ISO 12122-1:2014

Timber structures — Determination of characteristic values — Part 1: Basic requirements

ISO 12122-1:2014 gives methods for the determination of characteristic values for a defined population of timber products, calculated from test values. It presents methods for the determination of: characteristic value of mean-based properties; and characteristic value of 5th percentile-based properties.

Structures en bois — Détermination des valeurs caractéristiques — Partie 1: Exigences de base

General Information

• Status: Published
• Publication Date: 24-Feb-2014
• ICS: 91.080.20 - Timber structures
• Technical Committee: ISO/TC 165 - Timber structures
• Drafting Committee: ISO/TC 165/WG 10 - Characteristic values and design specifications
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 03-Dec-2019

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 12122-1
First edition
2014-03-01
Timber structures — Determination
of characteristic values —
Part 1:
Basic requirements
Structures en bois — Détermination des valeurs caractéristiques —
Partie 1: Exigences de base
Reference number
ISO 12122-1:2014(E)
©
ISO 2014

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ISO 12122-1:2014(E)

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© ISO 2014
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ISO 12122-1:2014(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Reference population . 2
6 Sampling . 3
6.1 Sampling method . 3
6.2 Sample size . 3
7 Sample conditioning . 3
7.1 Sample moisture content . 4
7.2 Sample temperature . 4
8 Test data . 4
8.1 Test method . 4
8.2 Test data compatible with product description . 4
9 Evaluation of characteristic values for structural properties . 4
9.1 Structural properties . 4
9.2 Characteristic value based on the mean . 5
9.3 Characteristic value based on the 5th percentile test value . 5
10 Report . 5
10.1 General . 5
10.2 Reference population . 5
10.3 Sampling . 6
10.4 Test methods . 6
10.5 Analysis methods . 6
10.6 Characteristic values . 6
Annex A (normative) Analysis of data for characteristic values . 7
Annex B (informative) Commentary .12
Annex C (informative) Examples .22
Bibliography .27
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ISO 12122-1:2014(E)

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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 165, Structural Timber.
ISO 12122 consists of the following parts, under the general title Timber structures — Determination of
characteristic values:
— Part 1: Basic requirements
— Part 2: Sawn timber
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ISO 12122-1:2014(E)

Introduction
This International Standard sets out a framework to establish characteristic values from test results on
a sample drawn from a clearly defined reference population. The characteristic value is an estimate of
the property of the reference population with a consistent level of confidence prescribed in this part of
ISO 12122.
It is the intention that this part of ISO 12122 can be used on any structural product including but not
limited to: sawn timber, glulam, structural composite lumber, I-beams, wood-based panels, poles, and
round timber. Whenever it is used, this part of ISO 12122 alerts the user to the basic requirements
for the determination of consistent characteristic values, but for some classes of products, additional
requirements set out in other parts or Annexes to this part give further mandatory detail and explanation.
It permits the evaluation of characteristic values on testing of commercial sized specimens.
In some cases, characteristic values determined in accordance with this part of ISO 12122 may be
modified to become a design value.
This part of ISO 12122 has the following Annexes:
Annex A presents detail on a number of statistical methods that may be used in the evaluation of
