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This paper is intended to show the design of two composite bridges along the Orastie- Sibiu motorway, from the basic concepts, applied without the need for a clause-by- clause checking of codes and standards, to the construction methods.

The bridges are seismically isolated in the longitudinal direction, while transversally the seismic action is distributed among the piers.

Calculations have been carried out through state of the art procedures, taking into account form effect of the cross section. For this reason, different FE models have been set up to study different aspects of the behavior, with increasing degrees of approximation. For example, “beam” elements have been utilised to investigate global effects both in the linear and non linear range, while more accuate 2D and 3D elements have been used for refined cases such as stress checks and local buckling analyses.

The present paper goes into detail in particular for what concerns some of the most interesting parts of the design process for the specific case. Namely, time dependent properties of the materials have been considered, and extensive “staged construction” analyses have been carried out to ensure safety in each phase of the complex life of the bridges, while at the same time guaranteeing significant cost savings.


This paper describes the design and construction of a “balanced cantilever girder” bridge over the Danube-Black Sea channel, characterized by a central span of 155m with two symmetrical side spans of 77.5m. The total length of the bridge, including portions of the abutments support, is 312.0m.

The bridge main features, from calculation as well as construction points of view, are in particular the post-tensioning tendons, distributed both a top and bottom sides of the section along the bridge. The former ones play a key role in the construction phase, for the need of counterbalancing selfweight while subsequent segments are realized.

Tendons are symmetrical about midspan, with anchors positioned at the end of each segment.

Bridge deck is supported by two piers outfitted with friction pendulum seismic bearings, which develop friction both in static conditions to withstand static forces and small displacements, and in dynamic conditions, causing dissipation. Under severe earthquake load all structures (deck and piers) develop only elastic behavior.

This papers presents a detailed review of the design process as well as a time journey during construction