15 Mar 2022

What are 25 years in the life of a bridge?

The answer to this question can be manifold. But, we're going to focus on what a bridge actually represents. It is a link between two sides, but it connects the people more than that. We're talking about the bridge over the Dobra River in Ogulin, which was built a bit over 25 years ago. For the citizens of Ogulin, the construction of the bridge solved their long-standing issues of the Dobra River flooding Ogulin and separating the town centre and the western part of the town. In its current state, the city of Ogulin is exposed to frequent flood events due to the high waters of the river Gornja Dobra. In the last 15 years, a total of ten flood events have been recorded with various degrees of material damage, generating average annual damage of 102 million HRK in households and industry.

An informal celebration of the 25th anniversary of the bridge's construction was an opportunity to unite the people responsible for its construction at the time. The designer, dr. sc. Petar Sesar, on behalf of Institut IGH, Mr Igor Džajić, who was the Head of the construction site at the time, working for Viadukt, now a member of IGH Management Board on one side. And the clients, Mr Ivan Kolić, the Mayor of the City of Ogulin at the time, Ms Vesna Salopek Košutić, project manager for the city and her husband Mr Marinko Košutić who was an informal "witness of the time "and photographed the progress of the project.

Although they have new jobs and responsibilities today, the Bridge over Dobra is one of those special projects for all the parties involved. The reunion at the bridge was spent reminiscing and telling anecdotes, so even though it had been over 25 years, everyone agreed it seemed like it had been yesterday.

The design of the bridge was developed by Institut IGH based on an earlier solution, developed by perhaps the most well-known bridge designer in Croatia, the late professor Tonković, Viadukt was the contractor, and the client was the town of Ogulin. So, although this was neither the largest nor the most complex bridge IGH has designed or Viadukt had built, its construction speciality makes it an exciting project even today.

As mentioned, until 1996, an old, steel truss bridge stood in its place. It was constructed during the Austro-Hungarian Empire and so worn-out that all traffic other than pedestrians was forbidden over it already in 1990. The bridge was 42 meters long, 5 meters wide and over 30 meters above the Dobra River. Constructing the bridge in the exact location while at the same time removing the existing one was a challenge for the designers and construction workers. A solution was found in prefabricated longitudinal girders, made of two parts and then connected using a wet joint. After prestressing, they were placed over the old bridge, using a specifically made carriage whose wheels drove over the longitudinal steel girders placed right next to the gusset plates of the transverse girders of the old bridge. After this dragging procedure over the old bridge and a few additional and complex engineering works, the old bridge could be removed entirely, in one part from the place where it had stood for precisely 111 years. Transport and removing the old bridge in a special vehicle was a sentimental experience for many Ogulin residents.

Construction of the new bridge continued, and in November of 1996, the new bridge was officially opened for traffic. With 6 meter-wide carriageways and 1,1m wide arches on each side, the total bridge width of 12,5 meters. It is 43,2 meters long. The structural system of the load-bearing assembly is an arched beam: a prefabricated, prestressed concrete girder with a reinforced concrete arch. The two arch beams are placed along the very edge of the bridge and are interconnected with transverse girders. The arches are interconnected with cross-beams 0,4 meters long. The bridge furniture was designed under modern bridge durability and traffic comfort requirements.

During the recent reunion, we could see that, even after 25 years, the bridge still fulfils its central role, which is to connect and last. Of course, as with any infrastructure, there will be a time when the bridge will require certain repairs. But, let's leave that part for another time.

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