• Steel and Composite Structures
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• 제15권2호
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• pp.131-150
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• 2013

This paper presents the experimental results of axially loaded stub columns of slender steel hollow square section (SHS) strengthened with carbon fiber reinforced polymers (CFRP) sheets. 9 specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the CFRP sheet orientation. From the tests, it was observed that two sides would typically buckle outward and the other two sides would buckle inward. A maximum increase of 33% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 100 transversely. Also, stiffness and ductility index (DI) were compared between un-retrofitted specimens and retrofitted specimens. Finally, it was shown that the application of CFRP to slender sections delays local buckling and subsequently results in significant increases in elastic buckling stress. In the last section, a prediction formula of the ultimate strength developed using the experimental results is presented.

• Geomechanics and Engineering
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• 제14권3호
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• pp.233-240
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• 2018

Pullout tests are usually employed to determine the ultimate bearing capacity of reinforced soil, and the load-displacement curve can be obtained easily. This paper presents an analytical solution for predicting the full-range mechanical behavior of a buried planar reinforcement subjected to pullout based on a bi-linear bond-slip model. The full-range behavior consists of three consecutive stages: elastic stage, elastic-plastic stage and debonding stage. For each stage, closed-form solutions for the load-displacement relationship, the interfacial slip distribution, the interfacial shear stress distribution and the axial stress distribution along the planar reinforcement were derived. The ultimate load and the effective bond length were also obtained. Then the analytical model was calibrated and validated against three pullout experimental tests. The predicted load-displacement curves as well as the internal displacement distribution are in closed agreement with test results. Moreover, a parametric study on the effect of anchorage length, reinforcement axial stiffness, interfacial shear stiffness and interfacial shear strength is also presented, providing insights into the pullout behaviour of planar reinforcements of MSE structures.

• Steel and Composite Structures
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• 제32권1호
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• pp.59-66
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• 2019

Hollow steel-reinforced concrete-filled GFRP tubular member is a new kind of composite members. Firstly set the mold in the GFRP tube (non-bearing component), then set the longitudinal reinforcements with stirrups (steel reinforcement cage) between the GFRP tube and the mold, and filled the concrete between them. Through the axial compression test of the hollow steel-reinforced concrete-filled GFRP tubular member, the working mechanism and failure modes of composite members were obtained. Based on the experiment, when the load reached the ranges of $55-70%P_u$ ($P_u-ultimate$ load), white cracks appeared on the surface of the GFRP tubes of specimens. At that time, the confinement effects of the GFRP tubes on core concrete were obvious. Keep loading, the ranges of white cracks were expanding, and the confinement effects increased proportionally. In addition, the damages of specimens, which were accompanied with great noise, were marked by fiber breaking and resin cracking on the surface of GFRP tubes, also accompanied with concrete crushing. The bearing capacity of the axially compressed components increased with the increase of reinforcement ratio, and decreased with the increase of hollow ratio. When the reinforcement ratio was increased from 0 to 4.30%, the bearing capacity was increased by about 23%. When the diameter of hollow part was decreased from 55mm to 0, the bearing capacity was increased by about 32%.

• International Journal of Concrete Structures and Materials
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• 제18권2E호
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• pp.79-87
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• 2006

The main objective of this research is to examine the behavior of high-strength concrete(HSC) columns. Eight test columns in one-third scale were tested under the conditions of cyclic lateral force and a constant axial load equal to 30% of the column axial load capacity. The $200{\times}200mm$ square columns were reinforced with eight DB bars constituting a longitudinal steel ratio of 2.54% of the column cross-sectional area. The main experimental parameters were volumetric ratio of transverse reinforcement(${\rho}_s$=1.58, 2.25 percent), tie configuration(Type H, Type C, Type D) and tie yield strength($f_{yh}$=548.8 and 779.1 MPa). It was found that the hysteretic behaviour and ultimate deformability of HSC columns were influenced by the amount and details of transverse reinforcement in the potential plastic hinge regions. Columns of transverse reinforcement in the amount 42 percent higher than that required by seismic provisions of ACI 318-02 showed ductile behavior. At 30% of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 548.8 MPa. Correlations between the calculated damage index and the damage progress are proposed.

• Steel and Composite Structures
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• 제24권3호
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• pp.323-337
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• 2017

This paper presents the results of a comprehensive experimental investigation on the compressive behaviour of steel tube-confined concrete (STCC) stub columns with active and passive confinement. To create active confinement in STCC columns, an innovative technique is used in which steel tube is laterally pre-tensioned while the concrete core is simultaneously pre-compressed by applying pressure on fresh concrete. A total of 135 STCC specimens with active and passive confinement are tested under axial compression load and their compressive strength, ultimate strain capacity, axial and lateral stress-strain curves and failure mode are evaluated. The test variables include concrete compressive strength, outer diameter to wall thickness ratio of steel tube and prestressing level. It is shown that applying active confinement on STCC specimens can considerably improve their mechanical properties. However, applying higher prestressing levels and keeping the applied pressure for a long time do not considerably affect the mechanical properties of actively confined specimens. Based on the results of this study, new empirical equations are proposed to estimate the axial strength and ultimate strain capacity of STCC stub columns with active and passive confinement.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.396-408
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• 2019

