed a period
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