ISO/TR 21141:2022
(Main)Timber structures — Timber connections and assemblies — Determination of yield and ultimate characteristics and ductility from test data
Timber structures — Timber connections and assemblies — Determination of yield and ultimate characteristics and ductility from test data
The purpose of this document is to extract the methods for determining the yield and ultimate characteristics and ductility of joints and assemblies from test data by reviewing existing standards in Europe, North America and Far East Asia and to provide the basic data for unifying the evaluation methods of parameters by clarifying their similarities and differences. These parameters are applied for determining the seismic performance of timber structures. This document deals with the method for determining the mechanical properties of individual joints and assemblies, and it does not refer to the seismic performance of the entire structure.
Structures en bois — Assemblages et composants bois — Détermination des caractéristiques limites et ultimes et de la ductilité à partir des données d’essai
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 21141
First edition
2022-05
Timber structures — Timber
connections and assemblies —
Determination of yield and ultimate
characteristics and ductility from test
data
Structures en bois — Assemblages et composants bois —
Détermination des caractéristiques limites et ultimes et de la ductilité
à partir des données d’essai
Reference number
© ISO 2022
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ii
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 Determination of envelope curves.3
6 Determination of elastic stiffness . 3
7 Determination of yield point . 5
7.1 Determination of yield load . 5
7.2 Determination of yield displacement . 7
8 Determination of ultimate limit state . 7
8.1 Ultimate (failure) displacement . 7
8.2 Ultimate (failure) load . 7
8.3 Equivalent energy elastic-plastic load and stiffness. 8
9 Determination of ductility factor . 9
Annex A (informative) Examples of modelling of envelope curves.10
Annex B (informative) Examples of test data .12
Annex C (informative) Impairment of strength and energy dissipation .36
Bibliography .38
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 165, Timber structures.
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iv
Introduction
Timber shows generally brittle failure in tension and bending. This characteristic of wood may cause
serious damage to buildings due to the lack of energy dissipation during an earthquake. To avoid such
damage, it is expected that the joints connecting wooden members dissipate seismic energy instead
of the members themselves. Ductility of a structure is one of the most important factors in dissipating
seismic energy. In this technical report, the definitions of yield point, ultimate characteristics and
ductility factor used in various test standards are reviewed and methods of determining these
characteristics from quasi-static and reversed-cyclic loading test data are compared.
Better fits to envelope curves derived from testing, such as more detailed piecewise linearization
are permissible, and indeed desirable for whole building design. The derived load-deflection inputs
to structural analysis programs of the various structural elements are only applicable to the case of
assessing the maximum connection forces under earthquake loading and provide no guarantee that a
structure will remain stable beyond the ultimate strength of the system.
v
TECHNICAL REPORT ISO/TR 21141:2022(E)
Timber structures — Timber connections and assemblies
— Determination of yield and ultimate characteristics and
ductility from test data
1 Scope
The purpose of this document is to extract the methods for determining the yield and ultimate
characteristics and ductility of joints and assemblies from test data by reviewing existing standards
in Europe, North America and Far East Asia and to provide the basic data for unifying the evaluation
methods of parameters by clarifying their similarities and differences.
These parameters are applied for determining the seismic performance of timber structures. This
document deals with the method for determining the mechanical properties of individual joints and
assemblies, and it does not refer to the seismic performance of the entire structure.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
envelope curve
locus of extremities of the load-displacement hysteresis loops, either obtained separately for the
positive and negative loading directions, or obtained by averaging the absolute values of load and
displacement of the corresponding positive and negative envelope points for each cycle in the case of a
reversed cyclic loading test (see Clause 5)
3.2
stiffness
K
e
resistance to deformation of a specimen in the elastic range, which can be expressed as a slope measured
by the ratio of the resisted load, F , to the corresponding displacement, V (see Clause 6)
1 1
3.3
elastic range
stress range in which a material, upon unloading, will recover the deformation caused by the application
of a stress or force
3.4
yield point
point at which a joint or an assembly begins to deform plastically
3.5
yield load and displacement
F , V
y y
load and displacement corresponding to the yield point (3.4) (see 7.1)
3.6
maximum load
F
max
maximum value of the load recorded in a quasi-static test or the maximum value of the load on the
average envelope curve (3.1) in a reversed-cyclic test or the absolute maximum values of the load
recorded in positive and negative directions
3.7
ultimate limit state
failure limit state
state at which a joint or an assembly undergoes a sudden load drop or the load decreases gradually to
80 % of the maximum load (3.6), F , or an excessive deformation (displacement or rotation) occurs
max
(see 8.1 and 8.2)
3.8
ultimate displacement
V
u
failure displacement
displacement corresponding to the ultimate limit state (3.7) (see 8.1).
3.9
equivalent energy elastic-plastic curve
EEEP
ideal elastic-plastic curve circumscribing an area equal to the area enclosed by the envelope curve (3.1)
between the origin, the ultimate displacement (3.8), V , and the displacement axis (see 8.3)
u
3.10
equivalent energy elastic-plastic load
F
eeep
load corresponding to the upper limit of the equivalent energy elastic-plastic curve, EEEP, (3.9)
3.11
ductility
ability of joints or assemblies to undergo large amplitude displacement in the plastic range without a
substantial reduction of strength
3.12
ductility factor
μ
ratio between ultimate displacement (3.8), V , and yield displacement, V , (see Clause 9).
u y
3.13
equivalent energy elastic-plastic ductility factor
μ
eeep
ratio between ultimate displacement (3.8), V , and EEEP displacement, V , (see Clause 9).
u eeep
4 Symbols and abbreviated terms
The following symbols and units apply.
F , F any load within the elastic range of the curve, expressed in Newtons
1 2
F equivalent energy elastic-plastic (EEEP) load, expressed in Newtons
eeep
F equivalent energy bilinear ultimate load, expressed in Newtons
eebl
F maximum load, expressed in Newtons
max
F yield load, expressed in Newtons
y
F ultimate (failure) load, expressed in Newtons
u
K elastic stiffness, expressed in Newtons per millimetre
e
K equivalent energy elastic-plastic stiffness, expressed in Newtons per millimetre
eeep
V , V displacement corresponding to F , F within the elastic range, expressed in millimetres
1 2 1 2
V equivalent energy elastic-plastic yield displacement, expressed in millimetres
eeep
V yield displacement, expressed in millimetres
y
V ultimate (failure) displacement, expressed in millimetres
u
μ ductility factor
μ equivalent energy elastic-plastic ductility factor
eeep
5 Determination of envelope curves
The initial envelope curve for the reversed-cyclic tests is established by connecting the peak loads and/
or the peak displacements from the first cycle of each phase of the cyclic loading, whichever better
represents the backbone shape of the hysteretic response. The points on the hysteresis loops where the
absolute value of the displacement at the peak load is less than that in the previous phase are replaced
with points that better represent the hysteretic response.
The envelope curves for the second and subsequent reversed cycles of each phase may be also
established if necessary.
If the load-displacement relation is (point) symmetric, envelope curve may be obtained by averaging the
absolute values of load and displacement of the corresponding positive and negative envelope points for
each cycle (see examples in B.1, B.5, B.6 and B.7).
For joints and assemblies producing asymmetric response, the positive and negative envelopes are
analysed separately (see examples B.2, B.3, and B.4).
NOTE In Annex B, positive and negative envelope curves are obtained separately if the values of maximum
(peak) load or displacement in the positive hysteresis loops in each phase up to the ultimate displacement, V ,
u
differ more than 20 % from the absolute value of those obtained from the corresponding negative hysteresis
loops.
6 Determ
...
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