Simplified earthquake analysis of buildings including site effects

The September 19, 1985 Mexico City earthquake clearly illustrated the potentially dangerous modifying effect that soft soil profiles can have on the earthquake motions as they propagate from the bedrock level to the ground surface, and the importance of considering this phenomenon in the seismic analysis of building systems. The use of simple methods for the earthquake analysis of buildings founded on soft soil sites is investigated.; The topic of site response analysis is addressed including the development and implementation of efficient time domain numerical procedures which are incorporated into a one-dimensional site response analysis computer program, WAVES. A soft clay site in downtown Mexico City is modeled and analyzed with WAVES for various base input records and the computed results are compared to data recorded during the September 1985 earthquake.; An overview of conventional building response analysis procedures is followed by a discussion of the use of simple harmonic earthquake motions to represent the "near harmonic" motions frequently recorded at the surface of soft soil profiles. A study comparing the analytical response of a multi-degree-of-freedom representation for harmonic earthquake loading is presented and the extension of single-degree-of-freedom analysis to general two and three-dimensional systems is discussed.; A brief discussion of various soil-structure interaction analysis methods is followed by a presentation of the free-field formulation of the equations of motion for soil-structure systems. Simplified procedures which include the effects of site amplification and foundation flexibility, are suggested and applied in the investigation of a simple soil-structure system. For the "near harmonic" site motions used in this investigation, the maximum roof displacements and base shears computed using an efficient, single-degree-of-freedom representation of a two-dimensional frame system are shown to be within 20%, and in most cases, within 10% of those computed using a multi-degree-of-freedom representation.