ISO 13910:2014

INTERNATIONAL ISO
STANDARD 13910
Second edition
2014-05-01
Timber structures — Strength graded
timber — Test methods for structural
properties
Structure en bois — Bois classé selon la résistance — Méthodes
d’essai des propriétés structurelles
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Symbols and abbreviated terms . 2
3.1 General notation . 2
3.2 Subscripts . 3
4 Test specimens. 3
5 Test conditions . 3
6 Test configurations . 3
6.1 Density . 3
6.2 Bending strength and stiffness . 4
6.3 Tension strength parallel to the grain . 5
6.4 Compression strength parallel to the grain . . 6
6.5 Shear strength parallel to the grain . 7
6.6 Tension strength perpendicular to the grain . 9
6.7 Compression strength and stiffness perpendicular to the grain .11
6.8 Torsional shear modulus .13
7 Adjustment for non-reference test conditions .14
8 Test report .15
Annex A (informative) Adjustment factors for non-reference condition .16
Bibliography .17
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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electrotechnical standardization.
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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. www.iso.org/directives
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The committee responsible for this document is ISO/TC 165 Timber Structures.
This second edition cancels and replaces the first edition (ISO 13910:2005), which has been technically
revised.
iv © ISO 2014 – All rights reserved

Introduction
This International Standard provides requirements for testing of structural properties for a specific
grade and size of sawn timber. In accordance with the requirements of performance-based International
Standards, it is concerned with the measurement of properties similar to those that occur under service
conditions and are intended for deriving engineering properties in structural design codes. Hence, terms
such as “bending strength”, “shear strength”, “bearing strength”, etc. relate to the loading configuration
used and to the targeted mode of failure.
It is not the intent to imply that every property of every grade and size of timber used in building
construction needs to be assessed according to this International Standard. The requirements for any
assessment typically are specified in building regulations, quality manuals or other material standards
and specifications.
This document is an internationally-agreed reference standard for measurement of structural properties
of strength-graded timber. Other standards related to the measurement of structural properties may
be deemed to comply with this International Standard, provided that the adjustments necessary to
establish equivalency between this and other standards are applied appropriately
INTERNATIONAL STANDARD ISO 13910:2014(E)
Timber structures — Strength graded timber — Test
methods for structural properties
1 Scope
This International Standard specifies test procedures for full-size sawn timber that has been strength-
graded, for the derivation of design properties in codes dealing with structural engineering design. It is
applicable to sawn timber of rectangular cross-section subjected to a short-duration load.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
grade
population of timber with defined design properties in a design standard
2.2
piece of timber
timber of rectangular cross-section manufactured for construction purposes of a specific grade
2.3
test specimen
length of timber, cut from a piece, for purposes of testing to evaluate a timber property
3 Symbols and abbreviated terms
3.1 General notation
a distance between a load point and nearest support in a bending test set-up, expressed in mm
b thickness (smaller dimension of a cross section) of a rectangular piece or specimen of tim-
ber, expressed in mm
E modulus of elasticity parallel to direction of grain, expressed in MPa
F applied load, expressed in N
f strength, expressed in MPa
G shear modulus of rigidity, expressed in MPa
h width (larger dimension of a cross section) of a rectangular piece or specimen of timber,
expressed in mm
K stiffness, expressed in N per mm deformation
L length along a piece or specimen of timber, expressed in mm
L length of test specimen subjected to torsion forces, expressed in mm
T
l length cut from a specimen, expressed in mm
h
l lever arm of applied torsion load, expressed in mm
t
e displacement of beam, expressed in mm
m mass of specimen, expressed in kg
SH volumetric shrinkage of wood from green fibre saturation point (FSP) to oven-dry condition
v
w ratio of mass of water to mass of oven-dry wood, equivalent to moisture content
w moisture content at fibre saturation point
FSP
x data value
i
θ rotational deformation in a torsion test, in radians
ρ density, expressed in kg/m
ρ density, expressed in kg/m , at 12% moisture content
ρ density, expressed in kg/m , at time of test
test
2 © ISO 2014 – All rights reserved

