Bridge Over the River Tisa at Žabalj
The bridge over the Tisa at Žabalj is one of the first examples of composite – prestressed continuous girder (top prize at an anonymous competition). It was designed as a structure to be built on piers already existing in the riverbed. The carrying capacity of these piers was limited given their age and foundation method, so that the competition requirements called for a solution with the minimum possible weight in the section of the main span.
The main girder of the bridge is a continuous beam with a maximum span of 105 m. Over all of the inundation basin and a section over the river the main girder is a composite structure. In a cross section, which is located approximately at midpoint of the side span, where the bending moments are relatively small, it changes to a steel girder with an orthtropic deck. The connection point is shaped in a way ensuring the transmission of internal forces from one part of the structure to the other part reliably and without any considerable local stress.
The composite part of the continuous girder is prestressed with high-tensile steel cables, which pass through the slab, as well by the subsequent lowering of the central supports. The aim of this second measure is to eliminate negative moments in the field resulting from prestressing with cables. This solution fulfils the requirement of a reduced loading on the piers in the riverbed in addition to all the other advantages provided by a composite structure on the remainder of the bridge. The monolithic connecting of the two parts makes use of the favourable properties of the continuous girder as a whole.
From the statical point of view, the system is interesting in that the process of concrete creep and shrinkage which takes place in one part of the girder, in view of the firm connection, is transmitted also to the section with the pure steel girder.
As far as we are aware, a combination of a composite concrete-steel structure and a pure steel structure in a single structural statical system had not been performed anywhere in the world until then.
The bridge was completed and opened for traffic in 1963.