Timber structures - Strength graded structural timber with rectangular cross section - Part 2: Machine grading; additional requirements for type testing

This document specifies requirements, additional to those of EN 14081-1, for type testing of machine graded structural timber with rectangular cross-sections shaped by sawing, planning or other methods, and having deviations from the target sizes corresponding to EN 336. This includes requirements for strength grading machines.

Holzbauwerke - Nach Festigkeit sortiertes Bauholz für tragende Zwecke mit rechteckigem Querschnitt - Teil 2: Maschinelle Sortierung; zusätzliche Anforderungen an die Erstprüfung

Dieses Dokument legt Anforderungen, neben den in EN 14081-1 angegebenen, an die Typprüfung für maschinell sortiertes Bauholz für tragende Zwecke mit rechteckigem Querschnitt fest, welches durch Sägen, Hobeln oder andere Produktionsverfahren hergestellt wurde und die zulässigen Maßabweichungen nach EN 336 einhält. Dies umfasst Anforderungen an Maschinen, die nach Festigkeit sortieren.

Structures en bois - Bois de structure à section rectangulaire classé pour sa résistance - Partie 2 : Classement mécanique par machine; exigences supplémentaires concernant les essais de type

Le présent document spécifie les exigences, en complément des exigences établies dans l’EN 14081-1, concernant les essais de type du bois de structure à section rectangulaire classé par machine et façonné par sciage, rabotage ou d’autres méthodes, et dont les tolérances de dimensions au regard des dimensions cibles sont conformes à l’EN 336. Ceci comprend les exigences concernant les machines de classement de la résistance.

Lesene konstrukcije - Razvrščanje konstrukcijskega lesa pravokotnega prečnega prereza po trdnosti - 2. del: Strojno razvrščanje - Dodatne zahteve za preskušanje tipa

Ta evropski standard določa dodatne zahteve poleg zahtev iz standarda EN 14081-1 za preskušanje tipa strojno razvrščenega konstrukcijskega lesa s pravokotnim prečnim prerezom, oblikovanim z žaganjem, struženjem ali z drugimi metodami, in z odstopanji od ciljnih velikosti v skladu s standardom EN 336. To vključuje zahteve za stroje za razvrščanje po trdnosti.

General Information

Status
Published
Publication Date
23-Oct-2018
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
24-Oct-2018
Completion Date
24-Oct-2018

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SLOVENSKI STANDARD
SIST EN 14081-2:2018
01-december-2018
1DGRPHãþD
SIST EN 14081-2:2011+A1:2013
/HVHQHNRQVWUXNFLMH5D]YUãþDQMHNRQVWUXNFLMVNHJDOHVDSUDYRNRWQHJDSUHþQHJD

SUHUH]DSRWUGQRVWLGHO6WURMQRUD]YUãþDQMH'RGDWQH]DKWHYH]DSUHVNXãDQMH

WLSD

Timber structures - Strength graded structural timber with rectangular cross section -

Part 2: Machine grading; additional requirements for type testing
Holzbauwerke - Nach Festigkeit sortiertes Bauholz für tragende Zwecke mit

rechteckigem Querschnitt - Teil 2: Maschinelle Sortierung; zusätzliche Anforderungen an

die Erstprüfung

Structures en bois - Bois de structure à section rectangulaire classé pour sa résistance -

Partie 2 : Classement mécanique par machine; exigences supplémentaires concernant

les essais de type
Ta slovenski standard je istoveten z: EN 14081-2:2018
ICS:
79.040 Les, hlodovina in žagan les Wood, sawlogs and sawn
timber
91.080.20 Lesene konstrukcije Timber structures
SIST EN 14081-2:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 14081-2:2018
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SIST EN 14081-2:2018
EN 14081-2
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2018
EUROPÄISCHE NORM
ICS 79.040 Supersedes EN 14081-2:2010+A1:2012
English Version
Timber structures - Strength graded structural timber
with rectangular cross section - Part 2: Machine grading;
additional requirements for type testing

