Updating of the seismic fragility curves for RC buildings subjected to slow-moving settlements

The seismic assessment of reinforced concrete (RC) structures is commonly carried out neglecting potential previous damage induced by other phenomena, for example, those related to the actions of slow-moving settlements. Many efforts are dedicated by the research community in properly considering multi-hazard actions and their inter-relations on the structure, instead of a reductionist approach, to be included in the numerical models adopted for the assessment of the seismic vulnerability. Such consequences are increasingly becoming an important issue in the structural assessment, since several structures have an age close to, or higher than, their design life. In this work, a typological 3D case study RC building, chosen to represent gravity loads designed buildings constructed in Italy from the 1950s to the 1970s, is used. The seismic assessment of the building structural elements, caused by the design seismic action, is initially shown. Then, the seismic assessment is repeated, considering as point zero of the analysis the “damaged” building as consequence of slow-moving settlements, acting in different configurations, potentially due to different causes (e.g., landslides, subsidence). A novel comparison in terms of fragility curves is proposed between the safety condition of the building expected in both cases, with or without the consideration of the precedent induced displacements. The effect of the configuration of the previous slow-moving settlements on the seismic response is investigated, by showing that the application of the horizontal settlements has a stronger effect on the penalization of the seismic response of the building, but also the application of the vertical settlements produces a decreasing of the median seismic capacity.