• Journal of Korean Association for Spatial Structures
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• v.7 no.3 s.25
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• pp.79-86
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• 2007

Recently, as steel structures become higher and more long-spanned, construction of high-strength steels is increasing gradually. Application of high-strength steel can be possible to make a more light and economic steel structures by reducing thickness and space. To apply a high-strength steel to structure, criteria of high-strength steel for buckling is required. However, current specification is not sufficient for criteria of high-strength steels. In this paper, buckling behavior of high-strength steel truss columns with box sections is investigated by using three-dimensional elastic-plastic finite deformation analysis program. The criteria equation for allowable compressive stress of high-strength steel truss columns with box sections is proposed and confirmed the applicability. It is reasonable form analytical results that formulated equations after finding the upper limit of allowable axial direction compression stresses of high-strength steel truss columns. And new equation is suitable to buckling design of high-strength steel truss columns.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.297-304
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• 2012

For the assessment of the performance of a wind-turbine blade, a simulated loading test may be required. In this study, the blade behavior was investigated through numerical analysis using a dual-axis loading test, closely simulating the real operation conditions. The blade structure for the 100-kW-class wind-turbine system was modeled using the finite element (FE) program ANSYS. The failure criteria and buckling analysis under dual-axis loading were examined. The failure analysis, including fiber failure and inter-fiber failure, was performed with Puck's failure criterion. As the dual-axis load ratio increases, the relatively increased stress occurs at the trailing edge and skin surface 3300-3600 mm away from the root. Furthermore, it is revealed that increasing the dual-axis load ratio makes the location that is weakest against buckling move toward the root part. Thus, it is seen that the dual-axis load test may be an essential requirement for the verification of blade performance.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.750-758
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• 2002

Concrete is deformed by load and subjected to micro damage under allowable deformation because of non-homogeneous property. When micro damage is accumulated, it is cracked and finally fractured. Characterization of AE can be demonstrated the micro damage which it is not discovered from visual observation, and it become known to an advantage that was clearly discriminated from the existing NDT method. This study was carried out the analysis and evaluation of concrete damage by acoustic emission technique. As a results of damage analysis, it was found out that the more concrete strength has increased, the more concrete has subjected to micro damage at lower stress ratio for chylinder specimen, and this is possible only AE method which could be described the brittle properties. Also it was revealed that the kaiser effect and felicity effect were existed in reinforced concrete bending specimens and it is found out that the onset of interface debonding between concrete and steel could be conformed in comparison with felicity ratio, AE activity and load history. From the results of this study, it was conformed that the deteriorative degree of reinforced concrete structure should be evaluated using felicity ratios.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.65-73
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• 2002

Underground flexible pipes for electric cables are subject to external loads and surrounding soil pressure. Particularly, strain of flexible pipes is of great concern in terms of safety and maintenance for electric cables. In this paper, stress and strain of flexible pipes with various depth are compared using traditional formula, FEM analysis and model soil box test. The results show that theoretical values are more conservative in strain in comparison with model soil box test and FEM analysis. Considering the strain criteria - maximum 3.5%, flexible pipes can be buried at the depth of 40cm without additional soil improvement. From the result of this study, deformation formula compatible with the field condition was proposed.

• Journal of the Korean Geotechnical Society
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• v.31 no.6
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• pp.15-25
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• 2015

This study aimed at the strength increase of the soft ground and analyzed the strength characteristics of clay soil reinforced with hair fiber which is environmentally friendly. The study varied the length of hair fiber, the amount of hair fiber, the amount of cement, and curing days to investigate both the compressive and tensile strengths and the stress-strain relationship of hair fiber mixed clay soils. The test results indicated that both the compressvie and tensile strengths increased with hair fiber mixed, especially in the tensile strength. In addition, the hair fiber mixed clay soil allowed larger displacement to failure. Based on the test results, it is thought that the environmentally friendly hair fiber could be utilized practically to increase the clay strength in the future.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.96-102
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• 1990

