DEICON supplied two tuned mass dampers (TMDs) to mitigate vibration in a gymnasium (gym) floor system caused by rhythmic activities such as cycling as well as abrupt/impulsive and random events such as dropped weights and the movement of exercise machines.
Rhythmic activities set the gym floor to vibrate in a sustained fashion with the same rhythm as that of the activity and its higher order harmonics. Such vibration becomes excessive and turns into resonance, when the rhythm of the activity or one of its higher order harmonics matches or closely approaches one of the floor’s natural frequencies, primarily the first natural frequency.
Impulsive and random events set the gym floor to vibrate in a transient fashion, mainly with the same frequency as the first natural frequency of the floor. The lack of sufficient inherent damping in the floor causes transient vibrations to persist for too long, leading to significant annoyance.
Figure 1 One of the TMDs installed underneath the floor
DEICON modeled the floor system to predict its natural frequencies and mode shapes. The modeling efforts was followed to physical measurement of floor vibration, the results of which were used to verify the model. The verified first natural frequency was then used in tuning two 2000 lb tuned mass dampers, targeting the first mode of vibration of the floor. The corresponding mode shape was used to locate the installation location of the TMDs. Figure 1 shows one of the TMDs installed in its designated location underneath the floor.
The blue traces in Figure 2 show the power spectral density (top plot) and time trace (bottom plot) of floor acceleration, in response to a weight drop, measured at an anti-node, without the TMDs. The red traces in this figure show the same measurement, but with the TMDs installed.
The comparison of the red and blue traces in Figure 2 clearly demonstrates the effectiveness of the tuned mass dampers in introducing a sizeable amount of damping into the floor significantly reducing the vibrations
Figure 2 Measured vibration without and with the TMDs