• The Journal of the Petrological Society of Korea
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• v.26 no.2
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• pp.127-141
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• 2017

Jurassic granite from Geochang was analysed with respect to the characteristics of the rock cleavage. The multicriteria evaluation for the six directions of rock cleavages was performed using the microcrack spacing-related parameters derived from the enlarged photomicrographs (${\times}6.7$) of the thin section and the spacing-cumulative frequency diagrams. The results of analysis for the representative values of these spacing parameters with respect to the rock cleavage are summarized as follows. First, the analysis for deriving the main parameter indicating the order of arrangement among six diagrams was performed. The values of five parameters with respect to six directions of the rock cleavages were arranged in increasing or decreasing order for the above analysis. The decreasing order of the values of main parameter(mean spacing-median spacing, $S_{mean}-S_{median}$) and mean spacing are consistent with the order of H1, H2, G1, G2, R1 and R2 directions. These sequential arrangements of six directions of the rock cleavages can provide a basis for those of the six diagrams related to spacing. Second, the nine correlation charts between the above main parameter and various parameters were arranged in decreasing order of correlation coefficient ($R^2$). These related charts shows a high correlation of power-law function in common. The values of mean spacing, density (${\rho}$) and length of line oa are directly proportional to the value of main parameter, while the values of constant (a), exponent (${\lambda}$), spacing frequency (N), length of line oa', slope of exponential straight line (${\theta}$) and total length ($1mm{\geq}$) are inverse proportional. Third, the results of correlation analysis between the values of parameters for three planes and those for three rock cleavages are as follows. The values of frequency, total spacing, constant, exponent, slope and length of line oa' for three planes and three rock cleavages show an order of R' < G' < H' and H < G < R, respectively. On the other hand, the values of mean spacing, (mean spacing-median spacing), density and length of line oa show an order of H' < G' < R' and R < G < H, respectively. The correlation of the mutually reverse order of the values of parameters between three planes and three rock cleavages can be drawn. This type of correlation analysis is useful for discriminating three quarrying planes.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Tunnel and Underground Space
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• v.29 no.2
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• pp.124-134
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• 2019

Subcritical crack growth in rock material can occur under monotonic and cyclic loading. Subcritical crack growth plays an important role in evaluating the long-term stability of structures in rocks. This paper presents the results of studies conducted to determine subcritical crack growth parameters under monotonic and cyclic loading in rock-like material. The constant stress rate method was employed for monotonic loading. The subcritical crack growth parameter of n under cyclic loading was determined by the relation between the rate of crack growth per cycle and stress intensity factor range. The specimens contained pre-existing flaws with 45 and 60 degrees of inclination angle and flaws spacing and continuity were varied to arrange crack growth in shear or tensile manner. The results show that the parameter of n is almost constant regardless of the applied load conditions such as monotonic and cyclic or shear and tension.

• The Journal of Engineering Geology
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• v.11 no.1
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• pp.51-62
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• 2001

Jurassic granites of three sites, Pocheon, Geochang and Habcheon, were analysed with respect to the characteristics of the rock cleavage. Microscopic analysis for the oriented thin sections of the specimens was conducted by using the scanline survey technique to measure microcrack direction, spacing and length. The results showed that the preferred orientations of microcrack developed in quartz and feldspar arc coincident with the orientation of quarry planes. The length of microcrack is related to grain size. The length of microcrack in coarse-grained granite is longer than that in relatively fine-grained granite. In all granites, microcracks related to the preferred orientations are well developed in order of rift, grain and hardway planes in number, length and density.

• 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.

• Magazine of the Korea Concrete Institute
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• v.3 no.3
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• pp.129-139
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• 1991

The mechanical hehavior of relIlforced concrete beams with steel fibers is investigated 111 the present study. An expenmental program was set up and several series of rem forced concrete beams have been tested, including two senes of singly-reinforced concrete beams and one senes of doubly-reinforced concrete beams. It was found from th, :se measurements that the crack widths lIlcrease almost llIlearly With the lIlcrease of steel stress and that the crack Widths at the same loadlJ1g stages are greatly reduced as the contents of steel fibers increase. The present study also IJ1chcates that the ductiiIty and the ultJmate resistance are remarkably enhanced due to the addition of steel fibers. A theoretical mex1e1 for the flexural analysis of fiber-reinforced concrete beam which takes into account the effects of fibers JS also proposed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.2
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• pp.201-208
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• 2016

Recently, extensive research on crack analysis using extended finite element method(XFEM) which has main advantages in element re-meshing and visualization of cracks has been conducted. However, its application was restricted to the members of a single material. In this study, the applicability and feasibility of the XFEM to the multiple crack analysis of reinforced concrete beams were demonstrated. ABAQUS which has implemented XFEM was used for the crack analysis and its results were compared with test results. Enriched degree-of-freedom locking phenomenon was discovered and its causes and the ways to prevent it were suggested. The locking occurs when cracks in the adjacent elements simultaneously develop. A modelling technique for multiple cracking similar to test results was also proposed. The analysis with XFEM showed similar results to the tests in terms of crack patterns, spacing of cracks, and load-deflection relationship.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.9
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• pp.2183-2188
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• 2009

This paper describes an automatic mesh generation system for finite element analysis of three-dimensional cracks. It is consisting of fuzzy knowledge processing, bubble meshing and solid geometry modeler. This novel mesh generation process consists of three sub-processes: (a) definition of geometric model, i.e. analysis model, (b) generation of bubbles, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional crack structures. Bubble is generated if its distance from existing bubble points is similar to the bubble spacing function at the point. The bubble spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Practical performances of the present system are demonstrated through several mesh generations for 3D cracks.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.289-294
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• 2011

The installation of joint is to prevent random cracking due to drying shrinkage stress of concrete slab. However contraction joint spacing is empirically implemented into slab constructions without detail calculation based on quantitative criteria. In this study, shrinkage strain of concrete due to concrete shrinkage stress was measured to suggest joint spacing based on the study results. The test environmental conditions were applied temperature of $15^{\circ}C$ and relative humidity of 60%. The design compressive strength used was 30 MPa and 40 MPa, which are currently used in concrete slab designs. The drying shrinkage test result was applied to drying shrinkage models (ACI 209R, CEB MC 90, B3, GL 2000 and Sakata). The results showed that the most appropriate model was ACI 209R model. Based on the research findings, quantitative contraction joint spacing locations were calculated.

• Tunnel and Underground Space
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• v.20 no.2
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• pp.125-130
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• 2010

Model blast experiments of mortar blocks were performed to investigate the effect of the guide hole on crack growth. The mortar block specimens have a blast charge hole and 8 guide holes. Two of circular guide hole, notched guide hole, diamond shaped guide hole and diamond shaped guide holder are installed around 110 mm, 165 mm and 220 mm apart from the charge hole for each specimen. From the blast experiments, it was revealed that all the guide hole used in this study were effective for controlling the crack growth at the fracture control.