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Plywood



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
Links Providing information on Wood
  1. Wood Handbook -- Wood as an Engineering Material..Downloads ..Comprehensive Document (American ) Excellent
  2. Canadian Wood Council ..Excellent site on Wood Engineering - my words
  3. Wikipedia Plywood ..Compreshensive detailed information from Wikipedia.
  4. Plywooduk-specifying Plywood ..A value useful download from a UK supplier.

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Last Updated 8/05/2009