# Experimental and Numerical Analysis of an Innovative Combined String-Cable Bridge
## 5 Conclusions and Discussion  
The main objective of this article was to present an innovative combined string-cable bridge structure and investigate its behavior based on numerical calculations and experimental research. The experiment and FEA showed the effectiveness of this new combined bridge structural system in accepting both symmetric and asymmetric loads. Summarizing the conclusions, we can say that the innovative combined string-cable bridge structure, as shown by the numerical and experimental results, is best used when it is loaded with an asymmetric load, since the string \"constrains\" the kinematic displacements, as a result of which we have smaller total displacements. Additionally, a big advantage  
Figure 13: Displacements obtained numerically and experimentally with asymmetric loading, when \(T_{3}=1.506\) kN: (**a**) when \(\gamma=1\); (**b**) when \(\gamma=2\); (**c**) when \(\gamma=3\). is that we can pre-tension the string, which allows us to adjust both the tension forces and the displacements of the structure. Furthermore, it is necessary to remember that the string creates a straight line for the movement of transport, which allows such a structure to be adapted to various types of transport. Following the analysis of the behavior of the mentioned innovative bridge model, the following conclusions can be drawn:  
1. The bridge model was deformed symmetrically. 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. 2. 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. This is because the string has no initial sag and is extremely sensitive to displacements, which immediately induce axial forces in the string. 3. The bridge model deformed asymmetrically according to the placement of the live load (when the live asymmetric load was on the left side of the mode). The largest displacements occurred on the side loaded with an asymmetric load (nodes 3L, 5L, and 7L). These displacements increased proportionally to the values of the load ratio \(\gamma\). This means that in the case of asymmetric loading, kinematic displacements dominate. Since the string has no initial sag, it has no kinematic displacements, so it \"stabilizes\" the displacements caused by the asymmetric load of the entire bridge model (basically cable displacements). Increasing string pre-tension values also increases this \"stabilizing\" effect. This is evident from the obtained experimental results. 4. Displacements of the part of the model not loaded with live load (nodes 3R, 5R, and 7R) are directed upwards. The higher the values of the load ratio \(\gamma\), the larger these displacements are in absolute terms. However, in their absolute size, these displacements are significantly smaller than the vertical displacements of the loaded part. 5. The tensile forces in the string under asymmetric loading are higher than in the case of symmetrical loading. The cable forces increase with increasing pre-tension values. In this case, the axial forces of the cable change little and are smaller in absolute magnitude (at any value of \(\gamma\)) than the string axial forces. 6. In almost all cases, numerically obtained axial forces are higher than the experimentally obtained forces. We can also see that increasing the axial force in the string (if the load does not change) decreases the total displacements of the structure. This is shown by both experimental and numerical analysis data. Experimental and numerical studies of the new bridge were carried out under quasi-static loading only and under the assumption that the chords of the bridge are absolutely flexible. In real design, the flexural stiffness of the upper chord of such a bridge and the resulting bending moment in this chord should be evaluated.