Sakharov V. Interaction of engineering structures with nonlinear base under seismic loads

The object of study - the interaction of buildings and structures with a soil base under seismic loads, mathematical models of nonlinear environments and methods, algorithms and programs of numerical simulation based on the finite element method. Purpose of the study - the elements of the "soil base - foundation - building" system, as well as SSS of the structures with soil base under dynamic loads. Purpose - to improve the soil model describing nonlinear processes of soil base deformation, and to estimate changes in the real stress-strain state of soil base and foundations under dynamic, including seismic, loads; to develop and implement efficient algorithms solving nonlinear dynamic problems of geotechnical engineering, and to put them into practice of engineering calculations. Methods: Search of existing criteria as well as development of new models, methods and algorithms describing the dynamic behavior of the soil; conduct and control of test calculations; mathematical modeling of experimental control tasks followed by comparison of the results to other software complexes; laboratory and in-situ research methods followed by the numerical analysis of the stress-strain state; mathematical modeling of problems of interaction of elements of the "soil base - foundation - building" system under seismic loads, based on the developed system of nonlinear analysis. Novelty - developed and justified a new model of behavior of soil under dynamic loads, which takes into account the structural strength, the processes of visco-elastic-plastic deformation of the volume and shape, and the processes related to the pore pressure and filtration. This model provides realistic simulation of deformation processes in the soil bases and foundations under seismic loads; for the first time a technique of numerical investigations on the basis of an explicit modification of the method with non-uniform step in the spatial coordinates and spectral superelement is offered. This technique provides an effective solution to the problems of dynamics and reduces the computation time by a magnitude of up to ten times; it demonstrates that the inclusion of real visco-elastic-plastic properties of soil-base evaluates the position of the building during and after the end of the dynamic loads, and can lead to changes in SSS structures by up to two times; A new method and equipment have been developed for investigation of the dynamic stiffness and viscosity of soil over a wide range of load's velocity using the standard laboratory equipment including Oedometer; it has been shown that the use of the developed finite element visco-elastic-plastic and orthotropic properties for reinforced concrete and masonry allows to estimate the actual dynamic response of buildings and structures; it has been discovered that in the process the seismic action in piles stretch zone appear substantially lower than the pile heads, especially in the presence of weak (compressive strengths) layers, which leads to the necessity of reinforcing the entire depth of the piles; it has been found that under identical seismic loads the amplitude of oscillation of structures of multistory buildings with fewer floors can grow, as a result of resonance. Industry - construction.