Troja Bridge is a double-deck, bowstring arch-type bridge built over the Vltava River for the City of Prague, Czech Republic. It connects the central city to the Prague Ring Road in the Myslbekova – Pelc-Tyrolka section. It replaces the temporary bridge named ‘Ramusak’, built in 1980 connecting the banks of Vltava.

The bridge replacement work contract was worth £29m (approximately $48.5m) and was completed in 2014. The new bridge was officially opened in November 2014. The structure of the bridge consists of steel box sections with multiple webs. The bridge carries two lanes for pedestrian and cycle traffic, four road lanes, and two tram lines.

Troja bridge design

The bridge structure, designed by Excon, comprises two spans, including the 200m-long main span crossing the river and a 40.4m-long side span.

The main span is traversed by a flat steel network arch tied to the suspended concrete deck. A multiple box section is placed at the mid-span of the steel arch. The arch section divides into two legs close to the supports to allow the passage of the tramway.

The arch is connected with two steel-concrete composite main chords by the two inclined plans of tension bar networks. The arch bases at either side are placed on the concrete deck and the last massive in-situ cast transversal beam. The footings are filled with self-compacting concrete to carry heavy loads.

The side span of the bridge is a single-span, pre-stressed concrete structure. The deck is built with a 280mm-thick concrete slab supported by pre-stressed transversal beams tied with network hangers. Each beam is supported by two cables with nine strings.

The distinct structures of the main and side spans are based on individual bearings and linked on the intermediate pier through enlargement juncture. The diameter of inclined hangars varies between 76mm and 105mm. Four 15.7mm strands in flat ducts make the transversal pre-stressing tendon and each composite tie has six cables with 37 strands.

The unique criss-cross design of the hangers makes the bridge strong and enables architectural efficiencies relating to high length-to-height ratios in comparison with the standard bowstring arch bridges. The built-in sensors in the system also measure temperature, wind speed and humidity.

The exclusive fatigue-resistant thread form for the bridge was constructed according to EN 1993-1-11: 2006 and meets the Eurocode 3 requirement for fatigue connections in bridges.

Key players involved with the Troja bridge construction

Mott MacDonald and Koucky Architects devised the preliminary, tender and detailed designs for the Troja Bridge. The main contractor for the bridge is Metrostav, while Bilfinger MCE Slaný, as a subcontractor, supplied and assembled approximately 1,400t of steel construction, including the main section, arch and tie.

Novák & Partner was contracted to design the incremental setting-up of the construction procedure and temporary structures.

CCE Prague was also involved in the construction of the bridge since the preliminary stages, serving as the chief geodetic surveyor. Wireless inclinometers were utilised for verticality monitoring of the torsion bars which were used to lift individual bridge arch components.

Macalloy was contracted to supply Macalloy 520 tension bar system for the bridge replacement project. The durable 520 tension bar system is used for the bridge hangers. Macalloy has further supplied its Techno-Tensioner device used for the architectural steel bars. The device uses a turnbuckle connection for on-site stressing of the tension bars. Ovako was contracted to provide Macalloy with structural steel for the project.