SIST-TS ENV 14272:2004
(Main)Plywood - Calculation method for some mechanical properties
Plywood - Calculation method for some mechanical properties
This European Prestandard gives a calculation method for the estimation of some mechanical properties of
plywood (strength and stiffness) with a symmetrical composition.
The resulting values are intended as predictive only.
Sperrholz - Rechenverfahren für einige mechanische Eigenschaften
Diese Europäische Vornorm beschreibt ein Rechenverfahren für einige mechanische Eigenschaften (Festigkeit und Steifigkeit) von Sperrholz mit symmetrischem Aufbau.
Die berechneten Werte dienen lediglich zur Orientierung.
Contreplaqué - Méthode de calcul de certaines propriétés mécaniques
La présente Prénorme européenne donne une méthode de calcul pour l'estimation de certaines propriétés mécaniques (résistance et rigidité) du contreplaqué de composition symétrique.
Les valeurs qui en résultent n'ont qu'une valeur indicative.
Vezane plošče – Metoda izračunavanja nekaterih mehanskih lastnosti
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST-TS ENV 14272:2004
01-januar-2004
9H]DQHSORãþH±0HWRGDL]UDþXQDYDQMDQHNDWHULKPHKDQVNLKODVWQRVWL
Plywood - Calculation method for some mechanical properties
Sperrholz - Rechenverfahren für einige mechanische Eigenschaften
Contreplaqué - Méthode de calcul de certaines propriétés mécaniques
Ta slovenski standard je istoveten z: ENV 14272:2002
ICS:
79.060.10 Vezan les Plywood
SIST-TS ENV 14272:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST-TS ENV 14272:2004
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SIST-TS ENV 14272:2004
EUROPEAN PRESTANDARD
ENV 14272
PRÉNORME EUROPÉENNE
EUROPÄISCHE VORNORM
June 2002
ICS 79.060.10
English version
Plywood - Calculation method for some mechanical properties
Contreplaqué - Méthode de calcul pour certaines Sperrholz - Rechenverfahren für einige mechanische
caractéristiques Eigenschaften
This European Prestandard (ENV) was approved by CEN on 5 April 2002 as a prospective standard for provisional application.
The period of validity of this ENV is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the ENV can be converted into a European Standard.
CEN members are required to announce the existence of this ENV in the same way as for an EN and to make the ENV available promptly
at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the ENV) until the final
decision about the possible conversion of the ENV into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. ENV 14272:2002 E
worldwide for CEN national Members.
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SIST-TS ENV 14272:2004
ENV 14272:2002 (E)
Contents
page
Foreword.3
1 Scope .4
2 Normative references .4
3 Principle.4
4 Terms and definitions and symbols .4
4.1 Terms and definitions.4
4.2 Symbols .5
5 Calculation method.6
5.1 General.6
5.2 Basic values for the calculation method.6
5.3 Wood species.7
5.4 Factors for plywood composition .7
5.5 Calculation of characteristic values for strength and stiffness.8
5.6 Density .11
5.7 Example of use of calculation method .12
6 Conversion from strength and modulus of elasticity to capacity and stiffness .12
Annex A (informative) Example of the calculation of characteristic values for strength and elastic
properties of a plywood panel.13
Annex B (informative) Calculation of mechanical properties of plywood — Guidelines for the
derivation method of the basic values of the mechanical properties of the layers.21
Bibliography .25
2
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ENV 14272:2002 (E)
Foreword
This document ENV 14272:2002 has been prepared by Technical Committee CEN/TC 112 "Wood-based panels",
the secretariat of which is held by DIN.
The annexes A and B are informative.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following coun-
tries are bound to announce this European Prestandard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Swe-
den, Switzerland and the United Kingdom.
3
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SIST-TS ENV 14272:2004
ENV 14272:2002 (E)
1 Scope
This European Prestandard gives a calculation method for the estimation of some mechanical properties of
plywood (strength and stiffness) with a symmetrical composition.
The resulting values are intended as predictive only.
2 Normative references
This European Prestandard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Prestandard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
EN 635-2, Plywood — Classification by surface appearance — Part 2: Hardwood.
