OBJECTIVES

The General Objective is the development of new methods through the nonlinear analysis of mechanical-physical properties of stratification soil structures for evaluation of major effects produced by seismic sources, which influence the seismic waves propagation upon important sites subjected to high seismic risk.

The first objective is to emphasize the material nonlinearity from soil constitutive laws between stress and strain and the behavior of the seismic waves at the passing through soft soils.

The second objective refers to nonlinear effects that appear in complex stratified media:

nonlinear effects that appear in complex stratified media
introducing, for emphasizing nonlinear effects, spectral amplification factor (SAF), as a ratio between maximum spectral acceleration (Sa), velocity (Sv), relative displacement (Sd) and maximum values of acceleration, velocities, respectively displacements, from processed recorded accelerograms
„structural models” will be obtained. Furthermore, these models will be compiled by computer modeling

In the third objective will study the influence and nonlinear properties evaluation of sites upon spectral amplification factors:

the influence and nonlinear properties evaluation of sites upon spectral amplification factors
this theory is extended here to the study of resonance state, at the simplified derivation of spectral amplification factors for displacement, velocity and acceleration and at the shock state study, when the external force has a limited duration
can be made predictions upon such effects of amplification of seismic movements
in the estimation of the amplification factors an important role is played by the attenuation (dissipation coefficient), as well as by the resonant (or quasi-resonant) regime, local characteristics of the element of interest, especially their non-linear properties
the study and the computation of the amplification factors by using the model of a linear harmonic oscillator with attenuation subjected to the action of an external force
the equations of motion for the linear harmonic oscillator with attenuation and subjected to an external force will be established in their most general form, which will allow the spectral analysis of the response

The fourth objective proposes a comparative analysis of local seismic response computed in different used/developed approximations:

seismic input of a specific site will be computed and after it will be done at the modeling of seismic behavior of the local geological structure applying viscous linear/nonlinear models till we get the best fit with recorded available seisms on the site
the model obtained this way could be applied for evaluation of effects induced by local structure not only to past earthquakes, but also to forthcoming ones expected for that site
checking of the capacity of these models to predict the variation of the soil parameters (maximum acceleration) dependent on the site

The fifth objective is represented by:

the mathematical corrections brought to the approximation of the geometrical radius in wave propagation determining the seismic response of stratified media, with complex structure and high order nonlinear properties.
mathematical results of wave propagation in such situations, in special those referring to propagation of surface waves in semi-infinite laminar spaces, present very interesting nonlinear effects, in the way of amplifying the local effects as a result of the nonlinear state
this approximation, named also quasi-classic, being used usually in wave propagation is derived here through a new matricial method, based on dividing in infinitesimal strata of a weakly inhomogeneous medium
the method results from the previously developed techniques and researches and is considered a powerful method for the inclusion of the effect of an inhomogeneous medium in wave propagation, or of the defects, localized, extended, spatial correlated, and in general for corrections wave type to the geometrical radius approximation