# Damping Assessment of Lightweight Timber Floors Under Human Walking Excitations
## 3 Results and Discussion
### Fundamental Damping Ratios  
Figure 13 shows a boxplot with the damping ratios of all the floors evaluated with the EFDD and SSI-UPC methods. Figure 11: Measured fundamental vibration mode for the Lab-3.1-W floor (20.32 Hz Enhanced Frequency Domain Decomposition (EFDD) method). Extracted form ARTeMIS Modal Pro [21]. Figure 12: Measured fundamental vibration mode for: (**a**) Lab-2.4-W floor (26.45 Hz Enhanced Frequency Domain Decomposition (EFDD) method); (**b**) Field-3.1-W (16.38 Hz EFDD method). Extracted form ARTeMIS Modal Pro [21]. It can be seen from Figure 13 that there is a clear difference between the damping ratios of the laboratory floors and the in-situ floors. While the laboratory floors had damping ratios between 1.9% and 4.9%, the field floors reached values between 4.3% and 14.8%. Additionally, the SSI-UPC method presented average damping ratios that were 1.24 times greater than those of the EFDD method. Concerning the coefficients of variation of the damping ratios, it is observed that they are much higher than those obtained in the frequencies (Table 5); however, they remain at reasonable values (less than 25%) given the difficulty of estimating this dynamic property experimentally. To determine whether the differences in the damping ratios of the different laboratory floors were statistically significant, an analysis of variance (ANOVA) was applied. Using a level of significance of 0.05 for the results of the EFDD method, the ANOVA indicated that the differences between the means of laboratory and in-situ tests were not statistically significant (\(p=0.199>0.05\)). However, when applying the ANOVA to the damping ratios with the SSI-UPC method, statistically significant differences were obtained between the means of laboratory and in-situ tests (\(p=0.028<0.05\)). In particular, the SSI-UPC method detected that the Lab-3.0-W floor was significantly lower than the Lab-2.7-W and Lab-2.1-S floors. The above described situation could imply that for floors with distances close to 3 m, it would not be advisable to use wood-based supports, since ranges of damping ratios could be smaller than the general trend of the rest of the cases. Besides, these results demonstrate the importance of evaluating the damping ratios with different methods, as they complement each other and make it possible to detect trends that might not be observed with a single method. Table 6 shows the confidence intervals of the means (95%) obtained by the ANOVA for the laboratory floors. Figure 13: Boxplot of fundamental damping ratios. Other interesting results worth analyzing are the high levels of damping ratios that were found in the in-situ floors. On the Field-2.4-W floor, damping ratios were found to be twice as high as those of the laboratory floors. This increase is attributed to the interaction of the floors with some non-structural elements (for example, ceilings and partition walls), together with the higher level of restriction to the rotation of the floor supports due to the weight of the perimeter walls (Figure 5). All of these interactions more strongly activated some energy dissipation by friction mechanisms and therefore increased the values of the damping ratios. On the other hand, for the Field-3.1-W floor, the effect of the interaction with the non-structural elements was even more evident. The Field-3.1-W floor resembles the Field-2.4-W floor in that it also has a ceiling and partition walls in the perimeter of the floor. However, the more significant constructive difference is that the Field-3.1-W floor also has a partition wall that crosses all the timber joists in the third of its length. Besides, this partition wall directly supports a part of the roof structure of the house (Figure 6). Because of the presence of this unusual partition wall, the floor of the Field-3.1-W housing presents damping ratios three times greater than those of laboratory floors. The damping ratios found both for the laboratory floors and the in-situ floors are higher than those indicated by other researchers.