characteristic values.
Annex B presents a commentary on the provisions in this part of ISO 12122.
Annex C presents examples of the use of the statistical methods.
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INTERNATIONAL STANDARD ISO 12122-1:2014(E)
Timber structures — Determination of characteristic
values —
Part 1:
Basic requirements
1 Scope
This International Standard gives methods for the determination of characteristic values for a defined
population of timber products, calculated from test values.
It presents methods for the determination of
a) characteristic value of mean-based properties, and
b) characteristic value of 5th percentile-based properties.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
AS/NZS 4063.2, Characterisation of structural timber — Part 2: Determination of characteristic values
ASTM D2915, Sampling and data-analysis for structural wood and wood-based products
EN 14358, Timber structures — Calculation of characteristic 5th percentile values and acceptance criteria
for a sample
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
characteristic value
value of a property taken to represent the property of a designated population using a process of
sampling, testing of specimens, and analysis
3.2
characteristic value of mean-based property
two alternative presentations of characteristic value for mean-based properties are possible:
a) the mean property obtained from results of tests on the defined product;
b) the mean property with 75 % confidence obtained from results of tests on the defined product
3.3
characteristic value of 5th percentile-based strength property
5th percentile value with 75 % confidence strength property obtained from results of tests on the
defined product
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3.4
population
all of the structural timber product that meets the description of the population
Note 1 to entry: See Annex B for some examples of the use of the term population.
3.5
sample
number of single members of the population, selected to represent the population
Note 1 to entry: See Annex B for some examples of the use of the term sample.
3.6
specimen
single element used in a test; the element may be a complete member, a member that has been trimmed
to length, or a part of a member fabricated for a specific test
Note 1 to entry: See Annex B for some examples of the use of the term specimen.
4 Symbols and abbreviated terms
Symbols defined in the relevant ISO product or test standard shall be used.
In addition, the following apply:
f is the characteristic bending strength
m
k is a multiplier to give the mean property with 75 % confidence and is given in Table A1
mean, 0,75
k is a multiplier to give the 5th percentile value with 75 % confidence for a 5th percen-
0,05, 0,75
tile-based property and is given in Table A2
M is the moment capacity
n is the number of specimens in the test data
V is the coefficient of variation of the test data
X is the target difference between the reported characteristic value and the test result
Δ
5th percentile
X is a generalized test value
i
X is the average of the individual test values (X )
mean i
X is the mean property with 75 % confidence
mean, 0,75
X is the 5th percentile value from the test data
0,05
X is the 5th percentile value with 75 % confidence
0,05, 0,75
Z is the section modulus
5 Reference population
The population to which the characteristic value applies shall be fully described. The description shall
reference all of the attributes that may affect either the strength or stiffness and restrict the pieces to
the grouping for which the characteristic value is required. These include but are not limited to:
a) reference to the relevant product standard or specification;
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ISO 12122-1:2014(E)

