• Journal of the Korea Concrete Institute
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• v.13 no.6
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• pp.593-601
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• 2001

In RC structure, sufficient anchorage of reinforcement is necessary for the member to produce the full strength. Generally, conventional standard hook is used for the reinforcement's anchorage. However, the use of standard hook results in steel congestion, making fabrication and construction difficult. Mechanical anchor offers a potential solution to these problems and may also ease fabrication, construction and concrete placement. In this paper, the required characteristics and the design considerations of mechanical anchor were studied. Also, the mechanical anchor was designed according to the requirements. To investigate the pull-out behavior and properness of mechanical anchorage, pull-out tests were performed. The parameters of tests were embedment length, diameter of reinforcement, concrete compressive strength, and spacing of reinforcements. The strengths of mechanical anchor were consistent with the predictions by CCD method. The slip between mechanical anchor and concrete could be controlled under 0.2mm. Therefore, the mechanical anchor with adequate embedment could be used for reinforcement's anchorage. However, it was observed that the strength of mechanical anchors with short spacing of reinforcements was greatly reduced. To apply the mechanical anchor in practice (e.g. anchorage of the beams reinforcements in beam-column joint), other effects that affect the mechanical anchor mechanism, such as confinement effect of adjacent member from frame action or effects of shear reinforcement, should be considered.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.59-67
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• 2005

This paper presents experimental and numerical research results of centrifuge model tests performed to investigate the geotechnical engineering behavior of slag compaction pile as a substitute of sand compaction pile. For centrifuge model tests, bearing capacity of composit soil improved with slag compaction piles, stress concentrations in-between pile and soft clay, settlement characteristics, and failure modes were investigated with slags differing in their relative density. A slag was found to be a good substitute for a sand since the slag compaction pile model showed a greater yield stress intensity up to $30\%$ than the sand compaction pile model under the identical testing conditions. Stress concentration ratio tended to increase with the relative density of slag pile and the clear shear lines in the piles were observed at the depth of $2D{\sim}2.5D$ (D=dia. of model pile) from the top of the piles after loading tests. Numerical analysis with a software of CRISP, implemented with the modified Cam-clay model, was carried out to simulate the results of centrifuge model test. Test results about characteristics of load-settlement curves and stress concentration ratio are in relatively good agreements with numerical estimations.

• Journal of Korea Game Society
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• v.15 no.5
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• pp.143-152
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• 2015

Unlike simulating general 'particle-based fluid explosion', simulating fluid with elasticity requires various experimental methods in order to show the realistic deformation of the matter. The existing studies on particle-based viscoelastic fluid only focused on matters' plastic deformation which can be found in mud or paint, based on the maximum distortion energy theory and maximum shear stress theory. However, these former researches could not simulate the brittle deformation which can be seen from silicon or highly elastic rubber when great external forces above limits are applied. This study suggests a brittle simulation method based on the Coulomb-Mohr theory, the idea that a yield occurs when maximum stress on a matter reaches to its rupture stress. This theory has a significant difference from the existing particle-based simulations which measures the forces on a matter by length or volume. Using a strong-elastic semifluid which Coulomb-Mohr theory is applied, realistic deformation process of a matter was observed as its forced surface reached to the rupture stress. When semifluid hit the ground, the impact of deformation can be explained by using Coulomb-Mohr theory.

• Tunnel and Underground Space
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• v.26 no.3
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• pp.235-252
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• 2016

This study presents a methodology to reproduce the mechanical behavior of isotropic or transversely isotropic rock using the polygonal grain-based distinct element model. A numerical technique to monitor the evolution of micro-cracks during the simulation was developed in the present study, which enabled us to examine the contribution of tensile cracking and shear cracking to the progressive process of the failure. The numerical results demonstrated good agreement with general observations from rock specimens in terms of the behavior and the evolution of micro-cracks, suggesting the capability of the model to represent the mechanical behavior of rock. We also carried out a parametric study as a fundamental work to examine the relationships between the microscopic properties of the constituents and the macroscopic behavior of the model. Depending on the micro-properties, the model exhibited a variety of responses to the external load in terms of the strength and deformation characteristics. In addition, a numerical technique to reproduce the transversely isotropic rock was suggested and applied to Asan gneiss from Korea. The behavior of the numerical model was in good agreement with the results obtained in the laboratory-scale experiments of the rock.

