Influence of stiffened hangers on the structural behavior of all-steel tied-arch bridges

In tied-arch bridges, the way the arch and the deck are connected may become crucial. The deck is usually suspended from hangers made out of steel pinned cables capable of resisting axial forces only. However, a proper structural response may be ensured by fixing and stiffening the hangers in order to resist, additionally, shear forces and bending moments. Thus, this paper studies the effect of different pinned and stiffened hanger arrangements on the structural behavior of the tied-arch bridges, with the intention of providing designers with useful tools at the early steps of design. Longitudinally and transversally stiffened hangers (and the effect of hinges at the hangers and their locations) are studied separately because the in-plane and the out-of-plane behavior of the bridge are uncoupled due to its symmetry. As a major conclusion, regarding the in-plane behavior, hangers composed of cables (either with vertical, $Nielsen-L\ddot{o}hse$ or network arrangements) are recommended due to its low cost and ease of erection. Alternatively, longitudinally stiffened hangers, fixed at both ends, can be used. Regarding the out-of-plane behavior, and in addition to three-dimensional arrangements of cables, of limited effectiveness, transversally stiffened hangers fixed at both ends are the most efficient arrangement. A configuration almost as efficient and, additionally, cheaper and easier to build can be achieved by locating a hinge at the end corresponding to the most flexible structural element (normally the arch). Its efficiency is further improved if the cross-section tapers from the fixed end to the pinned end.