Structures en bois - Bois de structure à section Holzbauwerke - Nach Festigkeit sortiertes Bauholz für

rectangulaire classé pour sa résistance - Partie 2 : tragende Zwecke mit rechteckigem Querschnitt - Teil

Classement mécanique par machine; exigences 2: Maschinelle Sortierung; zusätzliche Anforderungen

supplémentaires concernant les essais de type an die Erstprüfung
This European Standard was approved by CEN on 13 August 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14081-2:2018 E

worldwide for CEN national Members.
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 4

Introduction .................................................................................................................................................................... 5

1 Scope .................................................................................................................................................................... 6

2 Normative references .................................................................................................................................... 6

3 Terms and definitions ................................................................................................................................... 6

4 Symbols and abbreviations ......................................................................................................................... 8

5 Requirements for strength grading machines ...................................................................................... 9

6 Derivation of settings for machine control systems ........................................................................ 10

6.1 Requirements on sampling ....................................................................................................................... 10

6.2 Requirements for grading process, destructive testing and calculation of grade

determining properties ............................................................................................................................. 11

6.2.1 Grading process ............................................................................................................................................ 11

6.2.2 Destructive testing ....................................................................................................................................... 11

6.2.3 Calculations of grade determining properties .................................................................................. 11

6.3 Requirements for a setting area ............................................................................................................. 12

6.3.1 General ............................................................................................................................................................. 12

6.3.2 Standardized areas ...................................................................................................................................... 12

6.4 Requirements for the derivation and verification of machine settings ................................... 12

6.4.1 Derivation of machine settings ............................................................................................................... 12

6.4.2 Verification of machine settings ............................................................................................................. 13

6.5 Fixed settings ................................................................................................................................................. 15

6.6 Reporting ........................................................................................................................................................ 15

7 Additional verification requirements for a new grading machine or a change in

scope of existing grading machines for machine control systems ............................................. 17

7.1 Repeatability .................................................................................................................................................. 17

7.2 Machine installation check ....................................................................................................................... 17

8 Derivation of settings for output control systems ........................................................................... 18

8.1 General ............................................................................................................................................................. 18

8.2 Initial machine settings.............................................................................................................................. 18

8.3 Verification of machine settings ............................................................................................................. 18

8.3.1 Sampling .......................................................................................................................................................... 18

8.3.2 Destructive testing and calculation of characteristic values........................................................ 18

8.3.3 Requirements for verification of machine settings ......................................................................... 18

8.4 Report ............................................................................................................................................................... 18

9 Requirements for adaptive settings ...................................................................................................... 19

9.1 Method ............................................................................................................................................................. 19

9.2 Conditions ....................................................................................................................................................... 20

Annex A (informative) Guidelines for sampling a growth area for deriving machine settings ...... 21

Annex B (informative) Prediction limit method .............................................................................................. 23

B.1 General ............................................................................................................................................................. 23

B.2 Model determination .................................................................................................................................. 23

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EN 14081-2:2018 (E)

B.3 Settings calculation ...................................................................................................................................... 24

Annex C (normative) Determination of the global cost matrix ................................................................... 25

C.1 Introduction.................................................................................................................................................... 25

C.2 Optimum grading .......................................................................................................................................... 25

C.3 IP grading ........................................................................................................................................................ 25

C.4 Calculation of size matrix .......................................................................................................................... 26

C.5 Calculation of elementary cost matrix .................................................................................................. 26

C.5.1 Introduction.................................................................................................................................................... 26

C.5.2 Factors for wrongly upgraded pieces .................................................................................................... 26

C.5.3 Factors for wrongly downgraded pieces .............................................................................................. 27

C.5.4 Examples of elementary cost matrices for C, T and D classes ....................................................... 27

C.6 Calculation of a global cost matrix.......................................................................................................... 30

Annex D (informative) Settings for C and T-classes ........................................................................................ 31

Bibliography ................................................................................................................................................................. 38

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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
European foreword

This document (EN 14081-2:2018) has been prepared by Technical Committee CEN/TC 124 “Timber

structures”, the secretariat of which is held by AFNOR.

