Introduction
Plywood is made up of softwood veneers . The veneers are glued together
so that the grain of each layer is perpendicular to the grain of its adjoining layers. Plywood as a structural material consists
of an odd number of layers (plies). Exterior grade plywood is generally made from fully weather-resistant adhesive.
The structrual properties of plywood are primarily dependent on the number and thickness of the plies, the grade of the plies and the arrangement of the plies.
Relevant Standards..For comprehensive list of standards Wood related Standards
BS 5268 -2 ;2002 Structural use of timber � Part 2: Code of practice for permissible
stress design, materials and workmanship : section 4 deels with plywood
Typical sectional properties of a Plywood
BS 5268-2 includes a number of tables providing sectional properties of a number of grades of plywood. A set of
properties is provided below showing the level of information available.
Section properties of Finnish birch faced plywood: sanded
| Nominal thickness |
Number of plies |
Minimum thickness |
Section properties for a 1 m width |
Approximate mass /unit area |
| Area |
Section Modulus |
Second Moment of Area |
| mm |
mm |
mm |
10 3mm2 |
10 3mm3 |
10 3mm4 |
kg/m2 |
| 6.5 |
5 |
6.1 |
6.1 |
6.2 |
18.9 |
4.4 |
| 9 |
7 |
8.8 |
8.8 |
12.9 |
56.8 |
6.2 |
| 12 |
7 and 9 |
11.5 |
11.5 |
22 |
127 |
8.1 |
| 15 |
9 and 11 |
13.9 |
13.9 |
32.2 |
224 |
9.9 |
| 18 |
11 and 13 |
17.1 |
17.1 |
48.7 |
417 |
11.6 |
| 21 |
11, 13 and 15 |
20 |
20 |
66.7 |
667 |
13.4 |
| 24 |
13, 15 and 17 |
22.9 |
22.9 |
87.4 |
1 001 |
15.2 |
| 27 |
17 and 19 |
25.2 |
25.2 |
106 |
1 330 |
17 |
| 30 |
17 and 21 |
28.1 |
28.1 |
132 |
1 849 |
17.1 |
Grade stresses and moduli for service classes 1 and 2 for Finnish conifer plywood thick veneer: sanded
<
| Stress type |
Nominal thickness (Number of Plies) |
| 6,5(5) |
9(7) |
12(9) |
15(11) |
18(13) |
21(15) |
24(17) |
27(19) |
30(21) |
| N/mm2 |
| Extreme fibre in Bending |
| ....Face grain parallel to span |
20,68 |
19,6 |
18,32 |
17,93 |
17,58 |
17,24 |
17,14 |
16,94 |
16,79 |
| ....Face grain normal to span |
10,54 |
12,46 |
13,59 |
13,79 |
13,99 |
14,23 |
14,28 |
14,33 |
14,43 |
| Tension |
| parallel to face grain |
20,78 |
19,75 |
19,16 |
18,86 |
18,62 |
18,42 |
18,32 |
18,22 |
18,12 |
| normal to face grain |
15,17 |
15,86 |
16,2 |
16,45 |
16,6 |
16,7 |
16,79 |
16,84 |
16,89 |
| Compression |
| parallel to face grain |
10,34 |
10 |
9,8 |
9,7 |
9,6 |
9,55 |
9,5 |
9,46 |
9,46 |
| normal to face grain |
8,08 |
8,42 |
8,62 |
8,72 |
8,82 |
8,86 |
8,91 |
8,91 |
8,96 |
| Bearing |
| on face |
3,93 |
3,93 |
3,93 |
3,93 |
3,93 |
3,93 |
3,93 |
3,93 |
3,93 |
| Rolling shear |
| ....in face veneer |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
| ....in back veneer |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
| ....At first glueline |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
1,23 |
Traverse shear-
bending |
| ....face grain parallel to span |
1,41 |
1,32 |
1,37 |
1,3 |
1,32 |
1,28 |
1,3 |
1,27 |
0,27 |
| ....face gain normal to span |
0,9 |
1,17 |
1,12 |
1,19 |
1,17 |
1,19 |
1,18 |
1,21 |
0,21 |
| Panel shear |
| ....Parallel and normal to face grain |
4,83 |
4,83 |
4,83 |
4,83 |
4,83 |
4,83 |
4,83 |
4,83 |
4,83 |
| Modulus of elasticity in bending |
| ....face grain parallel to span |
5 850 |
5 200 |
4 900 |
4 750 |
4 600 |
4 500 |
4 450 |
4 400 |
4 350 |
| ....face gain normal to span |
2 150 |
2 800 |
3 100 |
3 300 |
3 400 |
3 490 |
3 550 |
3 600 |
3 650 |
| Modulus of Elasticity (btension/compression) |
| parallel to face grain |
4 500 |
4 350 |
4 250 |
4 200 |
4 200 |
4 150 |
4 150 |
4 150 |
4 100 |
| normal to face grain |
3 500 |
3 650 |
3 750 |
3 800 |
3 800 |
3 850 |
3 850 |
3 800 |
3 900 |
| Shear modulus |
| ....Parallel and normal to face grain |
320 |
320 |
320 |
320 |
320 |
320 |
320 |
320 |
320 |
|