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181.
182.
Computational study of self‐centering buckling‐restrained braced frame seismic performance
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Recent research developed and experimentally validated a self‐centering buckling‐restrained brace (SC‐BRB) that employs a restoring mechanism created using concentric tubes held flush with pretensioned shape memory alloy rods, in conjunction with a buckling‐restrained brace (BRB) that dissipates seismic energy. The present computational study investigated how the SC‐BRB can be implemented in real buildings to improve seismic performance. First, a computational brace model was developed and calibrated against experimental data, including the definition of a new cyclic material model for superelastic NiTi shape memory alloy. A parametric study were then conducted to explore the design space for SC‐BRBs. Finally, a set of prototype buildings was designed and computationally subjected to a suite of ground motions. The effect of the lateral resistance of gravity framing on self‐centering was also examined. From the component study, the SC‐BRB was found to dissipate sufficient energy even with large self‐centering ratios (as large as 4) based on criteria found in the literature for limiting peak drifts. From the prototype building study, a SC‐BRB self‐centering ratio of 0.5 was capable of reliably limiting residual drifts to negligible values, which is consistent with a dynamic form of self‐centering discussed in the literature. Because large self‐centering ratios can create significant overstrength, the most efficient SC‐BRB frame designs had a self‐centering ratio in the range of 0.5–1.5. Ambient building resistance (e.g., gravity framing) was found to reduce peak drifts, but had a negligible effect on residual drifts. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
183.
Ronald C. Chaney Marnie D. Chapman William Miller III 《Marine Georesources & Geotechnology》2013,31(3):333-339
Geotechnical Aspects of Coastal and Offshore Structures. Edited by Yudhair and A. S. Balasubramaniam. Proceedings of the Symposium on Geotechnical Aspects of Coastal and Offshore Structures, Bangkok, December 14–18,1981. Rotterdam: A. A. Balkema, 1983. 280 pp. $40.00. The Seaside Naturalist: A Guide to Nature Study at the Seashore. Written and illustrated by D. A. Coulombe. Englewood Cliffs, N.J.: Prentice‐Hall, Inc., 1984. 246 pp. $12.95. Ichnology, Trace Fossils in Sedimentology and Stratigraphy. By A. A. Ekdale, R. G. Bromley, and S. G. Pemberton. Society of Economic Paleontologists and Mineralogists, Short Course No. 15. Tulsa, Okla.: S.E.P.M., 1984. 317 pp. S.E.P.M. members, $16.00; non‐members, $20.00. 相似文献
184.
David L. Strayer Stuart E. G. Findlay Daniel Miller Heather M. Malcom David T. Fischer Thomas Coote 《Aquatic Sciences - Research Across Boundaries》2012,74(3):597-610
The shore zones of the Hudson River, like those of many developed waterways, are highly varied, containing a mix of seminatural and highly engineered shores. Our goal was to document the biodiversity supported by different kinds of shore zones in the Hudson. We chose six common types of shore zones, three of them ??natural?? (sand, unconsolidated rock, and bedrock), and three of them engineered (riprap, cribbing, and bulkheads). We measured selected physical characteristics (shore zone width, exposure, substrate roughness and grain size, shoreline complexity) of three examples of each of these shore types, and also sampled communities of terrestrial plants, fishes, and aquatic and terrestrial invertebrates. Community composition of most taxa differed across shore types, and frequently differed between wide, sheltered shores and narrow, exposed shores. Alien plant species were especially well represented along engineered shores. Nevertheless, a great deal of variation in biological communities was not explained by our six-class categorization of shore zones or the physical variables that we measured. No single shore type supported the highest values of all kinds of biodiversity, but engineered shore zones (especially cribbing and bulkheads) tended to have less desirable biodiversity characteristics than ??natural?? shore zones. 相似文献
185.
