# Damping Assessment of Lightweight Timber Floors Under Human Walking Excitations
## 2 Materials and Methods
### Laboratory Tests  
Eight timber floors with four different span lengths (3 m, 2.7 m, 2.4 m, and 2.1 m), and two kinds of wall-to-joist connections (wood-based and steel-based), were built in laboratory-controlled conditions. The span lengths were selected in order to represent the typical ranges present in social housing and to study the effect of the vibration amplitude on the floor damping ratios. Meanwhile, the two types of wall-to-joist connections were chosen for analyzing the influence of different energy dissipation conditions due to support friction on the floor's vibration performance. All the floors were simply-supported on four sides, and none of them had additional non-structural elements, such as \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Density 1 (kg/m3)** & **E Parallel (MPa)** & **E Perpendicular (MPa)** \\ \hline Timber joist & 476 & 9545 & 621 \\ Timber blocking & 476 & 9545 & 621 \\ Timber battens & 476 & 7900 & 514 \\ Plywood board & 538 & 6921 & 2353 \\ Gypsum board & 750 & n/a & n/a \\ \hline \hline \end{tabular} \({}^{1}\) Corresponding to a 12% moisture content.  
\end{table} 
Table 1: Nominal density and Young’s modulus (E) of timber floor components. Figure 1: Typical construction details of timber floors in Chilean social housing. partition walls or ceiling sheathings. Temperature and relative humidity were not explicitly controlled, but were according to standard indoor spring seasonal conditions, i.e., 18 \({}^{\circ}\)C and 65%, respectively. Figures 2 and 3 and Table 2 show the construction details of the laboratory floors tested. As a vibration source, a set of 36 short-duration walks were performed on each floor considering the different body masses of the walkers (between 56 kg and 87 kg) and step frequencies (between 1.4 Hz and 2.2 Hz). A portable metronome helped to synchronize the step frequencies and to generate a more representative set of walks. Vertical accelerations were recorded for the walking tests through five uniaxial accelerometers screwed to the top surface of the floors. The sensors were evenly spaced and located at the center lines of the timber floors (i.e., 1/4 th, 2/4 th, and 3/4 th of both span length and floor width). Integrated circuit piezoelectric (ICP) accelerometers (model 603C01) were used, having  
Figure 3: (**a**) Wood-based wall-to-joist connections; (**b**) steel-based wall-to-joist connections. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Series** & **Span Length “L” (m)** & **Floor Width “B” (m)** & **Support Type** \\ \hline Lab-2.1-W & 2.1 & 4.0 & Wood-based \\ Lab-2.1-S & 2.1 & 4.0 & Steel-based \\ Lab-2.4-W & 2.4 & 4.0 & Wood-based \\ Lab-2.4-S & 2.4 & 4.0 & Steel-based \\ Lab-2.7-W & 2.7 & 4.0 & Wood-based \\ Lab-2.7-S & 2.7 & 4.0 & Steel-based \\ Lab-3.0-W & 3.0 & 4.0 & Wood-based \\ Lab-3.0-S & 3.0 & 4.0 & Steel-based \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Nomenclature, dimensions, and support details of laboratory timber floors. Figure 2: Layout and dimensions of a typical laboratory test specimen. a sensitivity of 100 mV/g. Accelerometer data acquisition was conducted through a multi-channel dynamic signal acquisition module (model NI 9234) gathered into a Compact DAQ chassis (model cDAQ-9174) and linked via USB to a laptop. For all tests, the sampling rate was set to 1652 Hz. The typical walking paths, accelerometer locations, and instrumentation setup are shown in Figure 4.  
In general, this study was looking for a methodology that would also allow field evaluations with a minimum number of sensors and the time for installing sensors and recording data to be  
Figure 4: (**a**) Walking paths and accelerometer locations, (**b**) test setup on laboratory timber floors, and (**c**) instrumentation diagram. optimized, especially in the case of in-situ tests performed in houses occupied by families. In all cases, we selected measuring points avoiding modal nodes to capture the highest possible number of vibration modes.