1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

High frequency motion is typically observed in experimental works on seismic soil behaviour in centrifuge and in 1-g laboratory tests even if single harmonic sinusoidal input motions are imposed at base. Often these high frequencies are associated with the imperfections of the experimental setups, such as imprecise actuating systems or interaction between specimen and soil containers. On the other hand, the most up-to-date advanced numerical studies suggested that such higher frequencies can also be generated by soil due to its nonlinear behaviour.
This work presents results of a numerical study on seismic soil-structure interaction representative of a typical experimental setup. Two advanced soil constitutive models are used. In detail, the results show that soil generates higher harmonics of motion in free field for a single harmonic sinusoidal input motion applied at base. Further, the presence of higher harmonics of motion on a kinematic pile embedded in soil is amplified and can be thought as a potential example of a superharmonic resonance, i.e. a resonance of a structure with one of the soil-generated higher harmonics. The results of the numerical study are compared with the results of a relevant experimental work from the past in order to validate the findings of this paper. The explanation of the higher harmonics of motion generated by soil is also briefly drafted.
Finally, the importance of soil generated high frequency motion is briefly discussed, especially in the context of masonry old buildings, often of heritage significance, which are commonly damaged due to high frequency content of recent earthquakes recorded in Europe.