# Effect of Stiff Hangers on the Longitudinal Structural Behavior of Tied-Arch Bridges
###### Abstract  
In the design process of an arch bridge, the designer may decide to stiffen the hangers linking the arch and the deck, usually in order to reduce the internal forces or the deflections. In this paper, the effect of stiffened hangers on the longitudinal in-plane structural behavior of arch bridges is studied. Then, the effect of the stiffness of the hangers and the relevance of the arch-deck relative stiffness are shown. The paper also describes how stiff hangers with a hinge--either at the bottom or the top--combine very high structural efficiency and ease of execution. Once the advantages of stiff hangers are described and a possible drawback is highlighted. The problem may arise for stiffened hangers, as the bending moments near the ends of the deck might become more adverse for symmetrical load cases than for asymmetrical load distributions, as this usually occurs in arch bridges. To address this problem, this paper suggests a novel solution by designing a combination of fixed and pinned hangers, which can be as efficient as a configuration where all the hangers are fixed, while simultaneously reducing the bending moment at the end zones of the deck.  
B 2018  
In the early steps of the design process of an arch bridge, the most adverse load combination is usually a live load acting upon half the deck, which causes bending moments both in the arch and the deck. It will be seen that when the hangers are pinned at both ends, it can be accurately assumed that the amount of bending supported by the arch is proportional to the ratio \(EI_{A}/(EI_{A}+EI_{D})\), i.e., to the ratio between the flexural stiffness of the cross-section of the arch with respect to the flexural stiffness of the arch and the deck (where \(E\) is the Young's modulus of steel, and \(I_{A}\) and \(I_{D}\) are, respectively, the second moments of the area of the arch and the deck). Therefore, during the design process, it may happen that the dimensions of the cross-sections cannot prevent the failure of the bridge. Similarly, it may happen that the deflection of the deck are beyond allowable values. At this point, the designer usually decides to redesign either the cross-section of the arch, the deck, or both, according to their professional experience. However, and as an alternative, the designer may decide to stiffen the hangers linking the arch and the deck, usually in order to reduce the internal forces or the deflections; such a decision is the object of this paper.  
In this paper, the effect of stiffened hangers on the longitudinal in-plane structural behavior of arch bridges is described. The study has been carried out for a reference bridge, taken as being representative of typical tied-arch bridges. Then, the effect of the stiffness of the hangers and the relevance of the arch-deck relative stiffness are shown. The paper also describes how stiff hangers with a hinge, either at the bottom or the top, combine very high structural efficiency and ease of execution. Since in-plane buckling is seldom the reason for the failure of arch bridges as described in [PERSON] [8]; its effect is not considered in this study.  
One of the most relevant contribution of this paper is to highlight a possible drawback of stiff hangers. The problem arises because, for stiffened hangers, the bending moments near the ends of  
Figure 1: Structural elements of a tied-arch bridge.  
Figure 2: Bridge for the Autobahn A-42. Rhine–Herne Canal. Photo: [PERSON] (reproduced with permission from Structurae [7], 2008).  
the deck might be more adverse for symmetrical load cases than for asymmetrical loads distributions, as it usually happens in arch bridges. To address this problem, this paper suggests a novel solution by designing a combination of fixed and pinned hangers, which can be practically as efficient as a configuration where all the hangers are fixed, and simultaneously reduces the bending moment at the end zones of the deck. Thus, this solution combines structural efficiency and ease of execution.