EN 635-3, Plywood — Classification by surface appearance — Part 3: Softwood.
EN 636-1, Plywood — Specifications — Part 1: Requirements for plywood for use in dry conditions.
EN 636-2, Plywood — Specifications — Part 2: Requirements for plywood for use in humid conditions.
EN 636-3, Plywood — Specifications — Part 3: Requirements for plywood for use in exterior conditions.
3 Principle
To derive by calculation the mechanical properties of a panel, using the corresponding mechanical properties of the
wood species compounding the layers. Each pair of layers (or layer) values are weighted by a geometrical factor
related to its weight in the panel cross section.
4 Terms and definitions and symbols
4.1 Terms and definitions
For the purposes of this European Prestandard, the following terms and definitions apply.
4.1.1
characteristic strength
population fifth percentile value relating to a temperature of 20 °C and a relative humidity of 65 %
4.1.2
characteristic stiffness
either the population fifth percentile or the mean value relating to a temperature of 20 °C and a relative humidity of
65 %
4.1.3
characteristic density
population fifth percentile value with mass and volume corresponding to equilibrium at a temperature of 20 °C and
a relative humidity of 65 % either of the wood species or of the panels, single species or mixed species
The density values found from calculation refer to the minimum acceptable density of veneers used in the lay-up of
plywood. In the case of single species plywood these values are taken as the characteristic values for the plywood.
4
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ENV 14272:2002 (E)
In the case of mixed species plywood the characteristic value of density of the panel is calculated from the charac-
teristic densities of the individual veneers according to the proportion of each species
4.1.4
basic value
characteristic value of properties to be used in the equations of the calculation method for each pair of layers (or
layer)
NOTE Characteristic values are mean values for modulus of elasticity and fifth percentile values for strengths and modulus
of elasticity.
4.2 Symbols
In the tables the following symbols are used:
4.2.1 Main symbols
A Area (b t ), in square millimetres
nom
f Strength, in newtons per square millimetre
E Modulus of elasticity, in newtons per square millimetre
G Modulus of rigidity, in newtons per square millimetre
b Unit width of panel, in millimetres
t Thickness of panel or a pair of layers, in millimetres
2
W Section modulus, equal to bt / 6 , in cubic millimetres
nom
Łł
3
I Second moment of area, equal to bt /12 , in millimetres to the fourth power
nom
Łł
r Density, in kilogramms per cubic metre
k Modification factor, appearance class
a
a Thickness of the layer (distance between the outer faces of a pair of layers), in millimetres
DL / L Relative elongation of the face plies (bending, tension and compression)
V Strength or modulus, in newtons per square millimetre
4.2.2 Subscripts
m Bending
t Tension
c Compression
v Panel shear
r Planar shear
w Applies to the plywood species with the lower ration strength/modulus (f / E) for a given property in a panel
with a lay-up mixing several species
nom Nominal
n Number of pairs of layers of the panel
j Pair of layers (or layer) under consideration starting from the face, associated to n, its value is comprised
between 1 and n
i Starting from the face, rank of pair of layers having the shortest relative elongation in failure (bending,
tension and compression)
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SIST-TS ENV 14272:2004
ENV 14272:2002 (E)
rDensity
0 Length of the plywood (direction of the grain of the outer layers)
90 Perpendicular to the length
05 5 percentile characteristic value
5 Calculation method
5.1 General
The estimate of the mechanical properties of plywood can be found by calculation.
The calculation method described can only be applied to plywood panels with a symmetrical composition.
For the classification of plywood see:
EN 636-1 for use in dry conditions
EN 636-2 for use in humid conditions
EN 636-3 for use in exterior conditions
5.2 Basic values for the calculation method
For calculation of an estimate of characteristic values of mechanical properties for different plywood compositions,
the basic values of the layers are derived from the characteristic values of the properties of single species plywood
panels.
NOTE Annex B gives a method for deriving basic values.
Depending on the purpose, the basic values for layers are derived from testing small or semi-size test pieces.
The needed basic values are as given in Table 1.
