1,720,977 research outputs found
Safety assessment of existing reinforced concrete beams using probabilistic methods at different levels
No full textSeveral reliability methods available in literature combined with various modelling approaches are compared in this current work in the context of two experimental reinforced concrete (RC) beams. One beam failed in bending while the other beam failed in shear due to diagonal tension. The structural behaviour is described by analytical models and nonlinear finite element models. The changes in predicted reliability of these structures with increasing loads are evaluated by different reliability methods and the results are compare
Anchorage of naturally-corroded, plain bars in Reinforced Concrete structures
Get PDFReinforced Concrete (RC) is the most common construction material in existing structures. However, RC structures are susceptible to deterioration over time, with corrosion of the reinforcing steel as most common mechanism. Corrosion reduces strength and ductility provided by the reinforcement bars and affects their interaction with the concrete. Research on the structural effects of corrosion commonly focuses on deformed bars and applies artificial corrosion. Performance is evaluated based on testing the bond between the bars and the concrete. Plain (smooth) reinforcing bars, as typical in older structures, are seldom studied. Plain bars interact differently with concrete, due to the absence of ribs. Additionally, doubts on the relevance of artificial corrosion methods have been raised. Thus, there is a lack of knowledge on the effects of corrosion of plain bars, and naturally corroded specimens are the ideal mean of acquiring it.This work investigates the bond of naturally corroded, plain reinforcement bars by testing specimens taken from the edge beams of a decommissioned, 80-year-old bridge. Pilot tests were performed to investigate possible test configurations, to which a total of 20 beams were subjected to displacement-controlled 3-point bending. The beams presented different levels of damage, and the corrosion level of each tensile reinforcement bar was afterwards measured using of a 3D scanner. All but three of the tested specimens were able to anchor the yield force of the bars after the opening of one or two major bending cracks in the middle. Bending failure, not bond strength, limited the load-carrying capacity for the majority of test specimens. At large deflections, end-slip of the reinforcement bars was observed; thus, anchorage limited the deformation capacity.The average bond strength was evaluated separately in the unyielded and in the yielded zones. The average bond strength in the unyielded zone was found to be equal to 7.4 MPa, with a standard deviation of 3.3 MPa. The casting position was identified as an important factor. Bottom-cast bars had higher bond strength when uncorroded, but were more prone to external cracks in the bond region and consequently loss of bond strength for small corrosion levels. Top-cast bars had lower bond strength when uncorroded, but reached higher bond strength with increasing corrosion levels, due to the absence of external cracks. These differences are likely the result of a higher density of the concrete surrounding the bottom-cast bars. In the yielded zones, substantial loss of bond strength was observed, with an average of 1 MPa. This affected the overall structural behaviour, which was observed to change from beam to arch action for larger deflections.To conclude, the results improve our understanding of the behaviour of older structures with plain bars and will enable, in the long run, improved assessment methods
Natural corrosion in reinforced concrete structures [Elektronisk resurs]
No full textAmong the threats to the durability of concrete structures, corrosion of the reinforcement bars is undoubtedly the most common one. Corrosion damages impair safety and durability of infrastructure, and assessment of the safety is challenging due to the complex nature of the corrosion process. Furthermore, research on the topic often requires adapting results from short-time laboratory tests, where corrosion of the reinforcement bars is induced using impressed current, to the reality of existing structures. The use of impressed current results in differences in type and distribution of corrosion products. Naturally corroded specimens are hence the necessary bridge between the knowledge acquired from artificially corroded specimens and the application to real structures. This works investigates the structural effects of natural, chloride-induced corrosion in reinforced concrete structures. Specifically, three research questions were investigated. First, the bond and anchorage of naturally corroded plain bars was studied using 3-point bending and pull-out tests. The tests were designed to be applied to specimens taken from a decommissioned bridge from the 1930s. The bond capacity of plain bars was observed to be significantly higher than in results obtained from laboratory tests on similar bars. Significant factors influencing the effect of corrosion damages on the bond were casting position and presence of stirrups. Finite element analyses were used to further investigate the bond-slip behaviour of the tested specimens. The results highlighted the effect of the loss of bond at yielding on the structural behaviour of the specimens. The second question looked into the characteristics of the corrosion products and the surrounding concrete; this is relevant to assess corrosion damages in existing structures. Neutron imaging and X-ray computed tomography were used to obtain qualitative and quantitative data on corrosion damages in a naturally corroded specimens, including iron to rust ratio. Comparison with an artificially corroded specimen showed differences in distribution of the corrosion products. Finally, possible correlations between transversal cracks and corrosion damages was investigated. A dataset was compiled from experiments available in literature. In the selected studies, corrosion of the steel reinforcement resulted from exposing laboratory specimens, pre-cracked in 3-point bending, to chloride environments. No clear correlation between surface crack width and corrosion characteristics was found, but corrosion pits were shown to likely appear in the proximity of transveral cracks. To conclude, this work highlights the complexity of the corrosion process and argues that a thorough understanding of the material and environmental characteristics influencing this process is necessary to properly assess existing structures. Tests on naturally corroded structures are a fundamental step towards acquiring this knowledge
