ISO 13912:2017

INTERNATIONAL ISO
STANDARD 13912
Second edition
2017-11
Structural timber — Machine strength
grading — Basic principles
Bois de structure — Classement par machine selon la résistance —
Principes de base
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 General . 1
5.1 Machine strength-graded timber . 1
5.2 Machine strength-grading operations . 1
5.3 Machine strength-grading quality procedures . 2
5.3.1 Machine-controlled system . 2
5.3.2 Output-controlled system . 2
6 Resource and sawn timber input requirements . 3
6.1 General . 3
6.2 Input requirements . 4
6.2.1 Resource . 4
6.2.2 Sawn timber . 4
6.3 Control of inputs . 4
6.4 Reprocessing of previously graded material . 4
7 Machine strength-grading requirements . 4
7.1 Machine checking requirements . 4
7.2 Machine acceptance criteria . 4
7.3 Machine strength-grading requirements . 5
7.4 Visual grading requirements . 5
7.4.1 General. 5
7.4.2 Automated visual grading . 5
8 Machine strength-graded timber structural properties . 5
8.1 General . 5
8.2 Initial evaluation . 5
8.3 Daily evaluation . 6
9 Product identification . 6
10 Documentation . 6
Annex A (informative) Example of a machine strength-grading timber standard .7
Annex B (informative) Use of the CUSUM procedure for daily evaluation.20
Annex C (informative) Strength-grading machine acceptance considerations .24
Annex D (informative) Training, supervision and oversight of grading .26
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 165, Timber structures.
This second edition cancels and replaces the first edition (ISO 13912:2005), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Annexes C and D have been added;
— Clauses 5 and 7 have been technically revised.
iv © ISO 2017 – All rights reserved

Introduction
The general principle of this document is that any type of machine strength-grading procedure is
acceptable, provided it is defined, controlled, and documented to the extent required to reflect the
degree of reliability intended for the structural application of the product.
The body of this document specifies the essential features common to all machine strength-grading
operations. The requirements are minimal so as to ensure maximum scope and flexibility in the
application of this document to the machine strength-grading process as applied to timber.
Annex A provides an example of a conformance standard reflecting the requirements of this document.
INTERNATIONAL STANDARD ISO 13912:2017(E)
Structural timber — Machine strength grading — Basic
principles
1 Scope
This document establishes the basic principles for rules and procedures governing the machine sorting
of timber for use in structural applications. This applies to conventional bending type strength-grading
machines as well as more recent machines that use other properties for strength-grading purposes.
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.
ISO 12122-1, Timber structures — Determination of characteristic values — Part 1: Basic requirements
ISO 12122-2, Timber structures — Determination of characteristic values — Part 2: Sawn timber
ISO 13910, Timber structures — Strength graded timber — Test methods for structural properties
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13910 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
4 Symbols and abbreviated terms
For the purposes of this document, the symbols and abbreviated terms given in ISO 13910 apply.
5 General
5.1 Machine strength-graded timber
Machine strength-graded timber is sawn wood that has been machine sorted according to selected
criteria allowing for classification into structural grades. The machine criteria shall identify mechanical
and/or physical properties that reflect the timber strength and can affect the utility of the product.
5.2 Machine strength-grading operations
A typical machine strength-grading operation shall be comprised of a grading machine that sorts an
input resource into one or more grades (see Figure 1).
The data recorded by the machine shall be processed so as to produce a sorting criterion, and this
sorting criterion shall be used as a basis for assigning a grade of machine strength timber.
Where applicable, visual requirements for the total piece of timber, the unscanned end portions, or
both shall be specified to supplement the information obtained by the machine.
NOTE 1 The “grading machine” comprises one or more devices that can measure properties along the length
of a piece of timber as it passes through the machine. For some machines, properties along the length of a piece
of timber are not measured, but rather properties are measured that relate to the piece of timber considered in
total as a single unit.
NOTE 2 Within the context of this document, the term “scanner” is used to denote the device used to measure
a property of the timber, and the term “scanned length” is used to denote that portion of the timber for which
measurements are made by the scanning device if it measures properties along the length of a piece of timber.
For conventional bending type strength-grading machines, end portions of the timber are not scanned [see
Figure 2 a)].
NOTE 3 In the use of the conventional bending type of strength-grading machine, the only parameter that is
measured (mechanically) along the length of each piece of timber (except for the unscanned end lengths) is the
local modulus of elasticity on flat.
NOTE 4 For a machine using single or multiple scanners, the data obtained is commonly used to produce a
prediction of strength along the length of a piece of timber [see Figure 2 b)]. For this case, the minimum predicted
strength value within the piece is usually taken to be the grade control criterion.
5.3 Machine strength-grading
...