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

232 Chapter Nine
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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 9-8 Recommended Maximum Pressure on Plyform Class I—Values in
Pounds per Square Foot with Face Grain Parallel to Supports
spans up to 16 in. and two spans for 20 and 24 in. These are general
rules as recommended by the APA.
There are many combinations of frame spacings and Plyform
thicknesses that may meet the structural requirements for a particular
job. However, it is recommended that only one thickness of plywood
be used, then the frame spacing varied for the different pressures. Plyform
can be manufactured in various thicknesses, but it is good practice
to base design on 19 ⁄32-, 5 ⁄8-, 23 ⁄32-, and ¾-in. Plyform Class I, because
they are the most commonly available thicknesses.
Tables 9-7 through 9-10 give the recommended maximum
pressures of concrete on plywood decking for Class I and Structural
I Plyform. Calculations for these pressures were based on
deflection limitations of l/360 and l/270 of the span, or on 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.
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