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ENV 14272:2002 (E)
Table 1 — Basic values for the calculation method
Property
2
Characteristic strength values, N/mm
f : Bending
m, 05
f : Tension
t, 05
f , : Compression
c 05
f : Panel shear
v, 05
f : Planar shear
r, 05
2
Mean stiffness values, N/mm
E : Bending
m
E : Tension
t
E : Compression
c
G : Panel shear
v
2
Characteristic stiffness values, N/mm
E : Bending
m, 05
E : Tension
t, 05
E : Compression
c, 05
G : Panel shear
v, 05
3
r: Density values, kg/m
, 05
5.3 Wood species
For calculating an estimate of the characteristic values of mechanical properties basic values for each wood
species concerned in the plywood composition shall be used.
5.4 Factors for plywood composition
The characterization of plywood composition is shown in Figure 1.
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ENV 14272:2002 (E)
NOTE If two or more plies are glued together in the same grain direction, they are considered as one single layer for the
purposes of calculation.
Figure 1 — Plywood composition
The calculations are based on the following equations:
V = E (stiffness) (1)
n-j n-j
or
V = f (strength)
n-j n-j
where E is the modulus and f is the strength of the n'th pair of layers in Figure 1.
n n
5.5 Calculation of characteristic values for strength and stiffness
5.5.1 Bending
General
5.5.1.1
V = V ⋅ (I ) / I (2)
n-j n-j
where V is defined in equation (1) and I is the moment of inertia of the full cross section of the panel per unit of
width.
I is the moment of inertia, per unit of width, of the pair of layer under consideration along (0) or across (90) the
j
grain.
V
Property along the grain (0) of the face layer per unit width:
0, n
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ENV 14272:2002 (E)
When the grain direction of the central layer is at right angles to the grain direction of the face layer, equation (3.1)
shall be used:
3 3 3 3 3 3
a-a a-a a-a
n
n-2 n-4 n-6 3 1
V =·V +·V + . + +·V (3.1)
0,n n n-4 3
3 3 3
a a a
n n n
When the grain direction of the central layer is parallel to the grain direction of the face layer, equation (3.2) shall be
used:
3 3 3 3
3 3 3
a-a a-a a-a a
n
n-2 n-4 n-6 5 3 1
V =·V +·V + . + +·V +·V (3.2)
0,n n n-4 5 1
3 3 3 3
a a a a
n n n n
Property V across the grain (90) of the face layer per unit width:
90, n
When the grain direction of the central layer is at right angles to the grain direction of the face layer, equation (3.3)
shall be used:
Ø3 3 3 3 3ø
a-a a-a a
Œn-2 n-4 n-6 n-8 1œ
V =·V +·V + . + +·V· (3.3)
90,n n-2 n-6 1Œœ3 3 3
a a a
n n nŒœºß
When the grain direction of the central layer is parallel to the grain direction of the face layer, equation (3.4) shall be
used:
Ø3 3 3 3 3 3 3 3ø
a-a a-a a-a a-a
Œn-2 n-4 n-6 n-8 7 5 3 1œ
V =·V +·V + . + +·V +·V· (3.4)
90,n n-2 n-6 7 3Œœ3 3 3 3
a a a a
n n n nŒœºß
where
a
n
= in case of strength calculation (3.5)
a
n-2
m= 1 in case of stiffness (modulus of elasticity) calculation
5.5.1.2 Strength (f )
m
The bending strength along the grain (0) of the face layer shall be calculated from the equations (3.1) or (3.2) by
substituting V defined in equation (3.6.1):
n-j
V = k ⋅ E ⋅ (a / a ) ⋅ [ f / E ⋅ (a / a )] (3.6.1)
n-j a n-j n-j n i i n i w
The bending strength across the grain (90) of the face layer shall be calculated from the equations (3.3) or (3.4)
using equation (3.6.2). See notation in 5.5.1.4.
