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The
Technique fo Early Striking
Early striking is a technique whereby the formwork
is removed 3 to 4 days after pouring a slab, but
the supporting structure of scaffolding or props
remains undisturbed until the concrete is strong
enough to support its own weight over its full
span.
Concrete generally takes 28 days to attain its
full constructional design strength. Most engineers
will only permit the complete support to be removed
after about 10 to 14 days, depending on the ambient
temperature and cube strength tests.
The first calcualtion opposite shows that the
load safety factor of the slab of 3 days, spanning
the short distances between the temporary supports,
is certainly greater than 10 to 14 days over its
full Span, although other factors may have to
be considered.
The most critical stress in early striking is
the punching shear at the drophead. The second
calculation, based on the most severe condition
of relatively light slab, shows a safely factor
of 5 to 1.
With today's high costs of formwork it is important
to use it as frequently as possible. Traditional
formwork locked in situ for 10 to 14 days with
a pouring cycle in excess of this is obviously
outmoded by Metriform with its facility to speed
the cycle of operations. This pracitice has been
widely accepted in Europe for more than a decade
where the rising costs of materials and labour
have proved that the Metriform system of early
striking is safe, efficient and truly cost-effective.
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