Nonlinear ground and structural response variability due to soil response modeling uncertainty

Abstract eng:
Limited guidance exists both in engineering practice and seismology regarding the mathematical model to be employed for the computationally efficient evaluation of site response. The soil model affects the prediction of ground motion at the surface and consequently is an additional source of uncertainty for the structural response predictions. We combine downhole observations and broadband ground motion synthetics for characteristic site conditions in the Los Angeles Basin, and we investigate the variability in ground motion and structural performance introduced by the site response assessment methodology. More specifically, we conduct elastic, equivalent linear and nonlinear site response simulations, and evaluate the ground surface response variability resulting from the selection of the soil response methodology. We quantify the variability by means of the COV of site amplification factors, defined as the ratio of the predicted peak ground acceleration and spectral acceleration at short and long periods to the corresponding ground motion intensity measure on rock-outcrop. Finally, a series of inelastic single-degree-of-freedom oscillators are subjected to the ground motion predictions obtained via the alternative site response methodologies. The results show that large sensitivity in the selection of site response methodology yields high bias and uncertainty in the assessment of the inelastic displacement ratio for nonlinear structural response predictions.

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