Bsi bs en 00519 1995 (1998)

www bzfxw com BRITISH STANDARD BS EN 519 1995 Structural timber — Grading — Requirements for machine strength graded timber and grading machines The European Standard EN 519 1995 has the status of a B[.]

This British Standard,

having been prepared under

the direction of the Sector

Board for Building and Civil

Engineering, was published

under the authority of the

Standards Board and comes

into effect on

15 October 1995

© BSI 12-1998

The following BSI references

relate to the work on this

standard:

Committee reference B/518/2

Draft for comment 91/14706 DC

The preparation of this British Standard was entrusted by Technical Committee B/518, Structural timber, to Subcommittee B/518/2, Solid timber, upon which the following bodies were represented:

British Timber Merchants’ AssociationBritish Woodworking FederationCouncil of the Forest Industries of British ColumbiaDepartment of the Environment (Building Research Establishment)Forestry Commission

Institute of Building ControlInstitution of Civil EngineersNational House-Building CouncilNordic Timber Council (UK)Southern Pine Marketing CouncilTimber Research and Development AssociationTimber Trade Federation

Trussed Rafter and Fabricators’ Association

UK Softwood Sawmillers’ Association

Amendments issued since publication

National annex NA (informative) United Kingdom requirement for

Figure NA.1 — Example of a mark on machine strength graded timber 19

This British Standard has been prepared by Subcommittee B/518/2 and is the

English language version of EN 519:1995 Structural timber — Grading —

Requirements for machine strength graded timber and grading machines

published by the European Committee for Standardization (CEN)

It supersedes the following sections and appendices of BS 4978:1988 Specification

for softwood grades for structural use: sections 4 and 5, B.3, B.4 and

appendices E, F and G These are in the process of being withdrawn by revision

1) In preparation.

Cross-references Publication referred to Corresponding British Standard

EN 336:1995 BS EN 336:1995 Structural timber — Coniferous and

poplar — Sizes — Permissible deviations

EN 338:1995 BS EN 338:1995 Structural timber — Strength classes

EN 384:1994 BS EN 384:1995 Structural timber — Determination of

characteristic values of mechanical properties and density

EN 408:1995 BS EN 408:1995 Timber structures — Structural timber

and glued laminated timber — Determination of some physical and mechanical properties

ICS 79.040

Descriptors: Wood, sawn timber, laminated board, timber construction, filing, mechanical strength, test equipment, specifications

English version Structural timber – Grading – Requirements for machine

strength graded timber and grading machines

Bois de structure — Classement —

Spécifications pour le bois classé par machine

pour sa résistance et les machines à classer

Bauholz für tragende Zwecke — Sortierung — Anforderungen an mashinell nach der

Festigkeit sortiertes Bauholz und an Sortiermaschinen

This European Standard was approved by CEN on 1995-02-22 CEN members

are bound to comply with the CEN/CENLEC 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 Central Secretariat 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

Central Secretariat has the same status as the official versions

CEN members are the national standards bodies of Austria, Belgium,

Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,

Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and

United Kingdom

CEN

European Committee for StandardizationComité Européen de NormalisationEuropäisches Komitee für Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels

© 1995 All rights of reproduction and communication in any form and by any means reserved in allcountries to CEN and its members

Ref No EN 519:1995 E

Foreword

This European Standard has been prepared by the

Technical Committee CEN/TC 124, Timber

structures, of which the secretariat is held by DS

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

August 1995, and conflicting national standards

shall be withdrawn at the latest by August 1995

In accordance with the CEN/CENELEC Internal

Regulations, the following countries are bound to

implement this European Standard: Austria,

Belgium, Denmark, Finland, France, Germany,

Greece, Iceland, Ireland, Italy, Luxembourg,

Netherlands, Norway, Portugal, Spain, Sweden,

Switzerland and United Kingdom

5 Requirements for machine

6 Requirements for the company

producing graded timber, on the

operation of strength-grading machines 5

7 Requirements for the acceptance

7.2 Additional requirements for

9.3 Procedure for testing samples

Page9.5 Use of cusum control charts

Annex A (informative) Additional requirements for the certification body on the operational control of grading

Annex B (informative) Example of

Annex C (normative) Measurement ofvisually-assessed characteristics 15

Figure 3 — Measurement of bow, spring and

Figure 4 — A Graph of variables A and B for

use in the determination of cusum controlconstants for modules of elasticity 12Figure B.1 — Cusum control from (in control) 16Figure B.2 — Cusum control from (out of

Figure B.3 — Cusum chart of data from Figure B.1 and Figure B.2 18Table 1 — Visual override requirement 6Table 2 — Visual override requirements for

