## 5 Results and Discussion
### Stresses and Failure  
The stresses presented in this section were expressed in megapascals in the figures. Normal stress maps for composites and laminated veneer lumber were juxtaposed with the typical failure modes obtained for experimental tests. The goal of that comparison was to prove the applicability of numerical simulations for predicting the location of the failure and indicating the weakest link in the composite-LVL chain. In the case of reference beams, the maximum stresses are equal to the assumed yield strength. The maximum tensile stresses were slightly higher than the compressive stresses. The destruction of unreinforced beams was attributed to the brittle fracture of the LVL in the tension zone (Figure 5). A slight deformation in the veneer was observed at the point of application of the concentrated force [16]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **LVL** & **A** & **AU** & **G** & **GU** & **C** & **CU** & **CH** & **CHU** \\ \hline Experimental & 0.655 & 0.722 & 0.710 & 0.738 & 0.734 & 0.815 & 0.834 & 0.851 & 0.868 \\ Theoretical & 0.647 & 0.685 & 0.711 & 0.683 & 0.707 & 0.780 & 0.858 & 0.825 & 0.921 \\ Numerical (EL) & 0.681 & 0.745 & 0.768 & 0.753 & 0.776 & 0.865 & 0.945 & 0.895 & 0.991 \\ Numerical (EL-PL) & 0.636 & 0.692 & 0.719 & 0.702 & 0.727 & 0.800 & 0.886 & 0.825 & 0.928 \\ Theo./Exp. & 0.99 & 0.95 & 1.00 & 0.93 & 0.96 & 0.96 & 1.03 & 0.97 & 1.06 \\ Num. (EL)/Exp. & 1.04 & 1.03 & 1.08 & 1.02 & 1.06 & 1.06 & 1.13 & 1.11 & 1.14 \\ Num. (EL-PL)/Exp. & 0.97 & 0.96 & 1.01 & 0.95 & 0.99 & 0.98 & 1.06 & 0.97 & 1.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of experimental [16], theoretical and numerical values of stiffness coefficient. Figure 5: **(a)** Normal stress S11 distribution at ultimate load; (b) tensile failure of non-strengthened beam [16]. For beams strengthened with relatively low modulus composite sheets bonded only on the underside (A and G series), the ratio between the maximum tensile and compressive stresses was comparable to that observed in the non-strengthened beams. In the U-scheme (AU and GU series) context, the values of the maximum tensile and compressive stresses were approximately equal when these materials were used. In the remaining cases of strengthened beams (C, CU, CH, and CHU series), a slight decrease in tensile stress relative to compression was evident (Figure 6). The mode of failure also underwent a transformation, shifting from brittle fracture to a more plastic failure due to crushing in the compressed zone (Figure 7). In each of the cases analyzed, there was a distortion of the normal stress distribution within the concentrated force--the disturbances result from the plasticization of the laminated veneer lumber. The nature of these disturbances was identical for all strengthened beams. The slight discrepancies in the dimensions of these zones were attributable to the distinctive properties of the reinforcement employed--the volume of the plasticized zone increases in direct proportion to the rise in the factors above. Figure 8 illustrates the typical normal stress S11 distributions observed in the composite materials subjected to the maximum loading force. The following relationships can be observed: (1) as the stiffness of the sheet increases, the normal stresses also increase; (2) for the U-type configuration, slightly higher normal stresses were obtained compared to the sheet bonded only on the underside; (3) the maximum normal stresses of the sheet bonded on the underside were obtained at the center of the span, while for the sheet in the U-scheme at the axis of the loading force. The stress values obtained for aramid, glass, and carbon sheets were lower than those presented by the manufacturer [18; 19; 20; 21]. Despite the absence of stresses over the specified limit in the simulations, composite failure was observed in the experimental tests.