This paper deals with the collapse behavior of a historical masonry arch bridge subject to combined seismic loads, by means of the limit analysis and shakedown theorems.
A finite element modal analysis and seismic load evaluation has been performed by developing a program code. The assessment of the collapse loads and shakedown multiplier, consisting of corresponding nonlinear constrained optimization problems, are analyzed using lower bound theorems of the limit analysis and shakedown theory. The lower bound theorem of the limit analysis and the shakedown lower bound theorem, also known as the Bleich-Melan theorem, endorse the efficacy of the technical solution of retrofitting adopted here. Another important result of this study is the observation that the seismic shakedown multiplier coincides with the minimum of the collapse load multipliers. This means that the nonlinear behavior of the structures is always stable, otherwise the incremental collapse cannot occur. Because the retrofitting of this structure cannot be performed in the intrados surface, the application of CFRP strips on the extrados of the arch is a useful and valuable technique, as shown by a significant increase of the limit and shakedown multipliers. The rehabilitation and conservation has shown in recent years the need of reliable methods for assessing masonry arch bridges: it is important not only to maintain ancient structures in good conditions, but also, when necessary, to be able to estimate their safety factor as accurately as possible. With reference to a case of study, a Roman stone arch bridge, is
presented also a numerical analysis performed by means of a nonlinear F.E.M. algorithm implemented in the ANSYS code in which the structural role of the spandrel walls and filling is also involved. The results of this F.E.M. analysis can be useful, in case of restoration of a masonry arch, by giving a qualitative map of the “intervention areas” that strongly depends by the exactness of mechanical parameters, which often are difficult to evaluate by experimental analyses, especially in the cases of monuments and historical buildings.