b) species or species grouping;
c) designation of grade of the product;
d) size or size range of the product;
e) moisture condition of the product;
f) treatment of the product;
g) period in which the product was manufactured.
The reference population shall be a grouping from which it is possible to draw a representative sample,
and on which it is possible to perform tests on specimens to characterize the required properties.
6 Sampling
6.1 Sampling method
The sampling method shall aim to produce a sample that is representative of the variants in the defined
reference population that may affect the tested properties. The sampling shall minimize selection bias,
and shall be appropriate to the purpose of the characteristic value and the nature of the reference
population.
The sampling method shall be documented. The documentation shall include details of the steps taken
to ensure that each of the variants listed in the population as described in Clause 5 is included in the
representative sample.
6.2 Sample size
The sample shall be large enough to cover variants of the product that impact on the tested properties,
and give statistical significance to the result.
NOTE 1 Materials with larger assumed or assigned population coefficient of variation, (V), of the tested
properties should have a larger sample size.
NOTE 2 Some product standards may define a minimum number of tests that must be undertaken to determine
characteristic values to be used with described products.
NOTE 3 Annex B gives some guidance on selecting sample size.
NOTE 4 For some populations, a number of different sub-groups within the population may need to be sampled
(e.g. different cross-sectional sizes). In these cases, the size of each of the sub-groups may have to be sufficient to
allow meaningful pooling of the results as indicated in Annex A.
NOTE 5 Where characteristic values are to support limit states (or LRFD) design, the sample size should be
appropriate for the statistical method selected to determine the 5th percentile value strength (full distribution
or tail-fit). However, where the data are used to support a full reliability design method, the sample size should be
appropriate to also enable the full statistical distribution of the property to be defined.
7 Sample conditioning
Test data from the samples shall be compatible with the definition of the population by
a) compliance with the specification of the reference population at the time of testing in accordance
with 7.1 and 7.2, or
b) adjustment of test data in accordance with 8.2 where compliance with 7.1 or 7.2 is not achieved.
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7.1 Sample moisture content
The sample shall be stored so that the moisture content at the time of test is appropriate to the description
of the reference population as detailed in Clause 5.
7.2 Sample temperature
The sample shall be stored and tested so that the temperature at the time of test is appropriate to the
description of the reference population as detailed in Clause 5.
8 Test data
8.1 Test method
The test data shall be derived in accordance with an appropriate test method for the properties and for
the reference population.
NOTE 1 For tests on some product types, discrimination of results on the basis of failure mode may be required
to ensure that the results are compatible with objectives of the test program and the property being determined.
NOTE 2 Test methods involve many variables that may affect results including loading configuration and rates,
specimen positioning and measurement methods. The selection of these variables must be appropriate to the
objectives of the testing, and may require some adjustments specified in 8.2.
8.2 Test data compatible with product description
Where the characteristic value is applicable to a standard size or moisture content, adjustments to
the raw test data may be required. Any adjustment shall be in accordance with appropriate behaviour
models and shall be detailed in the report.
NOTE Annex B gives examples of the types of adjustment that may be necessary in response to variation of
the specimens from the description of the reference population.
Where test data from a number of different data subsets are to be combined, the basis for the combination
shall satisfy the following requirements:
a) The data shall be derived from similar subsets that are standardized using the same adjustment
models, and shall satisfy statistical tests for combining the subsets into a single data set;
b) Transformation methods shall be in accordance with appropriate behaviour models and shall be
detailed in the report.
NOTE Annex A gives requirements for combining or pooling of data from a number of different test programs.
9 Evaluation of characteristic values for structural properties
9.1 Structural properties
Characteristic values for properties shall be reported in one of two ways according to the use of the
product:
a) Material properties — where the determined property is multiplied by a geometric parameter to
give a component capacity, or component stiffness;
b) Component properties — where the determined property is a component capacity or component
stiffness.
Characteristic values for structural properties shall be classified as those based on the mean of test
results and those based on the 5th percentile of test results in accordance with 3.2 and 3.3.
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9.2 Characteristic value based on the mean
The mean value of the test values shall be evaluated as either a) or b):
a) the arithmetic average of the test values as
X
∑ i
X = (1)
mean
n
where
X is the average of the individual test values (X );
mean i
X is a generalized test value;
i
n is the number of test values.
b) the mean value of a statistical distribution fitted through the test data
For mean-based strength characteristic values, the mean property with 75 % confidence obtained from
results of tests shall be evaluated.
NOTE Suitable methods for estimating the mean with 75 % confidence are presented in Annex A.
The characteristic values for modulus of elasticity or modulus of rigidity shall be the mean value.
9.3 Characteristic value based on the 5th percentile test value
The 5th percentile value of the test values shall be evaluated as
a) the non-parametric estimate of the 5th percentile of the test data found by ranking the test data and
from the cumulative frequency of the test data selecting the interpolated value at the 5th percentile
(see A.2.1 and A.2.2), or
b) the estimate of the 5th percentile of the test data found by fitting an accepted statistical distribution
through the test data and selecting the 5th percentile point from the fitted distribution (see A.2.3).
The 5th percentile value with 75 % confidence shall be evaluated.
NOTE Suitable methods for estimating the 5th percentile value with 75 % confidence are presented in
Annex A.
10 Report
10.1 General
The report shall include details of the reference population definition, sampling program, description
of test pieces, the test method and analysis methods used, and the characteristic values in accordance
with 10.2 to 10.6.
10.2 Reference population
The reference population shall be defined as given in Clause 5. Each attribute used to define the reference
population shall be detailed in the report. Each of the attributes in the reference population that may
affect either the strength or stiffness shall be presented in the report.
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ISO 12122-1:2014(E)

