Uncertainty propagation of relevant soil and masonry parameters to design a SHM for the Baptistery of Pisa

Mechanical modeling of historic structures is affected by uncertainties, particularly the parameters related to soil and masonry. Variations in these parameters can result in significant changes in structural response, but their consideration in the modeling stage greatly increases the computational burden. Although strategies have been developed to address this issue, they are marginally employed in the field of dynamic modeling of historic structures. In this paper, a surrogate gPCE-based model of a medieval building, the Pisa Baptistery, is developed to evaluate the impact of uncertainties in the input parameters (masonry and soil resistance) on the model outputs (natural frequencies and modal shapes). The surrogate model allows analytical calculation of Sobol indices and the definition of the input parameters most affecting the considered outputs. Such information is relevant for the design of a SHM system of the monument, and the definition of the minimum detectable parameter change detectable by the SHM system in terms of natural frequencies.