1,720,975 research outputs found
Structural and corrosion performance of concrete bridge decks reinforced with corrosion-resistant reinforcing steel
No full textDeterioration of bridge decks is a primary factor limiting the lifespan of bridges especially in cold climates where deicing salts are commonly used. While controlling deck cracking or decreasing the permeability and porosity of concrete can improve performance and service life, chloride and moisture ingress as well as cracking cannot be eliminated. Full-depth cracks which are caused by restrained shrinkage allow for corrosive conditions at early ages for both the top and bottom reinforcement mats. Therefore, the use of corrosion-resistant reinforcement is essential to mitigate deterioration of bridge decks. The objective of this research program is to evaluate both the structural and corrosion performance of concrete bridge decks reinforced with corrosion-resistant reinforcement. To achieve this objective, a three phase experimental investigation was conducted considering a wide range of corrosion-resistant reinforcing materials. These materials included stainless steel (316LN, Duplex 2205, Duplex 2304, and XM-28), MMFX II microcomposite steel, and coated steel (epoxy, hot-dip galvanized, zinc-clad, and dual-coated zinc and epoxy (Zbar)). Forty-five beam specimens with tension lap splices were tested in the first phase to evaluate the bond between corrosion-resistant reinforcement and concrete. The test data were combined with other data available in literature to construct a simple model for development and splice length considering the range of corrosion resistant bar types as well as unconfined and confined conditions. Twelve slab specimens were tested in the second phase to evaluate the cracking behavior of slabs reinforced with corrosion-resistant reinforcement. Finally, one hundred twelve modified macrocells were constructed in the third phase to evaluate corrosion resistance under uncracked and cracked conditions. Transverse steel was also tied to the longitudinal steel to simulate actual bridge deck conditions. Based on the results of this study, a simple model is recommended for the calculation of development and splice lengths for both conventional black and corrosion-resistant reinforcing steel with and without confinement. Test results indicate that stainless steel, MMFX II, galvanized, and dual-coated bars have bond strengths comparable with black bars. Modification factors were developed for development and splice length calculations when other bar types are used. Recommendations are also provided for the control of crack widths. Considering corrosion resistance, identical reinforcing materials should be used in the top and bottom reinforcing mats while inert ties or ties made of the same material as the reinforcing bars should be used to avoid galvanic coupling. Finally, to assist in the selection of corrosion-resistant reinforcement, a ranking of the corrosion performance of various corrosion-resistant bars is provided based on test results and a visual examination after 503 days of exposure
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Simulation and analysis of wind turbine loads for neutrally stable inflow turbulence
Full text linktextEfficient temporal resolution and spatial grids are important in simulation of the inflow turbulence for wind turbine loads analyses. There have not been many published studies that address optimal space-time resolution of generated inflow velocity fields in order to estimate accurate load statistics. This study investigates turbine extreme and fatigue load statistics for a utility-scale 5MW wind turbine with a hub-height of 90 m and a rotor diameter of 126 m. Load statistics, spectra, and time-frequency analysis representations are compared for various alternative space and time resolutions employed in inflow turbulence field simulation. Conclusions are drawn regarding adequate resolution in space of the inflow turbulence simulated on the rotor plane prior to extracting turbine load statistics. Similarly, conclusions are drawn with regard to what constitutes adequate temporal filtering to preserve turbine load statistics. This first study employs conventional Fourier-based spectral methods for stochastic simulation of velocity fields for a neutral atmospheric boundary layer.
In the second part of this study, large-eddy simulation (LES) is employed with similar resolutions in space and time as in the earlier Fourier-based simulations to again establish turbine load statistics. A comparison of extreme and fatigue load statistics is presented for the two approaches used for inflow field generation. The use of LES-generated flows (enhanced in deficient high-frequency energy by the use of fractal interpolation) to establish turbine load statistics in this manner is computationally very expensive but the study is justified in order to evaluate the ability of LES to be used as an alternative to more common approaches. LES with fractal interpolation is shown to lead to accurate load statistics when compared with stochastic simulation. A more compelling reason for using LES in turbine load studies is the following: for stable boundary layers, it is not possible to generate realistic inflow velocity fields using stochastic simulation. The present study presents a demonstration that, despite the computational costs involved, LES-generated inflows can be used for loads analyses for utility-scale turbines. The study sets the stage for future computations in the stable boundary layer where low-level jets, large speed and direction shears across the rotor, etc. can possibly cause large turbine loads; then, LES will likely be the inflow turbulence generator of choice.Civil, Architectural, and Environmental Engineerin
CIVE 440: Reinforced Concrete Design I: Faculty-led Inquiry into Reflective and Scholarly Teaching (FIRST) Course Portfolio
Full text linkThis Faculty-led Inquiry into Reflective and Scholarly Teaching (FIRST) Course Portfolio documents the instructor’s teaching practices and student learning for Reinforced Concrete Design I (CIVE 440) course. The contents of this course portfolio captures the CIVE 440 course that was taught on the Lincoln campus during the semester of Fall 2022. CIVE 440 is a structural engineering design elective offered every year in the Department of Civil and Environmental Engineering on both Lincoln and Omaha campus at University of Nebraska-Lincoln (UNL). The course objective is to help students to be able to use theory and experience to proportion and detail reinforced concrete members such as beams, columns, and one-way slabs. In order to achieve this course objective, teaching methods, course materials, and assessment strategies have been carefully designed and continuously modified throughout multiple semesters. In addition to lectures, peer discussions in class with active learning tools (Plickers; a free paper based online clicker tool), solving and reviewing examples/problems as a group, and in-class reading were utilized as teaching methods. These unique methods are not the conventional way many engineering design courses are typically taught and this course portfolio documents these particular aspects. A mix of formative assessments (recall questions, peer instruction, minute papers, and muddiest point) and summative assessments (fourteen assignments and four exams) were designed and completed for each module in this course to assess the student learning. In addition, for Fall 2022 semester, a modified “specifications grading” of pass/fail grading scheme was used for the assignments in this course which allowed a second attempt if the first trial was failed. This was rather to help students achieve the goal of mastering the learning objectives of each lesson and improve their student learning experiences rather than focusing only on assignment and test scores only. The course assessment data analysis summarizes how these unique teaching methods (peer instruction with Plickers, group activities solving design problems, in-class reading) and different assessment strategies (specifications grading, minute papers, and muddiest points) influenced the student learning. Positive changes are observed in student learning based on their improved formative and summative assessment results compared to the assessments in previous semesters
Automated Transverse Crack Mapping System with Optical Sensors and Big Data Analytics
Full text linkTransverse cracks on bridge decks provide the path for chloride penetration and are the major reason for deck deterioration. For such reasons, collecting information related to the crack widths and spacing of transverse cracks are important. In this study, we focused on developing a data pipeline for automated crack detection using non-contact optical sensors. We developed a data acquisition system that is able to acquire data in a fast and simple way without obstructing traffic. Understanding that GPS is not always available and odometer sensor data can only provide relative positions along the direction of traffic, we focused on providing an alternative localization strategy only using optical sensors. In addition, to improve existing crack detection methods which mostly rely on the low-intensity and localized line-segment characteristics of cracks, we considered the direction and shape of the cracks to make our machine learning approach smarter. The proposed system may serve as a useful inspection tool for big data analytics because the system is easy to deploy and provides multiple properties of cracks. Progression of crack deterioration, if any, both in spatial and temporal scale, can be checked and compared if the system is deployed multiple times
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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