10.3 Sampling
The sampling method used to select the test sample shall be described.
The justification of the sample size selected shall be presented. (See 6.2.)
10.4 Test methods
Reporting of testing methods shall either
a) refer to the test standard used, or
b) fully document the test procedures used.
Reporting of test specimen preparation shall include a statistical summary of the characteristics of the
sample (e.g. moisture content, temperature, grade marks). This data shall be in sufficient detail to enable
the data to be adjusted to different conditions if required.
The test results shall be presented in the report in enough detail to enable the statistical analysis to
be checked or repeated. Any adjustment of the test results to ensure compatibility with the product
description shall be fully documented, together with references for the modification methods and
factors used.
Where applicable for the reference population and the tests undertaken, failure modes in strength tests
shall be reported.
10.5 Analysis methods
The analysis method shall be described in detail. For characteristic strength values, the method for
estimation of the 5th percentile value with 75 % confidence shall be referenced.
Where pooled data are used, the method of combination of the data shall be described.
Where a distribution is fitted to the test data, all of the defining parameters of the fitted distribution
shall be reported, together with goodness of fit parameters.
10.6 Characteristic values
The characteristic values shall be reported together with the V of the data that led to their calculation.
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ISO 12122-1:2014(E)

Annex A
(normative)

Analysis of data for characteristic values
A.1 Evaluation of mean value with 75 % confidence
Where required, the lower single sided 75 % confidence limit on a mean property shall be found by
kV
 
mean,,075
XX=−1 (A.1)
 
mean,,075 mean
 
n
 
where
X is the characteristic value expressed as the mean value with 75 % confidence;
mean, 0,75
X is the average of the individual test values (X );
mean i
k is a multiplier to give mean value with 75 % confidence and shall be the value obtained
mean, 0,75
in Table A1;
V is the coefficient of variation of the test data found by dividing the standard deviation
of the test data by the average of the test data;
n is the number of specimens in the test data.
Table A.1 — k
mean, 0,75
Number of specimens
k
mean, 0.75
n
3 0,82
5 0,74
10 0,70
30 0,68
50 0,68
100 0,68
>100 0,67
A.2 Evaluation of 5th percentile value with 75 % confidence
A.2.1 Use of non-parametric data analysed using ASTM D2915
Where this method is used, the estimation of the 5th percentile value with 75 % confidence using the
non-parametric method of ASTM D2915 shall be used without modification.
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A.2.2 Use of non-parametric data analysed using AS/NZS 4063.2
Where this method is used, the 5th percentile of the test data shall be evaluated by ranking the test data
and determining the 5th percentile of the ranked data. The 5th percentile value with 75 % confidence
shall be evaluated from Formula (A.2).
 kV 
00,,50,75
XX=−1 (A.2)
 
00,,50,,75 005
 
n
 
where
n is the number of test values;
X is the 5th percentile value with 75 % confidence;
0,05, 0,75
X is the 5th percentile from the test data interpolated between the data ranks as neces-
0,05
sary;
k is a multiplier to give the 5th percentile value with 75 % confidence and is given in
0,05, 0,75
Table A2;
V is the coefficient of variation of the test data found by dividing the standard deviation of
the test data by the average of the test data.
Table A.2 — k
0,05, 0,75
Number of specimens k
0,05, 0,75
n
a
5 —
a
10 —
30 2,01
50 1,94
100 1,85
>100 1,76
NOTE Method of analysis: non-parametric AS/NZS 4063.
a
There are difficulties obtaining a reliable estimate of the 5th percentile value from small
data sets.
A.2.3 Evaluation by fitting data to a distribution
Where this method is used, the 5th percentile value with 75 % confidence shall be evaluated from
the 5th percentile value of the test data by fitting a distribution through the test data and applying
Formula (A.2) with V found by dividing the standard deviation of the test data by the average of the test
data.
For this analysis, k is the multiplier to give the 5th percentile value with 75 % confidence and
0,05, 0,75
is given in Table A3. The result will only be valid if the distribution is a good fit to the data. Where a
distribution is fitted to the data, goodness of fit parameters shall be evaluated in accordance with A.3.
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Table A.3 — k
0,05, 0,75
Method of analysis Log-normal Normal
Number of specimens n k k
0,05, 0,75 0,05, 0,75
a
5 1,34 2,05
a
10 1,28 2,04
30 1,18 2,01
50 1,13 1,97
100 1,07 1,91
>100 1,05 1,90
NOTE 1 Other distributions may be used as long as the values of k can be justified.
0,05, 0,75
NOTE 2 For the log normal distribution, V is the standard deviation of the original data
divided by the mean of the original data, not the ratio of the standard deviation of the
logarithms to the mean of the logarithms.
NOTE 3 The data presented in this table is sourced from PN 05.2024 FWPA Australia. The
data for the log-normal distribution was calibrated for V ranging from 5 % to 55 % and
for the normal distribution for V ranging from 5 % to 20 %. The log-normal factors give
equivalent results to the non-central student t-distribution presented in EN 14358 and US
practice within 1 % for sample sizes of 10 or more.
a
There are difficulties obtaining a reliable estimate of the 5th percentile value from small
data sets.
A.3 Goodness of fit tests for fitted distributions
A distribution is deemed to be a good fit to test data where the Kolmogorov-Smirnov goodness of fit test
is significant at the 0,05 or better level.
NOTE Where the data are not shown to be a good fit to the distribution or the data are a collection from a
number of distributions, an alternative distribution, or a non-parametric method should be used.
A.4 Pooling of data for analysis
A.4.1 General
Pooling involves the aggregation of data from a number of discrete data sets to capture sources of
variation that may not be present within a single subset. Such aggregations may include data from
different species of timber, different production methods, or different sized products.
In this clause, the term subset data refers to test data from a single size, grade, product test sample.
Pooled data are the sum of all valid subsets as represented in Figure A1.
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