• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.523-535
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• 2014

According to the capacity design concept underlying current steel seimsic provisions, the braces in concentrically braced frames should dissipate seismic energy through cyclic tension yielding and compression buckling. On the other hand, the beams and the columns in the braced bay should remain elastic for gravity load actions and additional column axial forces resulting from the brace buckling and yielding. However, due to the difficulty in accumulating the yielding and buckling-induced column forces from different stories, empirical and often conservative approaches have been used in design practice. Recently a totally different approach was proposed by Cho, Lee, and Kim (2011) for the prediction of column axial forces in inverted V-braced frames by explicitly considering brace buckling. The idea proposed in their study is extended to X-braced seismic frames which have structural member configurations and load transfer mechanism different from those of inverted V-braced frames. Especially, a more efficient rule is proposed in combining multi-mode effects on the column axial forces by using the modal-mass based weighting factor. The four methods proposed in this study are evaluated based on extensive inelastic dynamic analysis results.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.2
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• pp.37-46
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• 2009

In this study, the seismic performance of the Buckling Restrained Knee Bracing (BRKB) system was evaluated through a pin-connected 1-bay 1-story frame. The BRKB system using a bolted channel section developed was composed of a steel plate as a load-resisting core member and two channel sections as a restrainment of the local and global buckling of the core plate. The main purpose of the BRKB system is to be used as an effective tool to re-strengthen/rehabilitate old low- and mid-rise RC frame buildings, which do not have enough seismic resistance to earthquake loadings. The main variables for the test specimens were the size of the core plates, stiffeners and the use of guide plates. The test results showed that the size of the core plate, which was the main element for the load-resisting member, was the most important parameter to achieve ductile behavior under tension as well as compression, until the maximum displacement exceed twice the design drift limit given by the AISC Seismic Provisions.

• Journal of Korean Society of Steel Construction
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• v.15 no.1
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• pp.1-8
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• 2003

In locations where the cost of concrete is relatively high or in situations where the weight of concrete members has to be kept to a minimum, it may be more economical to use hollow reinforced concrete vertic al members. Hollow reinforced concrete colun-ms with a low axial load, a moderate longitudinal steel percentage and a reasonably thick wall were found to perform in a ductile manner at the flexural strength, similar to solid columns. Hollow reinforced concrete columns with a high axial load, a high longitudinal steel percentage, and a thin wall were found, however, to behave in a brittle manner at the flexural strength, since the neutral axis is forced to occur away from the inside face of the tube towards the section centroid and, as a result, crushing of concrete occurs near the unconfined inside face of the section. If, however, a steel tube is placed near the inside face of a circular hollow column, the column can be expected not to fail in a brittle manner through the disintegration of the concrete in the compression zone. A design recommendation and example through the moment-curvature analysis program for curvature ductility are herein presented. A theoretical moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted, providing that the stress-strain relation for the concrete and steel are known. In this paper, a unified stress-stain model for confined concrete by Mander is developed foi members with circular sections.

• Journal of Soil and Groundwater Environment
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• v.8 no.4
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• pp.1-11
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• 2003

In order to measure aperture variation dependent on normal stress and to characterize on relationship between aperture variation and hydraulic conductivity this study measured apertures of rock fractures under a high resolution confocal laser scanning microscope (CLSM) with application of five stages of uniaxial normal stresses. From this method the response of aperture can be continuously characterized on one specimen by different loads of normal stress. The results of measurements showed a rough geometry of fracture bearing non-uniform aperture. They also revealed different values of aperture variations according to the load stages on each position along a fracture due to the fracture roughness. Laboratory permeability tests were also conducted to evaluate the changes of permeability coefficients related to the aperture variations by different loads. The results of permeability tests revealed that the hydraulic conductivity was not reduced at a fixed rate with increase of normal load. Moreover, the rates of aperture variations did not match to those of hydraulic conductivity. The hydraulic conductivity calculated in this study did not follow the cubic law, representing that the parallel plate model is not suitable to express the fracture geometry corresponding to the results of aperture measurements under the CLSM.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.6
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• pp.897-908
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• 2019

The objective of this study is to evaluate the field support performance of highperformance lattice girder (BK-Lattice Girder) by using numerical analysis. Three types (50, 70, 95-type) of existing and high performance lattice girders were applied to the cross section of highway 2, 3, and 4 lane tunnels to compare the supporting performance. The numerical analysis was the finite element method and the lattice girder was modeled in three dimensions with an elasto-plastic frame. The ground was modeled as a spring receiving only compression. The load was applied as a concentrated load on the central ceiling of the tunnel section. The yield strengths of the lattice girders were determined from the numerical results to compare the supporting performance of lattice girder. In case of 50-type, the yield strengths of high-performance lattice girders were increased by 6.7~10.0% compared with those of the existing lattice girders. In the case of 70-type, the high-performance lattice girders increased yield strengths by 12.1~14.9% than the existing lattice girder. In the case of 95-type, the high-performance lattice girders increased yield strengths by 13.3~20.0% than the existing lattice girder. As a result of numerical analysis, it was considered that the high-performance lattice girder supported better than the existing lattice girder when only the lattice girders were constructed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.146-152
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• 2018

