• Steel and Composite Structures
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• 제28권6호
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• pp.719-734
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• 2018

Prior to the introduction of modern seismic guidelines, it was a common practice to provide straight bar anchorage for beam bottom reinforcement of gravity load designed building. Exterior joints with straight bar anchorages for beam bottom reinforcements are susceptible to sudden anchorage failure under load reversals and hence require systematic seismic upgradation. Hence in the present study, an attempt is made to upgrade exterior beam-column sub-assemblage of a three storied gravity load designed (GLD) building with single steel haunch. Analytical formulations are presented for evaluating the haunch forces in single steel haunch retrofit. Influence of parameters that affect the efficacy and effectiveness of the single haunch retrofit are also discussed. The effectiveness of the single haunch retrofit for enhancing seismic performance of GLD beam-column specimen is evaluated through experimental investigation under reverse cyclic loading. The single steel haunch retrofit had succeeded in preventing the anchorage failure of beam bottom bars of GLD specimen, delaying the joint shear damage and partially directing the damage towards the beam. A remarkable improvement in the load carrying capacity of the upgraded GLD beam-column sub-assemblage is observed. Further, a tremendous improvement in the energy dissipation of about 2.63 times that of GLD specimen is observed in the case of upgraded GLD specimen. The study also underlines the efficacy of single steel haunch retrofit for seismic upgradation of deficient GLD structures.

• 한국구조물진단유지관리공학회 논문집
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• 제8권4호
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• pp.239-246
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• 2004

충격하중에 대한 양단 고정보의 거동을 강 소성 모델을 이용하여 파악 하였다. 또한 손상을 발생시키는 정 역학적 붕괴하중과 이상임펄스에 대한 하중최대치 비와 임펄스 비를 이용하여 손상곡선을 작성하였다. 작성된 손상곡선으로부터 충격하중의 하중 최대치와 임펄스는 구조물의 안전에 중요 변수가 됨을 보였으며 또한 하중최대치 비와 임펄스 비로 작성된 손상곡선은 하중작용시간과 하중의 형태 그리고 구조물의 동적 특성이 함께 고려된 기준으로, 등가 동하중에 초점을 맞추어 일괄적으로 구조물의 안전성을 판단할 수 있는 방법이다.

• Earthquakes and Structures
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• 제11권5호
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• pp.841-859
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• 2016

Bridge bearings are important connection elements between bridge superstructures and substructures, whose health states directly affect the performance of the bridges. This paper systematacially presents a new method to identify the bridge bearing damage based on the neural network theory. Firstly, based on the analysis of different damage types, a description of the bearing damage is introduced, and a uniform description for all the damage types is given. Then, the feasibility and sensitivity of identifying the bearing damage with bridge vibration modes are investigated. After that, a Radial Basis Function Neural Network (RBFNN) is built, whose input and output are the beam modal information and the damage information, respectively. Finally, trained by plenty of data samples formed by the numerical method, the network is employed to identify the bearing damage. Results show that the bridge bearing damage can be clearly reflected by the modal information of the bridge beam, which validates the effectiveness of the proposed method.

• 대한기계학회논문집A
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• 제24권2호
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• pp.518-525
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• 2000

This paper presents a new wavelet-based structural diagnostic technique. A continuous Gabor wavelet transform is shown to a very effective method in detecting damage in a beam. The beam is excited by a broad-band excitation force. For satisfactory results, the selection of an optimal wavelet is very important though the wavelet transform outperforms existing techniques such as the Wigner-Ville distribution. A specific example is given in a solid circular cylinder with a small defect.

• 한국해양공학회지
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• 제9권1호
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• pp.22-35
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• 1995

A simplified numerical procedure have proposed to trace the dynamic behaviour of offshore tubulars subjected to lateral collision impacts. The local denting and overall bending deformation of the struck tubular are represented by a non-linear spring and an elastic visco-plastic beam respectively. In this method a temporal finite difference method and a spacial finite element method are employed. Using this method various boundary conditions are able to considered and their effects on the extent of damage can be quantified. The extent of damage due to collision can be obtained as results of the dynamic analysis. The predictions using the proposed method have been correlated with existing test results and then the reliability of the procedure has been substantiated. The characteristics of the dynamic response of tubulars under lateral impacts are compared for simply supported roller and fixed end conditions and their effects on the extent of damage are specfied.

