Walking induced floor vibration design and control

Disturbing walking-induced vibrations have been observed more frequently in recent times on long span lightweight floor systems as evidenced by the development of a number of new design guidelines for floor vibration assessment. Constraining vibration levels to meet human comfort criteria is a vital serviceability requirement in the design of floors. The aim of the present research is to minimise the adverse vibrations from footfalls in new floors by providing better estimation of expected response and in existing floors by the use of a new configuration of tuned mass damper (TMD). Current floor vibration guidelines are reviewed and modifications are proposed to enhance the accuracy of floor response prediction. A significant finding is the development of an empirical expression for a unique factor that incorporates all effects of the floor properties, pacing rate, resonant harmonic and non-resonant harmonic forcing components on the floor response. The peak response due to a moving multiharmonic force can now be easily computed as the multiplication of the proposed factor by the steady state response due to a stationary single-harmonic force. Also discussed are finite element (FE) and semi-FE approaches for predicting the worst-case response of floors. One major achievement of the present research is the application of an innovative multi TMD system as an effective solution for floor vibration control. A closed form solution for natural frequencies and steady state response of systems with multi TMDs is developed to facilitate preliminary design. A custom made distributed multiple viscoelastic TMD system has been developed and successfully installed on a real office floor where disturbing walking-induced vibrations were observed. Extensive FE investigations and various field tests performed on the real floor reveal that the response level of the damper-retrofitted floor is suppressed by at least 40% to an acceptable limit for human comfort. Another contribution of the present research is the characterisation of human walking force based on the experimental footfall data obtained from an Australian biomechanics research program. The descriptive statistics of basic gait parameters are determined and the intra- and inter-subject variability in gait parameters is examined from this footfall database. Moreover, design values are proposed for the dynamic load coefficients corresponding to the first ten harmonics of walking. Finally, a probabilistic vibration analysis of a floor with and without dampers is conducted with a large number of simulation cases considering the likely variations in loading within each walk and between different walks and the possible changes in the dynamic properties of the floor and dampers. This sensitivity analysis automatically covers the effect of damper off-tuning and further validates the effectiveness and reliability of the TMD method when demonstrating that the 90% and 95% fractile response levels of the floor can be reduced by about 43% using the dampers.