ISO/TR 21136:2017

Timber structures — Vibration performance criteria for timber floors

ISO/TR 21136:2017 provides a review of key floor vibration design criteria (human acceptability criterion using calculated parameters) developed in research studies on timber floor around the world over the last 30 years. Associated design methods are provided in the Annexes. The methods proposed in this report are intended to be used for establishing human acceptability criteria for timber floor vibrations induced by walking activities. The proposed methods are applicable to the following timber floors: lightweight floors made of timber joists and thin wood panel subfloor, heavy timber floors made of heavy timber beams with a thick timber deck, and mass timber slab floors such as cross laminated timber (CLT), nail laminated timber (NLT) and glued laminated timber.

Structures en bois — Critères de performance vibratoire pour les planchers en bois

General Information

• Status: Published
• Publication Date: 12-Apr-2017
• ICS: 91.080.20 - Timber structures
• Technical Committee: ISO/TC 165 - Timber structures
• Drafting Committee: ISO/TC 165/WG 7 - Connections and assemblies
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 14-May-2021

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 21136
First edition
2017-04
Timber structures — Vibration
performance criteria for timber floors
Structures en bois — Critères de performance vibratoire pour les
planchers en bois
Reference number
ISO/TR 21136:2017(E)
©
ISO 2017

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ISO/TR 21136:2017(E)

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ISO/TR 21136:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Background . 1
5 Mechanism of timber floor vibration response to human normal walking actions.6
5.1 Characteristics of footstep force . 6
5.2 Responses of timber floors to the footstep force . 7
5.3 Parameters correlated to human acceptability of timber floor vibration. 8
5.4 General forms of human acceptability criterion of timber floor vibration . 8
6 Comprehensive procedure using a large database . 8
6.1 General . 8
6.2 Subjective evaluation procedure and questionnaire for laboratory floors . 9
6.3 Subjective evaluation procedure and questionnaire for field timber floors .10
6.4 Statistical analysis to derive human acceptability criterion from timber floor
vibration database .10
6.5 V erification of the criterion derived using a new database .11
7 Simplified procedure using a small database .11
Annex A (informative) Subjective evaluation questionnaire for laboratory floors used by
FPInnovations, Canada .12
Annex B (informative) An example of the application of the comprehensive procedure to
establish acceptability criterion for light frame timber floors in Canada .14
Annex C (informative) Example of application of the simplified procedure to establish
acceptability criterion (design criterion) for cross laminated timber (CLT) floors
in Canada .19
Annex D (informative) EC5 design criteria and calculation methods for criterion parameters .24
Annex E (informative) Hamm et al. design criteria and calculation methods for
criterion parameters .26
Bibliography .28
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ISO/TR 21136:2017(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
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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
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details 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.
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ISO/TR 21136:2017(E)

