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

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Forms for Beams and Floor Slabs 327
Plywood
Thickness,
in.
¹ 5 ⁄32 1,385
(1,385)
½ 1,565
(1,565)
¹ 9 ⁄32 1,620
(1,620)
5
⁄8 1,770
(1,770)
23
⁄32 2,170
(2,170)
¾ 2,325
(2,325)
1 1 ⁄8 4,815
(4,815)
Support Spacing, in.
4 8 12 16 20 24
390
(390)
470
(470)
530
(530)
635
(635)
835
(835)
895
(895)
1,850
(1,850)
110
(150)
145
(195)
165
(225)
210
(280)
375
(400)
460
(490)
1,145
(1,145)
—
—
—
—
—
—
—
120
160
(215)
200
(270)
710
(725)
—
—
—
—
—
—
—
—
115
(125)
145
(155)
400
(400)
—
—
—
—
—
—
—
—
—
—
—
(100)
255
(255)
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Notes:
1. Courtesy APA—The Engineered Wood Association, “Concrete Forming,” 2004.
2. Deflection limited to l/360th of the span, l/270th for values in parentheses.
3. Plywood continuous across two or more spans.
TABLE 11-3 Recommended Maximum Pressure on Plyform Class I—Values in
Pounds per Square Foot with Face Grain Parallel to Supports
these pressures were based on deflection limitations of l/360 and l/270
of the span or on the shear or bending strength, whichever provided the
most conservative (lowest load) value.
When computing the allowable pressure of concrete on plywood
as limited by the allowable unit shearing stress and shearing deflection
of the plywood, use the clear span between the supports.
Size and Span Length of Joists
Figure 11-2 illustrated single-span joists for the support of decking for
concrete slabs. The selection of the size, length, and spacing of the
joists will involve one of the following:
1. Given the total load on the decking, the spacing of the joists
and the size and grade of the joists, determine the maximum
span for the joists.
2. Given the total load on the decking and the spacing of the
joists, determine the minimum-size joists required.
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