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 April 2019, and conflicting national standards shall be

withdrawn at the latest by April 2019.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document will supersede EN 14081-2:2010+A1:2012.

This document has been prepared under a mandate given to CEN by the European Commission and the

European Free Trade Association.

Compared to EN 14081-2:2010+A1:2012, the following main modifications have been made:

— new definitions added in Clause 3;
— new requirements for sampling, settings areas and minimum cross-section area;
— introduction of standardized areas;

— method for deriving settings is no longer normative, since several methods may be used; an example

of a method is given in Annex B;
— new method for verification of settings;

— cost matrix requirements are changed, to better allow settings that aim for reduced reject rather than

yield in the highest grade;
— new method for output control systems;
— introduction of adaptive settings;
— introduction of fixed settings.

This standard is part of a series of standards on Timber structures — Strength graded structural timber

with rectangular cross section ("EN 14081") that includes:
— Part 1: General requirements;
— Part 2: Machine grading; additional requirements for type testing;

— Part 3: Machine grading; additional requirements for factory production control.

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,

Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France,

Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands,

Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

the United Kingdom.
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
Introduction

Machine grading is in common use in a number of countries. There are two basic systems, referred to as

“output control” and “machine control”. Both systems require a visual override inspection to cater for

performance reducing characteristics that are not automatically sensed by the machine.

The output control system is suitable for use where the grading machines are situated in sawmills grading

limited sizes, species and grades in repeated production runs of around one working shift or more. This

enables the system to be controlled by testing timber specimens from the daily output. These tests

together with statistical procedures are used to monitor and adjust the machine settings to maintain the

required strength properties for each strength class. With this system it is permissible for machine

approval requirements to be less demanding and for machines of the same type to have non-identical

performance.

The machine control system was developed in Europe. Because of the large number of sizes, species and

grades used it was not possible to carry out quality-control tests on timber specimens drawn from

production. The system relies therefore on the machines being strictly assessed and controlled, and on

considerable research effort to derive the machines settings, which, under basic machine control

operation, remain constant for all machines of the same type.
Additional factory production control requirements are given in EN 14081-3.

This standard provides a new approach, applicable to both machine control and output control systems,

which permits fine adjustment of settings on a grading machine based on continuous monitoring of

Indicating Property (IP) data during grading. This approach is called “adaptive settings”.

The acceptability of grading machines and the derivation of settings rely on statistical procedures and

the results will therefore depend on the method used. For this reason this document gives appropriate

statistical procedures.

Grading assignments to strength classes are based on grading reports. When these grading reports are

evaluated and approved by CEN/TC 124 /WG 2 /TG 1, they become Approved Grading Reports (AGR).

The requirements in this European Standard are based on machines in current use and on future types

of machines as far as these can be foreseen. It is recognized that additional clauses or standards may be

required if unforeseen developments take place.

Since the previous version of this European Standard (EN 14081-2:2010+A1:2012), grading settings

work, and research data, have provided more information about the variation in wood properties. Several

new rules were created by CEN/TC 124 /WG 2 to update the procedures and ensure safety of grading –

particularly of settings covering many countries, and are referenced in the guidance paper (see Annex A).

This new version of the standard updates the procedures according to the guidance paper.

