ISO 24323:2023

INTERNATIONAL ISO
STANDARD 24323
First edition
2023-12
Timber structures — Design method
for vibrational serviceability of timber
floors
Structures en bois – Méthode de dimensionnement aux états limites de
service pour la vibration des planchers bois
Reference number
© ISO 2023
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Baseline timber floor vibrational serviceability design criterion .1
5 General models for calculating f and d . 2
1 kN
6 Simplified calculation procedures for light-frame timber joisted floors .4
6.1 Floor construction . 4
6.2 Calculation of first natural frequency and static deflection under a 1 kN load at
floor centre . 4
6.3 Effective composite bending stiffness, D . 5
ef
6.4 Transverse system stiffness factor, K . 6
t
7 Simplified calculation procedures for mass timber floors . 7
7.1 Floor construction . 7
7.2 Calculation of first natural frequency and static deflection under a 1 kN load at
floor centre . 7
8 Design values of floor components .8
Annex A (informative) Coupled criteria for timber floor vibrational serviceability design .9
Annex B (informative) Decoupled criteria for timber floor vibrational serviceability design .12
Annex C (informative) Explanatory notes .14
Bibliography .15
iii
Foreword
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iv
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. As a result, it is critical that the timber floor design
process takes into account vibrational serviceability. In the past, static deflection check indirectly
provided some degree of control, but it is not a complete solution to the vibration problem. Two ISO
publications have been developed over the last few years under the auspices of ISO/TC 165. The first
[1]
publication, ISO 18324 , is intended for testing of floor response parameters for the purpose of
[2]
evaluating vibrational serviceability of the floor. The second publication is ISO/TR 21136 , which
provides guidelines for developing floor vibration performance criterion.
Annexes A and B recommend limit values for coupled and decoupled criteria respectively. The
calculation equations presented herein are based on the assumption that the floor system has a single
span and simple support conditions.
This document provides flexibility for individual jurisdictions to develop their own performance levels
[2]
within the same performance criterion framework using the procedure described in ISO/TR 21136 ,
and for using other models to calculate the fundamental natural frequency and 1 kN static deflection if
desired.
v
INTERNATIONAL STANDARD ISO 24323:2023(E)
Timber structures — Design method for vibrational
serviceability of timber floors
1 Scope
The design method provided in this document addresses vibration induced by walking action of
occupants and covers the following timber floor systems:
a) Light frame floors built with timber joists spaced at a distance of no more than 610 mm with a
layer of structural wood-based subfloor that is connected to the joists using mechanical fasteners
or adhesive. The area density of a bare light frame floors without a screed (topping) and ceiling is
not greater than 25 kg/m . Figure 1 shows such a light frame floor.
b) Mass timber floors built with mass timber panels such as cross laminated timber (CLT).
This document consists of three elements:
a) a baseline vibrational serviceability design criterion for timber floors using fundamental natural
frequency and 1 kN static point load deflection as the design parameters including two types of
design criteria, coupled and decoupled criteria;
b) equations for calculating the design parameters;
c) guidelines for the design values of the physical and mechanical properties of floor components.
The design method is based on the assumption that the floor system has a single span and simple
support conditions.
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 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/
4 Baseline timber floor vibrational serviceability design criterion
Vibrational serviceability of a timber floor shall be evaluated by comparing its fundamental natural
frequency and the static deflection at floor centre under a point load of 1 kN applied at the same
location, with the criteria stated in either coupled criteria, see Formula (1), or decoupled criteria, see
Formulae (2) to (4). It is the users’ decision or preference to select the appropriate criteria that meet
their needs.
a) Coupled criteria.
Using the coupled criteria, the vibration performance a floor is considered acceptable if the condition
given by Formula (1) is satisfied:
X
f
≥Z (1)
Y
d
1 kN
where
f
is the fundamental natural frequency, Hz;
d
is the 1 kN static point load deflection at floor centre, mm;
1 kN
[2]
X, Y and Z are constants determined from subjective evaluation study as per ISO/TR 21136 .
[2]
It is recommended to perform a subjective evaluation study as per ISO/TR 21136 on at least two
floors to define suitable values for X, Y, Z for individual country. In the absence of any relevant data for
specific country or region, X = 1,56, Y = 1 and Z = 112,20 (see Annex A).
b) Decoupled criteria.
Using the decoupled criteria, Formulae (2) to (4), the vibration performance of a floor is considered
acceptable if the fundamental natural frequency, static deflection under a 1 kN load at floor centre and
the velocity meet the respective conditions shown below:
fC≥ (2)
dC≤ (3)
12kN
vC≤ (4)
where C , C and C are constants determined from a subjective evaluation study as per
1 2 3
[2]
ISO/TR 21136 . In the absence of any relevant data for specific country or region, C = 8 Hz may be
used (see Annex B). Annex B provides Formulae (B1) and (B2) to calculate C and C for residential
2 3
floors, respectively.
5 General models for calculating f and d
1 kN
The static deflection under a 1 kN point load at floor centre, d , and the first natural frequency, f, of a
1 kN
[3]
timber floor simply supported on all four sides can be calculated using orthotropic plate models . The
static deflection parameter in mm, d , can be calculated using the series-type Formula (5) shown
1 kN
[4]
below :
41× 01
d = (5)
1 kN ∑∑
4 42 4
abπ m mn n
     