S. A. Miller 《Geophysical Journal International》2008,173(1):334-338
Recently reported rain-triggered seismicity from three separate storms occurred exclusively in karst geology. In this paper, I discuss how the hydrogeology of karst controls rain-triggered seismicity by channeling of the watershed after intense rainfall directly into the karst network. Such channeling results in very large increases in hydraulic head, and more importantly, substantially increases the vertical stress acting on the underlying pore-elastic media. Rapid loading upon a pore-elastic media induces seismicity by increasing pore pressure at depth in a manner similar to that observed from reservoir impounding. Using a simple 1-D model of a pore-elastic medium, it is shown that the instantaneous fluid pressure increase at depth is a substantial fraction of the pressure step applied at the boundary, followed by time-dependent pore pressure increases associated with the typical linear diffusion problem. These results have implications for the change in fluid pressure necessary to trigger earthquakes, and leads to the following hypothesis to be tested: Unambiguous rain-triggered seismicity will only occur in karst regions. 相似文献
186.
Recent anti-systemic social movements have illustrated the central role of cities in social movement mobilization. We not only highlight the characteristics of urban social relations that make cities fertile ground for mobilization, but also point to the disjunctures between the geographies and spatialities of social relations in the city, and the geographies and spatialities of many systemic processes. Struggles for a more just society must consider the broad geographies and spatialities of oppression, which we illustrate with a brief analysis of the Occupy movement. Finally, we introduce the next five articles in this special issue, all illustrating the importance of the geographies and spatialities of urban social struggle. 相似文献
187.
ABSTRACTFloodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen 相似文献
188.
189.
The space–time prism demarcates all locations in space–time that a mobile object or person can occupy during an episode of
potential or unobserved movement. The prism is central to time geography as a measure of potential mobility and to mobile
object databases as a measure of location possibilities given sampling error. This paper develops an analytical approach to
assessing error propagation in space–time prisms and prism–prism intersections. We analyze the geometry of the prisms to derive
a core set of geometric problems involving the intersection of circles and ellipses. Analytical error propagation techniques
such as the Taylor linearization method based on the first-order partial derivatives are not available since explicit functions
describing the intersections and their derivatives are unwieldy. However, since we have implicit functions describing prism
geometry, we modify this approach using an implicit function theorem that provides the required first-order partials without
the explicit expressions. We describe the general method as well as details for the two spatial dimensions case and provide
example calculations. 相似文献
190.
Centennial-scale climate change from decadally-paced explosive volcanism: a coupled sea ice-ocean mechanism 总被引:1,自引:1,他引:0
Y. Zhong G. H. Miller B. L. Otto-Bliesner M. M. Holland D. A. Bailey D. P. Schneider A. Geirsdottir 《Climate Dynamics》2011,37(11-12):2373-2387
Northern Hemisphere summer cooling through the Holocene is largely driven by the steady decrease in summer insolation tied to the precession of the equinoxes. However, centennial-scale climate departures, such as the Little Ice Age, must be caused by other forcings, most likely explosive volcanism and changes in solar irradiance. Stratospheric volcanic aerosols have the stronger forcing, but their short residence time likely precludes a lasting climate impact from a single eruption. Decadally paced explosive volcanism may produce a greater climate impact because the long response time of ocean surface waters allows for a cumulative decrease in sea-surface temperatures that exceeds that of any single eruption. Here we use a global climate model to evaluate the potential long-term climate impacts from four decadally paced large tropical eruptions. Direct forcing results in a rapid expansion of Arctic Ocean sea ice that persists throughout the eruption period. The expanded sea ice increases the flux of sea ice exported to the northern North Atlantic long enough that it reduces the convective warming of surface waters in the subpolar North Atlantic. In two of our four simulations the cooler surface waters being advected into the Arctic Ocean reduced the rate of basal sea-ice melt in the Atlantic sector of the Arctic Ocean, allowing sea ice to remain in an expanded state for?>?100 model years after volcanic aerosols were removed from the stratosphere. In these simulations the coupled sea ice-ocean mechanism maintains the strong positive feedbacks of an expanded Arctic Ocean sea ice cover, allowing the initial cooling related to the direct effect of volcanic aerosols to be perpetuated, potentially resulting in a centennial-scale or longer change of state in Arctic climate. The fact that the sea ice-ocean mechanism was not established in two of our four simulations suggests that a long-term sea ice response to volcanic forcing is sensitive to the stability of the seawater column, wind, and ocean currents in the North Atlantic during the eruptions. 相似文献