• Smart Structures and Systems
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• 제17권5호
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• pp.709-724
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• 2016

This study investigates the optimum design parameters of a superelastic friction base isolator (S-FBI) system through a multi-objective genetic algorithm to improve the performance of isolated buildings against near-fault earthquakes. The S-FBI system consists of a flat steel-PTFE sliding bearing and superelastic NiTi shape memory alloy (SMA) cables. Sliding bearing limits the transfer of shear across the isolation interface and provides damping from sliding friction. SMA cables provide restoring force capability to the isolation system together with additional damping characteristics. A three-story building is modeled with S-FBI isolation system. Multiple-objective numerical optimization that simultaneously minimizes isolation-level displacements and superstructure response is carried out with a genetic algorithm in order to optimize S-FBI system. Nonlinear time history analyses of the building with optimal S-FBI system are performed. A set of 20 near-fault ground motion records are used in numerical simulations. Results show that S-FBI system successfully control response of the buildings against near-fault earthquakes without sacrificing in isolation efficacy and producing large isolation-level deformations.

• 대한토목학회논문집
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• 제33권3호
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• pp.875-888
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• 2013

최근에는 초탄성 형상기억합금을 구조물 일부에 설치하여 지진과 같은 외부 충격하중으로 인해 발생되는 영구적인 소성 변형을 줄이고 자동치유가 가능한 변위제어 시스템을 개발하는 연구가 활발하게 진행되고 있다. 초탄성 형상 기억합금은 상당량의 변위를 가하더라도 별도의 열처리 없이도 상온에서 단지 하중만을 제거하여도 원형으로 복원이 가능한 독특한 합성 금속재료이다. 뼈대 구조물에서 변형이 집중이 되는 부위에 기존에 사용된 강재를 대신하여 초탄성 형상기억합금을 사용한다면 시스템의 복원 효과를 극대화 시킬 수 있다. 따라서 본 연구는 내진성능이 우수한 좌굴방지 가새프레임에 초탄성 형상기억합금 소재를 접목시킨 새로운 구조 시스템을 제안하고 자 한다. 본 연구에서 제안된 구조시스템의 성능을 검증하기 위하여 현재 사용되는 설계코드를 참고하여 6층의 가새프레임 빌딩을 설계를 하고 2차원적인 유한요소 프레임 모델에 각각의 지진 위험도 레벨의 가속도 데이터를 사용하여 비선형 동적 해석을 실시하였다. 해석결과를 바탕으로 초탄성 형상기억합금 가새시스템을 사용한 프레임 구조물과 기존의 가새시스템을 성능적인 측면에서 서로 비교하였다. 해석결과는 지진하중 이후에 초탄성 형상기억합금 가새시스템은 구조물에 잔류 처짐을 감소하는데 매우 효율적임을 보여주고 있다.

• Smart Structures and Systems
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• 제24권2호
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• pp.157-171
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• 2019

This study investigated the effects of the geometric parameters of superelastic shape memory alloy (SE SMA) fibers on the pullout displacement recovering and self-healing capacity of reinforced cementitious composites. Three diameters of 0.5, 0.7 and 1.0 mm and two different crimped lengths of 5.0 and 10.0 mm were considered. To provide best anchoring action and high bond between fiber and cement mortar, the fibers were crimped at the end to create spear-head shape. The single fiber cement-based specimens were manufactured with the cement mortar of a compressive strength of 84 MPa with the square shape at the top and a dog-bone shape at the bottom. The embedded length of each fiber was 15 mm. The pullout test was performed with displacement control to obtain monotonic or hysteretic behaviors. The results showed that pullout displacements were recovered after fibers slipped and stuck in the specimen. The specimens with fiber of larger diameter showed better displacement recovering capacity. The flag-shaped behavior was observed for all specimens, and those with fiber of 1.0 mm diameter showed the clearest one. It was observed that the length of fiber anchorage did not have a significant effect on the displacement recovery, pullout resistance and self-healing capacity.

• Smart Structures and Systems
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• 제15권5호
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• pp.1271-1291
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• 2015

Helical structures made of superelastic shape memory alloys are widely used as interventional medical devices and active actuators. These structures generally undergo large deformation during expansion or actuation. Currently their behaviour is modelled numerically using the finite element method or obtained through experiments. Analytical tools are absent. In this paper, an analytical approach has been developed for analyzing the mechanical responses of such structures subjected to axial and torsional loads. The simulation results given by the analytical approach have been compared with both numerical and experimental data. Good agreements between the results indicate that the analysis is valid.

• 한국강구조학회 논문집
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• 제27권6호
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• pp.493-501
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• 2015

초탄성 형상기억합금은 상온에서 소성 범위를 초월하여 상당량의 변위를 가하더라도 하중을 제거 후에 별도의 열처리를 가하지 않더라도 원상태로 복원이 가능한 특수한 금속이다. 자동치유가 가능한 형상기억합금의 특유한 재료적인 성질로 인하여 구조물에서 변위가 집중되는 부분에 기존에 주로 사용되는 강재를 대체하여 이러한 특수 합금 재료가 널리 활용되기 시작하였다. 하지만 형상기억합금을 활용한 구조물의 기본적인 설계와 성능 검증을 하기 위해 고등적인 구조해석에 필요한 재료적인 모델의 개발과 연구의 노력이 부족하기 때문에 본 재료를 현장에서 적용하기에는 여전히 많은 제약을 받고 있다. 따라서 본 연구에서는 초탄성 형상기억합금의 거동을 수치해석적인 방법으로 재현이 가능한 구성적인 재료 모델의 소개와 프로그램 코딩에 대하여 다루고자 한다. 또한 본 연구에서 제시된 재료 모델의 타당성을 입증하기 위하여 수치해석적으로 재현된 물리적인 거동을 실험에서 얻어진 데이터에 비교 및 보정 작업도 수행하였다. 아울러 이러한 재료 모델로 구현된 초탄성 형상기억합금의 물리적인 물성치를 구조 해석에 적용하고 정확성을 검증하여 현장 적용의 타당성을 입증하였다.