Anchorage of naturally-corroded, plain bars in Reinforced Concrete structures [Elektronisk resurs]
No full textReinforced Concrete (RC) is the most common construction material in existing structures. However, RC structures are susceptible to deterioration over time, with corrosion of the reinforcing steel as most common mechanism. Corrosion reduces strength and ductility provided by the reinforcement bars and affects their interaction with the concrete. Research on the structural effects of corrosion commonly focuses on deformed bars and applies artificial corrosion. Performance is evaluated based on testing the bond between the bars and the concrete. Plain (smooth) reinforcing bars, as typical in older structures, are seldom studied. Plain bars interact differently with concrete, due to the absence of ribs. Additionally, doubts on the relevance of artificial corrosion methods have been raised. Thus, there is a lack of knowledge on the effects of corrosion of plain bars, and naturally corroded specimens are the ideal mean of acquiring it. This work investigates the bond of naturally corroded, plain reinforcement bars by testing specimens taken from the edge beams of a decommissioned, 80-year-old bridge. Pilot tests were performed to investigate possible test configurations, to which a total of 20 beams were subjected to displacement-controlled 3-point bending. The beams presented different levels of damage, and the corrosion level of each tensile reinforcement bar was afterwards measured using of a 3D scanner. All but three of the tested specimens were able to anchor the yield force of the bars after the opening of one or two major bending cracks in the middle. Bending failure, not bond strength, limited the load-carrying capacity for the majority of test specimens. At large deflections, end-slip of the reinforcement bars was observed; thus, anchorage limited the deformation capacity. The average bond strength was evaluated separately in the unyielded and in the yielded zones. The average bond strength in the unyielded zone was found to be equal to 7.4 MPa, with a standard deviation of 3.3 MPa. The casting position was identified as an important factor. Bottom-cast bars had higher bond strength when uncorroded, but were more prone to external cracks in the bond region and consequently loss of bond strength for small corrosion levels. Top-cast bars had lower bond strength when uncorroded, but reached higher bond strength with increasing corrosion levels, due to the absence of external cracks. These differences are likely the result of a higher density of the concrete surrounding the bottom-cast bars. In the yielded zones, substantial loss of bond strength was observed, with an average of 1 MPa. This affected the overall structural behaviour, which was observed to change from beam to arch action for larger deflections. To conclude, the results improve our understanding of the behaviour of older structures with plain bars and will enable, in the long run, improved assessment methods
Natural corrosion in reinforced concrete structures
Get PDFAmong the threats to the durability of concrete structures, corrosion of the reinforcement bars is undoubtedly the most common one. Corrosion damages impair safety and durability of infrastructure, and assessment of the safety is challenging due to the complex nature of the corrosion process. Furthermore, research on the topic often requires adapting results from short-time laboratory tests, where corrosion of the reinforcement bars is induced using impressed current, to the reality of existing structures. The use of impressed current results in differences in type and distribution of corrosion products.Naturally corroded specimens are hence the necessary bridge between the knowledge acquired from artificially corroded specimens and the application to real structures.This works investigates the structural effects of natural, chloride-induced corrosion in reinforced concrete structures. Specifically, three research questions were investigated. First, the bond and anchorage of naturally corroded plain bars was studied using 3-point bending and pull-out tests. The tests were designed to be applied to specimens taken from a decommissioned bridge from the 1930s. The bond capacity of plain bars was observed to be significantly higher than in results obtained from laboratory tests on similar bars. Significant factors influencing the effect of corrosion damages on the bond were casting position and presence of stirrups. Finite element analyses were used to further investigate the bond-slip behaviour of the tested specimens. The results highlighted the effect of the loss of bond at yielding on the structural behaviour of the specimens. The second question looked into the characteristics of the corrosion products and the surrounding concrete; this is relevant to assess corrosion damages in existing structures. Neutron imaging and X-ray computed tomography were used to obtain qualitative and quantitative data on corrosion damages in a naturally corroded specimens, including iron to rust ratio. Comparison with an artificially corroded specimen showed differences in distribution of the corrosion products. Finally, possible correlations between transversal cracks and corrosion damages was investigated. A dataset was compiled from experiments available in literature. In the selected studies, corrosion of the steel reinforcement resulted from exposing laboratory specimens, pre-cracked in 3-point bending, to chloride environments. No clear correlation between surface crack width and corrosion characteristics was found, but corrosion pits were shown to likely appear in the proximity of transveral cracks.To conclude, this work highlights the complexity of the corrosion process and argues that a thorough understanding of the material and environmental characteristics influencing this process is necessary to properly assess existing structures. Tests on naturally corroded structures are a fundamental step towards acquiring this knowledge
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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