Introduction

There are basically two methods of strength

grading: visual grading and machine grading This

standard deals with machine grading Machine

strength is in common use in a number of countries

Its greater predictive accuracy compared with

visual grading enables higher yields of higher

strength classes to be achieved The countries use

two basic systems, referred to as “output controlled”

and “machine controlled” Both systems require a

visual override inspection to cater for

strength-reducing characteristics that are not

automatically sensed by the machine

The output-controlled system is suitable for use

where the grading machines are situated in

sawmills grading particular sizes, species and

grades in repeated production runs of around one

working shift in duration This enables the system

to be controlled by testing timber specimens from

the daily output These tests together with the

cusum statistical procedure are used to monitor and

adjust the machine settings to maintain the

required strength properties for each strength class

If the cusum procedure indicates that the process is

in control then the machine settings may be

modified to maximize yield If the cusum procedure

indicates that the process is out of control then, after

further checks, the settings shall be modified to

ensure the strength requirements are met and the

timber may need to be re-graded 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-controlled system was developed in

Europe around 1969 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 machine settings, which remain constant

for all machines of the same type

The requirements in this 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

Because of the complexity of the subject, the

standard is structured to facilitate use by the

various interested parties as follows

a) A specifier or user of machine strength graded

timber, should refer to clauses 1 to 5 inclusive.

b) A company carrying out machine strength

grading should refer to clauses 1 to 6 inclusive

and Annex A and Annex C If it is intended to operate the machine in an “output-controlled”

system, then clause 9 and and Annex B should

also be studied

c) A company manufacturing grading machines, should be familiar with all clauses and annexes,

but, most importantly, clause 7.

d) A certification body should refer to all clauses and annexes

1 Scope

This European Standard specifies the requirements for assessing and operating machine strength grading systems, to strength grade structural timber and laminates for glulam

NOTE Whilst it is permitted to use this standard to determine machine settings and to grade to any possible strength profile for

a given species, this standard refers to the strength classes of

EN 338 to provide suitable strength profiles and dictate the visual override requirements necessary to make machine grading

to this standard possible.

In addition, guidance is given for the degree of quality control necessary to ensure the reliability of timber graded by strength grading machines These requirements are given for both

“machine-controlled” and “output-controlled” systems for grading timber

2 Normative references

This European Standard 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 Standard only when incorporated in it by

amendment or revision For undated references the latest edition of the publication referred to applies

EN 336, Structural timber — Coniferous and

poplar — Sizes, permissible deviations

EN 338, 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

timber of one species population and size graded in

one working shift

dimension perpendicular to the longitudinal axis of

a timber beam, in the plane of the bending forces

3.4

indicating property

measurement or combination of measurements

closely related to strength, from which the machine

determines the grade of each increment of length of

a piece of timber

3.5

machine-derived modulus of elasticity

value of modulus of elasticity calculated directly

from an indicating property measurement and

associated with the position of that measurement on

the piece of timber

NOTE The calculation formula may assume the timber to be

homogeneous within the machine’s measuring span and may

ignore the effects of shear deflection and minor end moments.

3.6

sample

number of specimens of timber of one size and

representative of one species population

3.7

settings

values associated with the variable controls of a

grading machine which determine the acceptance to

each strength class of timber graded by the machine

3.8

strength-reducing characteristic

weakness in a piece of timber resulting from natural

growth of the tree (e.g knots, slope of grain) or

changes in moisture content (e.g fissures) or

resulting from conversion of the log (e.g the

inclusion of wane) or caused by attack from fungi,

insects or mechanical damage

timber from an identifiable source and of a species

or species combination that is, or is intended to be, strength graded and marketed as a commercially defined product

3.11 timber size

sawn or processed dimensions with respect to the permitted tolerances given in EN 336

3.12 thickness

lesser dimension perpendicular to the longitudinal axis of a piece of timber

3.13 width

greater dimension perpendicular to the longitudinal axis of a piece of timber

4 Symbols

A cusum control parameter

B cusum control parameter

Ba cusum parameter associated with

acceptable quality level

Br cusum parameter associated with

rejectable quality level

b width of cross section (in mm)

E theoretical modulus of elasticity

(in N/mm2)

Ea actual modulus of elasticity measured in a

proof load test (in N/mm2)

Em modulus of elasticity in bending (in N/mm2)

Emac machine-derived modulus of elasticity

(in N/mm2)

E0,mean characteristic mean modulus of elasticity

parallel to grain (in N/mm2)

F applied force (in N)

