1,720,987 research outputs found
Thermo-mechanical properties and stress-strain curves of ordinary cementitious mortars at elevated temperatures
Full text linkThe mechanical behaviour of three bed-fixing mortars (one reference cement-lime mortar, cube strength approximate to 5 MPa and two cement mortars, cube strength approximate to 10 and 15 MPa) is investigated in this project in ordinary conditions and after being heated to 200, 400 and 600 degrees C, and up to 900 degrees C to evaluate the thermal diffusivity. The objectives of this study are two: (a) to extend the database on the high-temperature behaviour of ordinary cementitious mortars; and (b) to develop stress-strain relationships as a function of the temperature, that may be useful in the formulation of macro finite elements for masonry structures.On the whole, the heat-induced mechanical decay of the cementitious mortars investigated in this study (a) agrees with the experimental results available in the literature and (b) is very similar to that of ordinary concrete, as far as it concerns the compressive strength, tensile strength and elastic modulus. Compared to concrete at high temperatures, however, the mass loss in the mortars is higher, the thermal diffusivity is always smaller and the softening branch of the stress-strain curves indicates a definitely higher ductility.The test results allow calibrating an analytical stress-strain law in compression. The formulation is derived from that provided by Eurocode 2 for concrete at high temperature, but accounting for the smaller elastic modulus, the greater ductility and the gentler softening of the mortars at any temperature. (C) 2020 Elsevier Ltd. All rights reserved
Bond shear modulus in reinforced concrete at high temperature: A design-oriented approach
No full textModeling bond behavior in either ordinary or high-temperature conditions requires the knowledge of bond shear modulus—called also slip modulus or simply bond stiffness—that has received so far scanty attention because of the greater interest for bond as a guarantee of equilibrium at the Ultimate Limit State (and in fire conditions) than as a means to guarantee both equilibrium and compatibility at the Serviceability Limit State (and in fire/post-fire conditions). The limited knowledge of bond shear modulus makes it difficult to numerically model such phenomena as tension stiffening, that controls the structural behavior in both ordinary and fire conditions. The general trends identified by examining eleven experimental campaigns with anchored bars covering 27 different cases and temperatures ranging between 20 and 800°C are the starting point of the design-oriented laws proposed in this study about bond shear modulus as a function of concrete residual strength and temperature. A simple shear-lag model is introduced for bond shear modulus at room temperature, as its evaluation from test data is no simple matter due to initial chemical adhesion and different test procedures. Bond shear modulus is shown to be a decreasing function of concrete residual compressive strength and of the maximum temperature reached by the bar-concrete system. Design charts are proposed to allow the designer to identify the value of the bond stiffness on the basis of the max. temperature, of concrete residual strength and of bar diameter, making it possible to realistically model tension stiffening in fire-damaged RC structures
Crack patterns in double-wall industrial masonry chimneys: Possible causes and numerical modelling
No full textThe origin of crack patterns in industrial masonry chimneys is investigated. This information is of utmost importance in defining any preservation project, and designing suitable repair interventions. Attention is focused on a 66 m-tall chimney built at the end of the XIX century, which is representative of numerous coeval chimneys of similar geometry. The base and the shaft of the chimney are double-walled: vertical ribs and horizontal diaphragms partially connect the walls of the shaft; the crown is single-walled. Vertical cracks can be observed in the lower part, horizontal cracks in the upper part, and zig-zag cracks in the central part. The structural behaviour of the chimney was investigated by means of finite elements, under gravity loads and thermal variations. Most of the cracks can be explained by thermal effects, if the anisotropic strength of masonry is duly accounted for. Therefore, new cracking phenomena can be excluded, and suitable repair interventions may allow an adequate level of safety to be attained
Numerical analysis of the effects of fire with cooling phase on reinforced concrete members
No full textFire exposed structures may collapse during or after the fire decay phase, with risks for building occupants and firefighters; yet, understanding of the effects of the fire decay phase on structural loadbearing capacity remains limited. This paper describes a numerical investigation on the behavior of reinforced concrete columns, beams, and walls under natural fires including cooling down phases. Finite element models are benchmarked against experiments capturing the behavior during heating. The models are then used to simulate the structural response of the concrete members under fires with various cooling rates and load ratios. The analyses capture the irreversibility of material properties through tracing of the temperature history in the structure. The results show that temperatures and deformations continue increasing after the end of the fire heating phase. As a result, concrete columns, beams, and walls may fail during the cooling phase. Faster cooling rates reduce the likelihood of failure in cooling. For beams, failure can be inferred from the maximum reinforcement temperature reached throughout the fire, but for columns and walls a thermal–mechanical analysis of the member throughout the fire history is needed. A relationship is proposed to evaluate the burnout resistance from the fire resistance rating and cooling rate. The presented numerical method allows assessing the structural stability throughout a fire event, an important requirement for designing a fire resilient built environment
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
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