The tubes which are applied in jacket platforms as the supporting structure might be collided by supply vessels. Such kind of impact will lead to plastic deformation on tube members. As a result, the ultimate strength of tubes will decrease compared to that of intact ones. In order to make a decision on whether to repair or replace the members, it is crucial to know the residual strength of the tubes. After being damaged by lateral impact, the simply supported tubes will definitely loss a certain extent of load carrying capacity under uniform axial compression. Therefore, in this paper, the relationship between the residual ultimate strength of the damaged circular tube by collision and the energy dissipation due to lateral impact is investigated. The influences of several parameters, such as the length, diameter and thickness of the tube and the impact energy, on the reduction of ultimate strength are investigated. A series of numerical simulations are performed using nonlinear FEA software LS-DYNA. Based on simulation results, a non-dimensional parameter is introduced to represent the degree of damage of various size of tubes after collision impact. By applying this non-dimensional parameter, a simplified formula has been derived to describe the relationship between axial compressive residual ultimate and lateral impact energy and tube parameters. Finally, by comparing with the allowable compressive stress proposed in API rules (RP2A-WSD A P I, 2000), the critical damage of tube due to collision impact to be repaired is proposed.

• 콘크리트학회지
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• 제7권3호
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• pp.199-210
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• 1995

충전형 강관콘크리트 구조는 강관과 콘크리트 두 재료의 이질적인 재료특성을 상호 보완적으로 발휘하여 구조적 성능향상을 꾀한 것으로서 제구조 특성상 우수한 구조형식이라 할 수 있다. 강관으로 구속된 콘크리트가 중심축력을 받게 되면 내부의 콘크리트는 압괴에 의한 체적 팽창을 외부의 강관에 의해 구속 받게 되므로 3축 압축응력 상태로 되어 압축강도가 증대된다. 또한 콘크리트의 압괴에 의한 탈락 현상이 방지되므로서 단면의 결손이 없어져 내력 저하가 작아진다는 잇점을 가진다. 따라서 본 연구에서는 원형강관으로 구속된 내부 콘크리트의 구조적 거동 특성을 규명하기 위한 것으로서 폭두께비와 충전 콘크리트의 강도를 주요 변수로 하여 일련의 실험을 통하여 강관으로 구속(3축 응력)된 콘크리트의 구조적 거동 특성을 고찰하였다. 일련의 실험을 통하여 얻어진 결론을 요약하면 다음과 같다. (1)강관에 의한 콘크리트의 구속효과는 강관의 폭두께비와 충전 콘크리트의 강도가 낮을수록 현저하며, 원형강관으로 구속된 내부 콘크리트는 최대내력시의 변형능력에 있어서 횡방향 구속이 없는 콘크리트보다 4~7배 정도까지 증대시켜 연성효과를 높일 수 있을 것으로 기대된다. (2)콘크리트의 구속계수를 이용하여 강관으로 구속된 내부 콘크리트의 강도와 콘트리트 충전강관 기둥의 최대내력을 산정할 수 있는 식을 제시하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1088-1093
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• 2010

The Smart bi-directional pile load test with variable end plate overcomes the shortcoming of the Osterberg cell test. It is possible that the ultimate bearing capacity of piles can be known by using two different end plates. The first step is to measure end bearing capacity with smaller end plate and the second step is similar to the conventional O-cell test. In this study, model test was performed to evaluate the smart bi-directional pile load test in sand. Vertical displacement of the model pile were messured at the axial loading condition.

• 한국항해학회지
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• 제22권3호
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• pp.65-72
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• 1998

최근에는 고장력강의 사용증대와 함께 구조부재가 경량화추세에 있으며 이상부식이 발생한 구조부재는 강도가 크게 저하되리라 예상되지만 지금까지 이에 관한 연구가 거의 없는 상태이다. 본 연구에서는 단소성대변형유한요소법을 적용하여 국부이상부식을 가진 판이 면내압축하중을 받을 경우에 압축최종강도에 미치는 부식부영역의 크기. 부식부의 판두께 감소량 및 세장비의 영향에 대하여 연구하였다.

• 한국지반공학회논문집
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• 제31권8호
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• pp.39-49
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• 2015

본 논문에서는 jet grouting 공법을 적용한 파형 마이크로파일의 지지력 향상 효과 및 거동 특성을 분석하기 위한 연구를 수행하였다. 각 말뚝의 형상에 따른 거동을 비교하기 위해 일반 마이크로파일, 파형이 없는 jet grouted 말뚝 및 네 종류의 파형 마이크로파일의 모델을 제작하여 원심모형실험을 수행하였다. 실험 결과 일반 마이크로파일 대비 파형 마이크로파일의 지지력 향상 효과를 확인 할 수 있었으며, 특히 파형의 간격이 상대적으로 좁은 말뚝의 지지력 개선 효과가 큰 것으로 분석되었다. 또한 기존의 재하시험에 의한 지지력 예측 및 평가 방법을 토대로 파형 마이크로 파일의 지지력 산정 방안을 검토한 결과 P-S 곡선법과 25.4mm 전침하량기준이 파형 마이크로파일의 거동을 합리적으로 예측하는 것으로 나타났다.