Conceptual design of bowstring bridges with steel-concrete composite deck

The behaviour of tied-arch (bowstring) bridges is very sensitive to the conceptual design of arch and deck. The geometry of the arch shape and the arch-tie joint as well as the construction sequence can modify the global behaviour. When the arch geometry moves away from the anti-funicular shape, bending moments appear in the arch and in the deck even for dead loads; additional bending moments can increase the total value of tension in the deck becoming critical for a composite deck because of possible cracking of the upper concrete slab. The conceptual design of tied arches with composite deck is presented here, in order to reduce the danger of concrete slab cracking and the amount of reinforcement to be used in the deck for the crack widths. Acting on the geometry and construction sequence, the behaviour of the bridge can be optimized: an actual case of a bridge placed in Sicily is shown.