final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 51
Isolated struts in larger structures
Where isolated struts of larger dimensions are used
these should preferably be pin jointed at their ends
so that no moments can occur. The lateral stability of
the strut must then be ensured either by the external
bracing or by taking sideways loads to other elements
of the structure being built.
The bracing of lines of towers and bird cages
If the towers are independent they must each withstand the horizontal forces plus 1 % of the vertical
load or 3 % of the vertical load - whichever is greater,
and this may involve lateral support. If the towers are
in connected lines one brace along the line may cater
for several towers; for instance in a square arrangement of towers there may be one brace for each pair
of towers in each direction. This means that intermediate towers may not be individually braced. With
this situation the lacing must be strong enough in
bending to give stability to the unbraced lines and
strong enough to withstand the whole of the lateral
force if required to do so.
Structural bracing
The bracing must resist all the horizontal loads.
Some were discussed previously and there will be
others in different cases. In addition to resisting all
these, the bracing must also provide the lateral
stability described above and ensure the stiffening of
the strut to prevent its buckling.
In most cases wind and other major forces will be
greater than 3 % of the deadload, and the Interim
Report proposed adding 1 % as a safety factor over
and above those conscientiously assessed. But the
additional 1 % is no substitute for exhaustive consideration of loads. The total should never be less
than 3%.
An example of tho benefits of careful setting-out and design is shown in this large-scale falsework, where excellent bracing and
lacing is facilitated by the regular construction
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