Introduction
Timber floors are known to be prone to producing high level of vibration caused by human activities
due to the light-weight nature of these systems. Given that human tolerance to floor vibration is
rather subjective and could be influenced by a number of vibration response parameters, such as
frequency content, peak vibration level (e.g. displacement, velocity and acceleration), mean vibration
level and damping, there has not been any general agreement among researchers and code writers on
the human acceptability criteria for design against objectionable floor vibration. With the advent of
engineered timber floor products, it is necessary to provide generic guidelines on the establishment of
human acceptability criteria for specific floor construction product. With the appropriate calculation
procedures for response parameters, such human acceptability criteria can then be used by designers
to predict floor vibration performance at the design stage. Such human acceptability criteria can also
be used to evaluate floor vibration performance in the field or laboratory testing according to the test
[1]
procedures given in ISO 18324. To differentiate between these two types of human acceptability
criteria, in this report, the criterion uses the measured parameters is called “Performance criterion”,
and that uses the calculated parameters is called “Design criterion”.
Given that human tolerance levels to floor vibration may vary between countries due to cultural
differences, floor construction products, and construction practices, it is felt that floor vibration
performance criterion developed in one region may not be directly applicable to the others.
Consequently it is the view of the ISO/TC 165 that a more fruitful approach is to provide guideline
methods to individual countries and regions to develop their own human acceptability criterion. This is
the main purpose of this document.
The methods reviewed in this document are intended to be used for establishing human acceptability
criteria using the parameters that have been found to correlate well with human acceptability of
timber floor systems. Generally a study is required that includes measurement or calculation of these
parameters and a human subjective evaluation rating of the vibration performance of a number of floor
systems in the field or in the laboratory, and subsequent statistical analyses to determine the best human
acceptability criterion function. The proposed methods have been published in numerous research
reports and peer-reviewed papers based on significant research efforts over the last four decades. They
also have been validated by measurements and feedbacks on numerous field timber floors.
The potential floor vibration response parameters include fundamental natural frequency, static
deflection under a concentrated load, peak-velocity, peak-acceleration, and root-mean-square
acceleration. These parameters can be measured in the laboratory or in the field, and also can be
calculated.
A comprehensive procedure is provided to establish human acceptability criteria using the measured
or calculated response parameters and the subjective evaluation rating through advanced statistical
analysis of a large database of timber floors. If the categorical variables of the subjective rating
have more than two performance levels, a “Discriminant analysis” shall be used, while a “Logistic
regression” can be used for the case of two performance levels. A simplified procedure is also provided
for establishing human acceptability criteria using a relatively small database.
Annex A provides an example of questionnaire that was used in laboratory studies in Canada. Annex B
demonstrates the application of the comprehensive procedure to establish a performance criterion for
timber floors used in Canada (human acceptability criterion using measured criterion parameters).
Annex C shows the application of the simplified procedure to establish a design criterion (human
acceptability criterion using calculated parameters,) and the calculation formulae for the criterion
parameters for cross laminated timber (CLT) floors used in Canada. Annex D presents the design criteria
[5]
and the calculation formulae for the criterion parameters in EuroCode 5 (EC5). Annex E presents the
[8]
design criteria and the calculation formulae for the criterion parameters proposed by Hamm et al .
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TECHNICAL REPORT ISO/TR 21136:2017(E)
Timber structures — Vibration performance criteria for
timber floors
1 Scope
This document provides a review of key floor vibration design criteria (human acceptability criterion
using calculated parameters) developed in research studies on timber floor around the world over the
last 30 years. Associated design methods are provided in the Annexes. The methods proposed in this
report are intended to be used for establishing human acceptability criteria for timber floor vibrations
induced by walking activities.
The proposed methods are applicable to the following timber floors: lightweight floors made of timber
joists and thin wood panel subfloor, heavy timber floors made of heavy timber beams with a thick
