## 3 Results and Discussion
### Estimation of the Wood Density In Situ  
Despite the limitations of carrying out a superficial test, Pilodyn is an easy-to-use device with which a high number of readings can be obtained quickly. This feature makes it possible to discard the highest and the lowest values and thus obtain a very reliable average value. The wood density was estimated using the indirect needle penetration method based on the regression equation derived from the laboratory tests, as follows (Equation (4)):  
\[\rho_{i,\ in\text{-}situ}=-23.47\times NP_{i,corrected}+818.14 \tag{4}\]  
where  
* \(\rho_{i,\ in\text{-}situ}\) is the estimated density (kg/m\({}^{3}\)) of reading \(i\);
* \(NP_{i,corrected}\) is the reading \(i\) of the needle penetration tests, corrected by Equation (1) (mm). Equation (5), which results from integrating Equation (1) with Equation (4), provides an estimate of the density of an in situ wood element at \(u=12\%\), based on an average of the in situ NP readings and the water content measured on site during the tests:  
\[\rho_{i,in\text{-}situ}=-\frac{23.47\times NP_{i,in\text{-}situ}}{1+0.015 \times\Delta u}+818.14 \tag{5}\]  
where  
* \(\rho_{i,\ in\text{-}situ}\) is the estimated density (kg/m\({}^{3}\)) of in situ reading \(I\);
* \(NP_{i,in\text{-}situ}\) is the in situ reading \(i\) of the needle penetration tests (mm);
* \(\Delta u\) (%) is the moisture content difference (%) between the in situ and reference (12%) moisture contents. Table 3 presents the results for the penetration depth (NP) obtained on site and corrected to a reference (12%) moisture content (u) and the number of readings, and the estimated and real wood densities. The difference refers to the estimated density versus the \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline  & & & \multicolumn{2}{c}{**NPR Testing**} & \multicolumn{3}{c}{**Wood Density (kg/m\({}^{3}\))**} \\
**Identification** & \begin{tabular}{c} **Moisture** \\ **Content (u) In** \\ **Situ (\%)** \\ \end{tabular} & \begin{tabular}{c} **Number of** \\ **Readings In** \\ **Situ** \\ \end{tabular} & \begin{tabular}{c} **Percentage to** \\ **In Situ** \\ **Equation (1)** \\ \end{tabular} & \begin{tabular}{c} **Density** \\ **Estimated by** \\ **Equation (4)** \\ \end{tabular} & \
\begin{tabular}{c} **Core Drilling** \\ **(Measured** \\ **Density at** \\ **u = 12\%)** \\ \end{tabular} &
\begin{tabular}{c} **Difference** \\ **Between** \\ **Estimated and** \\ **Measured** \\ **Measured** \\ **Density (\%)** \\ \end{tabular} \\ \hline \hline \multicolumn{8}{l}{B–building from the mid-19 th century—outskirts of Lisbon} \\ \hline B1 & 12.1 & 5 & \(12.5\pm 0.5\) & 12.5 & 525 & 541 & 2.9 \\ B2 & 11.1 & 5 & \(13.3\pm 0.5\) & 13.5 & 502 & 499 & 0.5 \\ \hline \multicolumn{8}{l}{C—building from the 19 th century’s last quarter—historical center of Lisbon} \\ \hline C1 & 9.0 & 5 & \(17.2\pm 1.9\) & 18.0 & 395 & 387 & 2.2 \\ C2 & 8.6 & 7 & \(11.1\pm 0.9\) & 11.7 & 544 & 560 & 2.9 \\ C3 & 10.8 & 7 & \(13.5\pm 1.5\) & 13.7 & 495 & 470 & 5.4 \\ C4 & 10.4 & 5 & \(10.7\pm 1.0\) & 11.0 & 561 & 645 & 13.0 \\ \hline \multicolumn{8}{l}{D—building from the 1940s of the 20 th century—outskirts of Lisbon} \\ \hline D1 & 12.6 & 4 & \(13.2\pm 1.1\) & 13.1 & Ne ** & 421 & - \\ D2 & 11.7 & 4 & \(11.3\pm 0.5\) & 11.4 & 552 & 558 & 1.1 \\ D3 & 12.5 & 4 & \(12.8\pm 0.8\) & 12.7 & 520 & 511 & 1.8 \\ D4 & 12.3 & 4 & \(16.0\pm 1.0\) & 15.9 & 444 & 426 & 4.3 \\ D5 & 11.4 & 4 & \(13.5\pm 1.3\) & 13.6 & 498 & 509 & 2.1 \\ D6 & 12.1 & 4 & \(12.8\pm 1.2\) & 12.8 & 518 & 480 & 8.0 \\ \hline \multicolumn{8}{l}{Average} & & & 506 & 512 & 4.6 \\ \hline \multicolumn{8}{l}{Std} & & & 38 & 61 & 3.2 \\ \hline \multicolumn{8}{l}{Relative RMSE (\%)} & & & 5.6 \\ \hline \multicolumn{8}{l}{Normalized RMSE (\%)} & & 11.7 \\ \hline \hline \end{tabular}  
* Values were corrected to a moisture content (u) of 12%, compared to those of the measurement on site. ** Not estimated (ne) due to the presence of extensive resin pockets.  
\end{table} 
Table 3: _Cont._real (measured) density.