Influence of the stiffness ratio of the building and the multilayer soil foundation on the seismic response of the system

Introduction. Currently, in engineering practice, a model of a die lying on an elastic homogeneous base is used to evaluate the joint dynamic operation of buildings with a soil base. The presence of layers with sharply different stiffness, as well as the order of their location in the soil column, leads to significant changes in the spectrum of resonant frequencies and the magnitude of the dynamic response. Therefore, it is important to take into account the inhomogeneity and layered structure of the soil foundation for a correct assessment of resonance processes arising from joint vibrations of the structure and the foundation. The purpose of the study is to analyze the reaction of the “structure – multilayer base” system depending on the ratios of their stiffness, as well as to compare the results obtained by modelling a multilayer and equivalent homogeneous base.Materials and methods. A computational model of a horizontal layered medium is used. The structure as an element of a layered system with reduced stiffness characteristics. The seismic load in the form of a vertical propagating shear wave is modeled by a stationary random process. The amplitude-frequency characteristics of the system as a whole, as well as for each individual layer, spectral output densities and dynamic coefficients are used for analysis.Results. It was found that with a decrease in the rigidity of the building, its contribution to the overall amplitude-frequency response of the system increases. A numerical assessment of the change in the dynamism coefficient with changes in the system parameters has been performed. A comparison was made of the response of a structure on a multilayer base with a response on a single base with equivalent characteristics.Conclusions. The simplified representation of the soil as homogeneous, without taking into account its layered structure, reduces the value of the dynamism coefficient to 30 %. The resonant frequencies of the “building – hard layer – weak layer” system are mainly determined by the resonant frequencies of the weak lower layer, especially with an increase in the rigidity of buildings. A similar pattern is characteristic for a homogeneous base. In the “building – weak layer – hard layer” system, the resonant frequencies depend on the frequencies of the base layers, as well as on the natural frequencies of the building.

seismic load, “structure – base” system, impedances, multilayer base, resonant frequencies, amplitude-frequency response, free oscillations, resonant frequencies, dynamicity coefficient, probabilistic calculation