• Steel and Composite Structures
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• 제38권4호
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• pp.431-445
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• 2021

This paper presents experiments and theoretical analysis on shear behavior of eight concrete-encased square concrete-filled steel tube (CECFST) specimens and three traditional reinforced concrete (RC) specimens. A total of 11 specimens with the test parameters including the shear span-to-depth ratio, steel tube size and studs arrangement were tested to explore the shear performance of CECFST specimens. The failure mode, shear capacity and displacement ductility were thoroughly evaluated. The test results indicated that all the test specimens failed in shear, and the CECFST specimens enhanced by the interior CFST core exhibited higher shear capacity and better ductility performance than that of the RC specimens. When the other parameters were the same, the larger steel tube size, the smaller shear span-to-depth ratio and the existence of studs could lead to the more satisfactory shear behavior. Then, based on the compatible truss-arch model, a set of formulas were developed to analytically predict the shear strength of the CECFST members by considering the compatibility of deformation between the truss part, arch part and the steel tube. Compared with the calculated results based on several current design specifications, the proposed formulas could get more accurate prediction.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.419-437
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• 2023

The use of reinforced concrete (RC) shear walls (SW) as an efficient lateral load-carrying system has gained recent attention. However, creating openings in RC shear walls is unavoidable due to architectural requirements. This reduces the walls' strength and stiffness, resulting in the development of wall piers. In this study, the cyclic behavior of RC shear walls with openings, reinforced with carbon fiber reinforced polymer (CFRP) sheets in various patterns, was numerically investigated. Finite element analysis (FEA) using ABAQUS software was employed. Additionally, the retrofitting of sub-standard buildings (5, 10, and 15-story structures) designed based on the old and new versions of the Iranian Code of Practice for Seismic-Resistant Structures was evaluated. Nonlinear static analyses, specifically pushover analyses, were conducted on the structures. The best pattern of CFRP wrapping was determined and utilized for retrofitting the sub-standard structures. Various structural parameters, such as load-carrying capacity, ductility, stress contours, and tension damage contours, were compared to assess the efficiency of the retrofit solution. The results indicated that the load-carrying capacity of the sub-standard structures was lower than that of standard ones by 57%, 69%, and 67% for 5, 10, and 15-story buildings, respectively. However, the retrofit solution utilizing CFRP showed promising results, enhancing the capacity by 10-25%. The retrofitted structures demonstrated increased yield strength, ultimate strength, and ductility through CFRP wrapping and effectively prevented wall slipping.

• 콘크리트학회논문집
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• 제28권2호
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• pp.177-185
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• 2016

이 논문에서는 강섬유 보강 초고성능 콘크리트(UHPC)의 부재의 휨거동을 특성을 파악하고자 하였다. 하이브리드 강섬유보강 초고성능 콘크리트의 압축강도는 150 MPa이다. 부피비 1.5%의 하이브리드 강섬유 보강 초고성능 콘크리트의 휨거동 특성 실험을 수행하였다. 강섬유보강 콘크리트의 압축 및 인장거동 재료 특성은 구조거동 예측을 위해 매우 중요하다. 강섬유 보강 초고성능 콘크리트의 하중-균열개구변위 측정결과를 이용하여 인장거동 특성을 파악하였다. 실험결과는 하이브리드 강섬유 보강 UHPC는 균열제어에 유리한 것을 나타낸다. 또한, 강섬유 보강 UHPC 보의 연성지수는 1.6~3.0을 나타내어 연성거동에 효과적임을 나타낸다. 모멘트-곡률 관계 측정결과와 해석결과를 비교하였다. 휨철근을 배근하지 않은 UHPC 보에 대한 휨강도 예측결과는 측정 휨강도를 다소 과다평가하고 있다. 전반적으로 본 연구에서 제시한 강섬유 보강 초고성능 콘크리트 재료 및 휨 거동 모델링 제안기법에 의해 압축강도 150 MPa 급의 강섬유 보강 콘크리트 보의 합리적인 휨성능 예측이 가능하다.

