Ground motions that contain velocity pulses may cause greater structural damage than ground motions that do not contain pulses. The effects of pulse-like motions are best approximated in the time domain using nonlinear response history analysis. Current approaches for incorporating pulse effects are not reproducible since they largely rely on engineering judgment and often result in unrealistic representation of the hazard. This study extends a method by Shahi and Baker (2011) that incorporates the effects of pulse-like motions in probabilistic seismic hazard analyses (PSHA). It uses disaggregation information from the PSHA to construct suites of target spectra that are used for matching an appropriate proportion of pulse-like motions with characteristics (pulse amplitude and pulse period) representative of a desired hazard intensity level. The methodology has been successfully employed for several high-profile projects in California that were subjected to a rigorous peer review process, including the Transbay Tower in San Francisco.

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A nonlinear ground response analysis is conducted for the Niigata-ken Chuetsu-oki earthquake recorded at a free-field vertical array near the Kashiwazaki-Kariwa Nuclear Power Plant in Japan. A bidirectional site response analysis is carried out using LS-DYNA which allows user defined stress-strain relationships to dictate soil behavior subjected to dynamic loading. Dynamic soil behavior is characterized using a two-stage hyperbolic backbone curve implemented with modifications to consider the peak strength of soil layers as well as the strain at which the peak strength is fully mobilized. The effects of bidirectional input motions, strain rate, and the shape of the shear modulus degradation curves are investigated, and it is demonstrated that each factor can have a significant influence on the results.

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This study proposes a new set of methodologies to estimate the site fundamental frequency using the horizontal-to-vertical spectral ratio (HVSR) of recorded surface ground motions. Because of the lack of consensus in HVSR calculation among researchers, a wide range of methods are practiced in this area, yielding different site fundamental frequencies at a given site due to analyst subjectivity. In this study, current practices for combining horizontal components—geometric mean and RotD50—are examined first, and results show that both methods provide comparable HVSR curves. However, RotD50 has the advantage of being orientation independent. Second, the application of Fourier amplitude spectrum (FAS) and 5% damped pseudospectral acceleration (PSA) in computing HVSR is studied, and results are presented for one case study in which PSA-based HVSR seems to suffer from scenario dependency, whereas the FAS-based results appear stable. Different values for Konno–Ohmachi smoothing parameter b were evaluated, and its effect on estimating the site fundamental frequency was considered; using b = 40 is our preference. In previous studies, average HVSR curves were used to estimate a single number representing the site fundamental frequency without incorporating uncertainty. This study proposes four methodologies that use events’ individual HVSR curves to estimate the site fundamental frequency and its associated uncertainty in a completely automated manner. Methods 1–3 use individual HVSR curves to find the maximum-likelihood estimate of the site fundamental frequency (fml), whereas method 4 uses both individual and average HVSR curves to estimate the first resonance frequency (f0). To evaluate the automated methods, a subset of the Next Generation Attenuation-West2 dataset is used to study 50 stations, and the results are compared with an independent study demonstrating good consistency. The proposed methods are further illustrated using data from the Garner Valley Downhole Array (GVDA), which highlights the pros and cons of the presented methods.

A series of 1-g shaking table model tests were carried out to study the behavior of pile groups embedded in sloping ground subjected to lateral ‰ow of liqueˆed soil. Two diŠerent conˆgurations of pile groups: large (6×6 and 11×11) and small (3×3), were considered. The models were subjected to the liquefaction-induced large ground deformation to investigate the eŠect of several parameters on the response of pile groups and mechanism of lateral ‰ow. These parameters comprise amplitude, frequency, and direction of input motion; density and slope of ground; and the thickness of non-liqueˆable layer at the surface. The outcome of this parametric study reveals the importance of above mentioned factors which should be taken into account for analysis and design purposes. In addition, the results from the experiments clearly illustrate that in sloping ground conˆguration, both front (in upstream) and rear (in downstream) row piles receive greater lateral forces than middle row piles. Thisˆnding is attributed to the distribution of soil motion (displacement and velocity) of the liqueˆed soil in the model. As a result, installation of additional pile rows in front and behind an existing pile foundation can be considered as an eŠective retroˆtting technique. Finally, soil-pile interaction was evaluated by running experiments with diŠerent pile spacings, and reliability of the JRA 2002 design manual in estimation of liquefaction-induced lateral force on piles is evaluated.