The long span balcony (mezzanine) in an up-scale large custom-built, single-family residence, overlooking the large open area of floor below had an unacceptable vibratory attribute. The balcony is supported by a long, wide flange (W21) steel beam that supports approximately 600 square feet of tributary floor area.
As anticipated and evident from the measured data, the worst-case vibrations occurred at around 4.2 Hz (the first natural frequency of the long steel beam supporting the balcony edge). Moreover, the modal damping ratio of the structure corresponding the first mode of the structure was predicted to be around 1%.
DEICON designed and fabricated a narrow tuned mass damper for the balcony. The TMD was sized to have the nominal active mass of 450 Kg. The depth and height of the TMD were chosen so that it can fit within the W21x182 beam spanning the entire length of the balcony. The remaining parameters of the TMD namely the tuning frequency and damping ratio were selected based on the dynamic attributes of the balcony.
Comparison of the measured balcony vibration without and with the TMD pointed to an excess of 8 fold increase in the damping of the first (target) mode of the structure, from 1.1% (without the TMD) to 9% (with the TMD). Such an increase in damping lowered the walking induced vibration along the open edge of the balcony by the same factor.