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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
1 Scope

This document specifies requirements, additional to those of EN 14081-1, for type testing of machine

graded structural timber with rectangular cross-sections shaped by sawing, planning or other methods,

and having deviations from the target sizes corresponding to EN 336. This includes requirements for

strength grading machines.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements 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 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 14358, Timber structures — Calculation and verification of characteristic values

EN 13556, Round and sawn timber — Nomenclature of timbers used in Europe

EN ISO 3166-1, Codes for the representation of names of countries and their subdivisions — Part 1: Country

codes
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
assigned grade

grade to which a piece of timber is assigned when using the appropriate setting for that specific grade

3.2
characteristic value

representative value of a material property used for design, which is based either on 5-percentile values

(e.g. strength properties and density) or on a mean value (e.g. modulus of elasticity)

3.3
critical feed speed

speed, within the intended usable range, at which the grading machine is least accurate in measuring its

indicating property
3.4
depth

in the case of bending, the cross sectional dimension parallel to the direction of loading, and in the case

of tension, the width
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
3.5
grade combination
set of one or more grades plus reject graded together
3.6
grade determining property (GDP)

mechanical or physical property, for which a particular value of that property is required for the material

to be assigned to that grade

Note 1 to entry: E.g. bending strength, mean MOE and density for the C and D strength classes of EN 338.

3.7
growth area
source from which timber is intended to be strength graded
3.8
indicating property (IP)

measurement or combination of measurements made by the grading machine, used in estimating one or

more of the grade determining properties, and upon which the settings are based
3.9
optimum grade

grade to which a piece of timber is assigned, such that the highest possible yield is obtained in the highest

grade when using the GDPs as the indicating properties
3.10
p-percentile
value for which the probability of getting lower values is p %
3.11
sample

number of ungraded specimens of one timber species or species combination, one timber source, with

sizes and quality representative of the timber population (of the species/species combination from the

timber source)
3.12
setting (S)

value of the parameters used to set the machine to grade timber, which are mathematically related to the

indicating property
3.13
setting area

combination of countries and / or standardized areas for which the same settings are valid

Note 1 to entry: a setting area is usually part of a test area.
3.14
standardized area
countries that can be combined to one setting area without further justification
3.15
test area

combination of countries and / or standardized areas from which timber is to be tested to obtain a setting

area
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
Note 1 to entry: test area is part of a growth area.
3.16
thickness
lesser dimension perpendicular to the longitudinal axis of a piece of timber
3.17
timber source

identifiable geographical origin of a species or species combination from which timber is, or is intended

to be, strength graded
3.18
width
larger dimension perpendicular to the longitudinal axis of a piece of timber
4 Symbols and abbreviations

For the purposes of this document, the following symbols and abbreviations apply.

slope in the DENS formula
DENS
slope in the MOE formula
MOE
slope in the MOR formula
MOR
b thickness for edgewise bending and width for flatwise bending
intercept in the DENS formula
DENS
intercept in the MOE formula
MOE
intercept in the MOR formula
MOR
c load configuration constant
DENS density
DENS
required density
req
E modulus of elasticity parallel to grain
optimum modulus of elasticity
optimum
assigned modulus of elasticity
assigned
measured first-mode longitudinal resonant frequency
f strength
assigned characteristic strength
k,assigned
assigned strength
assigned
optimum characteristic strength
k,optimum
optimum strength
optimum
F force
h depth
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
IP indicating property
mean value of IP of the reference sample
mean,ref,grade
running value of IP
mean,prod,grade
l span
MOE modulus of elasticity parallel to the grain
MOE
required MOE
req
MOR bending strength
MOR
required MOR
req
correlation coefficient between IP and grade determining property in the whole
ungraded data set which is used for determination of initial settings
adaptive setting
adapt
standard error of density estimates
δ,DENS
setting for DENS
DENS
initial setting
ini
setting for MOE
MOE
standard error of MOR estimates
δ,MOR
standard error of the estimate
setting for MOR
MOR
t a factor from Student's t-distribution
u timber moisture content
achieved safety index
ach
target safety index
tar
δ generic deformation
µ mean value
ρ timber density
5 Requirements for strength grading machines

The machine shall be of a type that meets the requirements given in Clauses 6 and 7 if it is part of a

machine control system, or Clause 8 if it is a part of an output control system. It shall be installed and set

up according to the manufacturer's specification and to any additional requirements resulting from the

tests given here. The following information shall be provided in the manufacturer's specification for the

machine:

a) specification and description of the mechanical and electrical operation of the machine, and the

software used by the machine to grade timber (this includes information on data processing such as

smoothing of the output signals);
b) range of environmental conditions under which the machine will operate;
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)
c) installation, maintenance and operating instructions;

d) method, extent and frequency of calibration procedures, including the use of control planks if

applicable;

e) species populations, sizes and tolerances, surface finish, moisture content, grades, environmental

operating temperature range, throughput speed, and limits of warp of the timber to be graded;

f) checking and adjustment procedures for all components that may affect the machine’s grading

accuracy.

