• Proceedings of the Korea Concrete Institute Conference
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• 1991.04a
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• pp.69-74
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• 1991

This paper reviewed various methods of evaluating the toughness of fiber reinforced concrete materials by means of toughness indices and discussed the use of various multiples of first-crack deflection or first-crack secant compliance to define toughness indices. And a new method what is called effective toughness used to evaluate the toughness of steel fiber reinforced concrete. The proposed method determinded from the area below the load-deflection curve until deflection at the loading point becoms 1/150 of the span devided by the ligament area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.4
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• pp.41-49
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• 1989

Following the previous paper, the results of test are further presented. As partially prestressed concrete members permit cracks under the service state, deflection and crack control of partially prestressed concrete members is more important than that of reinforced or fully prestressed concrete members. By the test results of load-deflection relation, it can be shown that prestressing ratio significantly affects the behavior of partially prestressed concrete beams. Deflection prediction formula of some codes are tried, and test results are compared with various fomulae of crack spacing and crack width.

• Journal of Ocean Engineering and Technology
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• v.17 no.6
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• pp.47-52
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• 2003

To determine the effect of transverse open crack on the dynamic behavior of simply-supported Euler-Bernoulli beam with the moving masses, an iterative modal analysis approach is developed. The influence of depth and position of the crack in the beam, on the dynamic behavior of the simply supported beam system, have been studied by numerical method. The cracked section is represented by a local flexibility matrix, connecting two undamaged beam segments that is, the crack is modeled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section, and is derived by applying a fundamental fracture mechanics theory. As the depth of the crack is increased, the mid-span deflection of the simply-supported beam, with the moving mass, is increased. The crack is positioned in the middle point of the pipe, and the mid-span defection of the simply-supported pipe represents maximum deflection.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.958-963
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• 2003

In this paper a dynamic behavior of simply supported cracked pipe conveying fluid with the moving mass is presented. Based on the Timoshenko beam theory, the equation of motion can be constructed by using the Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. And the crack is assumed to be in th first mode of fracture. As the depth of the crack and velocity of fluid are increased the mid-span deflection of the pipe conveying fluid with the moving mass is increased. As depth of the crack is increased, the effect that the velocity of the fluid on the mid-span deflection appears more greatly.

• Journal of the Korea Concrete Institute
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• v.22 no.6
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• pp.761-768
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• 2010

When cracks occur in reinforced concrete structures, a steel carries all tensile force at crack section, while the concrete between cracks carries a part of the tensile force due to bond, so that the steel is less elongated. This is called the tension-stiffening effect, that plays an important role in verification of a serviceability limit state. But it is a complicated work to use a complex strain distribution between cracks, therefore an average strain is used to calculate deflection and crack width. In Eurocode 2, tension-stiffening effect expressed in the first order form or the second order form is used in calculating an average curvature for deflection. In this study for a flexural member deflection and crack width are calculated using various models for the tension-stiffening effect and the results are compared with the values of Eurocode 2 and KCI provisions. As results, the predicted values using the second order form are appeared to be well agreed with the experimental values and it could secure more analytical consistency.

• Journal of Mechanical Science and Technology
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• v.17 no.2
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• pp.215-220
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• 2003

Trepan prevents the wear of the inside part of a bearing when the initial shaft rotates. It continuously contacts with the eccentric part of the shaft in rotation and is loaded repeatedly. Therefore, even if an early crack of a trepan part is small, the crack may progress by the repeated load. If the crack progresses, very small chips come out. This Is put in the rotor and prevents the rotation of the compressor, There can be leaks in a microgroove and extreme wear can occur due to lack of oil on the surface contact part. Therefore, this study was carried out to compare and investigate the trepan strength and deflection characteristics between trepan locations and dimension changes using the finite element method and search a motor bearing for a model with bigger stiffness of a trepan part and the same deflection.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.327-332
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• 1997

This study is aimed to investigate the effect of load and deflection on steel fiber reinforced concrete slab. Slabs were made with Hooked and Straight types steel fiber and compared a change of steel fiber contents and fiber types. Test were carried out to evaluate he first crack load, maximum load and deflection of slab. At the result, the first crack load, maximum load and energy absorption capacity were increased remarkably as steel fiber contents wee increased. And we found that the deflection of slab at same load ere decreased as steel fiber contents were increased, too. As the aspect ration was increased, the first crack load, maximum load and energy absorption capacity were increased.

• Structural Engineering and Mechanics
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• v.22 no.2
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• pp.169-184
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• 2006

A close form solution of the maximum deflection for cracked columns with rectangular cross-sections was developed and thus the elastic buckling behavior and ultimate bearing capacity were studied analytically. First, taking into account the effect of the crack in the potential energy of elastic systems, a trigonometric series solution for the elastic deflection equation of an arbitrary crack position was derived by use of the Rayleigh-Ritz energy method and an analytical expression of the maximum deflection was obtained. By comparison with the rotational spring model (Okamura et al. 1969) and the equivalent stiffness method (Sinha et al. 2002), the advantages of the present solution are that there are few assumed conditions and the effect of axial compression on crack closure was considered. Second, based on the above solutions, the equilibrium paths of the elastic buckling were analytically described for cracked columns subjected to both axial and eccentric compressive load. Finally, as examples, the influence of crack depth, load eccentricity and column slenderness on the elastic buckling behavior was investigated in the case of a rectangular column with a single-edge crack. The relationship of the load capacity of the column with respect to crack depth and eccentricity or slenderness was also illustrated. The analytical and numerical results from the examples show that there are three kinds of collapse mechanisms for the various states of cracking, eccentricity and slenderness. These are the bifurcation for axial compression, the limit point instability for the condition of the deeper crack and lighter eccentricity and the fracture for higher eccentricity. As a result, the conception of critical transition eccentricity $(e/h)_c$, from limit-point buckling to fracture failure, was proposed and the critical values of $(e/h)_c$ were numerically determined for various eccentricities, crack depths and slenderness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.3
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• pp.316-325
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• 1986

Characteristics of fatigue crack propagation in martensite-ferrite duel phase steels have been investigated. In low .DELTA.K region, fatigue crack propagation resistance increases with increasing volume fraction of martensite, but the difference of crack propagation resistance resulted from the volume fraction decreases with increasing .DELTA.K. Also, threshold stress intensity factor range .DELTA.K$_{th}$ increases with increasing volume fraction of martensite, But fatigue crack propagation rates of dual-phase steels in terms of .DELTA.K$_{eff}$ are independent to volume fraction of martensite. These phenomena can be explained by the roughness induced crack closure due to crack deflection.n.n.

• Structural Engineering and Mechanics
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• v.44 no.6
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• pp.801-814
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• 2012

The strain rate effects on the interaction between a Mode I matrix crack and an inclined elliptic matrix-inclusion interface under dynamic tensile loadings were investigated numerically, and the results are in agreement with previous experimental data. It is found, for a given material system, that there are the first and the second critical strain rates, by which three kinds of the subsequent crack growth patterns can be classified in turn with the increasing strain rate, namely, the crack deflection, the double crack mode and the perpendicular crack penetration. Moreover, such a crack deflection/penetration behavior is found to be dependent on the relative interfacial strength, the inclined angle and the inclusion size. In addition, it is shown that the so-called strain rate effect on the dynamic strength of granule composites can be induced directly from the structural dynamic response of materials, not be entirely an intrinsic material property.