The floor system of a large room at the 3rd floor administration building of a large university with the square footage of around 1760 ft^2s consists of 3 bays exhibited excessive walking-induced floor vibration. This composite floor system is made up of 3 ½” regular weight concrete on 1 1/2” metal deck, supported by 9 wide flange beams.
Numerical analysis as well as vibration measurement revealed that the floor system vibrates at 3 different frequencies, corresponding to the natural frequencies of the first 3 modes of the structure, depending on where and at what pace the floor is walked on (perturbed). In modes 1 and 2 the three bays vibrate collectively, but in mode 3, each bay vibrates individually, although at the same frequency.
Reactive damping, provided by appending tuned mass dampers (TMDs) to the floor system, was decided on and implemented for abating the vibration. Six tuned mass dampers (TMDs) targeting 3 modes of vibration were designed, fabricated, and installed underneath the floor system. The couple most effectively with the floor system, the TMDs were installed at the locations where their target modes have the highest vibration level.
Following the installation of the TMDs, floor vibration at the target bays, without and with the tuned mass dampers operational, were measured. Comparison of the two sets of measurements, pointed to the effectiveness of the tuned mass dampers in adding substantial amount of damping to their three target modes, quieting the vibration of the floor system.