Appearances can be deceptive. At first glance, the Domovinski Most looks like a typical modern river bridge, with continuous box girder approach viaducts and a cable stay central span across the river itself. A second glance reveals the unusually low angle of the 'harpstyle' stay cables, around 12infinity, and the short pylons.
'Low pylons were preferred due to the proximity of the airport, ' client Grad Zagreb's chief designer Rajka Veverka explains. 'And the low angle of the stays means they carry virtually no traffic loads, which eliminates the risk of fatigue in the cables.'
A bridge design competition was held in 1997 and won by Veverka and her small team. The judges liked the superior aesthetics produced by the winning design's longer spans and constant depth deck, as well as looking for as few piers in the flood plain as possible.
Insitu concrete construction was the obvious choice, given the size of the cross-section. Longitudinally, the approach viaducts are prestressed by 'external' tendons inside the box girder, with transverse internal tendons in the top deck flange and pierhead deviator diaphragms. At the centre span 55% of the prestress comes from the external inclined cables, the rest from tendons inside the deck box.
For better long term durability the entire length of the box girder is constructed without expansion joints, with one fixed bearing only, at pier 9. Seismically the region is fairly active, and Eurocode 8 provisions have been applied. The solution, given the shortness and transverse stiffness of the piers, is to protect the bridge against seismic forces in the longitudinal direction only, with eight hydraulic dampers installed at each abutment.
This is the first Croatian bridge to rely entirely on dampers for seismic resistance. Indeed, Domovinski Most is the first crossing of its type in Croatia, and only three others are known of in the rest of the world. Main design/ build contractor Industrogradjna will build the bridge using the welltried balanced cantilever system.