• Steel and Composite Structures
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• 제46권6호
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• pp.793-804
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• 2023

In this study, cyclic loading tests were conducted to assess the seismic performance of cast-in-place (CIP) concrete-filled hollow core precast concrete columns (HPCC) constructed using steel ducts and rubber tubes. The outer shells of HPCC, with a hollow ratio of 47%, were fabricated using steel ducts and rubber tubes, respectively. Two combinations of shear studs & long threaded bars or cross-deformed bars & V-ties were employed to ensure the structural integrity of the old concrete (outer shell) and new CIP concrete. Up to a drift ratio of 3.8%, the hysteresis loop, yielding stiffness, dissipated energy, and equivalent damping ratio of the HPCC specimens were largely comparable to those of the solid columns. Besides the similarities in cyclic load-displacement responses, the strain history of the longitudinal bars and the transverse confinement of the three specimens also exhibited similar patterns. The measured maximum moment exceeded the predicted moment according to ACI 318 by more than 1.03 times. However, the load reduction of the HPCC specimen after reaching peak strength was marginally greater than that of the solid specimen. The energy dissipation and equivalent damping ratios of the HPCC specimens were 20% and 25% lower than those of the solid specimen, respectively. Taking into account the overall results, the structural behavior of HPCC specimens fabricated using steel ducts and rubber tubes is deemed comparable to that of solid columns. Furthermore, it was confirmed that the two combinations for securing structural integrity functioned as expected, and that rubber air-tubes can be effectively used to create well-shaped hollow sections.

• Computers and Concrete
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• 제14권5호
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• pp.613-633
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• 2014

A double-skinned composite tubular (DSCT) column, which consists of concrete and inner and outer tubes, was finally developed to overcome the weaknesses of concrete filled tube columns by reducing the self-weight of the column and confining the concrete triaxially. Research pertaining to the stiffness and strength of the column and the confining effect in a DSCT column has been carried out. However, detailed studies on the confining stress, especially the internal confining stress in a DSCT column, have not been carried out. Internal and external confining stresses should be evaluated to determine the effective confining stress in a DSCT column. In this paper, the confining stresses of concrete before and after insertion of an inner tube were studied using finite element analysis. The relationship between the internal or external confining stresses and the theoretical confining stress was investigated by parametric studies. New modified formulae for the yield and buckling failure conditions based on the formulae suggested by former researchers were proposed. Through analytical studies, the modified formulae were verified to be effective for economic and reasonable design of the inner tubes in a DSCT column under the same confining stress.

• Steel and Composite Structures
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• 제22권2호
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• pp.217-234
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• 2016

In order to investigate mechanical properties and load-bearing capacity of T-shaped Concrete-Filled Square Steel Tubular (TCFST) composite columns under eccentric axial load, three T-shaped composite columns were tested under eccentric compression. Experimental results show that failure mode of the columns under eccentric compression was bending buckling of the whole specimen, and mono column performs flexural buckling. Specimens behaved good ductility and load-bearing capacity. Nonlinear finite element analysis was also employed in this investigation. The failure mode, the load-displacement curve and the ultimate bearing capacity of the finite element analysis are in good agreement with the experimental ones. Based on eccentric compression test and parametric finite element analysis, the calculation formula for the equivalent slenderness ratio was proposed and the bearing capacity of TCFST composite columns under eccentric compression was calculated. Results of theoretical calculation, parametric finite element analysis and eccentric compression experiment accord well with each other, which indicates that the theoretical calculation method of the bearing capacity is advisable.

