Site Response of Organic Soils

A primary source of uncertainty in any evaluation of the seismic stability of the Sacramento-San Joaquin Delta levee system is the site response characteristics of the shallow organic soils that commonly underlay the levees. This paper provides an overview of recent research on the site response characteristics of organic soils using centrifuge and numerical modeling. The centrifuge modeling effort included the development of techniques to measure the shear wave velocity profile for a centrifuge model while in-flight. One-dimensional site response analyses using an equivalent linear procedure were performed with the measured shear wave velocity profiles and the modulus reduction and damping relationships determined from prior laboratory studies. Good agreement was obtained between the numerical simulations and the centrifuge model recordings

COVID‐19, nationalism, and the politics of crisis: A scholarly exchange

In this article, several scholars of nationalism discuss the potential for the COVID‐19 pandemic to impact the development of nationalism and world politics. To structure the discussion, the contributors respond to three questions: (1) how should we understand the relationship between nationalism and COVID‐19; (2) will COVID‐19 fuel ethnic and nationalist conflict; and (3) will COVID‐19 reinforce or erode the nation‐state in the long run? The contributors formulated their responses to these questions near to the outset of the pandemic, amid intense uncertainty. This made it acutely difficult, if not impossible, to make predictions. Nevertheless, it was felt that a historically and theoretically informed discussion would shed light on the types of political processes that could be triggered by the COVID‐19 pandemic. In doing so, the aim is to help orient researchers and policy‐makers as they grapple with what has rapidly become the most urgent issue of our times

Wear behaviour at 600°C of surface engineered low-alloy steel containing TiC particles

The work aimed to develop surfaces that could resist wear at high temperatures, thus achieving a prolonged component life. Surface modification of a low-alloy steel by incorporating TiC particles has been undertaken by melting the surface using a tungsten inert gas torch. The dry sliding wear behaviour at 600°C of the original and modified surfaces was compared. Microscopic examination of both surfaces showed glazed layers across the wear tracks, with differing amounts of oxide and homogeneity. Extensive wear occurred on the steel surface, which showed deformation of the wear scar tracks and a steadily increased friction coefficient. The TiC addition reduced the wear loss, coinciding with a glazed layer 33% thinner than that on the low-alloy steel sample

Engineering characterization of ground motion. Task I. Effects of characteristics of free-field motion on structural response

This report presents the results of the first task of a two-task study on the engineering characterization of earthquake ground motion for nuclear power plant design. The overall objective of this study is to develop recommendations for methods for selecting design response spectra or acceleration time histories to be used to characterize motion at the foundation level of nuclear power plants. Task I of the study develops a basis for selecting design response spectra, taking into account the characteristics of free-field ground motion found to be significant in causing structural damage

The Effects of Long-Duration Subduction Earthquakes on Inelastic Behavior of Bridge Pile Foundations Subjected to Liquefaction-Induced Lateral Spreading

Effective-stress nonlinear dynamic analyses (NDA) were performed for a large-diameter reinforced concrete (RC) pile in multi-layered liquefiable sloped ground. The objective was to assess the effects of earthquake duration on the combination of inertia and liquefaction-induced lateral spreading. A parametric study was performed using input motions from subduction and crustal earthquakes covering a wide range of motion durations. The NDA results showed that the pile head displacements increased under liquefied conditions, compared to nonliquefied conditions, due to liquefaction-induced lateral spreading. The NDA results were used to develop a displacement-based equivalent static analysis (ESA) method that combines inertial and lateral spreading loads for estimating elastic and inelastic pile demands