• Elastomers and Composites
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• 제41권2호
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• pp.125-130
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• 2006

To understand the effect of midsole on the bending stiffness of footwear, bending moment is studied with various hardness and thickness of polyurethane(PU) and poly(ethyl one-co-vinylacetate)(EVA) foams which composed in footwear midsole. The initial bending moment of footwear was appeared at $19^{\circ}$ on bending angle of footwear, and this bending angle was not depend on thickness and hardness of midsole. The bending moments of footwear were also increased with increase of the hardness and thickness of misole which were composed in footwear. Increased hardness and increased thickness of foam and midsole also cause a greater bending moment of the sports shoe, respectively.

• Journal of Korean Society of Steel Construction
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• 제11권1호통권38호
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• pp.69-78
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• 1999

When the lateral forces are applied to a frame, columns in the frame are usually accompanied with sidesway. If this sidesway is large, the frame is subjected to buckling and an early yielding of members which reduces the overall frame stiffness. In this study, numerical analysis of frames were conducted to evaluate the ultimate lateral strength of steel moment resisting frames permitted to sidesway under axial and lateral forces, and develope the procedure for determining the limits of column slenderness ratios. In the numerical analysis, the effects of the relative stiffness ratio between beam and column, deterioration of overall frame stiffness, slenderness ratio and loading conditions were considered. The elasto-plastic analysis method in which the $P-{\Delta}$effect is implemented, presented by the author previously, was adopted in the analysis. Incremental lateral forces were applied to the frame under constant axial loads and the generalized inverse is employed for the post-ultimate behavior.

• Journal of Korean Society of Steel Construction
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• 제17권2호통권75호
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• pp.161-171
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• 2005

When the in-plane flexural rigidity is small in relation to the applied load, the arch ribs may buckle to the in-plane direction. Designers should therefore determine the in-plane buckling strength. To determine the buckling strength of arch ribs, designers have to consider the material nonlinear response. But in the case of arch ribs having large slenderness ratio, arch ribs may buckle in the elastic range, and when the arch ribs have low slenderness ratio, elastic buckling strength is useful in the preliminary design. In this paper, elastic buckling strength of arch ribs, which are frequently used in practical design, is studied using nonlinear finite element method. In general, the relation between flexural rigidity and elastic buckling strength is linear. As seen from the results, however, when the arch ribs have low slenderness ratio, the relation between flexural rigidity and elastic buckling strength is nonlinear.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2011년도 정기 학술발표대회
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• pp.90-90
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• 2011

최근 전 세계적으로 지진의 발생 빈도가 증가하며 그 규모도 점차 커지는 경향을 보이고 있다. 대형지진의 발생 시 저층 구조물의 붕괴로 인한 인명 및 사회, 경제적 피해가 두드러짐에 따라 기존 저층 구조물의 내진보강기법에 관한 연구가 활발히 진행 중인 추세이다. 우리나라의 경우 강도증가형 내진보강공법이 주를 이루고 있어 다양한 내진보강기법의 개발 및 적용이 필요한 실정이다. 따라서 본 연구에서는 지진입력하중 저감형 내진보강기법으로서 강재댐퍼시스템을 제안하여 구조적 성능을 파악하고, 이를 적용한 보강 실험체와 비보강 실험체를 제작하여 정적가력실험을 통하여 그 성능을 비교하였다. 제안된 강재댐퍼시스템은 입력에너지를 소산시키는 내부의 슬릿형 댐퍼와 이를 지지하는 기둥 및 외부 프레임으로 구성되며, 내부 댐퍼는 먼저 항복하여 에너지를 소산시키기 위하여 지지기둥 및 프레임에 사용된 강재보다 강성 및 강도가 적게 계획되었다. 강재댐퍼의 성능실험 결과, 비교적 안정적 거동을 하며, 강성과 강도 및 에너지 흡수능력이 우수하게 나타났다. 보강 및 비보강 실험체의 골조는 기존 학교 건축물의 표준도면을 기준으로 하여 골조의 일부를 대상으로 60% 축소율을 적용하여 계획하였으며, 보강 실험체는 미리 제작된 강재댐퍼시스템을 골조 내에 설치하여 에폭시 주입법으로 부착시공 하였다. 보강 및 비보강 골조 실험체의 정적가력 실험결과 비보강 실험체는 기둥의 휨 항복 후 변형의 증가에 따라 휨 및 전단 균열이 증가하면서 최종적으로 기둥이 전단파괴 되었으며, 보강 실험체는 비보강 실험체에 비하여 기둥 및 보의 균열이 적고, 골조에 골고루 분포되어 파괴 규모가 감소하였다. 최대 강도면에서 보강 실험체는 비보강 실험체에 비하여 약 3.4배 우수하였으며, 초기강성은 약 7배 가량 유리한 것으로 평가되어 제안된 강재댐퍼시스템이 강도면에서 우수한 성능을 나타냄을 알 수 있었다. 또한 두 실험체의 기둥 주근 및 띠철근의 변형률을 비교한 결과, 비보강 실험체는 대부분의 철근이 항복하여 큰 변형을 일으킨 반면, 보강실험체에서는 철근의 항복현상이 나타나지 않았고 댐퍼가 항복을 하면서 큰 변형을 일으켰다. 이를 통해 지진하중 입력 시 댐퍼에서 입력 에너지를 흡수하여 큰 하중을 부담하며, 기존의 구조부재에는 입력 에너지가 낮아 손상이 보다 적게 발생함을 확인하였다.