• 국제초고층학회논문집
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• 제7권4호
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• pp.313-325
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• 2018

Concrete-filled steel tubular (CFST) members are commonly used as composite columns in modern construction. However, the current guidelines for members' fire design (EN1994-1-2) have been proved to be unsafe in case the relative slenderness is higher than 0.5. In addition, the simplified design methods of Eurocode 4 are limited to circular and square CFST columns, while in practice columns with rectangular and elliptical hollow sections are being increasingly used because of their architectural aesthetics. In the last years a large experimental research has been carried out at Coimbra University on the topic. They have been tested concrete filled circular, square, rectangular and elliptical hollow columns with restrained thermal elongation. Some parameters such as the slenderness, the type of cross-section geometry as well as the axial and rotational restraint of the surrounding structure to the column have been tested in order to evaluate their influence on the fire resistance of such columns. In this paper it is evaluated the influence of the boundary conditions (pin-ended and semi-rigid end-support conditions) on the behavior of the columns in case of fire. In these tests it could not be seen a marked effect of the tested boundary conditions but it is believed that the increasing of rotational stiffness increases the fire resistance of the columns.

• Steel and Composite Structures
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• 제50권4호
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• pp.475-487
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• 2024

The usage of fiber-reinforced polymer materials increases in the construction sector due to their advantages in terms of high mechanical strength, lightness, corrosion resistance, low density and high strength/density ratio, low maintenance and painting needs, and high workability. In this study, it is aimed to improve mechanical properties of GFRP box profiles, produced by pultrusion method, by filling the polymer concrete into them. Within the scope of study, hybrid use of polymer concrete produced with GFRP box profiles was investigated. Hybrid pressure and bending specimens were produced by filling polymer concrete (polyester resin manufactured with natural sand and stone chips) into GFRP box profiles having different cross-sections and dimensions. Behavior of the produced hybrid members was investigated under bending and compression tests. Hollow GFRP_xx profiles, polymer-filled hybrid members, and nominative polymeric concrete specimens were tested as well. The behavior of the specimens under pressure and bending tests, and their load bearing capacities, deformations and changes in toughness were observed. According to the test results; It was deduced that hybrid design has many advantages over its component materials as well as superior physical and mechanical properties.

• 한국지진공학회논문집
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• 제10권4호
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• pp.85-94
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• 2006

지진지역의 교량교각에 대한 설계에서 요구연성도는 가장 중요한 요소이다. 철근콘크리트 교각의 내진성능 향상을 위해서 강관으로 교각을 감싸거나 후프철근과 같은 횡방향 철근을 이용하여 교각을 구속함으로써 교각의 연성도를 증가시키는 방안이 필요하다. 강재 매입형 교각을 이용하는 것은 RC 교각 내진성능을 향상시키는 유용한 방법중의 하나이다. 이 논문에서는 강재 매입형 합성교각의 내진성능을 평가하기 위하여 단일강재와 복수강재가 매입된 합성교각에 대하여 준정적 실험을 수행하였다. H형강이 매입된 실험체와 부분 충진된 원형강관이 매입된 단면으로 구성되어 총 8기의 실험체를 제작하였다. 실험변수는 심부구속 철근비, 매입 강재의 종류와 양으로서 이에 대한 변위연성도를 분석하였다. 실험결과 강재매입으로 인하여 교각의 변형능력이 증가하였으며 특히 원형강관이 매입된 교각의 변위연성도와 횡방향 강도가 가장 크게 나타났다.

• 한국강구조학회 논문집
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• 제28권1호
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• pp.23-34
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• 2016

