# Improving the Structural Behavior of Tied-Arch Bridges by Doubling the Set of Hangers
## 1 Introduction
When properly used, this strategy has the advantage where the cross-sections, both of the arch and the deck, do not need to be enlarged. In fact, they can often be lightened, as will be shown in Section 4. Furthermore, it is shown how this cable arrangement does not worsen the structural behavior of the bridge in the vertical plane under symmetric loads with respect to those of bridges with a single centered set of hangers, and it will be  
Figure 1: (**a**) Vertical and (**b**) Nielsen hanger arrangements. seen how, in the studied cases, the structural behavior improves. With the purpose of studying the advantages of this type of cable arrangement, the structural behavior of a series of tied-arch bridges has been studied both with vertical and Nielsen hangers and for bridges with one set of central hangers attached to the centerline of the deck (Figure 3a) and for two sets of lateral hangers anchored to its edges (Figure 3b). In Figure 3,\(f\) corresponds to the maximum vertical separation between the arch and the deck, i.e., the rise of the arch. This paper begins by defining, in Section 2, the so-called reference models, which are two common bridge configurations (two tied-arch bridges, one with vertical hangers and the other with a Nielsen-type arrangement) on which all the bridges shown in this paper are based. Section 3 studies the behavior, in the vertical plane, of bridges with a single set of hangers under symmetric loads. The results of this section are compared with the results of the studies carried out in Section 3, Section 4, Section 5, Section 6, Section 7. In addition, it is shown how the cables anchored to the axis of the deck are not able to reduce the deflections due to the torsional twist of the deck. Section 4 introduces bridges that differ from those studied in Section 3 in that they have two sets of hangers attached to the edges of the deck. Their deflections and forces are studied. It is shown not only that their structural  
Figure 3: (**a**) One set of central hangers attached to the centerline of the deck. (**b**) Two sets of lateral hangers attached to the edges of the deck. Figure 2: Tied-arch bridge in Tartu over the Emajogi river (Estonia). Photor [PERSON], Wikimedia Commons. behavior improves under eccentric loads but also that the behavior for symmetric loads improves with respect to that of the bridges with one central cable arrangement. Based on the results obtained in Section 4, Section 5 identifies the structural systems that support symmetric and nonsymmetric loads, i.e., actions contained within the plane of the arch and out-of-plane actions. The effect of the second set of hangers in the vertical response of the bridges will be discussed. In addition, it will be seen how some structural systems, such as the transversal and torsional stiffness both of the arch and the deck, become active under out-of-plane loads when the arch is linked with two sets of hangers to the deck. Section 6 shows how, in Nielsen-type bridges, due to nonsymmetric loads, the end hangers can be put into compression and loosen and how this problem can be solved by forking the ends of the arch. Section 7 discusses the buckling of this type of structure and shows how attaching the arch to both edges improves the out-of-plane buckling resistance of the arch. Furthermore, it is shown how forking the ends of the arch, as it happens, for example, in the Wittenberg Bridge (Figure 4), may also be a solution to improve the buckling resistance of the arch since its buckling length is reduced. The paper ends with the Conclusions section (Section 8).