## 4 Discussion
A 1.4% reinforcement of the circular grooves in the tension zone resulted in an average increase in stiffness by 11.2% and 13.9% and an average increase in the bending moment of 68% compared to unreinforced beams. Meanwhile, 2.8%reinforcement increased the stiffness by 22% and 29.6% and the average bending moment by 98.5% compared to unreinforced glued beams. In this study of the A series of beams, all unreinforced beams primarily failed in the tension zone due to fracture of the timber fibers--fiber twist or if there was a defect because of the KW class--in place of natural defects, just as one beam failed in the compression zone. It should be noted that already prestressed and reinforced beams were already failing due to bending and shear. Figure 9 shows the cracking of the timber fibers in the tension zone of a prestressed reinforced beam. It should be noted that the introduction of the BFRP bars also resulted in a change of the failure mode to plastic failure in compression in some beams (B-1 beam). This was very evident, especially in steel reinforced and prestressed beams (D-2 beam). It should also be noted that the tests did not cause the bars to break due to their high strength. Similarly, the epoxy adhesive only became loose, not detached. This could have been caused by the anchoring used at the ends of the bars and the connection of these bars along the axis of the beam. The results of the experimental tests are also analyzed in Table 5. It can be seen that the failure load had improved very significantly for both reinforced and prestressed glulam beams. The test results are also summarized in Table 4. It can be seen from Table 4 that the ultimate load had improved significantly for both reinforced and prestressed glulam beams. Increases of 58%, 32%, and 27% were achieved for the reinforced prestressed glulam beams. It should be noted that this increase was 58% for steel, 32% for basalt, and 27% for glass compared to unreinforced uncompressed beams, which represents a significant improvement for the same reinforcement ratio. Likewise, in terms of beam deflection, when 1/250 of the beam span was reached, the improvement was even more significant considering gulam prestressed beams. This increase was at the level of 10.7%, 10.1%, and 7.8%. This increase in stiffness was beneficial for strengthening as well as prestressing. The different levels of improvement in reinforcement efficiency were also related to the different elastic modulus of the reinforcement itself. In the case of prestressed steel bar rods, the failure was more abrupt, with a sudden but significant increase in load capacity and stiffness being achieved. In some beams, there was also shearing of the timber fibers, and compression shear occurred. In the case of beams reinforced with prestressed basalt bars, the failure was also abrupt but less than that of steel; an increase in load capacity of 32% was obtained, but the stiffness was comparable to steel. In the same way, most of the timber fibers got fractured in the tension zone, and some also failed in the compression zone. In the case of prestressed beams with glass reinforcement, significant increases in load capacity and stiffness were also achieved, but failure was most common in the tension zone. The numerical analysis of the normal stress values of the timber and composite bars in the tension zone also showed very good correlation with the laboratory analysis, as shown in Table 7. It should be noted that in the case of prestressed reinforced elements, for this class, the difference was small. In the same way, the values of the normal stresses in the composite bars were almost equivalent. The resulting small differences between the results obtained from the numerical analysis and the laboratory tests may be due to the fact that wood is a complex organic material exhibiting anisotropy of mechanical properties. There are structural complexities in wood (e.g., irregularities in the structure, wood defects, etc.) because it is a natural element; what affects it is impossible to control.