• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.487-492
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• 2003

High-strength concrete(HSC) is a new construction material with enormous potential. Structures using high-strength concrete are to be coming more and more popular. But high-strength reinforced concrete columns show brittle behavior. It, therefore, is necessary to improve the ductility of HSC members. The purpose of this study is to investigate the ductility and strength of high-strength columns with variable lateral confinement under concentric axial load. Five HSC columns with compressive strength 68㎫ are designed with variable lateral confinements such as carbon fiber sheet(CFS), glass fiber sheet(GFS), and metal lath. Test results indicate that specimen confined by CFS show 11% higher maximum strength, 2.74 times ductility than A specimen using hoop. On comparing with the specimen A and B confined metal lath instead of hoop, strength decrease of 3%, and ductility increase of 1.21 times were observed.

• Steel and Composite Structures
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• 제19권5호
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• pp.1237-1258
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• 2015

This paper proposes a simple inelastic analysis approach to efficiently map out the complete nonlinear post-collapse (strain-softening) response and the maximum load capacity of axially loaded concrete encased steel composite columns (stub and slender). The scheme simultaneously incorporates the influences of difficult instabilizing phenomena such as concrete confinement, initial geometric imperfection, geometric nonlinearity, buckling of reinforcement bars and local buckling of structural steel, on the overall behavior of the composite columns. The proposed numerical method adopts fiber element discretization and an iterative M${\ddot{u}}$ller's algorithm with an additional adaptive technique that robustly yields solution convergence. The accuracy of the proposed analysis scheme is validated through comparisons with various available experimental benchmarks. Finally, a parametric study of various key parameters on the overall behaviors of the composite columns is conducted.

• 한국공작기계학회논문집
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• 제17권4호
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• pp.67-74
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• 2008

The important dynamic specifications in the aluminum automobile body design are the vibrations and crashworthiness in the views of ride comforts and safety. Thus, considerable effort has been invested into improving the performance of mechanical structures comprised of the interactive multiple sub-structures. Most mechanical structures are complex and are essentially multi-criteria optimization problems with objective functions retained as constraints. Each weight factor can be defined according to the effects and priorities among objective functions, and a feasible Pareto-optimal solution exists for the criteria-defined constraints. In this paper, a multi-criteria design based on the Pareto-optimal sensitivity is applied to the vibration qualities and crushing characteristics of front structure in the automobile body design. The vibration qualities include the idle, wheel unbalance and road shake. The crushing characteristic of front structure is the axial maximum peak load.

• 한국공간구조학회논문집
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• 제23권1호
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• pp.15-23
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• 2023

In this work, we deal with the feasibility of structural topology optimization for beam designs using retrofits that optimally allocates the reinforcement to the web under the condition that designers set bolt regions for H-beams of different dimensions. Mean compliance or minimal strain energy is considered for the optimization. Volume fraction is given to the design space to assign appropriate steel material quantities. The purpose of this study is to evaluate optimal shapes of stiffeners with the maximum rigidity that improves the axial and shear performance of the H-beam and to satisfy a given safety design standard of H-beam and stiffeners in case arbitrary load effect and resistances. Finally, the effectiveness of stiffness-based topology optimization on stiffeners is verified with several practical applicable examples.

• 한국강구조학회 논문집
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• 제13권3호
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• pp.223-232
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• 2001

본 연구에서는 높은 축력을 받는 기둥재에 사용 가능성이 큰 고장력 용접구조용 압연강재인 SM570의 압축좌굴내력을 평가하기 위해서 중심압축실험을 실시하였다. 단 주압축 실험결과 강구조 계산규준이 정하고 있는 판폭두께비의 제한치를 만족시키는 기둥부재의 최대내력은 국부좌굴에 의해 결정되며, 판폭두께비의 제한치를 만족시키지는 못하는 경우에는 최대내력이 도달하기 전에 국부좌굴에 의해서 급격히 저하하였다. 또한 압축 좌굴내력이 SM570 강재의 설계기준값인 $4.1tonf/cm^2$보다 높게 나타났다.

• Journal of Welding and Joining
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• 제14권2호
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• pp.36-45
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• 1996

Fatigue strength of the spot welded lap joint is considerably influenced by corrosive environments. Particularly, the chloride and the sulfide are most injurious to strength of the spot welded lap joint. Therefore, there is a need to evaluate its effect to corrosion fatigue strength for safe life design of spot welded structures. In order to evaluate their corrosion fatigue strength, corrosion fatigue tests on the spot welded lap joints of the uncoated and the coated high strength steel sheets were conducted in air and in 10% NaCl solution. Corrosion fatigue strength of the uncoated specimens were entirely lower than the coated one in NaCl solution, but those of the coated specimens in NaCl solution were lower than in air. And stress distribution in single spon welded lap joint subjected to tension-shear load was investigated by the finite element method. Using these results, we tried to evaluate corrosion fatgue strength of the various spot welded lap joints with maximum stress $\sigma_{max}$ at edge on loading side of the spot welded lap joint. We could find that corrosion fatigue strength could be quantitatively and systematically rearranged by $\sigma_{max}$.