Fp proof load (in N)

fm,k characteristic bending strength (in N/mm2)

fp proof stress (in N/mm2)

h depth of cross section (in mm)

K cusum control parameter

w deflection or deformation (in mm)

Y cusum control parameter

Z cusum control parameter

5 Requirements for machine strength

graded timber

5.1 The grading system shall operate in either a

machine-controlled or output-controlled system

5.2 The visual characteristics of each piece of timber

shall meet the requirements of Table 1 and Table 2

when measured in accordance with Annex C

Where a machine does not fully grade to the ends of

each piece of timber (as in bending-type machines)

these non-fully graded portions shall be visually

examined If the diameter of knots and slope of grain

in the non-fully graded portions exceeds the size of

such defects in the fully graded portion of the same

piece of timber, and exceeds the limits given in

Table 2, then the piece shall be rejected

5.3 The timber shall meet the requirements of

EN 336 including one of the two tolerance classes

5.4 Each piece of machine-graded timber shall as a

minimum give the following information clearly and

indelibly indicated by marking or stamping on one

face or edge:

a) grade and/or strength class;

b) species or species combination;

c) number of this standard;

d) information whereby the company and the

machine responsible for the grading may be

identified

In exceptional circumstances the end use of timber

may require marking to be omitted for aesthetic

reasons In such cases, when the customer

specifically requests/orders timber to be free from

marks, each parcel of timber of a single class shall

be despatched under the cover of a certificate of

compliance stating the following minimum

information in addition to that listed in a), b), c)

and d) above:

e) serial number and date of the certificate;

f) customer’s name and address;

g) customer’s purchase or order number;

h) timber dimensions and quantities;

i) date the timber was graded;

j) signature of the operator of the grading

machine

5.5 If the grading has been carried out before

processing, provided that the processing reduction

is not greater than 3 mm from the target size or not

greater than 5 mm from the target size for

dimensions over 100 mm, the grade shall not be

considered to have been changed

If the marking or stamping is removed by such processing, the timber shall be re-marked orre-stamped with its original grade or strength class, the species or species combination, the standard to which it is graded and the name of the surfacing company

6 Requirements for the company producing graded timber, on the operation of strength-grading machines

6.1 Machine strength grading operations shall be carried out by personnel and grading companies, under the supervision of a certification body

NOTE Requirements essential to the operational control of grading machines for inclusion in the procedures of certification bodies are given in Annex A.

6.2 The number of grades or strength classes that can be graded on one pass through the machine will depend upon the accuracy and capabilities of the machine and the settings available Timber rejected

by a machine must not be re-graded unless the method of determining settings has made allowances for the changed species population

6.3 The strength-grading machine shall be calibrated in accordance with the manufacturer’s

7.1 Requirements for all systems 7.1.1 To enable acceptance to be considered, the manufacturer of the machine shall provide a specification to the certification body which shall include the following information:

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

b) range of environmental conditions under which the machine is to operate;

c) maintenance and operating instructions;d) frequency and extent of calibration procedures;e) species populations, sizes, tolerances, surface finish, moisture content, strength classes, grades, temperatures, throughput speed and limits of distortion of the timber to be graded

Table 1 — Visual override requirement

Table 2 — Visual override requirements for non-fully machine-graded portions (see 5.4)

Strength class according to EN 338 C18 and below Above C18

Max permissible length

of fissuresa

Through the thickness Not greater

than 600 mm in any 1 m length

Twice width of piece

Not through the

Maximum distortion

(in mm) over 2 m of

lengthb (see Figure 3)

Bow SpringTwist

dimensions to less than 2/3 of the basic dimensions

of the pieceResin pockets and bark

pockets Not through the thickness

Through the thickness

Unlimited if shorter than the width of the piece otherwise the same limits as for fissures Unlimited if shorter than half the width of the piece, otherwise the same limits as for fissures

are not permitted and worm and pin holes shall be assessed as abnormal defects

abnormal defect is obviously less than caused by other defects permitted by this table, the piece may

be accepted provided the defect is of a type that will not increase after conversion and drying

NOTE Sapstain is not a structural defect and is acceptable without limitation.

a Limitations on fissures may be disregarded if research confirms that they have no effect on strength.

b Limits of distortion will be less if required by the method of operation of the grading machine.

These maximum limits are only applicable where the size of knots and slope of grain in the non-fully graded portion exceeds the size of similar characteristics in the fully graded portion of the same piece.

Strength class according to EN 338

Knot diameter on face 1/2 × width of piece 1/4 × width of piece

Knot diameter on edge 3/4 × thickness of piece 1/2 × thickness of piece

NOTE The knot diameter is measured perpendicular to the longitudinal axis of the piece of timber For arris knots the above limits apply to the portion of the knot visible on the particular face or edge being considered.

