ISO 16598:2015

INTERNATIONAL ISO
STANDARD 16598
First edition
2015-09-01
Timber structures — Structural
classification for sawn timber
Structures en bois — Classification structurelle pour bois sciés
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Timber population and structural property data . 2
5 Primary properties . 2
5.1 Framework . 2
5.2 Bending or tension property evaluation . 3
5.2.1 General. 3
5.2.2 Exception . 3
5.3 Density evaluation . 3
5.4 Class boundaries. 3
6 Derived properties . 3
6.1 Framework . 3
6.2 Evaluation . 3
6.2.1 General. 3
6.2.2 Exception . 3
7 Allocation to a class . 4
7.1 Framework . 4
7.1.1 General. 4
7.1.2 Normalization of characteristic values . 4
7.2 Grading systems . 4
7.2.1 General. 4
7.2.2 Exception . 4
7.3 Design values . 5
8 Reporting . 5
Annex A (normative) Timber population and structural property data .6
Annex B (informative) Structural class example table . 9
Annex C (informative) Commentary .13
Bibliography .19
Foreword
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The committee responsible for this document is ISO/TC 165, Timber structures.
iv © ISO 2015 – All rights reserved

Introduction
The production of many different combinations of species and grades complicates timber specification
and structural design. Structural classification groups together species and grades of similar properties,
to make them interchangeable for structural purposes. The development of this International Standard
is intended to benefit industry, consumers, governments and distributors, by balancing the principles
of simplicity, product utility and structural reliability.
One of the key reasons for developing this International Standard is to provide a framework for
understanding and working on compatibility between approaches used in different regions, through
standardization of the basic elements of structural classes, including underlying assumptions and the
general method for setting up classes. An example table is presented in Annex B for illustration purposes.
This International Standard provides a model or template that may be modified before adoption
and it does not present final design values and adjustment factors. The scope includes evaluation of
structural properties; it does not cover suitability with regard to durability, fire resistance and other
timber properties.
INTERNATIONAL STANDARD ISO 16598:2015(E)
Timber structures — Structural classification for sawn
timber
1 Scope
This International Standard provides a basic international framework for establishing structural
classes for sawn timber.
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.
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
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
characteristic value
standard estimate of a structural property of a timber population (3.11) corresponding to a fractile,
tolerance limit or mean of sample test data after being adjusted to accepted reference conditions
3.2
derived property
structural property for which characteristic values are determined by correlation with one or more
primary properties, and not typically used in deciding how to classify a population
3.3
design value
numerical quantity assigned to a timber population for use in structural design, calculated from the
characteristic value and modified to suit provisions in the appropriate building code and standards
Note 1 to entry: Design values are not used directly in structural classes.
3.4
full-size specimen
timber test piece that is similar in size and characteristics to typical structural timbers and is prepared
and tested in a way similar to use in construction
Note 1 to entry: See also small clear specimen (3.7).
3.5
normalization
adjustment of data, beyond basic data breakdown and moisture and size corrections, to be on a
compatible basis with other data for evaluation in the same structural class system
3.6
primary property
structural property that is used to set criteria for allocating a timber population to a structural class
system, based on the characteristic value for that property
3.7
small clear specimen
timber test piece that is much smaller than typical structural timbers and normally prepared to be free
of visible defects
Note 1 to entry: See also full-size specimen (3.4).
3.8
species combination
two or more species or multiple data sets of the same species from different growth or production
regions, combined into a single marketing group on the basis of similar properties and property
relationships, or other applicable criteria
3.9
grade
solid sawn timber population produced with standardized rules that maintain well-defined limits on
strength-controlling characteristics or properties
3.10
structural classification
system for assigning shared structural properties to timber populations of similar capacities, for the
purpose of structural design and specification
3.11
timber population
solid sawn timber product of a grade and species or species combination intended for use in
structural applications
4 Timber population and structural property data
This International Standard is based on the timber population and structural property data estimates
conforming to those identified in ISO 12122-1 and ISO 12122-2.
NOTE See Annex A for additional information.
5 Primary properties
5.1 Framework
Primary properties shall be established on a standardized basis to ensure compatibility between
different sets of test data from accepted sampling and testing programs. Primary characteristic
properties include the following:
— bending strength: the modulus of rupture at the 5th percentile, with specified level of confidence;
— bending stiffness: the modulus of elasticity at the mean and 5th percentile levels;
— density: the density at the mean and 5th percentile levels.
NOTE 1 Strength properties are typically estimated as tolerance limits at the 5th percentile level with
confidence specified at 75 %. Stiffness and density properties are typically
...