Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

16 Chapter Two
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been properly tested with an appropriate American Society for
Testing and Materials (ASTM) standard test method designed to
indicate the compression strength of the concrete, and the test
results indicate that the concrete has gained sufficient strength to
support its weight and superimposed loads.
In general, forms for vertical members, such as columns and
piers, may be removed earlier than horizontal forms, such as beams
and slabs. ACI Committee 347 suggests the following minimum
times forms and supports should remain in place under ordinary
conditions. Forms for columns, walls, and the sides of beams often
may be removed in 12 hours. Removal of forms for joists, beams,
or girder soffits depends on the clear spans between structural
supports. For example, spans under 10 ft usually require 4 to 7 days,
spans of 10 to 20 ft require 7 to 14 days, and spans over 20 ft generally
require 14 to 21 days. Removing forms for one-way floor slabs
also will depend on clear spans between structural supports. Spans
under 10 ft usually require 3 to 4 days, spans 10 to 20 ft usually
require 4 to 7 days, and spans over 20 ft require 7 to 10 days.
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Building Construction and Economy
Careful planning in scheduling the construction operations for a
building and in providing the forms can assure the maximum economy
in formwork and also the highest efficiency by labor, both of
which will reduce the cost of formwork.
Consider the six-story building in Figure 2-1, to be constructed
with concrete columns, girders, beams, and slabs. The floor area is
large enough to justify dividing the floor into two equal or approximately
equal areas for forms and concreting. A construction joint
through the building is specified or will be permitted. If the structure
is symmetrical about the construction joint, the builder will
be fortunate. If the building is not symmetrical about the construction
joint, some modifications will have to be made in the form
procedures presented hereafter.
Each floor will be divided into equal units for construction purposes.
Thus, there will be 12 units in the building. One unit will be
completely constructed each week, weather permitting, which will
include making and erecting the forms; placing the reinforcing steel,
electrical conduit, plumbing items, etc., and pouring the concrete.
The carpenters should complete the formwork for unit 1 by the end
of the third day, after which time some of them will begin the formwork
for unit 2 while others install braces on the shores and other
braces, if they are required, and check; if necessary, the carpenters
will adjust the elevations of girder, beam, and deck forms. One or two
carpenters should remain on unit 1 while the concrete is being placed.
This will consume one week.
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