Health monitoring and seismic risk evaluation of an ancient artifact with non-linear behaviour

This work reports the research carried out on a middle-ages marble pulpit located in the church of S. Andrea in Pistoia, Italy. The pulpit is composed by a marble platform supported by seven columns of different length. The platform is linked to the columns top by a lead connection, as well as the column bases to their respective foundations, thus inducing a possible rocking behavior, which seems confirmed by a change of vibration frequencies during some light earthquakes occurred in the meantime. The pulpit has been monitored by means of six accelerometers and has been identified under dynamic conditions. A MatLab code has been developed to investigate its non-linear rocking behavior, and numerical simulations of major earthquakes (compatible with the location of the artifact) were carried out in order to evaluate the probability density function for the displacement of the platform, conditioned by the earthquake intensity and direction. A probability analysis of the earthquake intensities and occurrences was then combined with the displacement pdf of the platform, and eventually with a structural analysis which showed the most severely loaded elements of the artifact. A second-level risk analysis has therefore been carried out.