• 한국지진공학회논문집
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• 제8권4호
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• pp.1-10
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• 2004

반복 횡하중을 받는 콘트리트 충진 탄소섬유 튜브 기둥의 휨거동을 분석하기 위하여 실험을 수행하였다. 콘크리트 충진 각형 탄소섬유 튜부 기둥의 휨거동에 영향을 미치는 탄소섬유의 와인딩 각도와 두께를 변수로 선택하여 거동을 평가하였다. 콘트리트 충진 탄소섬유 튜브 기둥의 휨거동 보다 정확하게 분석하기 위하여 설정된 두 변수를 동시에 고려하였다. 실험의 결과에서 얻어진 하중-변형 곡선을 이용하여 콘크리트 충진 각형 탄소섬유 튜브 기둥이 휨강도, 변형능력 및 에너지 소산능력을 조사하였다. 또한 기존 구조물과의 비교를 위하여 철근콘크리트 조적벽과 콘크리트를 충진한 각형 탄소섬유 튜브 기둥과의 연성 능력을 비교 평가하였다.

• 한국지진공학회논문집
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• 제8권3호
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• pp.13-22
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• 2004

반복 횡하중을 받는 콘크리트 충진 탄소섬유 튜브 기둥의 휨 거동을 분석하기 위하여 여섯 개의 시험체에 대한 실험을 수행하였다. 콘크리트 충진 탄소섬유 튜브 기둥의 휨 거동에 영향을 미치는 탄소섬유의 와인딩 각도와 두께를 변수로 선택하여 거동을 평가하였다. 콘크리트 충진 탄소섬유 튜브 기둥의 휨 거동을 보다 정확하게 분석하기 위하여 설정된 두 변수를 동시에 고려하였다. 실험의 결과에서 얻어진 하중-변형 곡선을 이용하여 콘크리트 충진 탄소섬유 튜브 기둥의 휨강도, 변형능력 및 에너지 소산능력을 조사하였다. 또한 기존 구조물과의 비교를 위하여 철근콘크리트 조적벽과 콘크리트를 충진한 탄소섬유 튜브 기둥과의 연성 능력을 비교 평가하였다.

• Steel and Composite Structures
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• 제36권2호
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• pp.197-211
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• 2020

Application of the steel ring as a type of seismic fuse has been one of the efforts made by researchers in recent years aiming to enhance the ductility of the bracing systems which in turn, possesses various advantages and disadvantages. Accordingly, to alleviate these disadvantages, an innovative bracing system with a diamond scheme equipped with a steel ring is introduced in this paper. In this system, the braces and yielding circular damper act in parallel whose main functionality is to increase ductility, energy absorption and mitigate drawbacks of the existing bracing systems, in which the braces and yielding circular damper act in parallel. To conduct the experimental tests, specimens with three types of rigid, semi-rigid and pinned connections were built and subjected to cyclic loading so that their performance could be analyzed. Promisingly, the results indicate both great applicability and efficiency of the proposed system in energy absorption and ductility. Moreover, it was concluded that as the braces and damper are in parallel, the use of a steel ring with smaller size and thickness would result in higher energy absorption and load-resisting capacity when compared to the other existing systems. Finally, to assess the potential of numerically modeling the proposed system, its finite element model was simulated by ABAQUS software and observed that there is a great agreement between the numerical and experimental results.

• Earthquakes and Structures
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• 제18권1호
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• pp.15-25
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• 2020

The seismic behaviour of reinforced concrete (RC) columns made from high-strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength stirrups (HSSs) and three with normal-strength stirrups (NSSs), were tested under a combination of high axial and reversed cyclic loads. The effects of stirrup strength and the ratio of transverse reinforcement on the cracking patterns, hysteretic response, strength, stiffness, ductility, energy dissipation and strain of transverse reinforcement were studied. The results indicate that good seismic behaviour of an RC column subjected to high axial compression can be obtained by using a well-shaped stirrup. Stirrup strength had little effect on the lateral bearing capacity. However, the ductility was significantly modified by improving the stirrup strength. When loaded with a large lateral displacement, the strength reduction of NSS specimens was more severe than that of those with HSSs, and increasing the stirrup strength had little effect on the stiffness reduction. The ductility and energy dissipation of specimens with HSSs were superior to those with NSSs. When the ultimate displacement was reached, the core concrete could be effectively restrained by HSSs.

