A STUDY ON TWO DIMENSIONAL NONLINEAR ANALYSIS OF SITE RESPONSE
(Thesis Supervisor: Mustafa Erdik)
All phenomena in solid as well as in soil mechanics happen actually in nonlinear manner. There is no perfectly elastic material. No soil formations behave linearly, even at very low levels of shear strain. Although this reality is well known, idealizations and assumptions concerning the physical properties and constitutive models are frequently utilized for the purpose of simplification. With the methods of analysis and the high speed computers now available, it is in principle possible to evaluate the response of structure to any excitation of the base. However, mathematically precise analyses of complex structural models still require a major computational effort and are generally too costly for practical purposes and also, highly refined models and complex methods are more likely to misinterpretate and misuse than are the simpler method and tend to provide a false sense of accuracy. With the above remarks and based on many evidences, reflecting that soils behave generally as nonlinear, hysteretic (strain-rate independent) materials for the range of frequencies of interest during earthquakes, a computer program, considering the nonlinearity, is improved to conduct the soil response analyses in plane strain case. A finite difference approach is utilized to build the program structure. The mathematical models with varying irregular geometries and topographies are investigated for different fundamental frequencies and different intensity of input motions propagating at different incidence angles. The effects of nonlinearity to the amplification in irregular geometry of soil structure and topography are investigated. The analyses are performed in terms of total stresses and strains. Results from the two dimensional nonlinear soil response analyses with conclusions and recommendations for further work are given.