A GENERALIZED SEISMIC ENVIRONMENT FOR SOIL STRUCTURE INTERACTION (DYNAMICS, FILTER, WAVES, WAVE PROPAGATION)
Abstract
Critical structures located in the earthquake-prone regions of the world must be designed to resist seismic loads. For optimized design, soil-structure interaction (SSI) effects are considered, since the induced displacements and stresses are generally lower in comparison with the assumption of a rigid base. SSI analysis is performed using finite element computer codes. However, the design input motions are always assumed to consist of vertically propagating shear waves. This is an unreliable and often unjustified assumption. This study presents a methodology to assess the relative wave contents of actual recorded accelerograms. The recorded motions are separated into P-wave, S-wave, Rayleigh-wave and Love-wave motions. This is achieved by using a digital filtering technique which enhances wave motions according to how closely they compare with typical theoretical particle motions. These typical characteristics are based upon the solution of the wave equation for an elastic, homogeneous half-space. The theory can be extended to layered, non-linear media using the same principles. The ability to separate waves allows the specification of a "Generalized Seismic Environment". This would consist of inclined body and surface waves which have been shown to contribute to recorded surface motions. This generalized seismic environment can be used for SSI analyses. The results of examining 24 records from eight Californian earthquakes are discussed, including practical guidelines for specifying a general seismic environment. Also, a simple SSI analysis is presented to illustrate the significance of assumptions made for the seismic environment. The current state-of-practice method employing vertically propagating shear waves is compared with an analysis which uses the generalized environment discussed in this thesis. The analysis of a simple model suggests that an environment consisting of only shear waves will produce results which are different to those resulting from the use of a generalized seismic environment. This is attributable to the spatial variation of the free-field motions.
Degree
Ph.D.
Subject Area
Civil engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.