• Steel and Composite Structures
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• 제23권1호
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• pp.95-105
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• 2017

The use of superelastic shape memory alloys (SMAs) as reinforcements in concrete structures is gradually gaining interest among researchers. Because of different mechanical properties of SMAs compared to the regular steel bars, the use of SMAs as reinforcement in the concrete may change the response of structures under seismic loads. In this study, the effect of SMAs as reinforcement in concrete structures is analytically investigated for 3-, 6- and 8-story reinforced concrete (RC) buildings. For each concrete building, three different reinforcement details are considered: (1) steel reinforcement (Steel) only, (2) SMA bar used in the plastic hinge region of the beams and steel bar in other regions (Steel-SMA), and (3), beams fully reinforced with SMA bar (SMA) and steel bar in other regions. For each case, columns are reinforced with steel bar. Incremental Dynamic Analyses (IDA) are performed using ten different ground motion records to determine the seismic performance of Steel, Steel-SMA and SMA RC buildings. Then fragility curves for each type of RC building by using IDA results for IO, LS and CP performance levels are calculated. Results obtained from the analyses indicate that 3-story frames have approximately the same spectral acceleration corresponding with failure of frames, but in the cases of 6 and 8-story frames, the spectral acceleration is higher in frames equipped with steel reinforcements. Furthermore, the probability of fragility in all frames increases by the building height for all performance levels. Finally, economic evaluation of the three systems are compared.

• 대한기계학회논문집A
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• 제34권8호
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• pp.1083-1089
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• 2010

형상기억합금은 지능형 재료와 구조물에 널리 쓰인다. 큰 힘과 변위를 발생시키는 것이 특징이며 작동기, 소음 및 진동감쇠, 동역학적 튜닝, 형상의 변형 제어 등의 다양한 분야에 응용될 수 있다. 본 논문에 서는 형상기억합금튜브와 초탄성 스프링으로 구성된 형상기억합금 비틀림 작동기를 제안하였고 각각의 거동 특성을 알아보았다. 열전달 해석을 통해 저항열과 히터의 열을 동시에 형상기억합금튜브에 가하면 작동기의 성능을 더 향상시킬 수 있음을 확인하였다. 접촉 해석으로는 실제 작동기의 거동을 시뮬레이션하였고 정상적으로 작동함을 알 수 있었다. 3 차원 형상기억합금의 거동을 표현하기 위해 비선형 구성방정식을 유한요소 법으로 풀고 ABAQUS 의 U-MAT 기능을 이용하여 비선형 해석을 수행하였다.

• Computers and Concrete
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• 제25권4호
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• pp.293-302
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• 2020

Connections play a significant role in strength of structures against earthquake-induced loads. According to the post-seismic reports, connection failure is a cause of overall failure in reinforced concrete (RC) structures. Connection failure results in a sudden increase in inter-story drift, followed by early and progressive failure across the entire structure. This article investigated the cyclic performance and behavioral improvement of shape-memory alloy-based connections (SMA-based connections). The novelty of the present work is focused on the effect of shape memory alloy bars is damage reduction, strain recoverability, and cracking distribution of the stated material in RC moment frames under seismic loads using 3D nonlinear static analyses. The present numerical study was verified using two experimental connections. Then, the performance of connections was studied using 14 models with different reinforcement details on a scale of 3:4. The response parameters under study included moment-rotation, secant stiffness, energy dissipation, strain of bar, and moment-curvature of the connection. The connections were simulated using LS-DYNA environment. The models with longitudinal SMA-based bars, as the main bars, could eliminate residual plastic rotations and thus reduce the demand for post-earthquake structural repairs. The flag-shaped stress-strain curve of SMA-based materials resulted in a very slight residual drift in such connections.

• Smart Structures and Systems
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• 제24권5호
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• pp.641-648
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• 2019

The authors investigate the feasibility of applying a vision-based displacement-measurement technique in the characterization of a SMA damper recently introduced in the literature. The experimental campaign tests a steel frame on a uni-axial shaking table driven by sinusoidal signals in the frequency range from 1Hz to 5Hz. Three different cameras are used to collect the images, namely an industrial camera and two commercial smartphones. The achieved results are compared. The camera showing the better performance is then used to test the same frame after its base isolation. U-shaped, shape-memory-alloy (SMA) elements are installed as dampers at the isolation level. The accelerations of the shaking table and those of the frame basement are measured by accelerometers. A system of markers is glued on these system components, as well as along the U-shaped elements serving as dampers. The different phases of the test are discussed, in the attempt to obtain as much possible information on the behavior of the SMA elements. Several tests were carried out until the thinner U-shaped element went to failure.

• 한국공간구조학회논문집
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• 제18권2호
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• pp.109-119
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• 2018

In this paper a systematic numerical analysis is performed to obtain the energy dissipation and re-centering capacities of diagonal steel braced frames subjected to cyclic loading. This diagonal steel bracing systems are fabricated with super-elastic SMA (Shape Memory Alloy) braces in order to develop a recentering seismic resistance system without residual deformation. The three-dimensional nonlinear finite element models are constructed to investigate the horizontal stiffness, drifts and failure modes of the re-centering bracing systems.