mn==13,,51,,35
D +4 D + D
     
XXYYY
a ab b
     
where D is the equivalent system flexural rigidity in the span direction, in Nm as defined by Formula (6):
X
hE
X
D = (6)
X
12()1−νν
XY YX
D is the equivalent system flexural rigidity in the across-span direction, in Nm as defined by
Y
Formula (7):
hE
Y
D = (7)
Y
12()1−νν
XY YX
D is the equivalent system shear rigidity, in Nm as defined by Formula (8):
XY
hG ν D
XY YX X
D =+ (8)
XY
12 2
where
E is the modulus of elasticity of plate in x direction (span) in N/m ;
X
E is the modulus of elasticity of plate in y direction (across-span) in N/m ;
Y
G is the in-plane shear modulus of plate in N/m
XY
h is the plate thickness in m
ν is the Poisson’s ratio with stress applied in x direction and strain measured in y direction
XY
ν is the Poisson’s ratio with stress applied in y direction and strain measured in x direction
YX
a is the span of floor in m;
b is the width of floor in m.
The fundamental natural frequency, f, in Hz can be calculated from the following Formula (9):
42 4
π 1 11
     
fD= +4D +D (9)
     
XXYY
a ab b
2 ρ
where ρ is the mass per unit floor area, kg/m .
For light wood frame joisted floor systems, the simplified method presented in Clause 6 can be used.
For mass timber panel floor systems, the simplified method presented in Clause 7 can be used.
NOTE See Annex C for background on orthotropic plate models.
6 Simplified calculation procedures for light-frame timber joisted floors
6.1 Floor construction
Figure 1 shows the construction details of the type of light-frame timber floor system addressed by this
simplified method.
Key
A topping layer
B subfloor panel
C floor joist
Figure 1 — Applicable light-frame timber floor system
6.2 Calculation of first natural frequency and static deflection under a 1 kN load at floor
centre
The fundamental natural frequency, f, in Hz, of a floor shown in Figure 1 can be calculated using the
[5][6]
following Formula (10) :
D
π
ef
f = (10)
m
2l l
The static deflection at floor centre under a concentrated load of 1 kN applied at the same location, d ,
1kN
[3][4]
in millimetres, can be calculated using the following Formula (11) :
1 000Pl
dK= (11)
1 kN t
48D
ef
where
l is the floor span in m;
P is the point load of 1 000 N;
D is the effective composite bending stiffness of the joists in the span direction in Nm (in
ef
[7]
6.3 );
[7]
K is the transverse system stiffness factor to account for the two-way action of a floor (in 6.4 );
t
m is the linear mass of the composite cross section of the floor that accounts for the joist,
l
subfloor and topping in kg/m, calculated as follows:

mm=+ρρtb + tb (12)
lJ ss 11cc
where
m is the mass of joist per unit length in kg/m;
J
b is the joist spacing in m;
ρ
is the density of topping in kg/m ;
c
ρ is the density of subfloor panel in kg/m ;
s
t is the thickness of topping in m;
c
t is the thickness of subfloor panel in m.
s
6.3 Effective composite bending stiffness, D
ef
The effective composite bending stiffness, D , in Nm of the joist can be calculated using Formula (13),
ef
which accounts for the contribution of subfloor and, if present, the topping layer
DD=+Bh −Ay (13)
ef u 11
where
DD=+bD +D (14)
()
uj 1 sc⊥
where
D is the apparent bending stiffness of bare joist in Nm ;
j
b is the joist spacing in m;
D is the bending stiffness of 1 m wide subfloor panel in span direction in Nm;
s⊥
D
c is the bending stiffness of a 1 m wide topping in Nm. D equal Et /12 where E is the mod-
c cc c
ulus of elasticity of topping in N/m and t is the topping thickness in m.
c
bB
B = (15)
bB
11+ 0
sL
where
B is the
...