SIST EN 14272:2012
(Main)Plywood - Calculation method for some mechanical properties
Plywood - Calculation method for some mechanical properties
This European Standard specifies 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 Norm enthält ein Rechenverfahren für Sperrholzplatten mit beliebiger Zusammensetzung und mit symmetrischem oder nicht symmetrischem Aufbau zur Ableitung von sowohl einigen mechanischen Eigenschaften (Festigkeit und Steifigkeit bei Biegung, Zug, Druck, Schub/Scheren rechtwinklig zur Plattenebene und Schub/Scheren in Plattenebene) als auch der Rohdichte aus dem Holz, aus dem sich die Lagen zusammensetzen.
ANMERKUNG Üblicherweise haben die Platten einen symmetrischen Aufbau; jedoch sind das Aussehen der Oberfläche der Vorderseite und das Aussehen der Oberfläche der Rückseite sehr oft unterschiedlich, daher bestehen Unterschiede bei den mechanischen Eigenschaften der jeweiligen Furniere. Deshalb ist in diesem Fall die Zusammen-setzung nicht mechanisch symmetrisch, und es ist ein von der Symmetrie unabhängiges Rechenverfahren erforderlich.
Unter der Voraussetzung, dass für die Lagen konstruktive charakteristische Werte angesetzt werden, können die sich für die Platten ergebenden Werte als charakteristische Werte entsprechend den Anforderungen von EN 1995-1-1 verwendet werden.
Demgegenüber sind in Anhang A die Verfahren zur Ableitung der Eigenschaften von Furnieren bei Biegung, Zug und Druck festgelegt, entweder durch Prüfen von Platten nach EN 789 und EN 1058 oder Prüfen von Bauholz nach EN 408 oder durch die Ableitung aus in EN 338 festgelegten Werten.
Anhang B enthält praktische Kalkulationstabellen, die Anwendungen der im Hauptteil dieser Norm angege-benen Gleichungen darstellen.
Im Anhang C ist ein Beispiel für die Berechnung der Biegefestigkeit nach Anhang B angegeben.
Contreplaqué - Méthode de calcul pour certaines caractéristiques mécaniques
La présente Norme européenne donne, pour des panneaux de contreplaqué de composition symétrique ou non symétrique, une méthode de calcul pour la détermination de certaines propriétés mécaniques (résistance et rigidité en flexion, traction, compression, cisaillement roulant et cisaillement de voile) ainsi que la masse volumique du bois composant les couches.
NOTE En général, la composition des panneaux est symétrique mais, très souvent, il y a une différence entre l'aspect du parement et l'aspect du contreparement, d'où une différence entre les propriétés mécaniques des placages respectifs. En conséquence, dans ce cas, la composition n'est pas mécaniquement symétrique et une méthode de calcul indépendante de la symétrie est nécessaire.
Sous réserve que des valeurs caractéristiques structurales soient prises pour les couches, les valeurs résultantes pour les panneaux peuvent être utilisées comme des valeurs caractéristiques requises par l'EN 1995-1-1.
A l'inverse, l'Annexe A définit les modes opératoires pour déterminer les propriétés des placages, en flexion, traction et compression, à partir d’essais sur des panneaux conformément à l'EN 789 et à l'EN 1058, à partir d'essais effectués sur le bois conformément à l'EN 408, ou à partir de valeurs imposées spécifiées dans l'EN 338.
L'Annexe B fournit des feuilles de calcul pratiques qui sont des applications des formules indiquées dans la partie principale de la présente norme.
L'Annexe C fournit un exemple pour le calcul de la résistance en flexion, conformément à l'Annexe B.
Vezan les - Računske metode za nekatere mehanske lastnosti
Ta evropski standard podaja računske metode za vezan les vseh kompozicij, namenjene izpeljavi nekaterih mehanskih lastnosti (moč in togost pri upogibanju, napetost, tlačna obremenitev, strižni paneli in strižna deformacija) in gostote lesa, ki sestavlja plasti. Če se vrednosti konstrukcijskih značilnosti izmerijo na plasteh, je mogoče izračunane vrednosti za plošče uporabiti kot karakteristične vrednosti v skladu z zahtevami iz standarda EN 1995-1-1. Nasprotno dodatek A določa postopke za izpeljavo lastnosti furnirja na področju upogiba, napetosti in tlačne obremenitve iz preskušanja plošč v skladu s standardoma EN 789 in EN 1058, preskušanja lesa v skladu s standardom EN 408 ali predpisanih vrednosti iz standarda EN 338. Dodatek B podaja praktične preglednice, ki predstavljajo uporabe formul iz osnovnega dela tega standarda. V dodatku C je naveden primer izračuna upogibne trdnosti v skladu z dodatkom B.
