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Exploitation problems with particular road and railway composite bridges in Bulgaria

Composite steel-concrete bridges are having wide implementation in the present bridge practice due to their advantages. On the other hand, composite bridges have complex time dependent behaviour due to long term processes in concrete – creep and shrinkage. Stress strain state is a function of the sequence of their construction. In general, building an effective composite bridge needs relatively higher level of knowledge, precision and responsibility from designers, contractors, and relevant authorities. Implementation of composite bridge superstructures in Bulgaria is discussed in this paper. The influence of some problems related with design and construction of particular road and railway bridges on their behaviour during exploitation are analysed. Exploitation problems of three bridges are discussed. Conclusions for reasons leading to these problems and variants for avoiding them in future projects are analysed.