Response of high frequency floors: A literature review

This article reviews the process of estimating the response of high frequency floors (HFFs) to footfalls. The article begins by describing the evolution of the various forcing models. Originally, analyses were conducted using the harmonic methods that use the Fourier components of a walking time history. After the fourth harmonic of a footfall (approximately 10 Hz) very little energy exists and the harmonic methods were found not to be suitable for design of these ‘HFFs’. This was the reason for the development of some alternative force models. These models are discussed and their accuracy compared with real recorded footfall time histories. The article then continues to review the estimation of the floors dynamic properties, starting with hand calculations and evolving into using finite element analysis combined with modal superposition to estimate the floor’s response. The mechanisms of damping and the reason for why it is not possible to estimate damping with respect to the material properties are discussed. The article ends with a review of response criteria, describing how criteria for sensitive occupancy, for which many HFFs are used for, were developed. It was found that there is much discussion about the cut-off frequency between high and low frequency floors. A solution would be to develop an universal forcing function that is suitable for both the methods. Even with an accurate forcing function, there is little guidance on how to model floors in general; some floors can have many bays, which can result in large number of modes proving costly in computing time using the present methodologies. The response of these floors is usually evaluated using Bolt Beranek and Newman’s (BBN’s) vibration criteria (VC) curves, which was developed as an extension of human vibration criteria using the signal analysers that were available at the time. This may not be the most efficient means of designing a floor, and criteria specific to the floors occupancy may be a better option in certain cases.