## 6 Comparison of Experimental and FE Based Strain Values
### Demec Mechanical Strain Gauge Measurements on the Concrete Surface  
The comparison between the six FE models and the experimental results from the mechanical strain gauges mentioned in Section 4.3 are shown in Figure 10 for the measurements at 200 mm from the bottom and in Figure 11 for these at 245 mm from the bottom of the girder. Due to convergence issues, the FE results MAX-0.9 are omitted from Figures 10 and 11. It is clear that there is a good fit between the experimental and numerical results of the horizontal strain in the end zone, more specifically for the FE models with a coefficient of friction of 0.7. In the transmission zone (i.e., the ascending branch), the differences are limited, while beyond the transfer length, a larger scatter of the DEMEC measurements is noticeable. The fact that on average 10 to 15% larger strains than predicted are found in the horizontal branch (i.e., beyond the transmission zone) can be attributed to an incorrect value of the concrete stiffness used in the FEA. This results from the strict relation between concrete stiffness and strength as implemented in all codes and normative documents, which does not allow a numerical adjustment of the modulus of elasticity only. An analysis with only an adjustment of the concrete stiffness (modulus of elasticity \(-10\%\) to \(+10\%\) of coded value simulated) was performed in [PERSON] et al. [21], indicating that the simulated horizontal strains on the concrete surface are practically a linear function of the modulus of elasticity. Should a smaller modulus of elasticity have been adopted in the analyses shown in Figures 10 and 11, the FEA curves would have been shifted slightly to larger strain values, and a coefficient of friction of 0.5 to 0.7 can be proposed.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Age (Day)** & **Condition** & \(\mathbf{f_{4,R}}\) [N/mm\({}^{2}\)] & \(\mathbf{f_{4,R}}\) [N/mm\({}^{2}\)] & \(\mathbf{f_{4,R}}\) [N/mm\({}^{2}\)] & \(\mathbf{f_{4,Rup}}\) [N/mm\({}^{2}\)] & \(\mathbf{f_{4,Rup}}\) [N/mm\({}^{2}\)] & \(\mathbf{f_{4,Rup}}\) [N/mm\({}^{2}\)] & \(\mathbf{f_{4}}\) [N/mm\({}^{2}\)] \\ \hline \multirow{8}{*}{7} & \multirow{8}{*}{net to girder (outside)} & 5.32 & & & & 4.88 & & \\  & & & & & & 4.53 & & \\  & & 5.49 & & & & 4.68 & & \\  & & net to girder (outside) & & & & & 4.21 & & \\  & & 5.35 & & 5.64 & & 3.39 & & 4.57 & 4.61 & 4.15 \\  & & & & & & 5.13 & & \\  & & 6.41 & & & & 4.73 & & \\ \cline{2-10}  & & 5.92 & & & & 5.34 & & \\  & & 6.07 & & & & 4.43 & & \\  & under water (lab) & 7.27 & & & & 5.18 & & \\  & & 6.41 & & 3.84 & & 4.57 & 4.94 & 4.45 \\  & & 7.27 & & & & 5.21 & & \\  & & 6.37 & & & & 4.63 & & \\  & & & & & & 5.48 & & \\ \hline \multirow{4}{*}{14} & \multirow{4}{*}{under water (lab)} & 7.96 & & & & 6.33 & & \\  & & 8.09 & & & & 5.67 & & \\  & & 7.11 & & & & 5.67 & & \\  & & & & & & 6.34 & & \\ \hline \multirow{4}{*}{28} & \multirow{4}{*}{under water (lab)} & 7.68 & & & 6.78 & & & \\  & & & & & 6.00 & & \\ \cline{1-1}  & & 8.32 & & 7.79 & & 5.96 & 6.00 & 5.40 \\ \cline{1-1}  & & 7.37 & & & & 5.46 & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Results of the flexural and splitting tensile tests.  
From the FE results it may also be observed that the transmission length is smaller with a higher coefficient of friction and higher early age compressive and tensile strengths, which is in agreement with earlier findings from [PERSON] et al. (2018).