00078 Lin Hu - Timber Design Society

3 RESULTS
3.1 KEY CONSTRUCTION AND DESIGN
PARAMETER
Based on data analysis, it was found that the
combination of fundamental natural frequency with 1 kN
static deflection, or with acceleration, or with velocity
was well correlated to human perception. It is
understood that the fundamental natural frequency is
mainly controlled by the longitudinal stiffness and the
mass, while the 1 kN static deflection is determined by
the entire stiffness of the CLT floor in both the
longitudinal and lateral directions. The acceleration or
velocity is determined by the excitation, the entire
stiffness and by damping ratio. It has been wellrecognized
that determining the damping ratio accurately
and to a certain reliability level of is not easy.
Reproducibility is another issue. Besides, damping is
largely controlled by the floor constructions details such
as the joints, connections, and support conditions, and
the non-structural components such as potions, flooring,
toppings, insulation materials, furniture, etc. Moreover,
the modal test results showed that, for the bare CLT
floors tested, the measured damping ratio did not vary
from one assembly to another as it was quit constant
with a value of around 1%.
Based on the laboratory study results, it has been found
that in meeting the safety requirements for the supports
and joints, the vibration performance of CLT floors were
largely controlled by the CLT stiffness along the
longitudinal direction and by the mass. The type of joints
between the CLT panels did not significantly affect the
measured fundamental natural frequencies, the 1 kN
static deflections, and the subjective ratings. Therefore,
it was decided to use the stiffness in the longitudinal
direction and the mass as the key parameters in the
design method to control CLT floor vibrations through a
combination of fundamental natural frequency and 1 kN
static deflection.
3.2 PROPOSED DESIGN METHOD
The proposed design method to control CLT floor
vibrations consists of a design criterion and the relevant
equations to calculate the design parameters.
3.2.1 Scope
At this point, the scope of the proposed design method to
control vibrations of CLT floors covers the following
1. bare floors with finishing, partitions and
furniture, but without heavy topping,
2. vibrations-induced by normal walking,
3. well-supported floors,
4. well-jointed CLT panels, and
5. inclusion of the self weight of CLT panels only
(i.e. without live load).
cover various types of toppings and ceilings, and other
floor design options.
3.2.2 Advantages
The proposed design method is focused on target
features, which include, among others
1. simple for hand calculation,
2. user-friendly,
3. mechanics-based using the design values CLT
panels available in producer’s specification,
4. reliable to prevent CLT floors from excessive
vibrations induced by normal walking.
3.2.3 Design Criterion
Based on the understanding of the fundamentals of floor
vibrations and the special features of CLT floor
vibrations, and following the laboratory test results, a
proposed simple design criterion using fundamental
natural frequency and 1 kN static deflection of a simple
1-m wide CLT panel as design parameters has been
developed.
The design criterion is expressed in Equation (1).
f
d
0.7
13.0
Or
1.43
f
d
39
where f = fundamental natural frequency calculated
using Equation (2) in Hz, and d = 1 kN static deflection
calculated using Equation (3) in mm.
3.2.4 Equations to Calculate the Design Parameters
f
3.142
2
2l
EI
1m
eff
A
(1)
(2)
where, f = fundamental natural frequency of 1m CLT
panel simply supported in Hz, l= CLT floor span in m,
EI 1
m
eff
= effective apparent stiffness in the span direction
which is published by the producers for 1m wide panel
in N-m 2 , = density of CLT in kg/m 3 , and A = crosssection
area of 1-m wide CLT panel, i.e. thickness*1m
width in m 2 . The static deflection under 1 kN load can be
calculated using Equation (3) below.
3
1000Pl
(3)
d
1m
48EI eff
where, d = static deflection at mid-span of the 1m wide
simply supported CLT panel under 1 kN load in mm,
and P = 1000 N.
However, because of the mechanics-based feature, it is
possible to expand its scope to include other construction
details. A study has been planned to extend the scope to