Structural analysis of a medieval leaning masonry tower considering multi-leaf materials uncertainty

In this paper, the structural analysis of a medieval leaning masonry tower is conducted by means of a geometrically accurate 3D finite element (FE) model considering multi-leaf material uncertainty. The study focuses on the Garisenda Tower in Bologna (Italy), which has recently raised structural concerns. The tower leans about 4°, and it has multi-leaf walls, consisting of an inner infill (rubble core) and outer leaves (gypsum stone block masonry and clay brick masonry). Dynamic identification of the tower is performed based on ambient vibration measurements to identify reference modal parameters. The FE model of the tower is based on a solid CAD geometry developed in two steps. Initially, the CAD geometry, whose details are derived from a comprehensive point cloud (capturing both internal and external surfaces), is developed without inclination. Then, the tower inclination is innovatively estimated through an iterative closest point algorithm between the point cloud and the CAD geometry, which also provides an a posteriori validation of the geometric accuracy, with residual discrepancies on the order of a few centimetres. The estimated inclination is then incorporated into the FE model, together with an explicit representation of the tower’s multi-leaf wall configuration. Additionally, a relevant volumetric portion of the soil is introduced to serve as a deformable constraint to the tower. Parametric eigenvalue analyses and nonlinear static (dead-load) simulations are conducted to investigate the sensitivity of the structural response to the multi-leaf material properties. Results show that multiple multi-leaf material configurations, including soft core-stiff outer leaves and stiff core-soft outer leaves, can accurately match the empirical dynamic features. Accordingly, significantly different stress distributions in the tower can be obtained in nonlinear static analyses, leading to various possible structural responses that should be considered in the absence of in-situ elastic moduli characterization.