Soil Behavior: Dynamic Soil-Structure Interactions - Dynamic Behavior of Concrete and Seismic Engineering - page 143

Figure 4.10. Variation of hysteresis loops with the number of cycles
4.3. Linear soil-structure interactions
For the study of the soil-structure interaction in linear systems, the models
adopted to represent the soil are either the elastic model (section 4.2.1) or the
equivalent linear visco-elastic model (section 4.2.2). The non-linearities in the
behavior of the soil can be taken into account by selecting G shear modulus and E
damping modulus values compatible with the average strain induced in open field by
the seismic stresses. This approach involves neglecting additional non-linearities
linked to the soil-structure interaction, such as soil plastification at the ends of
superficial foundations, or along the pile shafts. Comparison of the results obtained
with non-linear calculations shows this approach gives acceptable results when
foundations show sufficient safety regarding their ultimate load.
4.3.1. Illustration of the soil-structure interaction effect
The influence of soil-structure interactions on the response of a building can be
illustrated using the analog model shown in Figure 4.11 [WOL 85]. The structure is
represented by a mass and a spring placed at a height h above the foundations. The
bond between the structure and its foundations is represented by a stiff bar. The
latter is lying on the ground, and its interaction is modeled via an impedance
function for the foundations. In this model, what stands out is the simplified
representation of impedance functions as springs and dashpots that are independent