# Effect of Primary Spruce Lamella Aging on the Bending Characteristics of Glulam Beams
## 3 Results and Discussion
### Bending Characteristics of Glulam Beams Affected by Aging of Lamellas
lamellas were made from naturally aged prisms with a greater degree (GD) of bio-attack (72.78 MPa; a decrease of 10.8%) or if the middle lamellas were artificially aged at a maximum temperature of 220 \({}^{\circ}\)C or in the presence of ZnCl\({}_{2}\) and (NH\({}_{4}\))\({}_{2}\)SO\({}_{4}\) (68.29-73.08 MPa; decreases of 16.3-10.5%). Figure 4: Examples of the 3-point bending test of three-layer glulam beams ((**a**): **a1** = SSS; **a2** = SAS, if A aged at T-200 \({}^{\circ}\)C), showing typical damages in the bond joints and/or wood lamellas ((**b**): **b1** = SSS; **b2** = SAS; **b3** = ASA; **b4** = AAA, if A always aged at T-220 \({}^{\circ}\)C) and details of these damages ((**c**): **c1** to **c4**). In accordance with the theoretical assumption, the lowest MOR were obtained for gplulam beams of the third group and fourth group, in which aged lamellas were localized in the surface \"tension and compression\" zones. For example, the MOR decreased by 25.9-23.3% if such lamellas were prepared from the outer greater bio-attacked zone of naturally aged prisms (\(\sim\)60.5 MPa), or if these lamellas were artificially aged at a maximum temperature of 220 \({}^{\circ}\)C (\(\sim\)62.6 MPa). The determination of similar values of the MOR for the third group (A-S-A) and the fourth group (A-A-A) of gplulam beams created from lamellas aged (A) artificially at 220 \({}^{\circ}\)C or aged naturally with a greater attack by _A. punctatum_ is in good accordance with the theory that for the bending strength of beams, including gplulam beams, the most important zones are their tension and compression zones. The MOE of gplulam beams depended less, compared to the MOR, on the method of spruce lamella aging and their locations in gplulam beams. This was determined by [PERSON]'s tests (Table 1). Quite high MOEs, approximately from 9000 to 11,000 MPa, were obtained for various gplulam beam types, i.e., not only in the first and second groups but, in some cases, also from the third and fourth groups. Apparently lower MOEs, from 8000 and 9000 MPa, were observed for some gplulam beams in which aged lamellas were localized (1) in the middle \"neutral\" zone of the second group--aged by (NH\({}_{4}\))\({}_{2}\)SO\({}_{4}\); (2) in the surface \"tension and compression\" zones of the third group--with a GD of bio-attack or aged by H\({}_{3}\)BO\({}_{3}\); (3) in all three zones of the fourth group--aged at 220 \({}^{\circ}\)C. The lowest MOE, only 7540 MPa, was obtained for gplulam beams in the fourth group consisting of three lamellas with a greater degree (GD) of bio-attack by _A. punctatum_. Generally, a decrease in the bending properties of gplulam beams made from aged lamellas can be explained (1) by the creation of poorly glued joints, as well as (2) by the presence of deteriorated wood in beams having lower strength and stiffness. Poorly glued joints are created when using wood with a more hydrophobic surface or a surface weakened by bio-, thermal and/or chemical attacks. Worse bending properties of wood damaged by larval galleries were found by [PERSON] and [PERSON] [42]. Temperatures from 160 \({}^{\circ}\)C to 220 \({}^{\circ}\)C cause only a minor change (\"increase or decrease\") in the MOE but a large decrease in MOR from 10% to 50% with a rise in temperature [56; 57; 58]. The mechanical properties of wood decrease after its attack by acids, bases and other aggressive chemicals [40]. For example, the negative effect of wood impregnation with compounds of trivalent boron on the strength of glued joints and the strength of wooden composites significantly depends on the type of wood and the type of polymer used as the glue or coating [59; 60].