Bridges and Viaducts

BRIDGE “KRKA” ON HIGHWAY A1

ZAGREB-SPLIT-DUBROVNIK

The River Krka, a jewel among rivers of the Adriatic drainage area, probably the most beautiful and attractive among them and well known for its waterfalls, was bridged when the A1 Highway was built, at a point few kilometres downstream from the town of Skradin by an impressive arch bridge. The bridge is located between the nods Skradin and Šibenik, and immediately behind it there is a rest area with a restaurant and viewpoint, from where the view of the bridge and the town of Skradin can be enjoyed. Especially attractive is the view at the bridge for yachtsmen heading to Skradin. The total length of the bridge is 391 m, the width is 22.5 m and it rises 66 meters above the sea level. The main span construction of the bridge over the river Krka is a hollow ferroconcrete arch of 204 m, i.e. 4 m bigger than the bridge of Maslenica (200 m). The cross-section of the arch is 3x10m, with the walls of 0.5 m. As much as 2988 m3 of concrete and 747 t of reinforcement have been built into the bridge, which was constructed according to cantilever principle and with cable support. The structure of the bridge above arch is composed of the grid of steel longitudinal and cross beams with cantilever projections and with rim beams. The longitudinal beams are coffered with cross-section of 0.75x1.7 m and a span of 32 i.e. 28 m. On the described grid a ferroconcrete slab of roadway of 25 cm has been laid. The described structure above arch contains 1700 tonnes of steel, 2172 m3 of concrete and 630 tonnes of reinforcement and it leans on the terrain and the arch of the bridge, by means of pillars reaching up to 55 m. The pillars are of hollow cross-section varying from 3.2x2.5 to 1.8x2.2 m in dependence of their height. Each pillar position has two equal pillars.

It should be pointed out that in the construction of this bridge rational technical solutions have been applied which have made possible – by respecting all prescribed conditions - a savings on the total mass of the object of 35 % in relation to almost identical Maslenica bridge.

The designer of the bridge was Dr. sc .Zlatko Šavor, the supervisor was IGH Zagreb - Dr.sc. Z. Marić, and the bridge was built in the period 2002- 2005 by the company “Konstruktor inženjering Inc.” from Split with the steel part built by the company “Đuro Đaković Ltd.” from Slavonski Brod. The bridge was opened to traffic together with the opening to traffic of the highway Zagreb –Split in 2005.

VIADUKT “MODRUŠ 1” ON HIGHWAY A1

ZAGREB- SPLIT-DUBROVNIK

Viaduct „Modruš1“ is the first and the longest in the row of three viaducts of the same name at the road section Ogulin- Brinje of the Highway A1 Zagreb-Split- Dubrovnik, at approach to the tunnel Mala Kapela. The object is situated near the settlement and the ruin of the old town of Modruš which once was also the seat of the Modruška County and can be seen from the right side when driving toward Brinje. The viaduct bridges a deep valley at the height up to 50 m from the lowest point of the valley and has a total length of 516 m and a total width of 31.5 m, enabling thus in standard profile the traffic on highway in both driving directions. Due to that many drivers even do not notice that they have crossed over a remarkable road construction building. In order to get an impression of the size of this viaduct one should exit to a parallel state road D23. The construction actually consists of two parallel, almost identical viaducts each serving one driving direction, which are transversally interconnected for the purpose of checking and maintenance. The levelling line of the viaduct is ascending 4.8% toward the tunnel Mala Kapela. The viaduct consists of 13 sections with centre-to-centre distances of the props (pillars): 38+11x40+38m = 516m. Particular construction spans consist of four prestressed ferroconcrete pillars with coffer cross-section, 2.2 m high and 37 m long, interconnected with a roadway slab. Particular span constructions lean on beam heads of pillars, by means of separate bearings.

The lower structure of the viaduct consists of abutments and pillars based on laminated ferroconcrete foundations, in consideration of rocky basic grounds. The foundations of pillars are 10.0x8.0x2.0 m. The abutments with parallel wings are based in the similar way. The pillars of the viaduct are hollow, of outer cross-section of 2.4 x5.4 m and with the wall thickness of 0.3 m. Used materials are ferroconcrete and prestressed concrete.

The project of the viaduct was made by IGH-Institute for Concrete and Masonry Structures, the designers were Gordana Trogrlić-Uzelac, Stjepan Kralj and Dr. Sc. Petar Sesar. It was built by the company Bechtel-Enka with participation of Croatian companies. The viaduct was opened for traffic in 2005 on the occasion of opening of the A1 Zagreb- Split Highway.

Zvonimir-Zdenko Šimunjak