1,720,977 research outputs found
Long-term strength prediction of concrete with curing temperature
No full textThis paper describes a new strength time temperature prediction equation, which utilizes curing temperatures to improve the accuracy of estimates of long-term strength. To develop the model equation, existing data reported in the literature were collected and used. The data were converted into a relative strength ratio based on the strength at 28 days for 8 average curing temperatures in a range of -0.6 similar to 59.7 degrees C. The effect of the diffusion shell, which happens during cement hydration, on the long-term strength as a function of the curing temperature was considered using the rate constant model. Temperature influence factors such as rate constant, limiting strength, and reaction coefficient, which are functions of curing temperature, were incorporated in the new equation. Verification of the proposed model was performed by regression analysis. The results of regression analyses showed that the proposed model has higher reliability than existing model equations. The proposed model has higher accuracy at long-term ages the difference with existing models at an early age is not significant. (c) 2005 Elsevier Ltd. All rights reserved
Fracture characteristics of concrete at early ages
No full textThe purpose of this study is to experimentally investigate, at early ages, the fracture characteristics of concrete such as critical crack tip opening displacement, critical stress intensity factor, fracture energy, and bilinear softening curve based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge-splitting test for Mode I was performed on cubical specimens with an initial notch at the edge. By taking various strengths and ages, load-crack mouth opening displacement (CMOD) curves were obtained and these curves were evaluated by linear elastic fracture mechanics and finite element analysis. The results from the test and analysis indicate that critical crack tip opening displacement decreases and critical stress intensity factor and fracture energy increase with concrete ages from Day 1 to Day 28. By numerical analysis, four parameters of bilinear softening curves from Day 1 to Day 28 were obtained. In addition, it was observed that the parameters f(t) and f(l) increase and the parameters w(l) and w(c) decrease with increasing age. The obtained fracture parameters and bilinear softening curves at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages. (C) 2004 Elsevier Ltd. All rights reserved
Effect of specimen sizes on ACI rectangular stress block for concrete flexural members
No full textIt is important to consider the effect of concrete member sizes when estimating the ACI rectangular stress block of a concrete flexural member. The experimental data and analytical results, however are still insufficient for a proper evaluation. For all types of loading conditions, the trend is that the size of the ACI rectangular stress block tends to change when the member size changes.
In this paper the size variations of strength coefficients for ACI rectangular stress block (alpha(1) and beta(1)) and the stress block parameters (k(3), k(1)k(3), and k(2)) have been studied. The results from a series of C-shaped specimens subjected to axial compressive load and bending moment were adopted from other references.
The analysis results show the effect of specimen sizes on the strength coefficients for ACI rectangular stress block and the stress block parameters of a concrete member to be apparent. They also show that the current strength criteria-based design practice should be reviewed to include member size effect. More studies are needed in the future to verify that
Effect of specimen sizes on flexural compressive strength of concrete
No full textIt is important to consider the effect of member length when estimating the ultimate strength of a concrete flexural member. It is also essential to evaluate the effect of neutral-axis depth on the flexural compressive strength of a beam. The current experimental data is still insufficient, however for a proper evaluation. For all types of loading conditions, the trend is that the strength of a member tends to decrease when the member length and depth increase.
In this paper the length and depth variations of flexural compressive member have been studied experimentally. A series of C-shaped specimens subjected to axial compressive load and bending moment were tested. More specifically, four different length (h = 10, 20, 30, and 40 cm) and three different depth (c = 5, O, and 20 cm) concrete specimens are tested to investigate the size effect of member length h and neutral axis depth c, respectively. The thickness of the specimens was kept constant where the size effect in our-of-plan direction is not considered. The test results are curve fitted using Levenberg-Marquardt's least square method (LSM# to obtain parameters for the modified size effect law #MSEL) by Kim, Eo, and Park. The analysis results show that the effect of specimen length and depth on ultimate strength was apparent, but their effect on the ultimate strain was negligible. Finally, more general parameters for MSEL are suggested
Size effect on flexural compressive strength of concrete specimens
No full textIn estimation of the ultimate strength of a concrete flexural member, the effect of member size is usually not considered. For various types of loading, however, the strength always decreases with an increase of member sire.
In this study, the size effect of a flexural compression member was investigated by experiments. For this purpose, a series of C-shaped specimens subjected to axial compressive load and bending moment was tested using three different sizes of concrete specimens with a compressive strength of 52 MPa. The three different size specimens were varied in height and width of their cross sections, which had a 1:2:4 ratio. The thickness of the specimens were constant where the size effect in outplan direction is not considered.
The test results are curve fitted using least square method (LSIM) to obtain the new parameters for the modified size effect law (MSEL). The MSEL curve, graphed with new parameters, is compared with the uniaxial compressive strength of concrete cylinder test results; the results show a much stronger size effect in C-shapen member compared to the cylinder members
Size effect of concrete members applied with flexural compressive stresses
No full textIn this study, two types of special experiments are carried out to understand flexural compressive size effect of concrete members. The first type is an ordinary cylindrical specimen (CS) with a fully penetrated and vertically standing plate type notch at the mid-height of the specimen, which is loaded in compression at the top surface (e.g., in the parallel direction to the notch length). The second type is a general double cantilever beam (DCB), which is compression loaded in axial direction (e.g., in the parallel direction of the notch). For CS, an adequate notch length is taken from the experimental results obtained from the compressive strength experiment of various initial notch lengths. The trial tests to select the effective initial notch length show that CS with an initial notch length approximately greater than four times the maximum aggregate size fails without an additional increased load and in stable manner under Mode I failure mechanism. Therefore, the initial notch length to the maximum aggregate size ratio of 4.0 is used for all size specimens. For DCB, the eccentricity of loading points with respect to the axial axis of each cantilever and the initial notch length are varied. In both specimens, the compressive loads apply flexural compressive stresses on the crack tip region of the specimens. These two types of specimens fail by Mode I crack opening mechanism. By testing 3 geometrically proportional size specimens for CS and DCB, the experimental datum for flexural compression size effect of concrete are obtained. Using the obtained flexural compressive strength size effect datum, regression analyses are performed using Levenberg-Marquardt's least square method (LSM) to suggest new parameters for the modified size effect law (MSEL). The analysis results show that size effect is apparent for flexural compressive strength of specimens with an initial notch. For CS, the effect of initial notch length on flexural compressive strength size effect is apparent. For DCB, flexural compressive size effect is dependent on the eccentricity of loading points with respect to the axial axis of the cantilever beam. In other words, if DCB specimen is applied with greater tensile stress at the crack tip, the size effect of concrete becomes more distinct. The results show that the flexural compressive strength size effect of initial notch length variation of DCB exists but directly dependent on the loading location. This is due to the fact that the sizes of fracture process zone (FPZ) of all DCB specimens are similar regardless of the differences in the specimen slenderness ratio, but the flexural compressive and tensile stress combinations resulting in stress concentration at the crack tip region has direct effect on size effect of concrete members
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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