“Bowstring” Arches in Langer System Without Wind Bracing

Arch bridges are slender structures and can be efficiently used in the range of medium to large spans. These structures have an improved aesthetic aspect and in the same time a low construction height, with obvious advantages regarding reduced costs in the infrastructuers and their foundations.

For this type of structures usually composite or orthotropic decks are used. Lately, innovative solutions have been used in designing arch bridges, especially discarding the top wind bracing system. The level of axial forces and bending moments in the arches and tie imply the design of sections with sufficient stiffness and strength in both directions in order to ensure the general stability of the arches, without the need for top wind bracing. Moreover, the cross section of the arches is not constant, but shifts in accordance with the variation of the bending moments, in order to ensure their lateral stability.

This paper studies a road bridge with parallel Bowstring arches, with a span of 108m and a carriageway 7.00m wide, sustained by a deck made up of crossbeams 2m apart and a concrete slab. The main beams are held by ties arranged in the Langer system, 10 to 14m apart from each other. The sag of the arches is 18m high.

The analyzed structure was proposed for construction in the city of Oradea and is used for crossing the “Crişul Repede” river, between Oneştilor street on the left bank and the Sovata, Fagului and Carpaţi streets on the right bank.

The performed analyses have the following two main objectives: to establish the critical load for which the failure of the arches occurs by instability and to underline the influence of different wind bracing systems on the bridge’s collapse loads respectively.