# The Performance Assessment of a Precast, Panel-Segmented Arch Bridge with Outriggers
## 4 Analysis of Target's Structure Behavior
### The Result of the Behavior Evaluation of 3D Structural Analysis Model
#### 4.1.3 Precast Panel and Outrigger Thrust Line Calculations  
The thrust line expresses the flow of force, which is dependent on the internal force and the external load. As with the evaluation of the stability of the compression member, the stability of an arch structure can be evaluated depending on whether the thrust exists in the central kern of the elastic area [8,9]. In the case of the proposed arch bridge, as steel outriggers are installed on the outer part of the precast panel, the tensile resistance of the outriggers can ensure structural stability, even when the thrust line deviates from the underside of the precast panel. Therefore, given that the proposed precast, panel-segmented arch bridge with outriggers can have a relatively flexible structure depending on the effect of the segmented precast panels, its stability can be determined according to its structural behavior using the thrust line. To compare the thrust lines according to the conceptual arch behavior  
Figure 25: Horizontal displacement (U1) with respect to construction step and outrigger position for models with spans of: (**a**) 6 m; (**b**) 7 m; (**c**) 8 m.  
of the proposed arch bridge with the behavior exhibited during the structural analysis, the thrust lines were compared at each construction step using the stress results of the bridges with spans of 6, 7 and 8 m obtained from the 3D structural analysis. The axial forces acting on the outriggers and those acting on the precast panels were calculated from the structural analysis results; the thrust line for each construction step was calculated using a proportional equation according to the distance from the origin (Figure 26). As shown in Figure 26, the thrust line of the arch bridge proposed in this study demonstrated a similar behavior to the thrust line of the arch bridge conceptually shown in Figures 2-5. Under the self-weight condition, there was a relatively large displacement near the support of the bridge and arch crown, as indicated by the structural analysis results; thus, the thrust line was directed outward from the precast panels at the arch crown and the support. However, the load acting on the outer side of the precast panels was converted into a compressive force at the arch panels, and the thrust line acting on the proposed bridge also acted within the precast panels. Even in the final loading state, the same behavior was observed. As shown in Figure 26, with an increase in the span, there were relatively small changes in the thrust line behavior, which is similar to the case of the deformation of the arch bridge. Hence, if the rise ratio of the arch bridge is large, as in the deformation of the abovementioned arch bridge, the load on the arch bridge panels is relatively large; this causes the thrust line to be located outside of the arch bridge precast panels. However, with an increase in the span of the arch bridge, the arch thrust line changed such that it was located inside the concrete panels. This confirms that the structural stability of the target arch bridge can be secured through the tensile resistance effect of the outrigger installed externally to the precast concrete arch panel of the proposed arch bridge. Accordingly, the precast panel arch bridge with the proposed outrigger demonstrated a stable and structurally-effective performance.