V = k ⋅ E ⋅ (a / a ) ⋅ [ f / E ⋅ (a / a )] (3.6.2)
n-j a n-j n-j n i i n-2 i w
Where
f, E respectively are the strength and modulus of the layers
k is a modification factor related to plywood grades ; it is a factor depending on the appearance class in accor-
a
dance with EN 635-2 for hardwood and EN 635-3 for softwood (see Table 2). The k factor for the minimum ap-
a
pearance class in the composition shall be used.
a is the distance between the outer faces of the surface layers (thickness of the panel)
n
a is the distance between the outer faces of the pair of layers having the lowest DL / L factor
i
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ENV 14272:2002 (E)
th
a is the distance between the outer faces of the "j " pair of layers below the face layer
n-j
n-j is a subscript for the rank of any pair of layers
w is a subscript attached to the minimum factor
5.5.1.3 Modulus of Elasticity (E )
m
The modulus of elasticity in bending shall be calculated from the equations (3.1) or (3.2) and (3.3) or (3.4) substi-
tuting V by E . See notation in 5.5.1.4.
m
5.5.1.4 Notation
[ f / E ⋅ (a / a )] : minimum value taken by the factor in square brackets in the stack of layers compounding the
i i n i w
panel in the direction under consideration, i is the rank of this pair of layers, starting from the face.
NOTE This factor represents the DL / L of the face layers resulting from the failure of the weaker pair of layers within the
panel.
Table 2 — k factors
a
Class: E I II III IV
k factor: 1,0 1,0 1,0 0,85 0,75
a
5.5.2 Tension and compression
5.5.2.1 General
Only those layers with the grain direction parallel to the direction of forces are taken into account.
Property V along the grain (0) of the face layer per unit width:
0, n
When the grain direction of the central layer is at right angles to the grain direction of the face layer, equation (4.1)
shall be used:
a a a-a a-a-n n-2 n-4 n-6 3 1
V =·V +·V + . + +·V (4.1)
0,n n n-4 3
a a a
n n n
When the grain direction of the central layer is parallel to the grain direction of the face layer, equation (4.2) shall be
used:
a-a a-a a
n n 2 n-4 n-6 1-
V =·V +·V + . +·V (4.2)
0, n n n-4 1
a a a
n n n
Property V across the grain (90) of the face layer per unit width:
90, n
When the grain direction of the central layer is at right angles to the grain direction of the face layer, equation (4.3)
shall be used:
a-a a-a a
n-2 n-4 n-6 n-8 1
V =·V +·V + . +·V (4.3)
90,n n-2 n-6 1
a a a
n n n
When the grain direction of the central layer is parallel to the direction of the face layer, equation (4.4) shall be
used:
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SIST-TS ENV 14272:2004
ENV 14272:2002 (E)
a-a a-a a-a
n-2 n-4 n-6 n-8 3 1
V =·V +·V + . +·V (4.4)
90,n n-2 n-6 3
a a a
n n n
5.5.2.2 Strength (f , or f )
t c
The tension or compression strength along the grain (0) of the face layer shall be calculated from the equations
(4.1) or (4.2) by substituting V:
V = k ⋅ ( f / E ) ⋅ E (4.5)
n-j a i j w n-j
where
(f / E ) is the minimum value taken by the factor in brackets in the stack of layers compounding the panel in
i j w
the direction under consideration, where i is the rank of this pair of layers starting from the face.
NOTE This factor represents the lowest DL / L of the wood species involved in the panel composition.
The tension or compression strength across the grain (90) of the face layer shall be calculated from the equations
(4.3) or (4.4) using equation (4.5).
5.5.2.3 Modulus of Elasticity (E or E )
t c
The modulus of elasticity in tension or compression shall be calculated form the equations (4.1) or (4.2) and (4.3) or
(4.4) substituting V by E or E where E is for tension or E is for compression.
t c t c
5.5.3 Panel shear
The strength values given for f shall be used directly.
v
The modulus of rigidity for G shall be used directly.
v
If combinations of wood species groups are used the value from the lowest wood species group shall be used.
5.5.4 Planar shear
The strength values given for f shall be used directly.
r
The modulus of rigidity for G shall be used directly.
r
If combinations of wood species groups are used, the value from the lowest wood species group shall be used.
5.6 Density
The characteristic density (r) is calculated as follows:
05
n
= ∑·t / t
05 n n
n = 1Łł
where
th
t is the nominal panel thickness of the n pair of layers (layer)
n
th
ris the fifth percentile of the n pair of layers (layer)
n
t is the thickness of the panel
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5.7 Example of use of calculation method
An example of the use of the above meth
...
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