ISO 12122-6:2017

INTERNATIONAL ISO
STANDARD 12122-6
First edition
2017-07
Timber structures — Determination
of characteristic values —
Part 6:
Large components and assemblies
Structures en bois — Détermination des valeurs caractéristiques —
Partie 6: Composants assemblés
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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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 . 1
5 Reference population . 2
5.1 General . 2
5.2 Prediction of test results . 3
6 Sampling . 3
7 Sample conditioning . 4
8 Test data . 4
8.1 Loading specifications . 4
8.2 Testing arrangement . 4
8.3 Test measurements . 4
9 Evaluation of characteristic values for structural properties . 4
9.1 General principles . 4
9.2 Direct evaluation of characteristic value . 5
9.2.1 Sampling factor k .
n 5
9.2.2 Normal distribution . 5
9.2.3 Log-normal distribution . 6
9.3 Statistical determination of resistance models . 6
9.3.1 General. 7
9.3.2 Procedure . 7
9.3.3 Use of prior test data .11
10 Reporting .12
Annex A (informative) Commentary .13
Annex B (informative) Example of calculation according to 9.2 and 9.3 .21
Bibliography .23
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
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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
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URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 165, Timber structures.
A list of all parts in the ISO 12122 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved

Introduction
This document sets out a framework for establishing characteristic values from test results on a
sample drawn from a clearly defined reference population of large components and assemblies. The
characteristic value is an estimate of the property of the reference population with a consistent level of
confidence prescribed in the standard.
This document is to be used in conjunction with ISO 12122-1.
Since this document is dedicated to large components and assemblies, it has to deal with a specific
statistical issue, namely that the characteristic values are to be derived from a very small number of
test results.
In some cases, characteristic values determined in accordance with this document may be modified to
become a design value.
Annex A presents a commentary on the provisions in this document.
Annex B presents examples of the use of the statistical methods.
INTERNATIONAL STANDARD ISO 12122-6:2017(E)
Timber structures — Determination of characteristic
values —
Part 6:
Large components and assemblies
1 Scope
This document specifies methods of determination of characteristic values for a defined population of
large components and assemblies, calculated from test values.
It establishes two methods for the determination of characteristic values:
a) direct calculation from test values;
b) calculation from a resistance model, which is firstly calibrated from test results, including
calculation of error terms.
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
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
large components and assemblies
parts of a timber structure consisted of at least two members, assembled together by connections
4 Symbols
E(.) mean value of (.)
Var(.) variance of (.)
V coefficient of variation [V = (standard deviation)/(mean value)]
V coefficient of variation of X
X
V estimator for the coefficient of variation of the error term δ
δ
array of j basic variables X … X
X 1 j
array of mean values of the basic variables
X
m
array of nominal values of the basic variables
X
n
resistance function (of the basic variables X) used as the resistance model
gX
()
rt
k characteristic fractile factor
n
m mean of the n sample results
X
n number of experiments or numerical test results
r resistance value
r experimental resistance value
e
r extreme (maximum or minimum) value of the experimental resistance
ee
[i.e. value of r that deviates most from the mean value r ]
e em
r experimental resistance for specimen i
ei
r mean value of the experimental resistance
em
r characteristic value of the resistance
k
r
m
resistance value calculated using the mean values X of the basic variables
m
r nominal value of the resistance
n
r
t
theoretical resistance determined from the resistance function gX
()
rt
r
theoretical resistance determined using the measured parameters X for specimen i
ti
s estimated value of the standard deviation σ
s estimated value of σ
δ δ
δ error term
δ observed error term for test specimen i obtained from a comparison of the experimental
i
resistance r and the mean value corrected theoretical resistance br
ei ti
η reduction factor applicable in the case of prior knowledge
k
σ
 
standard deviation σ = variance
 
 
5 Reference population
5.1 General
The reference population is the population of large components or assemblies that the test program
is designed to represent. Prior to the carrying out of tests, a test plan shall be documented. It shall
contain the objectives of the test and all specifications necessary for the selection or production of the
2 © ISO 2017 – All rights reserved

test specimens, the execution of the tests and the test evaluation. The test plan shall cover the following
details of the reference population, including structural context for the loading of the specimens:
— objectives and scope;
— prediction of test results;
— specification of test specimens and sampling;
— description of expected restraint and boundary conditions in normal service;
— loading specifications;
— testing arrangement;
— measurements;
— evaluation and reporting of the tests.
The objective of the tests shall be clearly stated, e.g. the required properties, the influence of certain
design parameters varied during the test and the range of validity. Limitations of the test and required
conversions (e.g. scaling effects) shall be specified.
5.2 Prediction of test results
All properties and circumstances that can influence the prediction of test results should be taken into
account, including:
— geometrical parameters and their variability;
— geometrical imperfections;
— material properties;
— parameters influenced by fabrication and execution procedures;
— scale effects of environmental conditions taking into account, if relevant, any seq
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