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Sperrholz - Rechenverfahren für einige mechanische EigenschaftenContreplaqué - Méthode de calcul pour certaines caractéristiques mécaniquesPlywood - Calculation method for some mechanical properties79.060.10Vezan lesPlywoodICS:Ta slovenski standard je istoveten z:EN 14272:2011SIST EN 14272:2012en,fr,de01-april-2012SIST EN 14272:2012SLOVENSKI
STANDARDSIST-TS ENV 14272:20041DGRPHãþD
SIST EN 14272:2012
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 14272
December 2011 ICS 79.060.10 Supersedes ENV 14272:2002English Version
Plywood - Calculation method for some mechanical properties
Contreplaqué - Méthode de calcul pour certaines caractéristiques mécaniques
Sperrholz - Rechenverfahren für einige mechanische Eigenschaften This European Standard was approved by CEN on 1 October 2011.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,
B-1000 Brussels © 2011 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 14272:2011: ESIST EN 14272:2012
EN 14272:2011 (E) 2 Contents Page Foreword .41 Scope .52 Normative references .53 Principle .54 Terms and definitions .65 Symbols .65.1 Main symbols .65.2 Subscripts .76 Calculation method.86.1 General .86.2 Properties relevant to the calculation methods .86.3 Wood species .86.4 Factors for plywood composition .87 Characteristic values for strength and stiffness in bending, tension and compression . 117.1 General . 117.2 Bending . 117.2.1 General . 117.2.2 Modulus of elasticity . 117.2.3 Strength . 117.3 Tension and compression . 127.3.1 Stiffness and capacity of the layers in the cross section . 127.3.2 Stiffness and capacity of the panel. 137.3.3 Property of the panel (as if homogenized) . 137.4 Property values for layers . 137.4.1 General . 137.4.2 Modulus of elasticity (, ––––…………;;;; . 147.4.3 Resistance . 148 Shear properties . 158.1 Panel shear . 158.1.1 Panel shear rigidity (Gv) . 158.1.2 Panel shear strength (fv) . 168.2 Planar shear . 168.2.1 General . 168.2.2 Planar shear rigidity (Gr) . 168.2.3 Planar shear strength (fr) . 179 Ratio of strength upon modulus . 1710 Density . 1711 Conversion from strength and modulus of elasticity to capacity and stiffness . 18Annex A (normative)
Derivation for the veneer values (or basic values) . 19A.1 Scope . 19A.2 Principle . 19A.2.1 Option 1: Using plywood test results . 19A.2.2 Option 2: Using solid timber properties . 19A.3 Procedure for derivation of properties from testing plywood . 19A.3.1 General . 19A.3.2 Sampling . 20SIST EN 14272:2012
EN 14272:2011 (E) 3 A.3.3 Test pieces . 20A.3.4 Testing . 20A.3.5 Exploitation of the results . 21A.4 Derivation of estimated values for veneers . 25A.4.1 General . 25A.4.2 Values obtained by testing . 25A.4.3 Imposed values . 25A.5 Report . 25Annex B (normative)
Practical spreadsheets to derive the properties . 27B.1 General . 27B.2 Bending . 28B.2.1 General . 28B.2.2 Main tables . 28B.2.3 Tables for strength values . 31B.3 Tension and compression . 33B.4 Panel shear . 39B.5 Planar shear . 40B.5.1 General . 40B.5.2 Available veneer values . 40B.5.3 Veneer values not available . 42Annex C (informative)
Example of bending strength . 43C.1 Determination of the stress in the layers . 43C.2 Determination of the panel strength . 45Bibliography . 47 SIST EN 14272:2012
EN 14272:2011 (E) 4 Foreword This document (EN 14272:2011) has been prepared by Technical Committee CEN/TC 112 “Wood-based panels”, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by June 2012, and conflicting national standards shall be withdrawn at the latest by June 2012. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document supersedes ENV 14272:2002. Annex A and Annex B are normative. Compared to ENV 14272:2002, the following modifications have been made: a) calculation applies to panels of any composition, symmetrical or not; b) values resulting for the panels can be used for calculation as characteristics values as required by EN 1995-1-1; c) new Annex A (normative) provides the derivation for the veneer values (basic values); d) new Annex B (normative) provides practical spreadsheets to derive the properties; e) new Annex C (informative) gives an example of bending strength. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
SIST EN 14272:2012
EN 14272:2011 (E) 5 1 Scope This European Standard specifies, for plywood panels of any composition, symmetrical or not, a calculation method to derive some mechanical properties (strength and stiffness in bending, tension, compression, panel and planar shear) as well as density from the wood compounding the layers. NOTE Usually, the lay-up of the panels is symmetrical but, very often, the surface appearance of the face and the surface appearance of the back face differ, hence a difference between the mechanical properties of the respective veneers. Therefore, in this case, the composition is not mechanically symmetrical and a symmetry independent calculation method is needed.