콘크리트 충전강관 기둥은 강관의 구속효과에 의해 콘크리트의 압축내력 상승과, 콘크리트에 의한 강관의 국부좌굴 보강효과에 의해 부재내력이 상승하고 뛰어난 변형성능을 발휘한다. 하지만, 기둥단면이 커질 경우 합성효과를 발휘하기 위하여 스터드 볼트나 후 시공 앵커 볼트를 사용해야 하는 시공상의 문제점이 발생된다. 이를 극복함과 동시에 합성효과를 증대시키기 위한 방안으로 내부에 리브가 설치된 용접조립 기둥이 소개되었다. 내부 리브는 콘크리트와 맞물려 있어 리브의 변형은 콘크리트의 균열을 촉진시키는 역할을 동반하게 된다. 이러한 잠재적인 문제에 대한 해결책은 강관 리브의 변형에 저항할 수 있도록 콘크리트 인성을 증가시킬 수 있는 방안이 필요하다. 언급된 두 가지의 문제점이 효과적으로 해결될 경우 용접조립 각형강관 기둥은 내화성능 확보가 가능하다고 판단된다. 본 연구에서는 해결방안으로 내부 콘크리트를 강섬유와 혼입하여 기둥 자체의 연성과 인성을 증대시키는 것에 중점을 맞추고 있다. 내화성능 평가를 위한 시험체는 총 8개 로 하중비에 따른 재하가열 실험을 실시하고 화재 전후 거동과 열 변형 능력을 주요변수별로 분석하였다. 실험결과와 선행연구 비교를 통해 열 전달과 열응력 해석 모델의 신뢰성을 확보하였으며, 강섬유 혼입율에 따른 변수해석을 수행하였다.

• Structural Engineering and Mechanics
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• 제66권2호
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• pp.229-235
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• 2018

This study investigated the behaviour of the simply supported hollow steel tube (HST) beams, either concrete filled or unfilled when strengthened with carbon fibre reinforced polymer (CFRP) sheets. Eight specimens with varied tubes thickness (sections classification 1 and 3) were all tested experimentally under static flexural loading, four out of eight were filled with normal concrete (CFST beams). Particularly, the partial CFRP strengthening scheme was used, which wrapped the bottom-half of the beams cross-section (U-shaped wrapping), in order to use the efficiency of high tensile strength of CFRP sheets at the tension stress only of simply supported beams. In general, the results showed that the CFRP sheets significantly improved the ultimate strength and energy absorption capacities of the CFST beams with very limited improvement on the related HST beams. For example, the load and energy absorption capacities for the CFST beams (tube section class 1) were increased about 20% and 32.6%, respectively, when partially strengthened with two CFRP layers, and these improvements had increased more (62% and 38%) for the same CFST beams using tube class 3. However, these capacities recorded no much improvement on the related unfilled HST beams when the same CFRP strengthening scheme was adopted.

• 한국강구조학회 논문집
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• 제16권2호통권69호
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• pp.225-233
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• 2004

일반적인 합성보는 콘크리트 슬래브와 H형강 철골보 사이에 작용하는 수평전단력을 쉬어 코넥터로 긴결하여 휨 내력 및 강성을 증가시킨 구조이다. 본 연구에서 제안한 TSC 구조는 H형강 대신 U형 철골을 사용하고 그 속에 콘크리트를 채운 새로운 형태의 합성보 시스템으로 실험을 통하여 구조특성을 평가 분석 하였다. 또한 실험결과를 통해 T형 합성보(이하 TSC 보라 칭함)의 구조설계 및 시공에 필요한 기초 자료를 제시하고자 한다.

• Steel and Composite Structures
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• 제31권3호
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• pp.217-232
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• 2019

Modular steel buildings consist of prefabricated room-sized structural units that are manufactured offsite and installed onsite. The inter-module connections must fulfill the assembly construction requirements and soundly transfer the external loads. This work proposes an innovative assembled connection suitable for modular buildings with concrete-filled steel tube columns. The connection uses pretensioned strands and plugin bars to vertically connect the adjacent modular columns. The moment-transferring performance of this inter-module connection was studied through monotonic and cyclic loading tests. The results showed that because of the assembly construction, the connected sections were separated under lateral bending, and the prestressed inter-module connection performed as a weak semirigid connection. The moment strength at the early loading stage originated primarily from the contact bonding mechanism with the infilled concrete, and the postyield strength depended mainly on the tensioned strands. The connection displayed a self-centering-like behavior that the induced deformation was reversed during unloading. The energy dissipation originated primarily from frictional slipping of the plugin bars and steel strands. The moment transferring ability was closely related to the section dimension and the arrangements of the plugin bars and steel strands. A simplified strength calculation and evaluation method was also proposed, and the effectiveness was validated with the test data.