Bridge over the Ain River

Abstract

Owing to the construction of the new dam on the river Ain. the water of the river level has risen considerably above the earlier level of flow at the suspension bridge in the neighbourhood of Serrieres sur Ain. Hence it became necessary to substitute this structure by a more modern one, suitable to present day traffic demands. This paper summarises the main features of this new bridge. The new bridge spans the river by means of a reinforced concrete arch of 120 m span. The arch is circular, and the deck rests on a palissade supported by the arch. The maximum rise is 30 ms at the crown. The deck carries a roadway 7 ms wide and two sidewalks of 1 m width each, for pedestrians. The deck is supported by by four longitudinal beams, and the arch has a box section and 4 longitudinal stiffners. In the crown zone the stiffners, the deck and the cylindrical surfaces become integrated and enclose three hollow chambers. This structure has great stiffness. The depth of the arch is constant, except at the crown, and is 2.40 ms. This depth gives the arch a pleasing and slender aspect. The palissade consist of four rows of columns, of 0.80x0.20 ms section, at intervals of 12.50 ms. The radius of the arch is 78.80 ms, and its transversal box section has a total width of 8.60 ms. The thickness of the inner cylindrical surface is 0.20 ms. The springers consist of two large reinforced concrete blocks, of approximately 10 ms length and 4.70 ms height. The construction of the bridge was done with the aid of a Blondin cable, of 5 tns capacity, spanning 290 ms. The main constructional aid was a. wooden scaffolding, cantilevered from the sides, consisting of 10 trusses. The timber elements were nailed and bolted together. The top part of the framework supports a formwork, made with a double layer of boards, 27 mm in thickness, crossing each other at 45°. The scaffolding was erected in successive phases and a number of guy cables were employed to stabilise the structure against the deforming effect of the wind.