Operational accuracy of transducers shall ensure that production machines meet the requirements of this

European Standard, and are compatible with grade settings derived for the machine type.

The grading machine shall not damage the timber during the grading operation to an extent that it affects

the intended use of the timber. For example, in bending type machines, damage should not be caused by

large compression perpendicular to grain stresses and/or large bending stresses.

NOTE When approving a new machine, consideration of already approved machines having the same

technology can contribute to the approval procedure, including settings derivation.

Grading machines whose indicating property does not take account of the material properties along the

whole length of each piece of timber, but whose indicating property measurements are influenced by

strength reducing characteristics away from the measuring position (as in bending type machines), shall

measure the indicating property to within 800 mm of each end of the piece of timber. Where the

indicating property is influenced only by strength reducing characteristics at the measuring position (as

in radiation type machines), the measurements shall be made to within 150 mm of each end.

When a new species is required to be graded by a machine that has already been shown to meet the

requirements of this European Standard, those requirements given in this clause that are not likely to be

affected by species differences may be disregarded for the new species.

Machine settings that were derived in accordance with previous versions of this standard remain valid

unless there is evidence that the required grade determining properties are not met. In that case, new

settings shall be derived according to this version of the standard.
6 Derivation of settings for machine control systems
6.1 Requirements on sampling

Sampling shall be representative of the timber to be graded. The timber shall represent the timber source,

species, range of sizes and quality to be graded in production with the most demanding surface finish for

the performance of the grading machine.
NOTE 1 Annex A gives guidance on sampling.

For each species or species combination, the minimum number of specimens required for deriving or

expanding settings shall be taken from Table 1:
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SIST EN 14081-2:2018
EN 14081-2:2018 (E)

Table 1 — Minimum number of specimens required for deriving or expanding settings

Specimens Total number of samples Specimens per sample
Total settings area (see 6.4.2.2) ≥ 450 ≥ 4 ≥ 100
Expansion check:
≥ 150 ≥ 1 ≥ 100
for each additional country or
standardized area (see 6.4.2.3)

NOTE 2 Usually it is necessary to increase the total number of specimens to take into account the variability of

the timber source, the performance of the machine, and the range of sizes and grades to be produced.

The minimum size of a setting area defined in this standard is normally a country or standardized area.

Parts of countries or standardized areas may also be considered if they are clearly geographically defined.

Sampling for a setting area that includes more than one country shall contain at least one sample from

each country, unless information exists which verifies that timber from one country can be safely graded

using settings from another country without being included in the sampling.

The range of permitted thickness and width for which settings shall be used in production shall not be

extrapolated more than 10 % from the maximum and minimum thickness and widths tested. This

requirement should be considered when carrying out the sampling.

The minimum cross section area for which settings shall be used in production shall not be extrapolated

more than 10 % from the minimum cross section area tested. This requirement should be considered

when carrying out the sampling.

A minimum of 40 pieces shall be included in the sampling on all ends of the cross section thickness and

width. This means that at least 40 pieces shall be in the range of 10 % of the upper tested timber thickness

and width and at least 40 pieces shall be in the range of 10 % of the lower tested timber thickness and

width.

A minimum of 40 pieces shall be included in the sampling for the smallest cross section area.

6.2 Requirements for grading process, destructive testing and calculation of grade

determining properties
6.2.1 Grading process

Each piece shall be graded by the machine at the critical feed speed while documenting the moisture

content, all variables necessary for calculating the IP, and any other variables
...

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