Probabilistic Seismic Hazard Analysis for Maximum Seismic Shear Stresses in Soils Using Improved Ground-Motion Parameters: Fid-Bau Portal

Probabilistic Seismic Hazard Analysis for Maximum Seismic Shear Stresses in Soils Using Improved Ground-Motion Parameters

Kishida, Tadahiro / Tsai, Chi-Chin

Abstract

Abstract

Maximum seismic shear stresses ( $τ_{max}$ ) have been recognized as one of the important parameters in design practice. This study develops ground-motion parameters for $τ_{max}$ and implements these in probabilistic seismic hazard analysis to provide the $τ_{max}$ distribution of deep soil layers for design purposes. The application of improved ground-motion parameters for $τ_{max}$ is demonstrated at the Oakland International Airport, where a thick Young Bay Mud deposit exists under the artificial fill. Model biases in the predictive equations of seismic shear-stress reduction coefficients ( $r_{d}$ ) are evaluated by comparison with the site response analyses performed with a wide range of input ground motions. Based on these results, we introduce improved ground-motion parameters for $τ_{max} (I_{tau})$ as a linear combination of spectral accelerations, implemented in probabilistic seismic hazard analysis to calculate seismic hazard curves. Conditional mean spectra are calculated, given $I_{tau}$ at 10% in 50 years to illustrate the variations in frequency contents with depth compared with the uniform hazard spectra. Finally, $τ_{max}$ is calculated with depth by using hazard values of $I_{tau}$ and compared with the peak-ground-acceleration-based and uniform-hazard-spectra-based calculations. Analysis results show that $τ_{max}$ will be underestimated for deep soil layers by peak-ground-acceleration-based calculation if the median value of $r_{d}$ is used in design practice.