Simulation and Application of Spatiallyvarying Non-Stationary Subsurface Motions

Abstract eng:
This paper presents stochastic simulations and application of spatially-varying non-stationary motions at subsurface sites. The motions are compatible to the sites in terms of both spatialvariation and earthquake energy. The stochastic Fourier spectrum characterizing the energy accounts for source spectrum, attenuation, geometrical spreading and source-to-site amplification. Earthquake magnitude, geometrical properties of the source and the site, and mechanical properties of the source and path rocks and the subsurface soil are the input data. The spatial-variation in amplitude is characterized by a common lagged coherency function with a set of site-compatible parameters estimated by Dinh et al. (2012). Both wave passage effect and arrival time perturbations are included in the phase spatial-variation. In the case study, where a large earthquake and three subsurface sites are considered, the averaged spectra of a few simulated samples match well with the target spectrum. A deep-foundation two-span bridge subjected to the simulated spatially-varying accelerations (SVA) is analyzed. Figure 1a shows that the maximum deflection of the left mid-span of the rigid-base support model (RBS) by SVA is considerably larger than the response by uniform accelerations (UA). There is phase difference in the second half of the time history. The vibration periods of the flexible-base model (FBMS) are considerably larger that of RBS as observed in Figure 1b. Contrary to the response of the RBS, the displacement amplitude of the FBMS is initially small and much amplified in the second half of the duration. When the soil damping is not accounted for, the amplitude peaks in the FBMS are larger than that of the RBS. As subsurface motions are hardly recordable, the numerically simulated motions are necessary for the seismic analyses of deepfoundation, underground structures with soil-structure interactions.

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