Piro, Annachiara (2021) Soil-Structure Interaction effects on seismic response of masonry buildings. [Tesi di dottorato]

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Abstract

In the recent years, due to the high vulnerability of masonry buildings, especially to local mechanisms of collapse, i.e. out of plane mechanisms, important tools have been develop to: (i) investigate the nonlinear response of masonry structure under earthquakes; (ii) analytically assess the 'seismic fragility' of such constructions in order to evaluate the expected damage. Usually, the models used for the seismic assessment consider the structure fixed at their base, neglecting the soil contribution. The interaction between soil and structure can significatively influence the seismic behaviour of masonry building and on the corresponding seismic fragility. Based on those motivations the aim of this research study is to evaluate how the soil-structure-interaction influence the out of plane loaded masonry walls in elevation, in terms of: (i) linear dynamic properties; (ii) nonlinear behaviour and corresponding fragility; and (iii) analysis of real case studies of existing masonry buildings, at both territorial and local scale. To evaluate the influence in terms of linear properties, the numerical results of linear analyses on advanced 2D coupled soil-foundation-structure (SFS) interaction models were performed and compared with the analytical prediction based on the replacement oscillator approach. Regression models and a relative soil-structure stiffness parameter are proposed to quickly predict the frequency reduction induced by soil-structure-interaction, accounting for the presence of an embedded foundation, and a layered soil. To evaluate the soil-structure-interaction on the nonlinear behaviour and the corresponding seismic fragility. Several archetype structures are considered, accounting for the variability in geotechnical and structural properties such as soil type, masonry type, and number of building stories. This selection reflects the most recurrent properties observed in the Italian and European built heritage. Advanced 2D coupled SFS nonlinear models are developed for each considered archetype building. A set of real records is used as input to cloud-based nonlinear time histories analyses (NLTHA), and the analysis results are used (1) to select optimal intensity measures (IMs) for the considered structural types; and (2) to generate fragility relationships for various structure-specific damage states, up to collapse. The comparison between the fragility relationships obtained for the different combinations of soil, masonry type and number of stories allows an explicit assessment of the influence of the SFS interaction on the seismic response and damage of masonry buildings.

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