Development of a viscoelastic tuned mass damper to reduce walking induced vibrations in building floors

Excessive floor vibration due to human excitations has become a significant serviceability concern for office floors in the last two decades. The use of lightweight and high strength materials, nominal furniture and open layouts have resulted in lighter floors with less damping and hence an increase in vibration related problems. In office floors, this may lead to unacceptable floor response due to walking excitation and hence annoyance problems. When excessive vibrations are encountered in existing floors, there are few options available as remedial actions. If a change of floor layout or stiffening is not practical, the use of a Tuned Mass Damper (TMD) to increase floor damping is one of the attractive possible solutions. Currently, conventional viscous Tuned Mass Dampers (TMDs) to treat floors experiencing small displacements due to walking is not practically available. The main aim of this research was to develop a cost effective and simple TMD that can deal with floor systems with small vibration displacements. A new innovative TMD in the form of a cantilever beam with an end mass was developed to suppress floor vibrations. The cantilever beam consists of a viscoelastic layer constrained by two constraining layers. The new viscoelastic TMD can be fitted within the false floor or false ceiling spaces. Based on extensive analytical modelling, Finite Element (FE) analysis, laboratory testing and investigation of a real office floor, the following conclusions could be made: i) the new viscoelastic TMD is simple and cost effective as it can be constructed from commercially available rubber. ii) an analytical model was developed which can be used to design the new TMD for floor applications. As expected, the performance of the viscoelastic TMD is highly dependent on the geometry and properties of the materials used in its construction particularly the dissipation loss factor of the rubber as it acts as the damping element of the TMD. iii) prototype viscoelastic TMDs were tested on simply supported steel and concrete beams and it was found that the viscoelastic TMDs were very efficient in reducing the levels of vibration generated from a mechanical shaker and human excitations. iv) for full scale floors where a single damper may be too large to fit in the available space, multiple damper solutions were developed and tested. The multiple dampers can be located at one spot or distributed. v) the viscoelastic TMD solution in the form of multiple distributed dampers was successfully applied to a real office floor experiencing excessive vibrations. The new TMD was able to reduce the vibrations by at least a factor of 1/3. The new viscoelastic damper offers design engineers a non intrusive and cost efficient solution to reduce excessive vibrations in floor systems. In a distributed form, the TMDs can be reasonably small in size and easily tuned.