The effect of fatigue on the arrangement of hangers in tied arch bridges

The arrangement of the hangers in tied arch bridges is one of the key issues in optimizing the design of this typology of bridges. Bending moments in the arch and the tie and axial forces in the hangers are usually the parameters on which attention is focused. The hangers are particularly vulnerable to fatigue phenomena but the variation of axial forces in hangers is not deeply studied despite the fact that it is an important parameter in relation to the fatigue behaviour of the hangers. In this context, this paper mainly deals with the reduction of fatigue stressing in hangers of road arch bridges. The analysis is carried out by varying the vehicular load position along the deck; the assumed parameters are the maximum variation and the average variation of the hanger force. Various hanger arrangements are considered: vertical, fan and network arrangement with inclined hangers having multiple intersections. One of the main results is that, on the one hand, vertical and fan arrangements are better than network ones if the fatigue in the hangers is considered as the only parameter, and, on the other hand, network arrangements are globally the best if the bending moments in the arch and the tie and the absolute values of the axial forces in hangers are also considered. Therefore, the work also focuses on decreasing the fatigue stressing of vertical, fan and network arrangements without increasing the bending moments in the arch and the tie. The results suggest that a slight modification of the radial arrangement near the arch springing points, namely using steeper hangers, leads to a smaller force variation in the hangers without increasing the bending moments in the arch and the tie.