Rocking response and vulnerability of the pulpit by Giovanni Pisano in Pistoia (Italy)

The pulpit of Giovanni Pisano lies in the church of S. Andrea in Pistoia, Italy, and is one of the most outstanding marble artifacts of the late middle ages in Italy. It is composed by seven columns supporting a platform. The columns have different lengths, since they rest on pedestals located at different heights, in a way for the column tops to be at the same height and therefore form a support for the arches, which in turn support the platform above. All the components are linked to each other by means of thin layers of lead; as a consequence, such connections cannot resist traction and the whole artifact is likely to exhibit rocking behavior, especially during earthquakes. This paper describes the development of a ®MatLab code and its utilization to take into account the rocking response of the pulpit. The model has been identified making use of the dynamic recordings performed by a permanent monitoring system composed of 6 accelerometers mounted at the base of the pulpit itself and on its platform. The first natural frequencies have been used to determine the compressibility of the lead layers. Subsequently, some artificial earthquakes were numerically generated to obtain an estimation of the fragility curves of the artifact, and eventually an estimation of its seismic vulnerability.