Bridge Monitoring and Performance Evaluation     

Timothy O. Lawrence  Chad T. Ritter  Janos Gergely 《Geotechnical and Geological Engineering》2011,29(5):919-926

Over fifty percent of our nation’s 560,000-plus bridges are obsolete or structurally deficient. To upgrade or replace these structures would require a serious budget. In order to shorten this list of bridges and to improve their ratings, state DOTs are investigating new repair techniques and better performance evaluation tools in order to implement the new drive to sustainability within the infrastructure. The research presented herein focused on the evaluation of current US bridge analysis and rating procedures for the North Carolina Department of Transportation (NCDOT). To evaluate these procedures, several bridges were rated with commercially available software and a newly developed spreadsheet program. In parallel, the bridges were also load tested for comparison, from which, it was concluded that the NCDOT’s bridge rating software directly follows the latest AASHTO requirements. The experimental results, however, also proved that the bridges had significant strength reserves associated to several factors, such as, girder/deck composite action, impact and distribution factors, material strength, and contribution of non-structural elements. In this research, a simplified bridge testing protocol was developed from which it was concluded, that a relatively simple instrumentation setup could be effective in the load rating of bridges through testing. The data gathered through these instruments provide vital performance data for normal traffic conditions, as well as during extreme loading conditions and evacuations, which could lead to less restrictive load ratings and removal of the structurally deficient classification, yielding a more sustainable structure.  相似文献   

Sedimentary stable carbon isotope evidence of late Quaternary vegetation and climate change in highland Costa Rica     

Chad S. Lane  Sally P. Horn  Claudia I. Mora  Kenneth H. Orvis  David B. Finkelstein 《Journal of Paleolimnology》2011,45(3):323-338

Continuous terrestrial records of paleoclimate and paleovegetation that extend to the late Pleistocene are rare for the circum-Caribbean uplands. In this study we analyzed the bulk and compound-specific carbon isotope composition of lake sediments spanning this period from Lago de las Morrenas 1 (LM1), a glacial lake in the highlands of southern Costa Rica, for evidence of climate and vegetation changes that may not have been apparent in previous analyses. The stable carbon isotope ratios of n-alkanes typically derived from terrestrial plants (δ¹³C_C27–C33) indicate an increased abundance of C₄ plant taxa during the late Pleistocene and earliest Holocene that may be related to decreased atmospheric carbon dioxide concentrations, increased aridity, or habitat availability. These n-alkane isotope ratios also provide evidence of more arid conditions during the early and late Holocene, and more mesic conditions during the middle Holocene, a pattern prevalent in other paleoclimate records from the region that is thought to be related to millennial-scale dynamics of the intertropical convergence zone (ITCZ). The sensitivity of the LM1 paleorecord to trade wind dynamics provides further support for the role of millennial-scale shifts in ITCZ dynamics in driving neotropical environmental change, and indicates that the effects of ITCZ migration were not limited to the lowlands.  相似文献   

Propagation of 0.7–2.5 Hz Rayleigh waves in Scotland     

Colin D. Macbeth  Paul W. Burton 《Geophysical Journal International》1986,84(1):101-120

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DENIS: A deep near-infrared survey of the southern sky     

N. Epchtein  B. De Batz  E. Copet  P. Fouqué  F. Lacombe  T. Le Bertre  G. Mamon  D. Rouan  D. Tiphène  W. B. Burton  E. Deul  H. Habing  J. Borsenberger  M. Dennefeld  A. Omont  J. C. Renault  B. Rocca Volmerange  S. Kimeswenger  I. Appenzeller  R. Bender  T. Forveille  F. Garzon  J. Hron  P. Persi  M. Ferrari-Toniolo  I. Vauglin 《Astrophysics and Space Science》1994,217(1-2):3-9

The DENIS project is the first attempt to carry out a complete digitized survey of the southern sky in the range 1–2.5µm. The main objectives of the programme and the main specifications of the camera and of the data processing stream are briefly outlined  相似文献   

Physical links between crustal deformation, seismic moment and seismic hazard for regions of varying seismicity     

Ian G. Main  Paul W. Burton 《Geophysical Journal International》1984,79(2):469-488

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Single-station attenuation measurements of high-frequency Rayleigh waves in Scotland   总被引：1，自引：0，他引：1  

Colin D. MacBeth  Paul W. Burton 《Geophysical Journal International》1987,89(3):757-797

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Daily accumulation rates of marine debris on sub-Antarctic island beaches     

Cecilia Eriksson  Harry Burton  Stuart Fitch  Martin Schulz  John van den Hoff 《Marine pollution bulletin》2013,66(1-2):199-208

