This thesis develops a simple mass–spring–dashpot-based system of soil–foundation–structure interaction, called the 3DOF SFS model, for calculating the foundation-base motion that accounts for dynamic interaction between soil, foundation and building. The results from simulations confirm that motion may amplify at the foundation depending on period of the building, soil deposit and the predominant period of input motion. Time history simulations of soil-building system have been carried out for varied parameters in 2D continuum finite element models using computer program ABAQUS. It was obvious that the amplification of the motion cannot be captured by the procedure. The estimations of variation of motion by the ASCE procedure are not in good agreement, even for the cases of reduction of foundation-base motion. Analysis of records among 26 buildings that have shallow rigid foundation shows that foundation motions are reduced in two-third cases and amplified in one-third cases. In this research study, investigation is carried out on the records of past earthquakes from sites of instrumented buildings over a wide range foundation configurations and site conditions in California. A large number of instrumented buildings that have experienced a numbers of earthquakes in the past provide an opportunity to investigate the SFSI effects and evaluate the methods of estimating the foundation motion based on field data. It implies that SFSI is beneficial and can be conservatively neglected in regular building design practice. Recent guidelines, standard and codes including FEMA-440 and ASCE/SEI41-06 also recognize that foundations with interconnected grade beams or concrete slab will always reduce the free-field motions. Past procedures for analysing the effect of the foundation on the free-field input motions are all based on the assumptions that the foundation slabs always reduce the motion.
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Soil-foundation-structure interaction (SFSI) in buildings during earthquakes is characterized by several aspects including the variation between the free-field and foundation motions.