timber deck, and mass timber slab floors such as cross laminated timber (CLT), nail laminated timber
(NLT) and glued laminated timber.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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
4 Background
A substantial amount of research efforts has been undertaken to develop human acceptability criterion
for timber floor vibration control. Table 1 summarizes the most influential human acceptability criteria
using calculated parameters, which is simply called “Design criteria”. Table 1 also summarizes the
method used to develop the criterion, and the pros and cons of the criterion.
The Canadian National Building Code (NBC) presents provisions to control lumber joist floor vibration
[2]
through limiting the floor deflection under a 1 kN load, see Table 1. The NBC design criterion
[3]
was developed based on research efforts by FPInnovations scientists between 1970s and 1990s.
Across Canada survey was conducted in 1970s. The survey included field testing and interview of the
occupants using a comprehensive questionnaire. The questionnaire was developed in conjunction with
statisticians and psychologist. A conversational approach was used so that the interview did not alert
the occupants to the suspicion that the floor performance was likely to be of interest in the survey. The
questionnaire included the following factors:
— previous experience of the evaluator on performance of floor,
— mechanical vibration of the floor by his/her own sensing and caused by others’ walking action,
— noise generated by the floor movement,
— visual effect caused by floor vibration.
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A prompted approach was used by providing the occupant with a list of clues, as given in the
questionnaire for three floor motion effects – hearing, feeling and seeing, and their potential causes.
For each response, the interviewee can choose up to three causes. This approach ensures that the
evaluator’s response is not influenced by his/her awareness that the performance of his/her property
is being assessed, and that there is consistency across all units. The detailed questionnaire consisting
[3]
of 57 questions can be found in .
The interview information obtained in each house included:
a) country of adult life of those born outside North America,
b) ethnic origin of ancestor,
c) place of birth,
d) size of childhood community,
e) number of adults living in the home,
f) respondent has children in certain age groups,
g) distribution of male respondents by age group and cities surveyed,
h) ownership status,
i) original owner,
j) total family income,
k) monthly rent,
l) cost of house,
m) age of property,
n) year that property was bought or built,
o) type of housing lived in most of life,
p) last previous housing type lived in,
q) present housing type,
r) satisfaction with neighbourhood,
s) satisfaction with house,
t) satisfaction (parts of the house),
u) summary of number of dislikes about components of house,
v) when floor motion, squeak, slope, cold, and noise was first noticed,
w) occupant’s acceptability ratings of floors for which squeaking, slope, coldness, or noisiness was
noted (unprompted responses),
x) estimated weight of respondent
y) respondent’s gait
z) condition of property.
More than 600 field single-family floors were studied. The floors were built with lumber joists with
finish and subfloor, with or without lateral elements and with or without gypsum board ceiling. The
finish materials included hardwood flooring, carpet and tile. The subfloor materials included lumber
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plank and plywood. The lateral elements included bridging, blocking and strapping. The nails or nail
and glue connections were used to attach the subfloor to joists. The ceilings were made of gypsum
boards attached to the bottom of the lumber without use of resilient channels.
Field tests were also conducted on the selected houses to measure the point-load static deflections
and the peak dynamic displacement responses to an impulse. The objective of the field tests was to
verify the computational models to predict the floor static deflection and the peak displacement
response of the floor. Finally the calculated 1 kN static deflection was selected as the parameter for the
design criterion. “Discriminant analysis” software was used to derive the design criterion. The design
criterion along with the calculation formula to estimate the floor deflection has been adapted in NBC
[2]
since 1990 .
This NBC 1 kN static deflection design criterion is simple and reliable for the types of floor systems
studied. Besides the joist and subfloor stiffness, it also accounts for the contributions of stiffening
features, including use of glue, bridging, blocking, strapping, and gypsum board ceiling. However, floor
construction products and practices have changed in Canada since the 1980s. For example multi-family
construction and floors with heavy concrete topping are now more common.
[4]
In the USA Dolan at al proposed a design criterion of floor fundamental natural frequency of 15 Hz
for unoccupied floors, and 14 Hz for occupied floors to control floor vibration. The design criterion was