• 한국지반공학회지:지반
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• 제11권4호
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• pp.99-110
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• 1995

본 연구에서는 정규압밀 건조 모래 지반내의 연직 강체 지반앵커에 대한 모형 인발실험을 실시해서 앵커 표면의 마찰각을 실측했다. 마찰각은 앵커 표면의 깊이 방향으로 설치된 다수의 2 방향 로드셀을 사용해서 측정된 수직응력, 전단응력으로 구했다. 실험은 평면변형률 앵커와 축대칭 앵커에 대해서 실시했는데 실험 분석 결과, 앵커표면의 최대마찰각은 평면변형률 압축시험에 의한 무신축방향의 면상의 응력경각의 최대치와 거의 일치한다는 것을 알았다. 이 결론은 모래의 강도 이방성과 구속압 의존성 등을 고려하여 얻은 것으로 앵커 표면 마찰각에 모래의 전단저항각을 적용해서 설계하면 위험측이 된다는 것도 알 수 있다.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.337-354
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• 2020

Reinforced concrete beam-column (RCBC) joints of laterally loaded unbraced frames are sometimes controlled by their shear behavior. This behavior relies on multiple and interdependent complex mechanisms. There are already several studies on the influence of some parameters on the shear strength of reinforced concrete joints. However, there are no studies methodically tackling all the most relevant parameters and quantifying their influence on the overall joint behavior, not just on its shear strength. Hence, considering the prohibitive cost of a comprehensive parametric experimental investigation, a nonlinear finite element analysis (NLFEA) was undertaken to identify the key factors affecting the shear behavior of such joints and quantify their influence. The paper presents and discusses the models employed in this NLFEA and the procedure used to deduce the joint behavior from the NLFEA results. Three alternative, or complementary, quantities related to shear are considered when comparing results, namely, the maximum shear stress supported by the joint, the secant shear stiffness at maximum shear stress and the secant shear stiffness in service conditions. Depending on which of these is considered, the lower or higher the relevance of each of the six parameters investigated: transverse reinforcement in the joint, intermediate longitudinal bars and diagonal bars in the column, concrete strength, column axial load and confining elements in transverse direction.

• Steel and Composite Structures
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• 제19권2호
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• pp.441-465
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• 2015

This paper presents the experimental results of flexural and compression steel members strengthened with carbon fiber reinforced polymers (CFRP) sheets. In the flexural test, the five specimens were fabricated and the test parameters were the number of CFRP ply and the ratio of partial-length bonded CFRP sheets of specimen. The CFRP sheet strengthened steel beam had failure mode: CFRP sheet rupture at the mid span of steel beams. A maximum increase of 11.3% was achieved depending on the number of CFRP sheet ply and the length of CFRP sheet. In the compression test, the nine specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the length of the specimen. From the tests, for short columns it was observed that two sides would typically buckle outward and the other two sides would buckle inward. Also, for long columns, overall buckling was observed. A maximum increase of 57% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 60 transversely.

• International Journal of Fluid Machinery and Systems
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• 제4권3호
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• pp.334-340
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• 2011

Turbo-pumps have weak points, such as the pumping operation is unstable on the positive slope of the head curve and/or the cavitation occurs at the low suction head. To improve simultaneously both weak points, the first author invented the unique pumping unit composed of the tandem impellers and the peculiar motor with the double rotational armatures. The front and the rear impellers are driven by the inner and the outer armatures of the motor, respectively. Both impeller speeds are automatically and smartly adjusted in response to the pumping discharge, while the rotational torques between both impellers/armatures are counter-balanced. Such speeds contribute to suppress successfully not only the unstable operation at the low discharge but also the cavitation at the high discharge, as verified with the axial flow type pumping unit in the previous paper. Continuously, this paper investigates experimentally the effects of the tandem impeller profiles on the pump performances and the rotational speeds against the discharge, using the impellers whose loads are low and/or high at the normal discharge. The worthy remarks are that (a) the unstable operation is suppressed as expected and the shut off power is scarcely large in the smart control, (b) the blade profile contributes to determine the discharge giving the maximum/minimum rotational speed where the reverse flow may incipiently appears at the front impeller inlet, (c) the tandem impeller profiles scarcely affect the rotational speeds, while the loads of the front and the rear impellers are same, but (d) the impeller with the low load must run faster and the impeller with the high load must run slower at the same discharge to take the same rotational torque, and (e) the reverse flow at the inlet and the swirling velocity component at the outlet of the front impeller with the high load require making the rotational speed of the rear impeller with low load fairly faster at the lower discharge.