Provided that structural characteristic values are taken for the layers, the resulting values for the panels can be used as characteristic values as required by EN 1995-1-1. Conversely, Annex A defines the procedures to derive the veneer properties, in bending, tension and compression, either from testing panels according to EN 789 and EN 1058 or from timber testing according to EN 408 or from imposed values defined in EN 338. Annex B provides practical spreadsheets, which are applications of the equations in the main part of this standard. Annex C provide an example for the calculation of bending strength, in accordance with Annex B. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 325, Wood-based panels — Determination of dimensions of test pieces EN 338:2009, Structural timber — Strength classes EN 384, Structural timber — Determination of characteristic values of mechanical properties and density EN 408, Timber structures — Structural timber and glued laminated timber — Determination of some physical and mechanical properties EN 789, Timber structures — Test methods — Determination of mechanical properties of wood based panels EN 1058, Wood-based panels — Determination of characteristic 5-percentile values and characteristic mean values EN 12369-2, Wood-based panels — Characteristic values for structural design — Part 2 Plywood EN 14358, Timber structures — Calculation of characteristic 5-percentile values and acceptance criteria for a sample 3 Principle Using the mechanical properties of the wood species, which compound the layers (in this standard referred to as veneer or basic values), it consists in deriving, by calculation, the mechanical properties of a panel.
For bending, tension and compression, each layer property value, along and across the length of the panel, is weighted by a geometrical factor related to its weight in the panel cross section.
SIST EN 14272:2012
EN 14272:2011 (E) 6 In this standard, where a value for a given property of the veneers is derived with a specified test method (including exploitation of the results), the models in this standard will provide a panel value for that property as if derived with the specified test method. EXAMPLE For instance, if, in a panel composition, a specified percentile of a bending property of veneers is determined with EN 789 and EN 1058, the calculated value of the bending property of the panel will be its specified percentile as if determined by using EN 789 and EN 1058. 4 Terms and definitions For the purposes of this document, the following terms and definitions apply. 4.1 characteristic strength population fifth percentile value relating to a temperature of 20 °C and a relative humidity of 65 % 4.2 characteristic stiffness either the population fifth percentile or the mean value relating to a temperature of 20 °C and a relative humidity of 65 % 4.3 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 NOTE 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. In the case of mixed species plywood the characteristic value of density of the panel is calculated from the characteristic densities of the individual veneers according to the proportion of each species 4.4 veneer value or basic value characteristic value of a property to be used for each layer in the equations of the calculation method
NOTE Characteristic values of the wood species, along and across the grain, are fifth percentile values for strength but either mean values or fifth percentile values for stiffness (modulus of elasticity). 4.5 reference panel value value of a given mechanical property of a panel composition NOTE
It is to be used to derive the veneer value (or basic value) of the property.