The worlds’ oceans contain a large but unknown amount of plastic debris. We made daily collections of marine debris stranded at two sub-Antarctic islands to establish (a) physical causes of strandings, and (b) a sampling protocol to better estimate the oceans’ plastic loading. Accumulation rates at some beaches were dependent on tide and onshore winds. Most of the 6389 items collected were plastic (Macquarie 95%, Heard 94%) and discarded or lost fishing gear comprised 22% of those plastic items. Stalked barnacles (Lepas spp.) were a regular attachment on Macquarie debris but not at Heard Island. The daily accumulation rate of plastic debris on Macquarie Island was an order of magnitude higher than that estimated from monthly surveys during the same 4 months in the previous 5 years. This finding suggests that estimates of the oceans’ plastic loading are an order of magnitude too low.  相似文献   

A numerical scheme and benchmark tests for non-isothermal two-fluid ambipolar diffusion     

David A. Tilley  Dinshaw S. Balsara Chad Meyer 《New Astronomy》2012,17(3):368-376

Stars form in magnetized molecular clouds composed primarily of neutral gas with a trace amount of ions. We present a semi-implicit strategy for incorporating the equations that describe the coupled ion and neutral two-fluid equations, with a full energy equation, into the RIEMANN code that uses a TR-BDF2 algorithm to stably handle the stiffness of the source terms. We demonstrate that the numerical implementation works through the use of a suite of test problems that we catalog here. We show that reproducing the analytic dispersion analysis for the propagation of waves in a two-fluid plasma is an especially strong code test. We also present a two-fluid analogue of the Noh wall-shock problem and demonstrate the performance of the code on the Wardle instability. We also present a novel blast wave test, showing that the results reduce to the single fluid results under strong coupling, yet differing considerably when the coupling is weak. These test problems demonstrate that the numerical implementation can accurately capture the dissipation rate of waves and reproduce the structure of a C-shock.  相似文献   

Expansion of the northern hemisphere subtropical high pressure belt: trends and linkages to precipitation and drought     

Bohumil M. Svoma  Daniel S. Krahenbuhl  Chad E. Bush  Jonny W. Malloy  Joshua R. White  Melissa A. Wagner 《自然地理学》2013,34(3):174-187

A critical issue in research concerning long-term climate change is the relationship between circulation features and global temperature variations. We establish that the annual areal size of the northern hemisphere subtropical high pressure belt (SHPB), as defined by seven 500-hPa height isohypses, shares over 70% of the variability with global annual near-surface air temperature since 1948. The area enclosed by the 5850-m isohypse of the 500-hPa surface in the northern hemisphere has more than doubled since the 1950s, with greatest increases over northern Africa, the Middle East and India. A long-term historical run of a coupled global climate model shows rapidly increasing SHPB annual sizes, since the mid-1970s. Since the SHPB’s descending air produces increased aridity, SHPB expansion may transition humid regions to more arid lands. To examine this aspect, first, variations in recorded precipitation using a gridded database for the region experiencing expansion of the SHPB show a decrease in precipitation (though significant only at the 88% confidence level) over the last 60?years. Second, variations in a 0.5° spatial resolution monthly drought index, the Standardized Precipitation Evapotranspiration Index, are highly correlated (+0.78) with annual variations in the area enclosed by the 500-hPa height isohypses. These results support those of previous investigations that suggest further northward expansion of the northern hemisphere subtropical dry zones with continued global climate change.  相似文献   

Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling   总被引：1，自引：1，他引：0  

Chad J. Pritchard  Peter B. Larson 《Contributions to Mineralogy and Petrology》2012,164(2):205-228

An array of samples from the eastern Upper Basin Member of the Plateau Rhyolite (EUBM) in the Yellowstone Plateau, Wyoming, were collected and analyzed to evaluate styles of deposition, geochemical variation, and plausible sources for low δ¹⁸O rhyolites. Similar depositional styles and geochemistry suggest that the Tuff of Sulphur Creek and Tuff of Uncle Tom’s Trail were both deposited from pyroclastic density currents and are most likely part of the same unit. The middle unit of the EUBM, the Canyon flow, may be composed of multiple flows based on a wide range of Pb isotopic ratios (e.g., ²⁰⁶Pb/²⁰⁴Pb ranges from 17.54 to 17.86). The youngest EUBM, the Dunraven Road flow, appears to be a ring fracture dome and contains isotopic ratios and sparse phenocrysts that are similar to extra-caldera rhyolites of the younger Roaring Mountain Member. Petrologic textures, more radiogenic ⁸⁷Sr/⁸⁶Sr in plagioclase phenocrysts (0.7134–0.7185) than groundmass and whole-rock ratios (0.7099–0.7161), and δ¹⁸O depletions on the order of 5‰ found in the Tuff of Sulphur Creek and Canyon flow indicate at least a two-stage petrogenesis involving an initial source rock formed by assimilation and fractional crystallization processes, which cooled and was hydrothermally altered. The source rock was then lowered to melting depth by caldera collapse and remelted and erupted. The presence of a low δ¹⁸O extra-caldera rhyolite indicates that country rock may have been hydrothermally altered at depth and then assimilated to form the Dunraven Road flow.  相似文献