developed through testing of 86 laboratory and field timber floors. The study included measurement
of the fundamental natural frequencies of the floors, and subjective evaluation. The floor vibration
performance was judged by several researchers while standing on the floor during a heel-drop test.
The evaluator would then feel the response and indicate whether he/she felt that the vibration was
annoying (unacceptable), marginal, or acceptable. The floors were made of lumber or engineered wood
joists and a subfloor of plywood or oriented strandboard (OSB). A formula was provided to calculate the
fundamental natural frequencies of these floors. The formula accounts for only the mass and stiffness
of the joists and the subfloor. Parameter of “Relative power” was used along with the measured
fundamental natural frequency to separate the unaccepted floors from accepted floors. Relative power
was defined as a measure of how much energy is in the system, e.g. fundamental frequency times
displacement. The 14/15 Hz criterion is simple, and works for certain span-range floors, but it may be
conservative for long span floors and floors with a heavy topping.
[5]
EuroCode-5 (EC5) requires the checking of three design criteria for timber floor vibration control.
The three criteria set limits on the minimum fundamental natural frequency of 8 Hz, the maximum
deflection to 1 kN concentrated load, and the peak velocity to 1 Ns impulse. The criteria are provided
in Table 1. Annex D provides the criteria and the formulae to calculate the frequency and peak velocity
in details. EC5 does not specify how to calculate the 1 kN static deflection, and the stiffness of the floor
along floor span and across floor width directions. Therefore, it is unknown whether the topping,
ceiling, and the vibration enhancements are included in the criteria. It was understood that the EC5
[6] [7]
design criteria were evolved from the original work by Ohlsson and . Limited information was
[6]
found on the approach of the development of the design criterion. It was briefly mentioned in that
the poor vibration performance of timber floors reported by the designers and owners of houses
were investigated. The feedback was used to set up the criterion limits. It is known that subsequently
European and New Zealand researchers conducted laboratory and field tests to evaluate Ohlsson’s
work, in an attempt to modify the EC5 criteria. It should be noted that calculation of the peak velocity
requires assumptions of floor width and damping ratio. Assumptions also are needed to decide the
1 kN concentrated load and the peak velocity limits.
[8]
Recently Hamm et al proposed a design method to control vibration for a broad range of timber
floors. The design criteria were set for two-level performance: 1) higher demand performance floors
and 2) lower demand performance floors. The design criteria consist of three single variable criterion:
1) deflection under a 2 kN concentrated load less than 0.5 mm for higher demand and 1.0 mm for
lower demand;
2) fundamental natural frequency larger than 8 Hz for higher demand, and 6 Hz for lower demand; and
2
3) for frequency less than 8 Hz floors, the maximum acceleration less than 0.05 m/s for higher
2
demand and 0.1 m/s for lower demand.
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Formulae were provided to calculate the static deflection, fundamental natural frequency and
maximum acceleration. Table 1 b briefly summarizes the criteria. Annex E presents the design criteria
and the calculation formulae. The criteria were developed using floors in existing buildings, including
57 timber beam floors, 42 with heavy screed, 8 with light screed and 7 without any floor finish, 16
timber-concrete composite floors and 38 massive timber floors, 20 of them with heavy screed and 7
with light screed and 11 without any finish. The formulae to calculate the floor stiffness along and
across span directions for the broad range of timber floors studied are not given. The limit for each
criterion was identified by plotting the data on an x-y plane where x-axis is the calculated deflection,
or frequency, or maximum acceleration, and the y-axis is the subjective rating (categorical variable).
The performance limits were manually identified. The calculation of the maximum acceleration and
deflection requires knowledge of damping ratio, and is iterative.
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Table 1 — A summary of floor vibration design criteria for timber floors
Criterion Design criterion Method of Pros and cons Reference
parameters development of the
criterion and database
d for span < 3 m: — Field survey and For timber joisted National
1kN
d ≤ 2 mm, subjective evaluation floors without Building Code
1kN
where d
1kN
topping: of Canada
for span ≥ 3 m: — More than 600
(NBC)[1]
= deflection under a
1.3
d ≤ 8/span lumber joisted single-family — simple
1kN
1 kN load in mm
floors in Canada
— reliable
— Approximate formula
For timber joisted
to calculate the 1 kN static
floors with
deflection
topping:
— Use commercial
— may be liberal
advanced statistical
software “Discriminant
analysis” to derive the de-
sign criterion
f for unoccupied — Testing and For timber joisted Dolan et al[4]