In this study, to improve the performance of asphalt mixtures for plastic deformation occurring mainly in Korea, complex modifiers were prepared by mixing powders and liquid type modifiers. The main constituents were powdery diatomaceous earth, mica and carbon black, and liquid type solid 70% SBR latex. The tensile strength ratios for the two asphalt mixtures used in the test were above 0.80 for the Ministry of Land Transportation (2017) asphalt mixture production and construction guidelines. The effects of increasing the tensile strength in the dry state was more than 14% when the composite modifier was added. The deformation rate per minute by the wheel tracking test load was an average of 0.07 to 0.147 for each mixture. The strain rate per minute was improved by the modifier, and the dynamic stability was improved by almost 100% from 295 to 590. In addition, the final settling was reduced from 11.38 mm to 9.57 mm. A plastic deformation test using the triaxial compression test showed that the amount of deformation entering the plastic deformation failure zone at the end of the second stage section and in the third stage plastic deformation section was 1.76 mm for the conventional mixture and 1.50 mm for the complex modifier mixture. The average slope of the complex modifier asphalt mixture mixed with the multi-functional modifier was 0.005 mm/sec. The plastic deformation rate is relatively small in the section where the road pavement exhibits stable common performance, i.e. the traffic load.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.126-132
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• 2018

This paper discusses about results of advanced buckling strength design for several kinds of perforated plated in the twin-hull car-ferry. For medium / small sized high speed vessels with a length of more than 50 meters and a length / width ratio of more than 12, such as car-ferries, it is highly possible that the buckling strength becomes weak due to the relatively thin thickness and the use of low strength capacity such as mild steel. Especially, it becomes big problem about weak buckling rigidity around the opening to access purpose in the perforated. As regarding safety design point of view for perforated plate, it is necessary to clarify buckling strength and ultimate strength by the distribution of in-plane load distribution around the opening. In this study, nonlinear series analysis using ANSYS was performed to clarify the influence of parameters such as aspect ratio, opening ratio and opening shape affecting the buckling and ultimate strength characteristics of the perforated plate under axial compression and we are derived the optimum design as buckling strength point of view. Based on these results, the governing factor determining the buckling strength of the perforated plate was the opening ratio, and the aspect ratio and the shape of the hole were not influenced.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.429-435
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• 2020

Different methods are used for determining the output of engines to obtain the indicated horsepower by measuring the combustion pressure of cylinders, and to obtain the shaft horsepower by measuring the shaft torque. It is difficult to examine the shaft torque using the condition of the cylinder, and the most accurate method used for determining the combustion pressure involves examining the combustion state of the cylinder to evaluate the engine performance and analyze the combustion of the cylinder. During the measurement, the combustion pressure is the most important parameter used for accurately determining the cylinder angle because the cylinder pressure is indicated based on the angle of the crankshaft. In this study, an encoder was used as the crank angle sensor to measure the cylinder pressure on the generator engine of the actual operating ship. The reasons for the differences between the top dead center (TDC) recognized by the encoder (TDC_encoder) and the TDC recognized by the compression pressure (TDC_comp) were considered. The dif erences between the TDC_comp and TDC_encoder of the cylinders measured at idle running, 25 %, 50 %, and 60 % loads were analyzed to determine for the crankshaft production effect, the crankshaft torsion effect owing to the increased rotational resistance from the increased load, and the coupling damping effect between the engine and generator. It was confirmed that the TDC error occurred up to 3° crank angle as the load of the generator increased.

• Geophysics and Geophysical Exploration
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• v.14 no.4
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• pp.324-334
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• 2011

Seismic wave velocity change has been monitored due to the accumulation of micro-cracks by uniaxial loads on the rock samples from Seokmo Island with stepwise increase in 5 stages. After the load was applied up to 95% of UCS, P- and S-wave velocities varied in ranges of 0.9 ~ 18.3% and 2.8 ~ 14.8% of fresh rock sample velocities, respectively. Unlike seismic velocity of the dry rock samples that showed overall decreases after the loading, velocity changes of saturated rock samples were much more complicated. These seemed to be due to the mixture of two contradictory mechanisms; i.e. accumulation of micro-crack causes an increase in porosity and a decrease in wave velocity, while saturation causes an increase in wave velocity. Most of tested rocks showed a trend of velocity increase with low axial load and then velocity decrease at later stages. Starting stage of velocity decrease differs from samples to samples. After the failure of rock occurred, noticeable increases of porosity and decreases of wave velocity have been observed. It showed overall trend that the more the quartz contents and the lower the silicate, the higher the Young's modulus.

• Journal of Korean Association for Spatial Structures
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• v.4 no.3 s.13
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• pp.65-75
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• 2004

A shell structure, having a curvature with a curved surface, is an extremely efficient mechanical creation regard to the external load. A basic structural resistance mechanism is the structural system, which is resisted the out-of-plane direction load by in-plane forces using the structure's curvature. Therefore, it has a merit to make thin and lightweight large spacial structures using minimum materials. Among the large spare structural system, the rapid development of the membrane structures, cable structures and the hybrid structures are watched recently. But, this kind of structural system shows the unstable phenomenon by snap-through or bifurcation according to the shape of structure, and the understanding of the collapse mechanism by this phenomenon is very important to the design process. In this study, I investigated the unstable characteristics of the Geiger-type, Zetlin-type and flower-type hybrid cable dome structures, which is the lightweight hybrid structures using compression and tension elements continuously, according to the difference of structural system.