• International Journal of Precision Engineering and Manufacturing
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• 제7권4호
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• pp.34-39
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• 2006

High-precision centerless grinding machines are emerging as a means of finishing the outer diameter grinding process required for ferrules, which are widely used as fiber optic connectors. In this study, a structural characteristic analysis and evaluation were carried out using a virtual prototype of a centerless grinding machine to realize systematic design technology and performance improvements required to manufacture ferrules. The prototype consisted of a concrete-filled bed, hydrostatic grinding wheel (GW) and regulating wheel (RW) spindle systems, a hydrostatic RW feed mechanism, a RW swivel mechanism, and on-machine GW and RW dressers. The loop stiffness values of the centerless grinding machine were estimated based on the relative displacements between the GW and RW caused by grinding forces. The simulated results illustrated that a concrete-filled bed considerably improved the structural stiffness and accuracy of a high-precision centerless grinding machine.

• Steel and Composite Structures
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• 제4권4호
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• pp.265-280
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• 2004

In view of the mounting cost of rehabilitating deteriorating infrastructure, further compounded by intensified environmental concerns, it is now obvious that the evolvement and application of advanced composite structural materials to complement conventional construction materials is a necessity for sustainable construction. This study seeks alternative fill materials (polymer-based) to the much-limited cement concrete used in concrete-filled steel tubular structures. Polymers have been successfully used in other industries and are known to be much lighter, possess high tensile strength, durable and resistant to aggressive environments. Findings of this study relating to elasto-plastic characteristics of polymer concrete filled steel composite beams subjected to uniform bending highlight the enormous increase in stiffness, strength and ductility of the composite beams, over the empty steel tube. Moreover, polymer based materials were noted to present a wide array of properties that could be tailored to meet specific design requirements e.g., ductility based design or strength based design. Analytical formulations for design are also considered.

• Steel and Composite Structures
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• 제4권4호
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• pp.303-315
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• 2004

Frame composed of concrete-filled steel tubular columns and I-shaped steel beam has been researched in order to development reasonable connection details. The present paper describes the results of an experimental program in four different connection details. The connection details considered include through-bolt between I-shaped steel beams and concrete-filled steel tubular columns and two details of welded connections. One of the welded connection details is stiffened by angles welded in the interior of the profile wall at the beam flange level. The specimens were tested in a cruciform loading arrangement with variable monotonic loading on the beams and constant compressive load on the column. For through-bolt details, the contribution of friction and bearing were investigated by embedding some of the bolts in the concrete. The results of the tests show that through-bolt connection details are very ductility and the bearing is not important to the behavior of these moment connections. The angles welded in the interior of the profile wall increase the strength and stiffness of the welded connection detail. In addition, the behavior curves of these connections are compared and some interesting conclusions are drawn. The results are summarized for the strength and stiffness of each connection.

• Steel and Composite Structures
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• 제22권1호
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• pp.63-77
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• 2016

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

• Structural Engineering and Mechanics
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• 제56권5호
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• pp.727-743
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• 2015

According to former studies, the mechanical properties of reinforced concrete filled tubular steel (RCFT) columns differed greatly from that of concrete filled steel tubular (CFT) columns because of interaction of inserted reinforcement in RCFT. Employing an experiment-based verification policy, a general FE nonlinear analysis model was developed to analyze the mechanical behavior and failure mechanism of RCFT columns under uniaxial compression. The reasonable stress-strain relationships were suggested for confined concrete, reinforcements and steel tube in the model. The mechanism for shear failure of concrete core was found out in the numerical simulation, and a none-conventional method and equation for evaluating the confinement effect of RCFT were proposed.

• 상하수도학회지
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• 제23권6호
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• pp.727-733
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• 2009

This study was performed to investigate the physical characteristics like compressive strength, permeability, porosity and the water quality removal characteristics of permeable concrete pavement filled with microbial-soil sheet to remove SS, organic matter and nutrients in artificial rainfall. As a result, it can show the removal efficiency is SS 90~95%, COD 85~93%, BOD 80~83%, T-N 61~75%, T-P 71~78% on WAPS I(W1) and WAPS II(W2). Therefore, permeable concrete pavement filled with microbial-soil sheet shows higher removal efficiency(SS 10%, organic matter and nutrients 30%) than a conventional porous concrete(W3). By filling microbial-soil sheet to permeable concrete pavement, we confirm that the function and efficiency are improved significantly and that a naturally-friendly facility can be developed and applied to treat non-point sources.

