Effects of deck girder slenderness on lateral elastic stability of tied arched footbridges

The aim of the paper is to investigate how the deck girder slenderness could affect the lateral critical load of a tied arched steel bridge. Previous models in the literature consider the deck girder infinitely stiff in the out-of-plane direction but, if we look at the challenges of modern footbridge engineering, the search for new dramatic shapes involves the deck itself, leading to more and more slender decks. This leads to the need to remove the tightening hypothesis of an infinitely stiff deck: this removal will produce a new formulation for the lateral buckling of the slender tied arch, describing the behaviour in terms of opportune geometric parameters. It will be shown that tied arched bridges must be investigated as global structures: this means the lateral behaviour of the curved members cannot be studied separately from that of the substructure, due to a coupled dependence and an exchange of influences. If usually these influences had to be studied with specific FEM analysis “at hoc”, now some manageable expressions are given to carry out accurate predictions since the early stage of the preliminary conceptual design. The results will then be applied to test the current Eurocode 3 instructions for preliminary stability checks: some inaccuracies will be found in the latter and the necessary modifications will be proposed.