• Computers and Concrete
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• 제15권2호
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• pp.141-166
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• 2015

In the present study, a Finite Element Model has been developed and used to study the effect of diameter to wall thickness ratio (D/t) of steel tube filled with concrete under axial loading on its behavior and load carrying capacity. The model is verified by comparing its findings with available experimental results. Influence of thickness and area of steel tube on strength, ductility, confinement and failure mode shapes has been studied. Strength enhancement factors, load factor, confinement contribution, percentage of steel and ductility index are defined and introduced for the assessment. A parametric study by varying length and thickness of tube has been carried out. Diameter of tube kept constant and equals to 140 mm while thickness has been varied between 1 mm and 6 mm. Equations were developed to find out the ultimate load and confined concrete strength of concrete. Variation of lateral confining pressure along the length of concrete cylinder was obtained and found that it varies along the length. The increase in length of tubes has a minimal effect on strength of tube but it affects the failure mode shapes. The findings indicate that optimum use of materials can be achieved by deciding the thickness of steel tube. A better ductility index can be obtained with the use of higher thickness of tube.

• Structural Engineering and Mechanics
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• 제19권2호
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• pp.185-198
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• 2005

In the design of reinforced concrete beams, it is a standard practice to use the yield stress of the steel reinforcement for the evaluation of the flexural strength. However, because of strain hardening, the tensile strength of the steel reinforcement is often substantially higher than the yield stress. Thus, it is a common belief that the actual flexural strength should be higher than the theoretical flexural strength evaluated with strain hardening ignored. The possible increase in flexural strength due to strain hardening is a two-edge sword. In some cases, it may be treated as strength reserve contributing to extra safety. In other cases, it could lead to greater shear demand causing brittle shear failure of the beam or unexpected greater capacity of the beam causing violation of the strong column-weak beam design philosophy. Strain hardening may also have certain effect on the flexural ductility. In this paper, the effects of strain hardening on the post-peak flexural behaviour, particularly the flexural strength and ductility, of reinforced normal- and high-strength concrete beams are studied. The results reveal that the effects of strain hardening could be quite significant when the tension steel ratio is relatively small.

• 대한토목학회논문집
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• 제35권2호
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• pp.287-297
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• 2015

철근콘크리트 부재의 연성을 확보하기 위하여 콘크리트구조기준에서는 철근의 최소 허용 변형률에 대한 지침을 두고 있고, EC2에서는 중립축 깊이와 유효 깊이의 비(c/d)를 제한하고 있다. 일반적으로 철근콘크리트 부재의 연성 능력은 항복변위와 극한변위의 비로서 표현되는 변위 연성도를 통해 평가하는데, 변위 연성도를 정확하게 산정하기 위해서는 항복변위와 극한변위에 대한 정립이 필수적이다. 그러나 실제 부재의 변위는 부재의 다양한 특성에 영향을 받으므로 이들 값을 정확하게 산정하는 것은 어렵다. 이 연구에서는 철근콘크리트 부재의 항복변위 및 극한변위를 휨모멘트-휨곡률 관계를 통해 직접 계산하여 변위 연성도를 산정하였다. 해석의 주요 변수는 콘크리트 압축강도, 주철근 항복강도, 주철근 비, 횡철근 간격, 축력비 및 콘크리트 극한변형률이다. 해석 결과 콘크리트 압축강도가 증가할수록 변위 연성도는 증가하였다. 반면에 주철근의 항복강도, 주철근 비, 횡철근 간격 및 축력비가 증가할수록 변위 연성도는 감소하였다. 그리고 변위 연성도는 기둥의 내진설계에 사용되는 응답수 정계수(R)의 산정에 필수적이므로 변위 연성도를 정확하게 산정하는 것이 필수적이라고 판단된다.