The role of foundations in structural seismic risk assessment

摘要

Seismic protection of civil structures may be carried out at various levels. The first level concerns the prediction of a seismic event that has a reasonable probability of occurring during the life of the structure. A second level is based on the idea of pro-viding additional strength, damping and ductility to the structure. A third level concerns seismic isolation at foundation level, which is generally carried out by inserting isolators and dissipators. In some cases, seismic mitigation can also be carried out by designing the foundation in such a way as to reduce the participation of the whole structure in the ground motion. To investi-gate this aspect, the seismic response of a rigid structure (shear-wall) was studied by means of a hybrid approach. Firstly, the equivalent non-linear foundation stiffnesses were evaluated by means of a pseudo-static approach, by using 3D FEM numer-ical modelling; later, dynamic analyses were carried out on the structure, which was provided with non-linear base restraints. Two typologies of foundation, directly embedded in the ground or resting on micropiles, and two different granular soils, were considered. Due to the considerable height and stiffness of the wall, it was possible to study the soil-structure interaction under coupled shear and bending loadings. Some aspects concerning the role of the foundation in mitigating the seismic vulnerability of the structures were highlighted.