1,721,102 research outputs found
Fatigue crack growth of high-strength concrete in wedge-splitting test
No full textIn this study, a wedge-splitting testing was carried out for the investigation of fatigue crack growth behavior of high strength concrete. Selected test variables were concrete compressive strength (28, 60, and 118 MPa) and stress ratio (6, 13%). In order to apply the target stress ratio, the maximum acid the minimum fatigue loadings were 75-85 and 5-10% of ultimate static load, respectively. Fatigue testing was preceded by crack mouth opening displacement (CMOD) compliance calibration, acid then the fatigue crack growth was computed by crack length vs. the CMOD compliance relations acquired by the CMOD compliance calibration technique. In the fatigue test, the frequency of loading cycle was 1 Hz, and the initial notch length a(0) was 30% of specimen height. To verify the applicability of the CMOD compliance calibration technique to wedge-splitting testing, the crack lengths measured by this method were compared with those predicted by linear elastic fracture mechanics (LEFM) and dye penetration testing. On the basis of the experimental results, an LEFM-based empirical model for fatigue crack growth rate (da/dn - Delta K-I relationship) that takes strength into account was suggested. The fatigue crack growth rate increased with the strength of concrete. It appeared that the da/dN - Delta K-I relationship depended on stress ratio, and the effect was evaluated by the proposed equation. In addition, the comparisons between the CMOD compliance calibration technique and the other methods supported the validity of this technique in the wedge splitting test. (C) 1999 Elsevier Science Ltd. All rights reserved
Experimental study of the fatigue behavior of high strength concrete
No full textIn this study, cylindrical concrete specimens with various strength levels were tested to investigate the fatigue behavior of concrete in compression. Selected test variables were compressive strength with 4 levels (26 Mpa, 52 Mpa, 84 Mpa, 103 Mpa) and maximum stress with 4 levels (75%, 80%, 85%, 95%), 160 specimens (phi 100 x 200 mm) were cast for the test. The reference for the fatigue strength was the ultimate static strength acquired just before the fatigue testing. The moisture contents of specimens were preserved during the fatigue testing. In fatigue tests, the first cycle of loading was loaded at standard rate, and the other cycles were loaded in the frequency of 1 Hz. Test results show that the fatigue life decreased with increasing the concrete strength, and a model for S-max-N-f relationship considering the effect of the concrete strength was proposed. While fatigue strain of high strength concrete was smaller than that of low strength concrete, the rate of fatigue strain increment of high strength concrete was greater than that of low strength concrete. Copyright (C) 1996 Elsevier Science Lt
Analytical studies on creep of sealed concrete under multiaxial stresses using a microplane model
No full textThe Poisson ratio resulting from multiaxial creep of concrete, which has been reported by some experimental works, is controversial. When calculated from measured strains, Poisson ratio is very sensitive to small experimental error. This sensitivity makes it difficult to determine whether the ratio varies with time or remains constant, and whether it has a different value with stress states. To understand precisely the properties of multiaxial creep of concrete, a new approach is needed. In this study, microplane model is applied to optimally fitting test data extracted from experimental studies on multiaxial creep of concrete. Double-power law is used as a model to represent volumetric and deviatoric creep evolutions on a microplane. Six parameters representing the volumetric and deviatoric compliance functions are determined from regression analysis, and the optimum fits accurately simulate the test data. Poisson ratio is calculated from the optimum fits and its value varies with time. Regression analysis is also performed on the assumption that multiaxial creep of concrete is isotropic. Four parameters are determined for this condition, and the error between the optimum fits and the test data is slightly larger than that for the six-parameter regression results. The constant Poisson ratio with time is obtained from the results of the four-parameter analysis, and the constant value can be used in practice without serious error
Long-term behaviour of square concrete-filled steel tubular columns under axial service loads