• Journal of the Korean Geotechnical Society
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• v.35 no.5
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• pp.5-19
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• 2019

Considering the natural phenomenon in which steep slopes ($65^{\circ}{\sim}85^{\circ}$) consisting of rock mass remain stable for decades, slopes steeper than 1:0.5 (the standard of slope angle for blast rock) may be applied in geotechnical conditions which are similar to those above at the design and initial construction stages. In the process of analysing the stability of a good to fair continuum rock slope that can be designed as a steep slope, a general method of estimating rock mass strength properties from design practice perspective was required. Practical and genealized engineering methods of determining the properties of a rock mass are important for a good continuum rock slope that can be designed as a steep slope. The Genealized Hoek-Brown (H-B) failure criterion and GSI (Geological Strength Index), which were revised and supplemented by Hoek et al. (2002), were assessed as rock mass characterization systems fully taking into account the effects of discontinuities, and were widely utilized as a method for calculating equivalent Mohr-Coulomb shear strength (balancing the areas) according to stress changes. The concept of calculating equivalent M-C shear strength according to the change of confining stress range was proposed, and on a slope, the equivalent shear strength changes sensitively with changes in the maximum confining stress (${{\sigma}^{\prime}}_{3max}$ or normal stress), making it difficult to use it in practical design. In this study, the method of estimating the strength properties (an iso-angle division method) that can be applied universally within the maximum confining stress range for a good to fair continuum rock mass slope is proposed by applying the H-B failure criterion. In order to assess the validity and applicability of the proposed method of estimating the shear strength (A), the rock slope, which is a study object, was selected as the type of rock (igneous, metamorphic, sedimentary) on the steep slope near the existing working design site. It is compared and analyzed with the equivalent M-C shear strength (balancing the areas) proposed by Hoek. The equivalent M-C shear strength of the balancing the areas method and iso-angle division method was estimated using the RocLab program (geotechnical properties calculation software based on the H-B failure criterion (2002)) by using the basic data of the laboratory rock triaxial compression test at the existing working design site and the face mapping of discontinuities on the rock slope of study area. The calculated equivalent M-C shear strength of the balancing the areas method was interlinked to show very large or small cohesion and internal friction angles (generally, greater than $45^{\circ}$). The equivalent M-C shear strength of the iso-angle division is in-between the equivalent M-C shear properties of the balancing the areas, and the internal friction angles show a range of $30^{\circ}$ to $42^{\circ}$. We compared and analyzed the shear strength (A) of the iso-angle division method at the study area with the shear strength (B) of the existing working design site with similar or the same grade RMR each other. The application of the proposed iso-angle division method was indirectly evaluated through the results of the stability analysis (limit equilibrium analysis and finite element analysis) applied with these the strength properties. The difference between A and B of the shear strength is about 10%. LEM results (in wet condition) showed that Fs (A) = 14.08~58.22 (average 32.9) and Fs (B) = 18.39~60.04 (average 32.2), which were similar in accordance with the same rock types. As a result of FEM, displacement (A) = 0.13~0.65 mm (average 0.27 mm) and displacement (B) = 0.14~1.07 mm (average 0.37 mm). Using the GSI and Hoek-Brown failure criterion, the significant result could be identified in the application evaluation. Therefore, the strength properties of rock mass estimated by the iso-angle division method could be applied with practical shear strength.

• The Journal of Engineering Geology
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• v.8 no.2
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• pp.115-130
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• 1998

An analysis on landslide types and susceptibilities associated with geomorphic characteristics has been conducted with 916 landslide inventories in Yeonchon-Chulwon District, where two day's heavy rainfall was concentrated on July, 1996. The precipitation during the 2 days, which is equivalent to 0.372 of event cofficient, can cause large landslides based on Olivier's equation. Sliding materials are dominantly composed of debris mixed with rock fragments and soil derived from colluvium and residual soils. 66% of the landslides are belong to debris flow md 23% are due to sediments flow, in accordance with the classification of sliding materials. Most of landslides(> 90%) are small and shallow, less than l00m in length and about 1m in depth, and classified as transitional type. Granite is more susceptible as much as 4.7 times than metamorphic rocks and 2.7 times than volcanic rocks, probably due to higher weathering grade of granite. The highest landslide frequency is concentrated on the areas between 200 and 300m in height and on the slopes between $10-20^{\circ}$ in dgree. More than 50% of landslides occurred under these geomorphic conditions. Consequently, colluviums and residual soils distributed on the gentle slopes are most susceptible to the landslides of the area.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.73-80
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• 2022

