Soil-foundation modelling in laterally loaded historical towers

The seismic stability analysis of historical towers requires reliable soil-structure interaction (SSI) modelling. To avoid the complexity of non-linear dynamic computations, engineers frequently resort to simplified static approaches, such as the so-called pushover analyses. Their outcomes are deeply affected by the foundation response under horizontal/moment (HM) loading. This paper encompasses a comprehensive SSI modelling process, taking as a reference case study the embedded shallow footing of the Ghirlandina tower in Modena, Italy. First, a finite-element (FE) soil-foundation model is developed with an inhomogeneous distribution of the undrained soil strength, related to the in situ inhomogeneity of the stress state. Total stress FE analyses are then performed to derive the undrained failure locus of the footing and numerical data about its pre-failure performance. This locus is found to exhibit distorted HM cross-sections, depending on the vertical load and hardly reproducible through standard analytical formulae. The FE evidences are then condensed into a simple elasto-plastic HM ME model, reproducing the outcomes of the inhomogeneous FE model, and employable for the pushover seismic analysis of historical towers.