• Journal of Korean Society of Steel Construction
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• 제20권2호
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• pp.303-312
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• 2008

In this paper, the seismic behavior of shear wal-frame systems is analyzed. The governing equations of the wall-frame systems with outrigger truss are formulated through the continuum approach and the whole structure is idealized as a shear-flexural cantileverwith rotational spring. The effect of shear deformation and flexural deformation of the wall-frame and outrigger trusses are considered and incorporated in the formulation of the wall-frame structures with and without outriggers are compared by using finite element analysis incorporated with the Newmark-${\beta}$ method. Numerical results are obtained and compared with the finite element package MIDAS. The proposed method is found to be simple and efficient, and provides reason ably accurate results in the early design stage of tall building structures.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1452-1457
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• 2010

Recently, coal ash is used as resources to make controlled low-strength material (CLSM) which a self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. Pozzolanic reaction is strongly related with self-cementation of coal ashes. However, this reaction depends on pozzolanic content in fill materials and is disappeared in 2-3 days after placement of coal ash fill. Therefore, state of coal ash fill is commonly very loose and not appropriate for foundations of structures without special treatments. In this study, a coal ash placement device was developed to place coal ashes effectively to improve density of coal ash fills. The device consists of a ribbon type mixer to obtain homogeneous materials mixture and a piston type pump for density control of fill materials. Based on several laboratory test results, more stable coal ash fill state can be obtained with controlling placement pressure.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제36권7호
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• pp.731-738
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• 2012

In this study, the evaluation of the aerodynamic characteristics of the NREL Phase VI Rotor System has been performed, for the 7 m/s upwind case using commercial FEA and CFD tools which are ANSYS Mechanical 12.1 and CFX 12.1. The initial operating conditions of the rotor blade include a $3^{\circ}$ tip pitch angle. A numerical simulation was carried out on only the rotor parts, excluding the tower structure based on the equivalent stiffness model, to consider the aeroelastic effect for the numerical simulation using the loosely coupled 2-way fluid-structure interaction method. The blade root bending moment was monitored in real time to obtain reasonable results. To verify the analysis results, the numerical simulation results were compared with the measurements in the form of the root bending moment and the pressure distributions of the NREL/NASA Ames wind tunnel test.

• Composites Research
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• 제24권1호
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• pp.17-23
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• 2011

The failure of composite sandwich joints was experimentally investigated. A total of 30 joint specimens of 5 different types were tested with various fastening methods and core materials. In the NomexTM core sandwich joints, the core shear buckling was commonly observed in all the specimens which was followed by the slope change of the load-displacement curve. After the shear buckling, however, the joints carried additional loads of 50~200% over the buckling loads and then finally failed in the upper face breakage. The joints of PMI foam core showed the shear failure of the core instead of shear buckling and experienced the sharp drop of the carried load. Considering the failure modes, while both the core and face properties are important in the $Nomex^{TM}$ core joints, core shear strength seems to be the critical factor for the foam core joints.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제37권9호
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• pp.1077-1082
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• 2013

To improve cycling performance, the power output of the rider and the sources of resistance (e.g., air resistance, frame stiffness, and cycle mass) must be considered. From a mechanical viewpoint, we consider how the bike frame performance can be increased while decreasing the resistance. First, to improve the competitive ability of a racing track cycle, we should consider the stiffness of the bike frame including the pedal loading and aerodynamic effects when riding. Therefore, we obtained the cross-sectional area of each part of the bike frame and then aimed to minimize the drag force through an aerodynamic parametric study. In addition, the frame should remain safe under the loading applied by the rider. Under the guidelines of the UCI (union Cycliste Internationale) regulations, the bike frame has been evaluated under the proposed loading condition, and we developed a racing track cycle for elite cyclists.

• Journal of Korean Society of Steel Construction
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• 제14권5호통권60호
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• pp.641-646
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• 2002

A new damage detection technique using static displacement data was developed, in order to assess the structural integrity of bridge structures. In conventional damage assessment techniques using dynamic response, the variation of natural frequencies is intrinsically insensitive to the damage of the bridge: thus, it is usually difficult to obtain them from the measured data. The proposed detection method enables the estimation of the stiffness reduction of bridges using the static displacement data that are measured periodically, without requiring a specific loading test. Devices such as a laser displacement sensor can be used to measure static displacement data due to the dead load of the bridge structure. In this study, structural damage was represented by the reduction in the elastic modulus of the element. The damage factor of the element was introduced to estimate the stiffness reduction of the bridge under consideration. Likewise, the proposed algorithm was verified using various numerical simulations and compared with other damage detection methods. The effects of noise and number of damaged elements on damage detection were also investigated. Results showed that the proposed algorithm efficiently detects damage on the bridge.