This paper investigates the critical issues of the collapse of two italian bridges: the “S. Stefano” viaduct in Siciliy and the “Annone” overpass in Lombardy. First, a short discussion about the structural aspects and the load conditions of both collapses is carried out. Then, the numerical results of structural analysis are discussed. The nonlinear analysis, simulating the deterioration of the structural material (steel and concrete) characteristics, are used to explain the cause of failures and help to understand how the different level of corrosion can influence the serviceability of structural elements. Finally, by varying the degree of corrosion and therefore of deterioration, one can see how the response of the element varies and can affect the overall bearing capacity.