5 Symbols 5.1 Main symbols A area (b · tnom), in square millimetres f strength, in Newtons per square millimetre E modulus of elasticity, in Newton per square millimetre Fs shear forces in a bending panel, in Newtons SIST EN 14272:2012
EN 14272:2011 (E) 7 G modulus of rigidity, in Newtons per square millimetre b width of panel (equal to 1 in the equations), in millimetres t, thickness of layers, in millimetres T thickness of panels, in millimetres W section modulus, equal to()6/.2nomtb, in cubic millimetres I second moment of area, equal to()12/.3nomtb, in millimetres to the fourth power ρ
density, in kilograms per cubic metre ka modification factor, appearance class grade z distance of the axis of a layer to the neutral axis of the panel, in millimetres Ζ
distance of the neutral axis from either face of the panel, in millimetres Ecc eccentricity factor, no dimension ∆L/L relative elongation of the layers (bending, tension and compression) P property V strength or modulus, in Newton per square millimetre Rw in the set of layers, the weaker ratio of strength upon modulus for the properties of the wood species involved in the composition of a panel Up stiffness of the panel s standard deviation 5.2 Subscripts m bending t tension c compression v panel shear r planar shear w applies to the lower ratio strength/modulus (f/E) of a property of a layer in a multi-species panel
nom, mean nominal value and mean value respectively n number of layers of the panel (from top face to bottom face) i rank of layers from top face ax stands for neutral axis in bending ρ density 0 parallel to length of the plywood (direction of the grain of the face layers) 90 perpendicular to the length SIST EN 14272:2012
EN 14272:2011 (E) 8 05 5 percentile characteristic value 6 Calculation method 6.1 General The mechanical properties of plywood, in bending, tension, compression panel shear and planar shear can be derived by calculation. The calculation method described in this standard can be applied to plywood panels of any composition, symmetrical or not. For the classification according to appearance classes of plywood, see EN 635-2 and EN 635-3. 6.2 Properties relevant to the calculation methods For calculation of characteristic values of mechanical properties for different plywood compositions, the values of the properties of the veneers compounding the layers shall be derived in accordance with Annex A. The relevant properties are as listed in Table 1. 6.3 Wood species For calculating the characteristic values of panel mechanical properties, test values shall be used where available for each wood species in the plywood panel composition; where not, imposed values from EN 338 shall be used. NOTE EN 338 values, related to the density of the wood species, are quite conservative and therefore should be used as a last resort option. 6.4 Factors for plywood composition The characterization of plywood composition is shown in Table 2. For the purposes of calculation, if two or more plies are glued together in the same grain direction, they can be considered as one single layer provided that they belong to the same wood species; otherwise they shall be considered as independent layers. The calculations are based on the following equations: iEiV=
(Modulus of elasticity of the ith layer in Table 2) (1) or
ifiV=
(Strength of the ith layer in Table 2) (2) SIST EN 14272:2012
EN 14272:2011 (E) 9 Table 1 — Property values for the calculation method Property Characteristic strength values, N/mm2
fm, 05: Bending
ft, 05: Tension
fc, 05: Compression
fv, 05: Panel shear
fr, 05: Planar shear Mean values for stiffness properties, N/mm2
Em: Bending
Et: Tension
Ec: Compression
Gv: Panel shear Characteristic values for stiffness properties, N/mm2
Em, 05: Bending
Et, 05: Tension
Ec, 05: Compression
Gv, 05: Panel shear
ρ, 05: Density values, kg/m3
SIST EN 14272:2012
EN 14272:2011 (E) 10 Table 2 — Plywood composition factors
Layer
rank Wood
Species ti (mm) Vi
(N/mm²)kai Grain direction 1
========== 2
lllllllllllllllllllll 3
========== ------------- ----------------- ----------------- ----------------- ----------------- ---------------------------------------- i -1
========== i
llllllllllllllllllll i+1
========== ------------- ----------------- ----------------- ----------------- ----------------- ---------------------------------------- n -2
========== n -1
lllllllllllllllllllll n
========== ti : layer thickness Vi : mechanical property of the ith layer ka : appearance factor ====== : grain along the length llllllllllllllll : grain across the length SIST EN 14272:2012
EN 14272:2011 (E) 11 7 Characteristic values for strength and stiffness in bending, tension and compression 7.1 General The properties of the panels are derived from those of their layers as if the panels were homogenous. The equations are based on strength of materials.
7.2 Bending 7.2.1 General The general equation to be used for the derivation of the second moment of area of a cross section is based on the area Ai of the elementary rectangles compounding the cross section of the panel: ∑∑====×+×=niiiiniiiitAzAI121212 (3) NOTE This equation can be applied to any composition, symmetrical or not. If calculation is based on a unit of width, Equation (3) becomes: ∑∑====+×=niiiniiiitztI131212 (4) 7.2.2 Modulus of elasticity The stiffness of the panel (as if homogenised) is equal to the sum of the stiffness of the compounding layers as defined by the following equation: ∑∑====×+××=×=×niiiminiiiimimmtVztVTEpIEp131231212 (5) 31131212×+×××=∑∑∑======niiiniiiminiiiimimttVztVEp (6) Width is assumed to be equal to 1 unit.
