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Modeling of Fourier amplitude spectra (FAS) of seismic motions has gained much attention in engineering seismology. In the past few years, several ground motion prediction equations (GMPEs) and inter-frequency correlation structure of FAS have been established. Due to many preferable characteristics of FAS, probabilistic seismic hazard/risk analysis is rapidly changing from ergodic, spectrum acceleration Sa(T0)-based approach to non-ergodic, site-specific, FAS-based approach. This paper presents time domain intrusive framework for probabilistic seismic risk analysis using GMPE of FAS. Methodology for time domain stochastic ground motion modeling based on GMPEs of FAS is presented in some detail. The simulated uncertain motions are modeled as a random process and represented by polynomial chaos Karhunen-Loève expansion. The random process excitations are further propagated into the uncertain structural system using Galerkin stochastic finite element method (SFEM). Probabilistic evolution of structural response is solved, and such solution is used to develop seismic risk for any damage state. The presented framework is illustrated through seismic risk analysis of a four-story building subjected to possible earthquakes from two strike slip faults. The influences of the epistemic uncertainties in source stress drop Δσ and site attenuation κ0 on seismic risk are investigated. The need for non-ergodic seismic risk analysis with source-specific and site specific characterizations is emphasized.

Tuned mass dampers (TMDs) can be used as vibration control devices to improve the vibration performance of high-rise buildings. The Shanghai Tower (SHT) is a 632-m high landmark building in China, featuring a new eddy-current TMD. Special protective mechanisms have been adopted to prevent excessively large amplitude of the TMD under extreme wind or earthquake loading scenarios. This paper presents a methodology for simulating behavior of the new eddy-current TMD that features displacement-dependent damping behavior. The TMD model was built into the SHT finite element model to perform frequency analysis and detailed response analyses under wind and earthquake loads. Furthermore, soil-structure interaction (SSI) effects on wind and seismic load responses of the SHT model were investigated, as SSI has a significant impact on the vibration performance of high-rise buildings. It was found that SSI has more significant effects on acceleration response for wind loads with a short return period than for wind loads with a long return period. Some of the acceleration responses with SSI effects exceed design limits of human comfort for wind loads with shorter return periods. As to the seismic analyses, it was found that SSI slightly reduces the displacement amplitude, the damping force, and the impact force of the TMD.

In soil-structure interaction modeling of systems subjected to earthquake motions, it is classically assumed that the incoming wave field, produced by an earthquake, is unidimensional and vertically propagating. This work explores the validity of this assumption by performing earthquake soil-structure interaction modeling, including explicit modeling of sources, seismic wave propagation, site, and structure. The domain reduction method is used to couple seismic (near-field) simulations with local soil-structure interaction response. The response of a generic nuclear power plant model computed using full earthquake soil-structure interaction simulations is compared with the current state-of-the-art method of deconvolving in depth the (simulated) free-field motions, recorded at the site of interest, and assuming that the earthquake wave field is spatially unidimensional. Results show that the 1-D wave-field assumption does not hold in general. It is shown that the way in which full 3-D analysis results differ from those which assume a 1-D wave field is dependent on fault-to-site geometry and motion frequency content. It is argued that this is especially important for certain classes of soil-structure systems of which nuclear power plants subjected to near-field earthquakes are an example.

The Center for Geotechnical Modeling at UC Davis operates a 9.1-m radius geotechnical centrifuge equipped with a 2 m x 1 m servo-hydraulic shaking table. This equipment has been used in geotechnical earthquake engineering research since 1994. In October 2000, UC Davis was selected as a host equipment site on the National Science Foundation's George E. Brown, Jr., Network for Earthquake Engineering Simulation. This four-year upgrade project represents a $5M investment in the UC Davis centrifuge facilities by NSF with an additional $1M from UC Davis. NEES at UC Davis capitalized on the size of the centrifuge and innovations in instrumentation and information technology to enable generation of higher resolution information (control, sensors, and images) and to create more realistic physical models. With NEES the Center for Geotechnical Modeling is working to implement advanced instrumentation, digital video, robotics, and geophysical testing to increase the quality and quantity of data that can be collected; to increase the capacity of the centrifuge; and to develop a biaxial shaking capability. These improvements will allow us to extract more detailed and more accurate information from experiments and simulations, maximizing the information and knowledge that can be gained from these experiments. The Center for Geotechnical Modeling facilities are intended for use by researchers from academia and industry, from both the US and abroad. The centrifuge at UC Davis will be a shared-use facility under NEES, with experiments being performed by teams of researchers. New hardware and software developments are currently being implemented as part of the NEESgrid System Integration project. These new resources will allow teams to collaborate regardless of their physical location. Remote researchers will be able to control their experiments at UC Davis as easily as local researchers. Further information about the UC Davis NEES site can be obtained at http://nees.ucdavis.edu, or by email to cgm@ucdavis.edu.