In this study, details of NRC beam-column connections were developed in which beam and columns pre-assembled in factories using steel angles were bolted on site. The developed joint details are NRC-J type and NRC-JD type. NRC-J type is a method of tensile joining with TS bolts to the side and lower surfaces of the side plate of the NRC column and the end plate of the NRC beam. NRC-JD type has a rigid joint with high-strength bolts between the NRC beam and the side of the NRC column for shear, and with lap splices of reinforcing bar penetrating the joint and the beam main reinforcement for bending. For the seismic performance evaluation of the joint, three specimens were tested: an NRC-J specimen and NRC-JD specimen with NRC beam-column joint details, and an RC-J specimen with RC beam-column joint detail. As a result of the repeated lateral load test, the final failure mode of all specimens was the bending fracture of the beam at the beam-column interface. Compared to the RC-J specimen, the maximum strength of the specimen by the positive force was 10.1% and 29.6% higher in the NRC-J specimen and the NRC-JD specimen, respectively. Both NRC joint details were evaluated to secure ductility of 0.03 rad or more, the minimum total inter-story displacement angle required for the composite intermediate moment frame according to the KDS standard (KDS 41 31 00). At the slope by relative storey displacemet of 5.7%, the NRC-J specimen and the NRC-JD specimen had about 34.8% and 61.1% greater cumulative energy dissipation capacity than the RC specimen. The experimental strength of the NRC beam-column connection was evaluated to be 30% to 53% greater than the theoretical strength according to the KDS standard formula, and the standard formula evaluated the joint performance as a safety side.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.781-792
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• 2004

Experiments were performed to study the cyclic behavior of framed steel walls with thin web plates. Five specimens of single-bay and three-story steel plate walls were tested for cyclic lateral load. The parameters for the test specimens included the plate thickness and the column strength. Based on the test results, the strength, deformability, and energy dissipation capacity of the framed steel walls were studied. The test results showed that the behavioral characteristics of the framed steel walls with thin web plates were different in many aspects from those of the conventional braced frame, and the steel wall with a stiffened web plate exhibited cantilever action, high strength, and low ductility. With the framed steel plate walls, local plate buckling and tension-field action developed in the thin web plates, and plastic deformation was uniformly distributed along the wall's height. As a result, the framed steel plate walls exhibited combined flexural and shear deformation, but they also showed high strength and energy dissipation capacity. Moreover, such walls have high deformability, which was equivalent to that of the conventional moment frame. Frame members such as columns and beams, however, must be designed to resist the tension-field action of the thin web plates. If the column does not have sufficient strength, and if its sections are not compact enough, the overall strength of the framed steel wall might be significantly decreased by the development of the soft-story mechanism. The framed steel walls with thin web plates have advantages, such as high deformability and high strength. Therefore, they can be used as ductile elements in earthquake-resistant systems.

• Korean Journal of Materials Research
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• v.4 no.6
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• pp.626-637
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• 1994

The relationship between microstructures and tensile properties depending on various solution treatment temperature and cooling rate of Ti-6A1-4V alloy have been investigated. The complex and random edge shaped $\alpha$ phases were formed after the 1st solution treatment at $\beta$ region and the 2nd solution treatment at $900^{\circ}C$, which was followed by furnace cooled. When the specimen was subjected to the 2nd solution treated at $950^{\circ}C$, and furnace cooled, $\alpha$ phase changed its morphology to equiaxed structure. The aspect ratio showing the appreciation basis of microstructual refinement decreases with the temperature of 1st and 2nd solution treatment. The slightly decrease in strength were observed in the Widmanstltten structures than in the bimodal structures. Also, ductility of the Widmanstatten structures was considerable lower than that of bimodal structures. The tensile-fractured surface of the Widmanstatten structures appears to be quasi-cleavage and dimple fracture, while that of the bimodal structures was the type of ductile fracture. The tensile fracture surface of the bimodal structures can easily be separated into cental crack areas lying generally perpendicular to the tensile axis and shear lip areas lying at angles of high shear(around 45 deg.) to the tensile axis.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.290-297
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• 2017

The flexural behavior tests of UHPC segmental U-girder and composite U-girder which has 160MPa compressive strength and 15.4m length were carried out. The test variables are volume fraction of steel fibers and slab over the U-girder. Each U-girder has longitudinal re-bars in web and lower flange. PS tendons which has 2 of 15.2mm diameter in upper flange and PS tendons which has 7 of 15.2mm diameter in lower flange were arranged and prestressed at onetime in U-girder connection stage. Enough strong prestressing force which applied to U-girder due to ultra high performance concrete strength can withstand the self weight and dead load in U-girder stage. By comparison with the brittle behavior of U-girder, composite U-girder showed the stable and ductile behavior. After the construction of slab over U-girder, flexural load capacity of composite U-girder can bear the design load in final construction stage with only one time prestressing operation which already carried out in U-girder stage. This simple prestressing method due to the ultra high strength concrete have the advantage in construction step and cost. The shear key which has narrow space has the strong composite connection between ultra high strength concrete U-girder and high strength concrete slab didn't show any slip and opening right before failure load.