3.2 Subscripts
0.1h value at deformation of 0.1h
0 property in a direction of 0° to the grain
90 property in a direction of 90° to the grain
c compression
m bending
t tension
ult value at failure
v shear
4 Test specimens
All test specimens are of full-size cross section. The length required for a test specimen shall be related
to the specific test (see Clause 6).
Unless otherwise stated, test specimens shall be selected from random locations within a piece of
timber. Specimens cut from pre-defined locations (centre of a piece of timber, a randomly selected end
within a piece or clear sections, etc.) may be deemed to comply with this requirement provided this does
not produce any bias in the measured properties.
Each test specimen for a given size, grade or property shall be cut from a different piece of timber and
more than one type of test specimen may be cut from each piece.
5 Test conditions
Unless otherwise specified in the description of the reference population, the reference moisture content
at the time of testing shall be consistent with conditioning at a temperature of 20°C (±2°C) and 65 %
(±5 %) relative humidity. Other test procedures and conditioning criteria may be used provided they
are more conservative; otherwise, an equivalency in performance for these alternative procedures and
conditions shall be established. The rate of loading shall be selected that targets average time-to-failure
in 1 min to 5 min.
NOTE The intent here is not to reject data for weak pieces that fail in a short time.
At the time of testing, the moisture content of the timber, the temperature of the timber, and the time to
failure shall be recorded.
6 Test configurations
6.1 Density
The specimens for the measurement of density shall be free of knots and comprise the full cross-section
of the piece of timber. The length of the test specimen shall be a minimum of 50 mm. The mass, m, and
moisture content, w, are measured for each test specimen. The density at the time of test, ρ , shall be
test
calculated from
m×10
ρ = (1)
test
Lbh
The density at 12 % moisture content, ρ , shall be calculated from
ρρ=−[,10 50(,w− 12)] (2)
12 test
where w is the moisture content at the time of test as determined by the oven-dry method.
Alternatively, it may be sufficiently accurate to measure moisture content by means of a moisture
meter, provided that the meter is calibrated against moisture content measurements determined by the
oven dry method. Where such moisture meter measurements are made, they shall be made at several
locations along each specimen.
NOTE If specific gravity (e.g. based on oven-dry mass and oven-dry volume, SG ) is desired, it can be
OD
estimated from wood density at test, ρ , moisture content, w, fibre saturation point, w , and wood volumetric
test FSP
shrinkage, SH , as follows:
v
(/1+wSHw )ρ
vFSP test
SG =
OD
1000()1+w
6.2 Bending strength and stiffness
The bending strength and stiffness test configuration shall be as shown in Figure 1. The beam specimen
shall be loaded at two points, equally spaced between the end supports, with each load equal to F/2.
The distance between load points shall be 6 h and the distance between a load point and the nearest
support, a, shall be 4,5 h to 7 h. The tension edge of the beam shall be chosen randomly. If the beam has a
slenderness where there could be a tendency for the compression edge to buckle during loading, lateral
restraints may be provided to the compression edge. Such restraints shall not resist any movement in the
direction of the loading. Bearing blocks at loading and support points (see Figure 1), shall be of sufficient
thickness and extend entirely across the beam thickness to eliminate high-stress concentrations at
places of contact between beam and bearing blocks. Load shall be applied to the blocks in such a manner
that the blocks may rotate about an axis perpendicular to the span. The slider bearing plate in Figure 1
shall allow rotation and horizontal movement whereas the bearing plate shall allow only rotation.
F/2
F/2
1 b
C
A
B
h
e
a
a
L
Key
1 slider bearing plate
2 bearing plate (rocker)
Figure 1 — Test set-up for measuring bending strength and stiffness
4 © ISO 2014 – All rights reserved

Modulus of elasticity, E, shall be calculated from measurement of e, the centre-point deflection of the
centre-line of the beam relative to the position of the centre-line at the ends of the beam, i.e. the deflection
of point B relative to points A and C as shown in Figure 1.
NOTE Centre-point deflection measured by referencing the displacement transducer against the top or
bottom edge of the beam or by using loading head movement usually contains unintended displacement component
due to the indentation of the wood material at the support and loading points, etc. Deflection measured by such
methods can be used for calculation of E provided it can be shown that it leads to more conservative result.
The applied load, F, shall be increased until the maximum load is reached.
To evaluate the modulus of elasticity in bending, E , the incremental deflection ∆e for an incremental
m
load ∆F shall be selected from the linear elastic part of the load-deformation graph. E is calculated
m
from:
a  ΔF 
E = ()34La− (3)
m  
Δe
4bh  
The range of 10 % to 40 % of the maximum load shall be used to determine ∆F/∆e. The deflection e
may be evaluated by the measurement of the movement of points other than those described above,
provided that an acceptable equivalency for these procedures is established, or it can be shown that the
alternative procedures produce conservative results.
NOTE The test set-up will lead to the determination of apparent modulus of elasticity. Shear-corrected
modulus of elasticity can be estimated by adjusting the measured deflection, Δs, using the following formula
assuming shear modulus is known (For structural timber, G can be assumed to be E/16.), and substituting Δe into
Formula (3):
3ΔFa
 
ΔΔes=−1
 
5ΔbhG s
 
The bending strength, f , shall be calculated from
m
3Fa
ult
f = (4)
m
bh
where F is the value of the applied load at failure.
ult
6.3 Tension strength parallel to the grain
NOTE The gauge length used is typically longer than the stated minimum to increase the likelihood that the
critical strength-reducing defect is captured within the gauge length.
b
F
F
h
Gauge length
Key
1 grip
Figure 2 — Test setup for measuring tension strength parallel to the grain
The tension strength f shall be calculated from
t,0
F
ult
f = (5)
t,0
bh
where F is the value of the applied load at failure.
ult
6.4 Compression strength parallel to the grain
The compression strength parallel to the grain test configuration shall be as shown in Figure 3. The test
specimen shall be the full length of the piece of timber. It shall be compressed axially by a load F until
failure occurs. The specimen should be restrained against lateral buckling with the spacing of the lateral
restraints not greater than 5h for buckling about the major axis and 5b for buckling about the minor
axis. The lateral restraint shall not provide any resistance in the direction of the loading.
< 5h
b
F
F
h
< 5b
Key
1 lateral restraint
Figure 3 — Test setup for measuring compression strength parallel to the grain using the full
length test specimen
The compression strength f shall be calculated from
c,0
F
ult
f = (6)
c,0
bh
where F is the value of the applied load at failure.
ult
An alternative test procedure using short compression specimen is permitted to be used provided that
the relationship between the full-length and short-length test st
...