Stay Cable and Tensioning Systems for a Water Pipeline Bridge
In 2001 the City of Zagreb decided to build its first ever wastewater treatment plant on the left bank of the Sava river in order to treat municipal wastewater according to current EU standards.
Context
The Sava River crosses the city of Zagreb and is heavily contaminated. The waste coming from this growing city (with a population of 900,000) and industrial zone located on the left bank near the airport has until now been discharged directly into the river.
The project, co-financed by EBRD (European Bank for Reconstruction and Development) and KfW (Kreditanstalt für Wiederaufbau, the German government development bank) and planed on a BOT basis for 28 years, incorporates not only the wastewater treatment plant, it also includes the supporting infrastructure such as access roads, collecting pipelines, and a bridge across the river.
The 840m-long "Domovinski" Bridge will not only ease traffic congestion between the inner city and the industrial and airport area, but also carry two water pipelines. One will transport the waste water from the inner city to the new wastewater treatment plant and the other will supply the areas on the river left bank with drinking water as the drinking water pumping sites are located on the right bank.
The bridge has spans of 48 m + 6x60 m + 72 m + 120 m + 72 m + 2x60 m + 48 m which also cross the former flood plain. The main span of 120 m across the river is constructed using the free cantilever method. The superstructure is 34m wide because the citys development plan required that the bridge deck provided enough space for a double-track tramway line, two separate double traffic lanes, as well as a footpath and a bicycle lane on each side.
Solution
The bridges superstructure was designed as a continuously prestressed five-cell hollow box girder. The superstructure is prestressed in the webs with 15x0.62" strand tendons, in the diaphragms with 12x0.62" strand tendons and in the deck slab in transverse direction with unbonded 0.6" monostrand tendons.
A total of 2x8 pairs of DYWIDAG Stay Cables consisting of 48x15.7 mm strands are used to carry the total load of the bridge deck. All approach spans were constructed span by span on scaffolding.
The project was completed in 2006.
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