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

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Patented Forms for Concrete Floor Systems 371
Plastic Forms
Plastic forms, which have been used to construct concrete slabs of the
one-way and two-way joist types, have several advantages, including
the following:
1. They are light, strong, and resistant to impact.
2. They are resistant to denting and warping.
3. They will not corrode or rust.
4. They produce smooth concrete surfaces.
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The products of one manufacturer, Molded Fiber Glass Concrete
Forms Company, are glass-reinforced plastics molded under heat
and pressure in steel molds. This company manufactures several
sizes of forms for use in constructing two-way joist or waffle-type
slabs. Table 12-1 gives representative dimensions and other information
for these forms. The specified dimensions apply to outside surfaces
of the forms. The size of voids indicates the width of the void left
in the concrete slab, and the overall size is the width of the flange.
The forms are installed, usually on solid decking, with the flanges
down and abutting the flanges of adjacent forms. One large-headed nail
driven into the decking at the juncture of four flange corners should hold
the forms in position. After the concrete has gained the desired strength,
the decking is stripped and the pans are removed by injecting a blast of
compressed air through each form into the space at the back of the form.
If the forms are handled with care, they can be used 25 times or more. If
a surface is damaged, it can be restored with a suitable plastic treatment.
Figure 12-9 shows these forms being installed on solid decking, and
Figure 12-10 illustrates how a form is removed by using compressed air.
Item
19-in.
System
24-in.
System
30-in.
System
41-in.
System
52-in.
System
Size of voids, in. 19 × 19 24 × 24 30 × 30 41 × 41 52 × 52
Joist center, in. 24 × 24 30 × 30 36 × 36 48 × 48 60 × 60
Joist width, in. 5 6 6 7 8
Range of depth
of voids, in.
Approx. weight
of 12- in.-deep
void, lb
TABLE 12-1
8, 10, 12,
14, 16
8, 10,
12, 14,
16, 20
8, 10, 12,
14, 16,
18, 20
12, 14,
16, 18,
20, 24
13 19 21 65 103
10, 12,
14, 16, 18,
20, 24
Representative Dimensions and Other Properties of Molded Fiber
Glass Forms (MFG Concrete Forms Company)
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