SMIP 2017 Seminar

We compile a California vertical array database of 21 sites. Weak motion transfer functions derived from data are compared to predictions from 1D ground response analyses performed using three damping models – geotechnical models, models for quality factor (Q) based on seismological inversion, and models derived from the site-specific site diminutive parameter (κ0). When compared to prior results for KiK-net sites in Japan, the California sites have, on average, improved match of empirical and theoretical transfer function shapes and more event-to-event consistency. Using κ0-informed damping results in a slightly better fit between predicted and observed transfer functions than alternative damping models.

This paper summarizes the results of a recently completed project on the one-dimensional (1D) site response analysis (SRA) of five geotechnical downhole arrays in California which were subjected to both strong and weak earthquake shakings. The arrays were initially assessed in terms of the effectiveness of the 1D SRA using taxonomy classification. Then, SRA was performed utilizing finite element program LS-DYNA to study the site effects at the selected arrays. Lastly, the predictions were compared with the recorded counterparts and the uncertainties of the 1D SRA models were evaluated using two methods namely the Goodness-of-Fit (GOF) and Amplification Factor (AF) residuals. The 1D SRA results of the selected arrays were interrogated on a site-by-site basis and discussions are made on the effectiveness of the employed nonlinear SRA models.

This research aims at assessing the validity of accidental torsion provisions in building codes. Uncertainty in stiffness is considered as the main source of possible eccentricity. Monte Carlo simulation is utilized to statistically assess the behavior of nine one-story symmetric-in-plan base systems with nine different translational to rotational period ratios (Ω). Three vibrational characteristics and equivalent design eccentricity are developed and compared with information obtained from CSMIP database. The effect of Ω, plan aspect ratio, and correlation in building stiffness on building displacement amplification due to torsion are investigated. Equivalent design eccentricity is quantified based on these results.

The dynamic response of a building structure to an earthquake excitation is the result of a complex interaction between the structural system and the underlying and surrounding geology. Since modeling the physics of the coupled soil-structure system is a complex undertaking, the state-of-practice has adopted simplified modeling procedures, such as the substructure method. Nevertheless, these procedures are often empirical and/or based on idealized assumptions, such as linear-elasticity. In this study, our objective is to develop a robust model inversion framework that can be utilized to extract information from the real-world building response measurements to back-calculate the model parameters that characterize the structural response and soil-structure interaction effects.

This paper presents interim results from a study on the identification of spatial variability in bridge Foundation Input Motions (FIMs) observed during the 2014 South Napa Earthquake. Bridges are especially prone to the spatial variability of ground motions because they extend over relatively long distances. The primary objective of this project has been to develop a framework to identify FIMs from response signals recorded at instrumented bridges, because, in general, FIMs cannot be measured directly. In this progress paper, we present the development and verification of a framework developed for this purpose and its application to a real-life case study—namely, the Golden Gate Bridge. This bridge was chosen, because initial analysis suggested that its behavior is not significantly affected by inertial soil-structure interaction effects, and thus, the identified FIMs could be—at least partially—validated. Results obtained from both verification (identification using simulated response signals) and validation (identification using real-life data) confirmed the applicability of the developed framework, which will be applied to the other long-span bridges affected by the 2014 South Napa Earthquake in a follow-up study.

The relationship between earthquake ground motion characteristics and embankment dam deformations is currently being investigated through a ground motion study using two validated non-linear deformation (NDA) embankment models. Presented in this paper are: (1) NDA results for one of the dams in this study, Lenihan Dam, against the 1989 Loma Prieta earthquake, and (2) current results of the ground motion study with this NDA model. The paper ends with major conclusions and plans for future work.

The 2014 South Napa mainshock caused significant damage in the Northern California Bay Area. Time series from a foreshock, mainshock, and three aftershocks were collected from various agencies. These were processed following the Pacific Earthquake Engineering Research Center (PEER) standard data-processing methods, and a ground-motion database was developed. Metadata such as fault style, source-to-site distance, average shear wave velocity in the top 30 m (Vs30), and basin depth were collected. Shear wave velocity profiles were also measured by the Spectral Analysis of Surface Wave Dispersion (SASW) technique at selected strong-motion stations. These datasets were combined in the ground motion database and compared to the Ground Motion Models (GMMs) from the NGA-West2 studies to evaluate the regional attenuation of these events. Time series at two geotechnical downhole array sites were also collected from 29 earthquakes to calculate apparent wave velocities from wave travel times and empirical transfer functions to understand wave amplification. Characteristics of pulse-like records from the South Napa and NGA-West2 databases were also analyzed to compare near-fault regions between these databases. The influence of pulse-like records was also investigated using inelastic response spectra to understand the damage potential on structures. These observed ground-motion characteristics are summarized in this study. The data produced in this study can be used to generate fragility curves that account for the presence of a pulse in the record.

This study evaluates several possible parameters used to quantify the intensity of grouns motions and its correlation with strong nonlinear structural response and collapse. In particular, it compares the dispersion of structural collapse capacities obtained using four different ground motion intensity measures (IMs): (1) Sa(T1); (2) Sa(T1) adjusted using ε ; (3) an IM consisting spectral acceleration averaged over a period range (Saavg); and (4) a new IM termed filtered incremental velocity (FIV). Results suggest that Sa(T1) is the least efficient IM whereas Saavg and FIV are the best IM parameters. Additionally, this paper investigates the influence that record scaling has on estimating probabilities of collapse of SDOF and MDOF systems. Results suggest that a systematic bias is introduced by scaling ground motions and that the bias is strongly dependent on the period of vibration and the lateral strength of the system.