# Effect of Primary Spruce Lamella Aging on the Bending Characteristics of Glulam Beams
## 3 Results and Discussion
### Shear Strength of Glued Joints Affected by Aging of Lamellas  
The shear strengths (\(\sigma\)) of glued joints in the first, second and third double-bonded sets prepared from naturally aged lamellas of type II (Section 2.1) and PUR glue (Sections 2.3 and 2.5) are presented in Table 2.  
According to [PERSON]'s test for the shear strength, no significant differences occurred between the first set prepared from two sound lamellas (\(\sigma\) = 10.82 MPa) and the second or third sets prepared from one or two naturally aged lamellas (\(\sigma\) from 9.90 to 11.02 MPa). This unexpected result was potentially caused by PUR glue possibly seeping into _A. punctatum_ larval holes when, after glue curing, quasi-pin joints between the jointed lamellas can be created with their orientation perpendicular or at a defined angle to shear forces, and thanks to which the shear strength of gulam beams from the naturally aged lamellas did not worsen. For this reason, the correlation analyses of MOR or MOE = f (\(\sigma\)) in Section 3.3 had to be performed without the sets of naturally aged lamellas and the groups of gulam beams made from them.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Double-Bonded Set** & **Shear Strength—\(\sigma\) (MPa)** \\ \hline
**1 st set (S-S)** & \\ Sound & 10.82 (1.39) \\ \hline
**2 nd set (S-A)** & \\ GD bio-attack & 10.85 (1.24) d \\ LD bio-attack & 11.02 (0.86) d \\ \hline
**3 rd set (A-A)** & \\ GD bio-attack & 9.90 (1.30) d \\ LD bio-attack & 10.94 (1.49) d \\ \hline \hline \end{tabular} Notes: Mean values are from 10 measurements. Standard deviations are in parentheses. [PERSON]’s tests were used to evaluate the shear strength of the 2 nd or 3 rd double-bonded set consisting of 1 or 2 aged “A” lamellas, relative to the 1 st (reference) double-bonded set consisting of 2 sound “S” lamellas, with indexes of significance: a—very significant decrease at 99.9% level; b—significant decrease at 99% level; c—less significant decrease at 99% level; d—significant change (decrease or increase) at +95% level.  
\end{table}
Table 2: The shear strengths (\(\sigma\)) of glued joints in the double-bonded sets consisting of Norway spruce lamellas of type II and PUR glue.  
Figure 5: Summary linear correlations between the bending characteristic MOR (**a**) or MOE (**b**) of the three-layer gulam beams belonging to the 2 nd, 3 rd and 4 th groups and the temperature during the artificial aging of spruce lamellas.  
The shear strengths (\(\sigma\)) of glued joints of the first, second and third double-bonded sets prepared from artificially aged spruce lamellas were published and discussed by [PERSON] et al. [55], who used thermally aged lamellas, and by [PERSON] and [PERSON] [12], who used chemically aged lamellas. In this work, the achieved shear strength values at Section 3.3 were applied in the correlation analyses of MOR or MOE = f (\(\sigma\)). The strength of the glued joints apparently decreased at the level of significance of 95% and as high as 99.9% when one lamella of the double set was aged at a temperature of \(\geq\)200 \({}^{\circ}\)C or in the presence of ZnCl\({}_{2}\) and H\({}_{3}\)BO\({}_{3}\), or when both lamellas of the double set were aged at a temperature of \(\geq\)160 \({}^{\circ}\)C or in the presence of one of the four used inorganic preservatives.