No full textThis paper presents experimental and analytical studies on the long-term behaviour of rectangular concrete-filled steel tubular (CFT) columns under central axial loading. Four loading cases are considered in this study: ( a) a load applied simultaneously on both the inner concrete and steel tube (SCE); (b) a load applied only on the inner core concrete (CE); ( c) a load applied on the steel tube and three quarters of the inner concrete (SCQ); and (d) a load applied on the steel tube and half of the inner concrete (SCH). The last two loading cases ( SCQ and SCH) simulate a diaphragm installed in the steel tube. Specimens measuring 600 mm in length were tested for the first two loading cases ( SCE and CE), and specimens of three different lengths, 600, 900 and 1200 mm, were tested for the last two loading cases in order to investigate the effect of the diaphragm size and the length of the specimen on the long-term behaviour of rectangular CFT columns. In addition to the experimental study, three-dimensional finite element models for each specimen were established and verified from a comparison of the test data and the analysis results. From the test and analysis results, a number of conclusions can be drawn. The magnitude of long-term deformation of a CFT column with a diaphragm that covers more than a half of the cross-sectional area of the inner concrete is identical with that of a column under a load applied simultaneously on the entire section of the steel tube and the inner concrete. The diaphragm confines the lateral deformation of the end surface of the column, and its influence range is limited only to the end part of the column, meaning it is limited only from the surface to a depth as long as the width of the CFT column. The confinement effect and stress variation along the longitudinal axis do not occur except in the influence range of the diaphragm. In the case of loading only at the inner concrete, the inner concrete is confined at the corner by the steel tube, and the slip between the inner concrete and the steel tube increases over time
Experimental studies on creep of sealed concrete under multiaxial stresses
No full textThe majority of research studies and prediction models on the creep of concrete have been concerned with the uniaxial stress state. Research on creep under multiaxial stresses, however has been relatively scarce even though concrete is subjected to multiaxial stresses in many structural members and structures. Although some experiments on the multiaxial creep of concrete have been performed, the results of these experiments, which mainly considered low-strength concrete, are controversial. Consequently, for today standards and practice-and for a better understanding of the properties of concrete-more experimental data are needed on the multiaxial creep of concrete with various strengths. In this study, multiaxial creep tests with 27 cubic specimens (200mm X 200 mm X 200 mm) were carried out for three different strengths of concrete, namely 26, 44 and 54 MPa, and creep strains were measured in three principal directions. From the measured strains, Poisson ratio at initial loading was obtained, as was Poisson ratio resulting from creep strain and Poisson ratio resulting from the combined creep strain and elastic strain. These Poisson ratios were approximately equal for each concrete mix. The Poisson ratio at initial loading and the Poisson ratio for the combined strain increased slightly as the strength of the concrete increased. The volumetric creep strain and deviatoric creep strain were linearly proportional to volumetric stress and deviatoric stress, respectively
Microstructural analysis of Ga-doped ZnO films grown on (0001) Al2O3 substrates by RF magnetron sputtering
No full textTensile and fiber dispersion performance of ECC (engineered cementitious composites) produced with ground granulated blast furnace slag
No full textAn engineered cementitious composite (ECC) produced with ground granulated blast furnace slag was developed for the purpose of achieving moderately high composite strength while maintaining high ductility, represented by strain-hardening behavior in uniaxial tension. In the material development, single fiber pullout tests and matrix fracture tests were performed, followed by micromechanical analyses to properly select the range of mixture proportion. Subsequent direct tensile tests were employed to assess the strain-hardening behavior of the composite, which exhibited high ductility and strength with the addition of slag. High ductility is most likely due to enhanced workability and fiber dispersion performance which is attributed to the oxidized grain surface of slag, as verified by fiber dispersion tests. These results suggest that, within the limited slag dosage employed in the present study, the contribution of slag to fiber dispersion outweighs the side-effect of decreased potential for saturated multiple cracking, including a slight increase in matrix fracture toughness and fiber/matrix bond strength. (c) 2007 Elsevier Ltd. All rights reserved.This study has been a research project supported by the
Korea Ministry of Construction and Transportation through the
Korea Advanced Institute Science and Technology (A06-04).
The authors wish to express their gratitude for the financial
support that made this study possible
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
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