Fragility curves of slender towers accounting for seismic soil-structure interaction

The paper proposes fragility curves of masonry towers accounting for Soil- Foundation-Structure (SFS) interaction under seismic loadings. The effects of structural slenderness and soil compliance were investigated by analyzing three structural schemes placed on different soil typologies. 3D models including the soil, the foundation and the structure were generated through the FLAC3D code, assigning a strain-softening constitutive law to masonry and an elasto-plastic hysteretic behavior to soil. The SFS predominant periods were firstly evaluated by analyzing the model response to a noise signal. Non-linear dynamic analyses were performed on the overall system excited by different input motions. The results highlighted the attainment in the masonry of the ultimate tensile and compression strain. Fragility curves, representative of the aforementioned mechanisms, were developed by applying the cloud-method procedure. Towers founded on soft soils resulted the most damaged, since soil deformability contributed to increase the seismic ground amplification as well as the structural displacements.