# Effect of Wood Densification and GFRP Reinforcement on the Embedment Strength of Poplar CLT
## 3 Results and Discussion
### Effect of Densification Ratio and Loading Direction on Embedment Strength
Concerning face side insertion in CLT, Uibel and Blab [15,46] evaluated the load-bearing capacity of dowels placed in manufactured with four distinct arrangements and computed the embedment strength. The CLT embedment strength prediction model was suggested based on the variable CLT lamination characteristics. \begin{table}
\begin{tabular}{c c c c} \hline  & \multicolumn{3}{c}{**Main Effects**} \\ \hline  & 0 & 29.8 (4.65) * & A ** \\ Densification ratio & 25 & 43.7 (3.4) & B \\  & 50 & 49.7 (4.76) & C \\ \hline Loading direction & T & 39.44 (9.29) & A \\  & L & 42.62 (9.41) & B \\ \hline \multicolumn{3}{c}{**Interaction effects**} \\ \hline
**Densification ratio** & **Loading direction** & **Embedment strength (MPa)** \\ \hline  & T & 28.24 (4.88) & A \\
0 & L & 31.33 (4.07) & A \\  & T & 42.52 (3.61) & B \\
25 & L & 44.8 (2.92) & BC \\  & T & 47.58 (4.19) & C \\
50 & L & 51.75 (4.54) & D \\ \hline \end{tabular}
* The values in parentheses represent standard deviation. ** The letters show Duncan test results.  
\end{table} 
Table 4: Main and interaction effects of densification ratio and loading direction on embedment strength of CLT samples with Duncan test results. The load displacement of control, densified, and GFRP-reinforced CLT specimens is shown are Figure 5. Accordingly, the yield points of the CLT samples in the L direction were more than those in T direction. The yield points of OL, 25L, 50L, and GFRP were 8636 (N), 11,900 (N), 16,080 (N), and 13,720 (N), respectively. The highest yield point in the L direction belonged to the CLT sample reinforced with 50% densified wood. On the other hand, the yield points of 0T, 25T, 50T, and GFRPPT were 7947 (N), 11,450 (N), 13,152 (N), and 12,120 (N), respectively. The highest yield point in the L direction belonged to the CLT sample reinforced with 50% densified wood. The failure modes of CLT specimens are depicted in Figure 6. The typical failure modes of tested CLT specimens are different in the situation where the lag screw is loaded in the L and T direction of the CLT specimens. Cracks occurred along the grain when the load was applied along with the L direction, as shown in Figure 6 (0L, 25L, and 50L). Cracks in 25L and 50L show that the densification reduced the length of the cracks compared to the unreinforced samples (0L). However, compression failure occurred in the embedment surface, as shown in Figure 6 (0T, 25T, 50T, GFRP, and GFRPT), or cracks appeared on both edges of the cross layers, as shown in Figure 6 (0T), when the CLTs were loaded in the T direction. The compression failure might occur layer by layer, which results in stress redistribution [1]. The results of the prediction models in comparison with experimental results are shown in Figure 7. NDS showed the most accurate results compared to the experimental findings, followed by the Ubel and Blub and then the [PERSON] and CSA formulas. Finally, the formula of [PERSON] et al. showed the lowest accuracy in terms of the prediction of experimental results. Previously, all of these equations were applied to predict the embedment strength of fasteners in EWPs, such as CLT. Accordingly, various results were obtained regarding the accuracy of these equations. The accuracy of the equations might be related to factors including moisture content, density, diameter of fastener, or the loading direction. Figure 4: Means and standard deviations of embedment strength of control, densified, and GFRP-reinforced CLT specimens. Figure 5: _Cont_. Figure 5: Load-displacement curves of the reinforced and unreinforced CLT samples. Figure 6: Failure modes of reinforced and unreinforced CLT specimens in L and T loading directions. Figure 7: Comparison of the observed and predicted values of the embedment strength. The MAPE of all models is detailed in Table 5. The NDS formula showed the highest accuracy (10.31%). After that, the Ubel and Blub formula showed the highest accuracy (21.3%). On the other hand, [PERSON] et al. 's formula showed the lowest accuracy (40.07%).