00078 Lin Hu - Timber Design Society

measurements were taken at each loading location to
ensure that stable results were obtained. The average of
three sets of the deflection profiles were used to plot the
deflection profile of the test floor under the person’s
weight. The deflection measurements were normalized
to 1 kN load.
to determine the natural frequencies, modal damping
ratios and mode shapes.
Figure 9: Modal test on a CLT floor specimen
Figure 7: Static deflection measurements using two
deflection gages under the CLT floor
Figure 8: Static loading using the tester’s weight
2.2.4 Modal Test
Modal test was conducted to determine the natural
frequencies, modal damping ratios, and vibration modes
of the CLT floor specimens.
Modal testing followed a standard procedure specified in
FPInnovations’ protocols [3]. Hammer excitation was
selected because of its simplicity and reliability. The
hammer impact was applied at the top of the floor by a
person sitting on a beam supported on the ground so that
the tester’s weight was not added to the floor. The
hammer impact was located on the side panel and was
offset from the mid-span of the test floor areas. At such
a location, it was unlikely that a nodal point of the first
three modes would occur. The floor vibration was
measured on each panel at one quarter of the span of the
test floor areas. Figure 9 shows a typical modal test setup
and the locations for the hammer and accelerometers.
The force and acceleration signals were recorded by a
multi-channel analyzer. The signals were post-processed
2.2.5 Forced vibration test
Forced vibration testing was conducted to determine the
dynamic responses including acceleration, velocity, and
displacement responses of the CLT floors to an impulse
similar to the heel impact force of the foot steps of
human normal walking.
Forced vibration testing followed the procedure
described in the FPInnovations’ test protocols [3]. The
excitation was triggered by dropping a 5 kg medicineball
on a force plate instrumented with the force
transducer. The ball drop impact was performed by a
tester while sitting on a stool. The ball was caught when
it rebounded to avoid multiple impacts. The ball drop
force was applied at the floor centre. An accelerometer
was also located at the impact location to measure the
maximum response of the floor. The impact force and
acceleration signals were recorded by the multi-channel
analyzer. The acceleration signals were then integrated
to obtain velocity or displacement responses. The impact
force signal was processed to determine the impulse,
which was further used to normalize the dynamic
responses to a 1 N-s impulse. Figure 10 shows the ball
drop impact test and the measurement setup.
Figure 10: Forced vibration test on a CLT floor specimen
using the ball drop as the excitation