Influence of environmental degradation on dynamic properties of masonry bridges

The paper presents some preliminary analyses devoted to the identification of suitable models able to provide the frequency decay of a damaged masonry structure on the basis of the observed damage pattern. In particular the analysis will be carried out with reference to some comparison FE models, and by introducing two distinct damage patterns, i.e. an elastic modulus decay of an external layer of the bridge arch, or a localised reduction of section due to impact or brick and stone detachments. The worked out examples allow checking of a very simple formulation based on the frequency evaluation through the static displacement equivalence of energy, and the splitting of the curvature diagram in the average part plus an added impulse term due to the presence of defects. The proposed formula is in good agreement with the FE analyses and sufficiently simple to be used for the detection of the damaged material properties, as a function of the average frequency decay.