• 복합신소재구조학회 논문집
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• 제1권3호
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• pp.10-16
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• 2010

건설분야에서 환경적, 사회적 요구의 변화로 인해 기존의 건설재료와 괸련된 다양한 문제점들을 극복하기 위해 새로운 건설재료가 필요하게 되었다. 따라서, 토목분야에서 토목구조물을 설계할 때 만족시켜야 할 요구조건 또한 다양화 되고 있다. 토목분야의 새로운 건설재료로서 섬유보강플라스틱은 탁월한 부식저항성, 높은 비강도/비강성 등을 갖고 있다. 그러므로 그러한 성질은 기존 건설재료의 사용에 따른 문제점을 완화시키는데 사용할 수 있다. 최근 신규 건설현장에 적용하기 위해 신형식 교각이나 해상파일 등이 연구되고 있으며, 그것들은 보통 섬유보강플라스틱 튜브에 콘크리트를 채우는 형식이다. 이 연구에서 압축 및 휨 강도를 향상시키기 위해 섬유보강플라스틱 튜브에 철근콘크리트를 채운 합성파일을 제안하고 실험과 해석을 바탕으로 하중재하성능에 대하여 검토하였다.

• Steel and Composite Structures
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• 제27권2호
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• pp.185-192
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• 2018

Fly ash can significantly improve concrete workability and performance, and recycling fly ash in concrete can contribute to a cleaner environment. Since fly ash influences pozzolanic reactions in concrete, mechanical behaviors of concrete containing fly ash differ from traditional concrete. Creep behaviors of fly ash concrete filled steel tube arch were experimentally investigated for 10% and 30% fly ash replacement. The axes of two arches are designed as circular arc with 2.1 m computed span, 0.24 m arch rise, and their cross-sections are all in circular section. Time dependent deflection and strain of loading and mid-span steel tube were measured, and long term deflection of the model arch with 10% fly ash replacement was significantly larger than with 30% replacement. Considering the steel tube strain, compressive zone height, cross section curvature, and internal force borne by the steel tube, the compressive zone height and structural internal forces increased gradually over time due to concrete creep. Increased fly ash content resulted in more significant neutral axis shift. Mechanisms for internal force effects on neutral axis height were analyzed and verified experimentally.

• Steel and Composite Structures
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• 제18권5호
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• pp.1129-1144
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• 2015

Based on the experiment, this paper focuses on studying flexural behavior of splicing concrete-filled glass fiber reinforced polymer (GFRP) tubular composite members connected with steel bars. The test results indicated the confinement effects of GFRP tubes on the concrete core in compression zone began to produce, when the load reached about $50%P_u$ ($P_u$-ultimate load), but the confinement effects in tensile zone was unobvious. In addition, the failure modes of composite members were influenced by the steel ratio of the joint. For splicing unreinforced composite members, the steel ratio more than 1.96% could satisfy the splicing requirements and the steel ratio 2.94% was ideal comparatively. For splicing reinforced specimen, the bearing capacity of specimen with 3.92% steel ratio was higher 21.4% than specimen with 2.94% steel ratio and the latter was higher 21.2% than the contrast non-splicing specimen, which indicated that the steel ratio more than 2.94% could satisfy the splicing requirements and both splicing ways used in the experiment were feasible. So, the optimal steel ratio 2.94% was suggested economically. The experimental results also indicated that the carrying capacity and ductility of splicing concrete-filled GFRP tubular composite members could be improved by setting internal longitudinal rebars.

• 한국지진공학회논문집
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• 제6권2호
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• pp.9-19
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• 2002

강합성교각과 강교각은 철근곤크리트교각에 비해서 우수한 연성, 작은 단면 및 빠른 시공속도에도 불구하고 이 같은 장점들을 활용할 필요가 있는 도시지역에서조차 철근콘크리트교각의 대안으로서 활용되지 못하였다. 이 논문은 강합성교각과 강교각의 내진성능 평가에 관한 연속된 두편의 논문 중 첫편으로 강교각과 강합성 교각의 연성과 강성을 평가 비교하기 위해 수행한 준정적 반복재하실험을 대상으로 하였다. 기존의 강교각 및 강합성교각의 실험과 더불어 채움콘크리트와 하부 다이어프램간의 부작을 개선한 상세를 실험하였다. 또한, 강합성교각의 연성과 강성을 산정하기 위한 간편한 수치해석방법을 찾기 위해 비선형 스프링과 쉘요소를 사용한 해석을 시도하였다. 도시내의 전형적인 오버패스구간의 교각을 모델로 한 실험결과, 강합성교각은 강교각에 비해서 우수한 강성과 에너지 소산능력을 가지고 있는 것으로 나타났으며 채움콘크리트의 부착과 응력집중부의 상세를 개선시기는 것이 강합성교각의 연성과 강성을 증가시키는데 효과적인 것으로 나타났다. 시도된 수지해석방법은 강합성교각과 강교각의 거동을 완벽하게 모사하지는 못했지만 추가적인 연구가 진행되면 연성과 강성을 평가하는 간편한 방법으로 사용될 수 있는 것으로 판단된다.