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍFigure 1 — Amounts of wane

Figure 2 — Fissures

7.1.2 The grading machine shall comply with the

manufacturer’s specification

7.1.3 A theoretical examination of the machine’s

principle of operation shall be carried out to

evaluate its sensitivity to isolated strength-reducing

characteristics within a piece of timber Where the

machine predicts strength by measuring a

machine-derived modulus of elasticity Emac, the

theoretical examination shall indicate that Emac is

not more than 45 % higher than the modulus of

elasticity E value assumed for the

strength-reducing characteristics In this

evaluation, the strength-reducing characteristics

shall be assumed to be 150 mm in length and have

an E value of 0,5 times that for the remainder of the

piece and situated at the most sensitive position in

the span

NOTE 1 The purpose of this clause is to assess theoretically the effects of a machine’s dimensions and configuration on its sensitivity to changes in modulus of elasticity caused by a defect

It is therefore assumed that for a piece of homogenous timber the

machine would measure E exactly, i.e E = Emac·

NOTE 2 Where the indicating property of a machine is completely independent of strength-reducing characteristics greater than 75 mm from the measuring position (unlike bending machines), sensitivity to isolated defects is limited by the

requirements of 7.2.3, 7.2.4 and 7.2.5 for machine-controlled

systems.

7.1.4 The grading machine shall not damage the timber during the grading operation In particular, damage shall not be caused by large compressions perpendicular to grain stresses and/or large bending stresses

Figure 3 — Measurement of bow, spring and twist

7.1.5 Ten pieces of timber of various cross-sectional

sizes shall be passed through the machine five times

in the same orientation to determine any differences

in the indicating property measurements at the

same position on the pieces The average value of

the maximum difference for each piece, at each

position it occurs, shall not be greater than 7 % of

the average indicating property values at each of

those positions Where the speed can be varied this

shall be carried out at two throughput speeds, i.e at

low speed and at the maximum speed

7.1.6 The effects on the indicating property of

timber size, surface finish, moisture content,

throughput speed, timber tolerances, distortion,

temperature and orientation (both end to end and

side to side) for use in determining grade settings

shall be established

7.1.7 The grading machine shall measure its

indicating property or properties, at increments of

not greater than 150 mm Grading machines 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) then the

measurements shall be made to within 500 mm of

each end

7.1.8 The grading machine shall be capable of

comparing each of its indicating property

measurements with pre-set boundary settings

which correspond to individual grades and of

marking each piece of timber according to the lowest

grade sensed within the length of that piece

7.1.9 All measuring transducers that are part of the

grading machine shall be accurate to within ± 3 % of

the actual measurements

7.1.10 For grading machines which measure their

indicating properties in digital form, the digital

increments shall represent not more than 6 % of the

actual indicating property measurements for any

size, grade and species within the range required for

the machine

7.1.11 The infeed and outfeed equipment shall

provide the correct height and angle of entry for the

timber into the grading machine and shall not

interfere significantly with the sensing of the

indicating property, even when the timber is

distorted within the limits given in item e) of 7.1.1.

7.1.12 The grading machine shall be fitted with a means to enable calibration of all measuring transducers and of parameters critical for the correct operation of the machine

7.2 Additional requirements for machine-controlled systems 7.2.1 All machines of the same type shall have an identical performance to within acceptable manufacturing tolerances

7.2.2 The machine shall have locking devices on the setting controls, and a means by which the grade settings are displayed in a form different from that used to insert the settings to help ensure that, as an additional check, the operator refers back to the tabulated setting data

7.2.3 For each species population given by the

manufacturer’s specification (see 7.1.1) a sample or

combination of samples of at least 200 specimens

shall be tested to verify the requirements in 7.2.4 and 7.2.5.

7.2.4 Where machine settings are estimated from an equation between the lower percentile bending strength, tested in accordance with EN 408, and the indicating property, then the equation shall be determined from the combined sample data for each species, to reduce the effects of sample variability The regression equation between bending strength and the indicating property for the combined sample shall have a coefficient of determination of not less

than 0,45 (see 7.2.3).

7.2.5 The relation between the bending modulus of

elasticity Em as measured in EN 408 and the machine’s indicating property shall have a coefficient of determination of not less than 0,5

(see 7.2.3).

7.3 Additional requirements for output-controlled systems

For output-controlled systems there are no

requirements in addition to those given in 7.1 It

follows that a machine approved for use in a machine-controlled system is automatically acceptable for use in an output-controlled system