Cracks found in pressure vessels have been reported to be mostly semi-elliptic surface cracks. The fatigue crack growth behaviour of the surface cracks on pressure vessel materials, SPV 50Q and API 5A-K55, was studied with the consideration of the crack opening character. To determine the crack opening loads for the surface cracks, the displacement/strain were measured at three positions; the center and the side of the surface crack, the back face of the specimen using CMOD gauge and strain gauges. The experimental results showed that the crack opening load levels measured at the side of the surface crack were generally a little higher than those measured at the back face. As for the crack growth rates at the different parts of the surface crack, the experiments also showed that, if .DELTA.K$_{eff}$ is used, the exponent n of the Paris' law obtained were the same for the rear and the side parts of the surface cracks.

• Journal of the Korean Society of Hazard Mitigation
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• v.2 no.2 s.5
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• pp.105-113
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• 2002

Steel-Concrete composite girders have been used since early in the 1920's due to their advantages, which are lower weight, increasement of stiffness, slenderness, long span. However, in designing short to continuous composite bridges, negative moment occurs in mid-support and creates problems such as cracks in the concrete slab. Therefore, partially composite bridges are considered. In this time, slab-anchor is used in these. If the stiffness of shear connectors is insufficient, slip would happen at the contact surface. Partial interaction is the case that takes account of slips. In this paper, the evaluation of initial shear stiffness of slab-anchor in composite bridges is obtained from Push-Out specimen. Also, finite element analyses which uses the initial shear stiffness of slab-anchor got the experiment are carried out on simple composite girder and continuous composite girder. Futhermore, the ratio of composite according to various shear stiffness are investigated and the classification according to the ratio of composite is proposed.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.961-972
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• 2002

Flat plate structures under lateral load are susceptible to the brittle shear failure of plate-column connection. To prevent such brittle failure, strength and ductility of the connection should be ensured. However, according to previous studies, current design methods do not accurately estimate the strength of plate-column connection. In the present study, parametric study using nonlinear finite element analysis was performed for interior connections. Based on the numerical results, a design method for the connection was developed. At the critical sections around the connection coexist flexural moment and shear developed by lateral and gravity loads, and maximum allowable eccentric shear stresses were proposed based on the interactions between the flexural moment and shear, The proposed method can precisely predict the strength of the connection, compared with the current design provisions. The predictability of the proposed method was verified by the comparisons with existing experiments and nonlinear numerical analyses.

• Journal of the Korean Geosynthetics Society
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• v.14 no.1
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• pp.11-21
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• 2015

This study aims at investigating of the behavioral characteristics of foundation ground subjected to a strip load in anisotropy. Using marine clays sampled at Shihwa area, a series of laboratory tests including triaxial compressive test, plane strain compressive and expansion tests that allows horizontal deformation only and zero strain (${\varepsilon}_2$) in the direction of intermediate stress (${\sigma}_2$) are conducted. In addition, a numerical analysis using parameters obtained from the tests is carried out. In the numerical analysis, Cam-clay model that simulates the behavior of natural deposited clay properly is adopted. The analysis results show that the vertical displacements of the plane strain compressive tests are relatively larger than those of triaxial compressive tests by 18-25%. Likewise, the horizontal displacements is 13-19% larger.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.141-154
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• 1987

The algorithm proposed utilizes the tow-levels technique. In the first level which consists of teeatment only the applied load and design stress as the random variables whose parent distribution has the normal distribution, the cross-sectional areas of the truss members such that the their probabilities of failure have the preseribed failure probabilites are optimized by transforming the nonlinear problem into SUMT, and solving it utilizing modified Newton-Raphson method. In the second level, the geometric shape of truss structure is optimized by utilizing the unidirectional search technique of Powell method which makes it possible to minimize only the objective function. The algorithm proposed is numerically tested for the several truss structures with various shapes and loading conditions. The numerical analysis shows that the rate of decreasing the weight of truss structures is dependent on the prescribed failure probability of the each member of truss structure and the covariance of the applied load and design stress.