A model to estimate the virgin and ultimate effective stiffnesses from the response of a damaged structure to a single earthquake

The paper presents a model describing the evolution of the effective stiffness of a 'mode' of a structure subjected to an earthquake engaging it in its non-linear phase of behaviour. Such models are available in the literature, however the proposed one allows the estimate of the effective stiffnesses both of the virgin state of the structure and of its ultimate state, even when the considered excitation does not act on an undamaged system nor leads it to ultimate conditions. Only the base input and the response at a significant location of the structure need to be known to apply the procedure. This is satisfactorily checked against the results of shaking table tests performed on masonry buildings.