As part of the new Prague Ring Road transportation link, a bridge was need to cross the Vltava River in Prague. The span would be 656 feet (200 meters) and 112 feet (34 meters) wide, enough to accommodate pedestrians and bicyclists as well as vehicles and a tram line.
Mott MacDonald provided a design for a steel-tied arch featuring a network arrangement of suspender rods.
The prestressed concrete bridge deck is suspended from the arch using two inclined planes of network hangers, which connect the arch to the two composite steel-concrete arch ties. The hanger arrangement provides four times the stiffness of a comparable tied arch using vertical suspender rods.
The Troja Bridge represents a major step forward in structural efficiency. By reconfiguring the hangers of the bowstring arch from a conventional vertical arrangement to a diagonal one, we dramatically improved the bridge’s performance.
The elegant design of the bridge results from the ratio of the rise to the span of the arch, accounting for its slenderness of 1:10, and the 1:180 ratio of the overall height of the arch to its span. The dense network of hangers made it possible to achieve these ratios by improving the strength and rigidity of the structure.