## 3 Results and Discussion
### Study on Cost in Relation to Mechanical Properties of Reinforced and Unreinforced Beams  
To compare the cost of beams, including mechanical properties, calculating a cost multiplier (\(C_{T}\)) was necessary, as determined by Equation (11):  
\[C_{T}=\frac{C_{BSH-CFRP}}{C_{BSH}} \tag{11}\]  
\begin{table} \begin{tabular}{c c c c c c c c} \hline \hline  & \(L\)/\(h\) & 21.43 & 18.75 & 16.67 & 15.00 & 13.64 \\ \multirow{2}{*}{\begin{tabular}{c} **Length** \\ **(m)** \\ \end{tabular} } & \(\begin{array}{c}L\)/\(h\) \\ **Stiffness** \\ \end{tabular}  & 21.43 & 18.75 & 16.67 & 15.00 & 13.64 \\ \multirow{2}{*}{ \begin{tabular}{c} **Stiffness** \\ **(m)** \\ \end{tabular}  } & \(\begin{array}{c}L\)/\(h\) \\ **Stiffness** \\ \end{tabular} & 21.43 & 18.75 & 16.67 & 15.00 & 13.64 \\ \multirow{2}{*}{ \begin{tabular}{c} **Stiffness** \\ **(m)** \\ \end{tabular}  } & \(\begin{array}{c}L\)/\(h\) \\ **Stiffness** \\ \end{tabular} & 21.43 & 18.75 & 16.67 & 15.00 & 13.64 \\ \multirow{2}{*}{\ \begin{tabular}{c} **Stiffness** \\ **(m)** \\ \end{tabular}  } & \(\begin{array}{c}L\)/\(h\) \\ **Stiffness** \\ \end{tabular} & 21.43 & 18.75 & 16.67 & 15.00 & 13.64 \\ \multirow{2}{*}{ \begin{tabular}{c} **Stiffnessness** \\ **(m)** \\ \end{tabular}  } & \(\begin{array}{c}L\)/\(h\) \\ **Stiffness** \\ \end{tabular} & 21. Looking at the increases in stiffness and load-bearing capacity as in the increasing glue laminated timber class, the cost increase in dependence on the BSH class increase was possible to be found. This can be substantial information, because these days, when demand for wood is high, acquiring a BSH class higher than GL24h is hard in a traditional production. Increasing stiffness by 5.22% leads to the BSH one class higher (GL26h), and 10.44% to two classes higher (GL28h), while one class growth in the case of load-bearing capacity may be completed by an 8.33% increase and 16.66% for two classes. When these features were known, based on the obtained results, creating a cloud of points representing the cost multiplier in dependence on class growth both for stiffness and load-bearing capacity was possible. Results presented in the mentioned manner are shown in Figures 9 and 10. Based on the point clouds, applying exponential approximating functions for both dependencies with a very good \(R^{2}\) fitting factor could be achieved. For cheap and expensive wood, the formulas are Equations (12) and (13). They made it possible to collect data in one graph and describe the basic differences (Figure 11). \[Stiffness:\subset_{\text{C}_{T,cheap}}=1.148\cdot e^{0.837\cdot x},\;\text{C}_{ T,expensive}=0.957\cdot e^{0.618\cdot x} \tag{12}\]  
\[Load\;bearing\;capacity.\;\text{C}_{T,cheap}=1.193\cdot e^{0.917\cdot x},\;\text{C}_{ T,expensive}=0.984\cdot e^{0.677\cdot x} \tag{13}\]  
Figure 10: Cost multiplier in dependence on glue laminated timber class increase based on load-bearing capacity. As it can be seen in Figure 11, the cost of increasing the BSH class based on stiffness was close but was slightly different from this for the load-bearing capacity. For the stiffness, the cost multiplier with expensive wood for BSH one class growth (GL26h) was 1.78 and 3.29 for two classes (GL28h), while for cheap wood it was 2.65 and 6.12, consecutively. Equally, the load-bearing capacity with expensive wood for one class growth was 1.94 and 3.81 for two, while with cheap wood it was 2.98 and 7.47, consecutively. To interpret the results in a clearer way, a column graph was prepared (Figure 12). It presents a BSH class increase in dependence on the wood price (cheap/expensive) and mechanical response (stiffness/load bearing capacity). For general summary, the results were averaged. It can be stated that improving the BSH standard class by one using CFRP tapes was associated with 1.86 BSH cost in the case of expensive wood or 2.81 in the case of cheap wood. Improving the class by two was connected with 3.55 BSH cost for the expensive wood, and 6.79 for the cheap wood.