Paul Osborne, engineering manager for supplier ">Macalloy Ltd., says the hanger order was the largest-ever bridge-component order for the Sheffield, U.K., firm. Infrastructure projects in Eastern Europe have helped fuel Macalloy’s 100% growth—to about $20 million a year—since its management buyout 10 years ago, adds Chris Willett, sales director.
Macalloy fatigue-tested the hanger turnbuckle system to withstand two million cycles under 130 mega-Newtons per sq m of stress, says Vladimír Janata, chief technical officer and chairman of Excon A.S., the bridge’s steelwork design subcontractor.
To erect the bridge, Metrostav considered various options, including assembling the whole span on one bank and pivoting it, with one end floating on pontoons over the river. A few years earlier in Slovakia, that technique had been used to place the 231-m-long arch of the Apollo bridge, also known as the Kosická, over the Danube in Bratislava, says Vítek. But in Prague, the Vltava River was too shallow.
Starting in late 2010, the contractor partially assembled the deck on a steelwork truss next to the river and launched it over temporary river piers. The deck structure comprises precast-concrete lateral beams hung from beneath the arches’ bottom chords at 4-m intervals. The beams are 0.5 m wide and taper up to 1.5 m deep.
Once the truss spanned the river, the contractor cast the 28-cm-thick deck in 16-m-long sections, loading the lateral pretensioning in each. Longitudinal tendons were stressed after the final, central deck section was cast.
Metrostav then assembled nearly 800 tonnes of steelwork for each of the two outer thirds of the arch on the deck and rotated them to the correct levels, propped by temporary towers. The central section followed, completing the self-supporting arch and allowing the towers to be removed.