1
floors: subjective evaluation of floors without
where f =
1
86 lumber and engineered topping:
fundamental f ≥15 Hz
1
wood joist floors
natural frequency — simple
for occupied floors:
in Hz — Approximate
— for certain span
formula to calculate the
f ≥14 Hz
1
range
fundamental natural
frequency
For timber joisted
floors with
topping:
— may be
conservative
f , d and V 1) d ≤ a — Limited poor — Require EC5[5]
1 1kN peak 1kN
performance field floors judgement by users
where V =peak 2) f ≥ 8 Hz
peak 1
to select certain
velocity due to unit — Theoretical reasoning
(f ξ −1)
parameters
3) Vpeak ≤ b
1
2
impulse in m/(Ns )
— Approximate
where — Complicated
formulae to calculate the
a =0.5-4mm, fundamental — Involve iteration
natural frequency and
— Formulae not pro-
b=50-150,
peak-velocity
vided to
“a” and ”b” need to
calculate deflection
be determined by
and floor stiffness
user based on the
in span and width
decision of perfor-
direction
mance level
f , d and a x For higher — Field study of 95 — Require Hamm et al[8]
1 2kN ma
demand: timber floors judgement by users
where d
2kN
to select certain
1) d ≤ 0.5 mm — Formulae provided to
2kN
= deflection under a parameters
calculate static deflection,
2 kN load in mm 2) f ≥ 8 Hz
1
fundamental natural — Complicated
2
frequency and
where a = 3) a ≤ 0.05 m/s
max max
— Involve iteration
maximum acceleration
Maximum if f ≤ 8 Hz
1
2
acceleration in m/s — Formulae not
For lower
provided to
demand:
calculate floor
1) d ≤ 1.0 mm stiffness in span and
2kN
width direction
2) f ≥ 8 Hz
1
2
3) a ≤ 0.1 m/s if
max
f ≤ 8 Hz
1
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5 Mechanism of timber floor vibration response to human normal walking actions
5.1 Characteristics of footstep force
[6,7,9-12]
Researchers have found that the footstep force generated by walking comprises two
components. One component is a short duration impact force induced by the heel of each footstep on
the floor surface, as illustrated in Figure 1. The duration of the heel impact varies from about 30 ms to
100 ms depending on the conditions and the materials of the two contact surfaces (the floor and the
shoes worn by the person walking), and on the weight and gait of the person. The second component is
the walking rate, a continuous series of footsteps consisting of a wave train of harmonics, at multiples
of about 2 Hz, Figure 2.
Key
t time (milliseconds)
F force (pounds)
Figure 1 — Forcing function based on an average of five heel drop forces on a concrete
[9]
surface
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Key
f frequency (Hz)
a magnitude
b harmonic
c Fourier amplitude spectrum
Figure 2 — Fourier transform spectrum of the loading time history of normal walking action by
[10]
one person
5.2 Responses of timber floors to the footstep force
How a floor responds to the footstep excitation described above depends on the floor’s inherent
properties such as mass, stiffness, and capacity to dissipate the excitation energy (i.e. damping of
the floor system.) The two components in the walking excitation can initiate two types of vibrations,
depending on the inherent properties of the floor and walking rate. The two types of vibrations are
transient vibration and resonance.
If the fundamental natural frequency of a floor is above 8 Hz and is far above the footstep frequency
(walking rate) and its predominate harmonics, then the vibration induced by the footstep forces is most
likely dominated by a transient response caused by the individual heel impact force from each footstep.
The transient vibration decays quickly, and takes place at multiples of the footstep frequency. The peak
values of a transient vibration are mainly governed by the stiffness and mass of the floor system.
On the other hand, if the floor fundamental natural frequency is below 8 Hz, and is in the range of
the footstep frequency and its predominate harmonics, then the floor most likely will resonate with
one of the harmonics, and the vibration will be constantly maintained by the action of the walking
excitation. The magnitude of the resonance is largely dependent on the damping ratio of the floor
system. Furthermore, if the floor fundamental natural frequency is around 2 Hz, which is close to the
footstep frequency, the magnitude of the resonance will be high because, as shown in Figure 2, most of
the energy in the walking excitation is concentrated at the walking frequency.
The fundamental natural frequency of a floor is largely governed by the system stiffness in the major
stiffness direction and its mass. It has been found that for the majority of the satisfied timber floors,
their fundamental natural frequency is above 8 Hz. Therefore, the responses of most of timber floors to
normal walking activities are of a transient nature.
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5.3 Parameters correlated to human acceptability of timber floor vibration
In general, humans are more tolerant to short duration vibration (e.g. transient vibration) than the longer
[3,4,6-8,13-17]
lasting resonance. Researchers have found that the vibration performance parameters of
timber floors such as floor static deflection, natural frequency, peak-velocity, pea
...