LESSONS LEARNED FROM SOIL-STRUCTURE INTERACTION

The paper deals with the recurrence that naturally occurs between deformable structures and the bearing soil. In one of his preserved sketches Leonardo da Vinci assumed that there are loaded beams that deform under nearly parabolic shapes. The first mathematical model about the beams on elastic foundation is due to the German railroad engineer Emil Winkler in 1867 when he was teaching Strength of Materials at the Polytechnic Institute in Prague. It is a linear model independently of time that seems inspired from the Law of Elasticity published by Robert Hooke in 1678 as Ut tensio, sic vis, and meaning As the extension, so the force. It looks like Winkler only replaced the tension by compression in Hooke’s Law. By coincidence, in the same year 1867 Joseph Monier from Versailles obtained in Paris his patent for reinforced concrete. Winkler’s Theory of beams on elastic foundations under static loads was gradually extended on thin and thick plates, piles and sheet piles, circular tanks and reinforced pipes. Later the elastic stability and dynamic behavior of the same structures was developed. In order to simplify the non-linear analysis in 1997 the finite difference theory was successfully introduced. All results of non-linear analysis are strongly influenced by the bilocal boundary conditions of Sturm-Liouville type. The practical consequence of this analysis consists in the need to provide appropriate joints between structures. There are simple joints with one degree of freedom only, for horizontal thermal contraction/expansion or vertical gravity settlement and seismic joints with six degrees of freedom, i.e. three translations and three rotations. For including in any analysis, the foundation soil should be carefully investigated by geotechnical and geology techniques. Particularly, the foundation soil in Bucharest requires high attention and competence in practical use. For evaluating the behavior in time of bearing soil, its viscous properties have to be accordingly considered in analyses. Soil-structure interaction is controlled by a legislation that satisfies the European Standards. All the existing study cases confirm that in Civil Engineering, sooner or later, any mistake should be paid.