Cross layers properties can be taken into account where the values are derived from timber. Emi shall be input as 0 wherever the cross layers are not taken into account in the determination of the basic values as defined in Annex A. Annex B provide practical spreadsheets to carry out this calculation (see Tables B.1 and B.2).
7.2.3 Strength The capacity of the panel (as if homogenised) is equal to the sum of the capacities of the compounding layers as defined by the following equations: SIST EN 14272:2012
EN 14272:2011 (E) 12 ZtVztVTTfpTIfpniiiminiiiimimm∑∑====×+××=××=×13123122122 (7)
ZtttVztVfpniiiniiiniiiminiiiimim×××+×××=∑∑∑∑========2121311312 (8) It can be simplified as: 211312212×××+×××=∑∑∑======niiiniiiminiiiimimtZtVztVfp (9) Width is assumed to be equal to 1 unit. NOTE 1 However, Equation (8) should be preferred because it allows the use of the same procedure of calculation as Equation (6), the difference between Equations (6) and (8) lying in the factor of eccentricity of the neutral axis Ecc = T/2Ζ
to be applied on the result yielded by Equation (5). ZtZTEccniii×==∑==221 (10) Ζ is the distance (or eccentricity) of the neutral axis to either face or back face. Where composition is not symmetrical, the bigger value shall be picked so as to be on the safe side; it is expressed as: −=∑==niiaxiaxZtZZ1;max (11) NOTE 2 For symmetrical composition Ζ = T/2 and the calculation can be made using Equation (6) where Epm value is substituted by fmp value. For safety in the determination of the ultimate limit state, cross layers properties shall not be taken into account. Annex B provide practical spreadsheets to carry out this calculation (see Tables B.1 to B.4). 7.3 Tension and compression 7.3.1 Stiffness and capacity of the layers in the cross section The stiffness or capacity of the panel is given by: SIST EN 14272:2012
EN 14272:2011 (E) 13 ∑==×=niiiiVtUp1 (12) 7.3.2 Stiffness and capacity of the panel ∑==×=×=niiictcttVpTVpUp1,, (13) 7.3.3 Property of the panel (as if homogenized) With Equations (12) and (13): ∑∑====×==niiiniiciticttVtTUpVp11,, (14) Width is assumed to be equal to 1 unit; Vi is entered as 0 where cross layers are not taken into account in the derivation of the basic values. Cross layers properties can be taken into account for stiffness under the same conditions as for bending (see 7.2.2). Annex B provides a practical spreadsheet to carry out this calculation (see Tables B.5 to B.10). 7.4 Property values for layers 7.4.1 General These values are derived according to the methods specified in Annex A. A modification factor ka related to surface appearance of the face veneers shall be applied to the characteristic value of modulus of elasticity and of strength in accordance with Table 3. Table 3 — Modification factor ka for the properties of the veneers Appearance class E I II III IV ƒ1,0 1,0 1.0 0,85 0,75
Where the inner layers are not appearance graded, class 4 (ka = 0,75) shall be assumed. NOTE This table is relevant where the basic values are derived from panels made of veneers with an appearance grade E, I or II. Where these values are derived from panels with faces with appearance class III, ka, if faces are classified IV, is derived according to: 88.0,,==basicalayeraakkk (15) where SIST EN 14272:2012
EN 14272:2011 (E) 14 ka,basic is ka of the veneers of the sample of panels for the derivation of the basic values; ka,layer is
ka of the veneer of the layer of the panel to be calculated. 7.4.2 Modulus of elasticity (, ––––…………;;;; For bending as well as for tension and compression, the basic value of the modulus of elasticity of the veneer of the plies of each layer is input, weighted with the appearance class, together with the thickness of the layer.
iaiiEkV×= (16) If the purpose is to derive a mean value or a 5th percentile for the panel, then the mean modulus or the 5th modulus respectively is input. 7.4.3 Resistance 7.4.3.1 General For strength properties, the veneer value of a specified layer depends on: the corresponding property of its wood species; its stress level.
7.4.3.2 Common procedure to bending, tension and compression Firstly, the 5th percentile value of the strength of the wood species of each layer is picked (in accordance with Annex A). Secondly, the stress level in the layer shall be derived prior to enter the stress value; though similar in principle, the procedure for tension-compression and bending differ slightly. Thirdly, in case of mixed species panels or of mixed grade single species panels, as the weaker layer(s) may fail before reaching the maximum load, the procedure of calculation shall be resumed. Once the first calculation is over, the weaker layer(s) and the corresponding panel strength is recorded in the relevant direction
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