# Experimental and Numerical Analysis of an Innovative Combined String-Cable Bridge
## 3 Test Results and Analysis
### Experimental Results
#### 3.1.1. Symmetrical Loading  
The displacement values of the symmetrically loaded bridge model are presented in Tables 3-5, respectively, according to the string pre-tension values: \(T_{1}\) = 0.472 kN; \(T_{2}\) = 1.084 kN; \(T_{3}\) = 1.506 kN. Vertical displacements are given at nodes only. As indicated in the scheme of the deflection gauges (see Figure 4), displacements were measured at the bottom of the struts.  
From the results presented in Tables 3-5, it can be clearly seen that the bridge model was deformed symmetrically enough, and the maximum difference between the displacements of the left (R) and right (L) sides is about 5%. It was experimentally established that, under symmetrical loading, the pre-tensioning of the string does not significantly affect the displacements of the nodes of the bridge model. Increasing the string pre-tension values from 0.472 kN to 1.506 kN practically did not change the displacement values.  
It is necessary to notice that in the case of symmetrical loading, increasing the pre-tension of the string causes a greater change in the axial force in the string, while the axial force in the cable does not change (see Table 6). This is because the string has no initial sag and is extremely sensitive to displacements, which immediately induce shear forces in the string [4]. The cable has an initial sag equal to 0.5 m and absorbs the forces acting from the struts with a smaller tensile force.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multicolumn{2}{c}{**Loading Type**} & \multicolumn{8}{c}{**Vertical Displacements, mm**} \\ \hline Measurement points of structure & 1L & 3L/9L & 5L/10L & 7L/11L & 7R/11R & 5R/10R & 3R/9R & 1R \\ Dead load & 0 & \(-\)1.82 & \(-\)2.45 & \(-\)2.84 & \(-\)2.9 & \(-\)2.57 & \(-\)2.08 & 0 \\ Live load, symmetrical & 0 & \(-\)3.32 & \(-\)4.72 & \(-\)5.9 & \(-\)5.91 & \(-\)4.57 & \(-\)2.95 & 0 \\ \hline \end{tabular}
\end{table}
Table 4: Vertical displacements of the structure under string prestressing force \(T_{2}\) = 1.084 kN.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multicolumn{2}{c}{**Loading Type**} & \multicolumn{8}{c}{**Vertical Displacements, mm**} \\ \hline Measurement points of structure & 1L & 3L/9L & 5L/10L & 7L/11L & 7R/11R & 5R/10R & 3R/9R & 1R \\ Dead load & 0 & \(-\)1.97 & \(-\)3.07 & \(-\)3.3 & \(-\)3.4 & \(-\)3.07 & \(-\)2.19 & 0 \\ Live load, symmetrical & 0 & \(-\)3.64 & \(-\)5.02 & \(-\)5.96 & \(-\)5.95 & \(-\)5.35 & \(-\)3.57 & 0 \\ \hline \end{tabular}
\end{table}
Table 5: Vertical displacements of the model under string prestressing force \(T_{3}\) = 1.506 kN.  
Figure 9: Numbering of measurement points of the bridge model.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multicolumn{2}{c}{**Loading Type**} & \multicolumn{8}{c}{**Vertical Displacements, mm**} \\ \hline Measurement points of structure & 1L & 3L/9L & 5L/10L & 7L/11L & 7R/11R & 5R/10R & 3R/9R & 1R \\ Dead load & 0 & \(-\)1.87 & \(-\)2.54 & \(-\)2.76 & \(-\)2.65 & \(-\)2.41 & \(-\)1.66 & 0 \\ Live load, symmetrical & 0 & \(-\)3.06 & \(-\)4.64 & \(-\)5.66 & \(-\)5.95 & \(-\)4.98 & \(-\)3.22 & 0 \\ \hline \end{tabular}
\end{table}
Table 3: Vertical displacements of the bridge model under string prestressing force \(T_{1}\) = 0.472 kN.