We present a novel technique for visualizing tensors in three dimensional (3D) space. Of particular interest is the visualization of stress tensors resulting from 3D numerical simulations in computational geomechanics. To this end we present three different approaches to visualizing tensors in 3D space, namely hedgehogs, hyperstreamlines and hyperstreamsurfaces. We also present a number of examples related to stress distributions in 3D solids subjected to single and load couples. In addition, we present stress visualizations resulting from single-pile and pile-group computations. The main objective of this work is to investigate various techniques for visualizing general Cartesian tensors of rank 2 and it's application to geomechanics problems.

Earthquake events are among the most devastating catastrophes on Earth. Besides human casualties, they are also responsible for large damage to a variety of man-built objects. Civil engineering thus has significant interest in understanding effects of earthquakes. Induced dynamic motions will cause significant oscillations in stress and strain tensors inside 3D solids (soils, concrete and steel). These fluctuations in stresses and strains can result in failure of one of the components of the civil engineering object which might eventually lead to the complete failure and loss of life. We use tensor visualization techniques to study seismic behavior of concrete pile foundations embedded in soil. We show results and limitations of current and new techniques leading to a discussion of possible further research.

This paper presents results of the finite element study on the behavior of a single pile in elastic-plastic soils. Pile behavior in uniform sand and clay soils as well as cases with a sand layer in a clay deposit and a clay layer in a sand deposit were analyzed using finite element modeling. Finite element results were used to generate p-y response curves, which were cross compared to investigate the soil layering effects. CE Database subject headings: Layered soils; Lateral loads; Piles; Finite element method; Elastoplasticity.

In this paper, we investigate the behavior of elastic-plastic specimens during testing in a triaxial apparatus. In particular, an investigation of the influence of a number of imperfections on the observed behavior of a specimen is performed. To this end, we present influences of end platen friction, end platen inclinations, and the shape of specimen on what we broadly understand by 'constitutive behavior.' We investigate the issues related to the constitutive as opposed to boundary value behavior or elastic-plastic specimens. We present a number of examples to illustrate the differences between different types of response, which are usually, and wrongly, just called the constitutive behavior. CE Database subject headings: Elastoplasticity; Constitutive relations; Geomaterials; Laboratory tests.

Six displacement-controlled, conventional, drained axisymmetric triaxial experiments on cohesionless granular soil specimens were conducted at very low effective confining stresses in a SPACEHAB module on the Space Shuttle during the STS-79 and STS-89 missions. Three specimens were tested on each mission. The specimens measured 75 mm in diameter by 150 mm long. The average grain size of the subangular Ottawa quartz sand was 0.22 mm. The specimens' relative density for the STS-79 mission was 86.5% ([+ or -] 0.8%); for the STS-89 mission it was 65.0% ([+ or -] 1.0%). The confining stresses in the six experiments were 0.05, 0.52, and 1.30 kPa. Very high friction angles in the range of 47.6 to 70.0 [degrees] were observed. The dilatancy angles were also unusually high, in the range of 30 to 31 [degrees], In spite of the very low effective stresses, high elastic moduli were observed.

In this paper, recently developed probabilistic elastoplasticity was applied in simulating cyclic behavior of clay. A simple von Mises elastic-perfectly plastic material model was used for simulation. Probabilistic soil parameters, elastic shear modulus (Gmax) and undrained shear strength (su), needed for the simulation were obtained from correlations with the standard penetration test (SPT) N-value. It has been shown that the probabilistic approach to geo-material modeling captures some of the important aspects-the modulus reduction, material damping ratio, and modulus degradation-of cyclic behavior of clay reasonably well, even with the simple elastic-perfectly plastic material model. [ABSTRACT FROM AUTHOR]

In this paper we discuss the use of the p-version of the finite element method applied to elastoplastic problems that exhibit sharp (but continuous) deformation gradients. The deformation theory of deviatoric, linearly hardening elastoplasticity with an iterative, displacement based finite element framework is used. The focus of this work is on assessing the applicability of the p-version to the analysis of localized deformation with continuous strain and displacement fields. Presented examples demonstrate that the method can be used reliably with a proper finite element mesh design. Possible extensions of the work are also discussed. Copyright © 1999 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]