BRIDGES AND VIADUCTS

The Old Bridge on the Kupa river in Sisak The city of Sisak, known as Siscia in antiquity, was an important Roman municipium - a trade and crafts centre with a mint - and in the Middle Ages, it was the seat of the Croatian duke Ljudevit Posavski. In the 16th century, Sisak was a strategic stronghold in the resistance against Turkish conquest. During the 19th century, the city was slowly evolving into a trade and transportation centre, thanks to its location on the navigable rivers Sava and Kupa. The development of the city accelerated with the emergence of marine steam engines, and later also with the railway (the Zidani Most – Zagreb – Sisak railroad opened in 1862). Road transportation was less developed and, at that time, still depended on horse carts. All the while, the absence of a firm crossing that would connect the old part of the city on the left bank of the Kupa with the new part on the right bank, was causing considerable difficulties. Despite that, it was only in 1862 that a standard wooden bridge was constructed, its several smaller spans and one larger span, presenting a major obstacle to waterborne transport. However, it served its purpose for a full 72 years until the raising of the Old Bridge, which exists to this day. At the beginning of the 20th century, three project versions for the construction of the new, modern bridge that was to replace the old dilapidated wooden one were created. The project conceived by the engineer Milivoj Frković (1887 – 1945) was accepted and the current bridge was built in its image. Together with its access ramps, the bridge measures almost 400 m in length and has 7 spans of 7.2 + 34.5 + 36.9 + 38.5 + 38.25 + 14 + 12 m, from the left bank to the right. Great segmented vaults bridge the Kupa, while smaller elliptical ones bridge the streets on the bank. The passage stretches from Rimska street on the left bank to Žitna street on the right. Together with piers and abutments, the bridge is 207 m long, while the overall width amounts to 9.3 m, the roadway being 5.1 m wide, the pavements 1.53 m each, two fences 0.36 m each, and two coronals 0.2 m in width. Pedestrians have access to the bridge over ramps and spiral staircases on both abutments, as well as on both sides of the bridge through access corridors from the river bank openings. The foundations of the river piers are resting on caissons, their dimensions being 4.8 x 13.6 x 14 m, and the foundations of the abutments are on soil stabilizing pilots. The construction of the bridge began in 1925 and it was opened to traffic on May 6th 1934. It was built by the company A. Payer. The basic building material of the bridge is concrete, while all the visible surfaces are made of brick and cut stone. Delicate, richly designed details on the piers, vaults and fences, as well as coronals supported by spikes, add to the beauty of the bridge. The Old Bridge on the Kupa river in Sisak, this masterpiece of Croatian bridge construction of the first half of the 20th century can compare with the bridges of the greatest European capitals, both as a project and in terms of execution, and it is hard to find its equal among our bridges from that period. Jezerane Viaduct On the A1 Zagreb-Split highway, not far from the exit of the Mala Kapela Tunnel, is the 655 m long Mokro Polje Viaduct and the 668 m long Jezerane Viaduct. The Jezerane Viaduct crosses a dry valley in a circular curve 900 m in radius, and it is 46 m tall at its highest point. It was named after the Jezerane village, located at the bottom of the valley, under the viaduct. The overall length consists of 16 spans and two abutments, in the following order: 12.0 + 38.05 + 14 x 40.0 + 38.05 + 20.0 m. Horizontally, we are talking about two identical, parallel objects, measuring 2 x 14.4 m in width, with a distance of 10 cm between them, amounting to an overall width of 28.9 m. The traffic profile of the objects consists of two driving lanes and one emergency lane, as well as inspection walkways, with a guard and pedestrian fence. The core span structure consists of typical U-cross-section beams, measuring 2.2 m in height and, on average, 36 m long. They are built of prestressed concrete and there are four of them in every object’s cross-section. Building the foundation of the viaduct piers was done on reinforced concrete plate-like foundations with 10 x 8 x 2 m dimensions. The pillars are hollow, 5.5 x 2.4 m in cross-section, with 30 cm thick walls, and their height reaches up to 46 m. They end with a cap supporting the beams of the span construction. The object was planned by the company IGH - Concrete and Masonry Institute, with the architects being Gordana Trogrlić, Stjepan Kralj and Petar Sesar, PhD. The viaduct was built by the company Bechtel-Enka with the considerable involvement of Croatian companies, and it opened to traffic in 2005 at the time of the opening of the A1 Zagreb-Split highway. The Jezerane Viaduct is a typical example of the construction of longer viaducts on highways where rationality, speed of construction and keeping costs low demand the application of a long series of typical elements, resulting in more than one viaduct on the highway being constructed using the same technology and project solutions. The Jezerane Viaduct is well-incorporated into the landscape, but to be able to see it in full, one must drive along the state highway D-23 and stop in the village of Jezerane. Zvonimir-Zdenko Šimunjak B. Sc. C. E.