# Damping Assessment of Lightweight Timber Floors Under Human Walking Excitations
## 4 Conclusions  
This paper has highlighted the importance of the damping ratio in the dynamic serviceability of lightweight timber floors that are typical in social housing projects, under human-walking excitations. The experimental campaign revealed ranges of values for damping ratios for both floors built in the laboratory and existing homes. The different dimensions and constructive details of the floors, together with the two operational modal analysis methods used for estimating the damping ratios, have allowed the current knowledge about this research topic to be extended.  
For the floors constructed in the laboratory, damping ratios were obtained in the range of 1.9% to 4.9%. In general, there were few statistically significant differences between the laboratory floors with different span lengths and types of support. Only the 3 m long floor with wood-based supports (Lab-3.1-W) had significantly lower values of damping ratios and a worse vibration performance, so its use in social housing projects is not recommended.  
For the floors evaluated in-situ, damping ratios were obtained in the range of 4.3% to 14.8%, presenting values between 2 and 3 times greater than those of the laboratory floors. The reason for these increases in damping was mainly due to the presence of non-structural elements, such as a ceiling and partition walls. This favorable effect of the non-structural elements in the damping ratio confirms what was indicated by other researchers.  
Concerning the methods used to calculate the damping ratio from experimental tests, the importance of using at least one that works in the frequency domain and another in the time domain is confirmed. On average, the SSI-UPC method obtained damping values that were 1.24 times higher than those of the EPDD method. Besides, the combined use of both methods provides further reliability to the results and detects tendencies that are challenging to find with a single method.  
Damping ratios higher than those indicated in other studies were obtained for both the floors built in the laboratory and those evaluated in-situ. These results show that the amplitudes of vibrations induced by walking are larger and activate more energy dissipation mechanisms in the floors than the ambient vibration or low-energy impact tests used by other researchers. However, these increases in the damping ratios were not only due to the activation of new energy dissipation mechanisms, but also due to the human-structure interaction that occurred during the walks. Therefore, it is desirable to carry out new numerical investigations to quantify the contributions of the different physical phenomena to the total damping of the timber floors.  
Finally, the positive influence of the damping ratio on the vibration performance of the floors was identified. For floors with similar vibration frequencies, it was observed that those with 2.1 times larger damping ratios had \(V\!DV_{day}\) values that were up to 48% lower. These results allowed some floors to move from unacceptable vibration levels for users to others where it is possible that users generate adverse comments, but within a tolerable range of vibrations.  
Conceptualization, A.O.-V. and C.O.-V.; methodology, A.O.-V. and C.O.-V.; software, A.O.-V. and F.M.-V.; validation, C.O.-V. and A.O.-V.; formal analysis, A.O.-V.; investigation, A.O.-V. and F.M.-V.; data curation, A.O.-V. and F.M.-V.; writing--original draft preparation, A.O.-V.; writing--review and editing, C.O.-V., visualization, A.O.-V. and F.M.-V.; supervision, C.O.-V.; project administration, A.O.-V.; funding acquisition, A.O.-V.  
This research was funded by the UNIVERSITY OF BIO-BIO RESEARCH DIRECTORATE, grant number DIUBB 151714 2/R.  
The authors gratefully thank the support of the Civil Engineering Doctoral Program at Universidad Catolica de la Santisima Concepcion (UCSC).  
The authors declare no conflict of interest.