A posteriori mechanical assessment of Risorgimento type arch bridges

Risorgimento Bridge (1911) is a 100 m span famous bridge over the Tiber river in Rome. The bridge was designed on the basis of the suggestions, experiences and patents of Francois Hennebique. Such was its importance that its name came to characterize a precise class of bridges. The so-called cellular arch bridges, or Risorgimento-type-bridges, look like very shallow arches and, at the origin, there was controversy in classifying them as true arches or, as strongly tapered beams. Their design was carried out mainly on the basis of previous experiences and experimental checks. In fact, the structural analyses and the numerical verifications carried out at that time were necessarily simple and did not fully demonstrate that these bridges possessed an adequate safety level. At the same time, the impressive appearance of these structures stimulated a wide range of both theoretical and experimental studies in many European countries. The main faults of the original engineering computations were due to many mechanical phenomena intuitively sensed, but still not rigorously framed: among these, the global structural behaviour (which cannot be dealt with the hypotheses of the slender beam theory), the redistribution effects due to the structural response of the reinforced concrete in the cracked state, and the role of concrete creep and shrinkage. The paper, after a short recall of the main historical mechanical interpretations of the Risorgimento bridges behaviour, presents a structural assessment of these type of structures (many of which are still in service) developed according to modern criteria of analysis. The results allow a deeper interpretation of the actual mechanical behaviour and contribute to assessing the soundness of the original intuitions of eminent pioneers.