Comparison of Time Series and Random-Vibration Theory Site-Response Methods

The random-vibration theory (RVT) approach to equivalent-linear site-response analysis is often used to simulate site amplification, particularly when large numbers of simulations are required for incorporation into probabilistic seismic-hazard analysis. The fact that RVT site-response analysis does not require the specification of input-time series makes it an attractive alternative to other site-response methods. However, some studies have indicated that the site amplification predicted by RVT site-response analysis systematically differs from that predicted by time-series approaches. This study confirms that RVT site-response analysis predicts site amplification at the natural site frequencies as much as 20%-50% larger than time-series analysis, with the largest overprediction occurring for sites with smaller natural frequencies and sites underlain by hard rock. The overprediction is caused by an increase in duration generated by the site response, which is not taken into account in the RVT calculation. Correcting for this change in duration brings the RVT results within 20% of the time-series results. A similar duration effect is observed for the RVT shear-strain calculation used to estimate the equivalent-linear strain-compatible soil properties. An alternative to applying a duration correction to improve the agreement between RVT and time-series analysis is the modeling of shear-wave velocity variability. It is shown that introducing shear-wave velocity variability through Monte Carlo simulation brings the RVT results consistently within +/- 20% of the time-series results.Nuclear Regulatory Commission NRC-04-07-122Civil, Architectural, and Environmental Engineerin

Recent Advances in Predicting Earthquake-Induced Sliding Displacements of Slopes

This paper summarizes recent research related to predicting earthquake-induced sliding displacements of earth slopes. Recently developed empirical models for the prediction of sliding displacements for shallow (rigid) failure surfaces are discussed, and comparisons of the different models demonstrate that including peak ground velocity, along with peak ground acceleration, reduces the median displacement prediction and the standard deviation of the prediction. Thus, peak velocity provides important information regarding the level of sliding displacement. A framework is developed such that the recently developed empirical displacement models for rigid sliding can be used for deeper, flexible failure surfaces, where the dynamic response of the sliding mass is important. This framework includes predicting the seismic loading for the sliding mass in terms of the maximum seismic coefficient (kmax) and the maximum velocity of the seismic coefficient-time history (k-velmax). The predictive models for kmax and k-velmax are a function of the peak ground acceleration (PGA), peak ground velocity (PGV), the natural period of the sliding mass (Ts), and the mean period of the earthquake motion (Tm). With a slight modification, the empirical predictive models for rigid sliding masses can be used, with PGA replaced by kmax and PGV replaced by k-velmax. The standard deviations for the modified predictive models for flexible sliding masses are slightly smaller than those for rigid sliding masses

Geotechnical Lessons Learned From Earthquakes

Geotechnical earthquake engineering is an experience-driven discipline. Field observations are particularly important because it is difficult to replicate in the laboratory, the characteristics and response of soil deposits built by nature over thousands of years. Further, much of the data generated by a major earthquake is perishable, so it is critical that it is collected soon after the event occurs. Detailed mapping and surveying of damaged and undamaged areas provides the data for the well-documented case histories that drive the development of many of the design procedures used by geotechnical engineers. Thus, documenting the key lessons learned from major earthquake events around the world contributes significantly to advancing research and practice in geotechnical earthquake engineering. This is one of the primary objectives of the Geotechnical Extreme Events Reconnaissance (GEER) Association. Some of GEER’s findings from recent earthquakes are described in this paper. In particular, the use of advanced reconnaissance techniques is highlighted, as well as specific technical findings from the 1999 Kocaeli, Turkey earthquake, the 2007 Pisco, Peru earthquake, the 2010 Haiti earthquake, and the 2010 Maule, Chile earthquake

Evaluation Nonlinear Soil Response In Situ

Evaluation of nonlinear soil properties is an important concern in geotechnical earthquake engineering. Typically, nonlinear properties are expressed in terms of the nonlinear reduction in shear and constrained moduli with strain and the nonlinear increase in material damping in shear and constrained compression with strain. At this time, there is essentially total dependency on laboratory testing to evaluate nonlinear soil properties. The accuracy and limitations involved in modeling in situ properties with laboratory evaluated properties remains to be studied. In an attempt to evaluate nonlinear soil properties directly in the field, an in situ test method is being developed at the University of Texas that dynamically loads a soil deposit while simultaneously measuring strains, soil properties, and pore water pressures. Initial testing with this method has focused on vertically loading an unsaturated sandy soil, evaluating the magnitude of induced strains, and assessing the variation of constrained modulus (in terms of compression wave velocity, VP) with effective vertical stress and vertical strain. Preliminary results show that the test method can be used to: (1) evaluate the increase in small-strain VP with increasing vertical effective stress, (2) induce nonlinear compressional and shear strains, and (3) evaluate the nonlinear reduction in VP with increasing vertical strain

Virtualizing the Stampede2 Supercomputer with Applications to HPC in the Cloud

Methods developed at the Texas Advanced Computing Center (TACC) are described and demonstrated for automating the construction of an elastic, virtual cluster emulating the Stampede2 high performance computing (HPC) system. The cluster can be built and/or scaled in a matter of minutes on the Jetstream self-service cloud system and shares many properties of the original Stampede2, including: i) common identity management, ii) access to the same file systems, iii) equivalent software application stack and module system, iv) similar job scheduling interface via Slurm. We measure time-to-solution for a number of common scientific applications on our virtual cluster against equivalent runs on Stampede2 and develop an application profile where performance is similar or otherwise acceptable. For such applications, the virtual cluster provides an effective form of "cloud bursting" with the potential to significantly improve overall turnaround time, particularly when Stampede2 is experiencing long queue wait times. In addition, the virtual cluster can be used for test and debug without directly impacting Stampede2. We conclude with a discussion of how science gateways can leverage the TACC Jobs API web service to incorporate this cloud bursting technique transparently to the end user.Comment: 6 pages, 0 figures, PEARC '18: Practice and Experience in Advanced Research Computing, July 22--26, 2018, Pittsburgh, PA, US

Recent Advances in Geotechnical Post-earthquake Reconnaissance

Field observations are particularly important in geotechnical engineering, because it is difficult to replicate in the laboratory the response of soil deposits built by nature over thousands of years. Detailed mapping of damaged and undamaged areas provides the data for the well-documented case histories that drive the development of many current design procedures. Thus, documenting key insights from earthquakes advance research and practice. This has been a primary goal of the National Science Foundation-sponsored Geotechnical Extreme Events Reconnaissance (GEER) Association since its inception almost 20 years ago. New technologies are continually employed by GEER teams to capture ground deformation and its effects. These technologies include Light Imaging Detection and Ranging (LIDAR) and Structure-from-Motion (SfM) image processing techniques for generating and visualizing three-dimensional point cloud data sets. New sensor deployment platforms such as Unmanned Aerial Vehicles (UAVs) are playing an integral role in the data collection process. Unanticipated observations from major events often catalyze new research directions. An overview of some of these recent integrated technology deployments and their role at the core of earthquake disaster analysis is presented. Important advancements are possible through post-event research if their effects are captured and shared effectively

Seismic Vulnerability and Post-Event Actions for Texas Bridge Infrastructure

0-6916The research investigates the seismic vulnerability of bridges in Texas by characterizing seismic hazards in the State, developing computational tools to estimate the likelihood of seismic damage to various bridge types, and providing the Texas Department of Transportation (TxDOT) tools to inform post-earthquake response planning and decision-making