• Computers and Concrete
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• 제3권5호
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• pp.285-299
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• 2006

The free vibration of stiffened and damaged coupled shear walls is investigated using the mixed finite element method. The anisotropic damage model is adopted to describe the damage extent of the reinforced concrete shear wall element. The internal energy of a locally damaged shear wall element is derived. Polynomial shape functions established by Kwan are used to present the component of displacements vector on each point within the wall element. The principle of virtual work is employed to deduce the stiffness matrix of a damaged shear wall element. The stiffened system is reinforced by an additional stiffening beam at some level of the structure. This induces additional axial forces, and thus reduces the bending moments in the walls and the lateral deflection, and increases the natural frequencies. The effects of the damage extent and the stiffening beam on the free vibration characteristics of the structure are studied. The optimal location of the stiffening beam for increasing as far as possible the first natural frequency of vibration is presented.

• Nuclear Engineering and Technology
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• 제56권8호
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• pp.3129-3138
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• 2024

The in-situ TEM irradiation experiments of zirconium alloy were conducted at 573 K, 673 K, and 773 K utilizing a 400 keV Kr + single beam and a 400 keV Kr+ and 30 keV He + dual beam. The results show that a large number of dislocation loops have been characterized in the matrix of the zirconium alloy under irradiation. With increasing the irradiation damage dose, some dislocation loops have reacted with one another to form a larger dislocation loop, which has finally formed dislocation lines or other defect structures. In zirconium alloys irradiated with Kr + single beam and Kr+ and He + dual-beam radiation, the proportion of <a> type dislocation loops with different Burgers vectors is essentially the same at low damage doses, but the proportion of interstitial type dislocation loops with the same Burgers vectors is obviously different. The amorphization of the second phase and the dissolution of the small-sized second phase were also pointed out. With the increase in temperature, the density of the dislocation loop in zirconium alloy gradually decreases, and the size of dislocation loop first increases and then decreases. Kr+ and He + dual beam irradiation increases the size of dislocation loops but decreases their density as compared with Kr + single beam irradiation.

• 한국강구조학회 논문집
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• 제22권5호
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• pp.477-485
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• 2010

다양한 모니터링 센서는 구조물의 손상측정과 예측에 많이 사용되고 있다. 광섬유센서, 압전소자(PZT) 센서, MEMS(Micro Electro Mechanical System)센서 등의 스마트 센서는 기존 센서를 대체하여 많은 분야에서 사용되고 있다. 본 논문에서는 PZT센서를 실험체에 부착한 후 충격하중을 가하여 PZT센서의 출력 전압의 특성을 이용하여 실험체의 손상을 예측하고자 하였다. PZT센서를 이용한 보 이음부의 손상실험에서는 $H-400{\times}200{\times}8{\times}13$ 철골을 이용하여 단순보를 제작하고 중앙에 볼트 이음을 하였으며, PZT센서의 민감도 측정을 위해 기존 가속도계의 가속도값과 PZT센서의 전압값의 FFT 결과를 비교하였다. 또한 이음부의 볼트풀림을 이용하여 단순보의 손상을 가정하고 손상계측실험도 병행하였다. 철골 플레이트 보의 손상계측 실험에서는 $PL600{\times}65{\times}5.8$로 단순보 실험체를 제작하여 세 곳에 손상을 주어 충격하중 실험을 하였다. 손상의 정도는 쇠톱을 이용하여 보 단면의 양쪽에 6~42 mm로 절단하였다. FFT를 사용하여 손상의 유무에 따른 고유진동수의 비(${\omega}_c/{\omega}$)를 구하여 손상을 파악하였고 모드에 따른 손상의 위치와 정도를 파악하였다.

• Structural Engineering and Mechanics
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• 제39권1호
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• pp.77-91
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• 2011

A simply structural damage detection software is developed to identification damage in beams. According to linear fracture mechanics theory, the localized additional flexibility in damage vicinity can be represented by a lumped parameter element. The damaged beam is modeled by wavelet-based elements to gain the first three frequencies precisely. The first three frequencies influencing functions of damage location and depth are approximated by means of surface-fitting techniques to gain damage detection database of forward problem. Then the first three measured natural frequencies are employed as inputs to solve inverse problem and the intersection of the three frequencies contour lines predict the damage location and depth. The DLL (Dynamic Linkable Library) file of damage detection method is coded by C++ and the corresponding interface of software is coded by virtual instrument software LabVIEW. Finally, the software is tested on beams and shafts in engineering. It is shown that the presented software can be used in actual engineering structures.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.367-374
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• 2005

The use of system identification approaches for damage detection has been expanded in recent years. Soft computing techniques such as neural networks have been utilized increasingly. Damage assessment using neural networks is presented in this study. Data set for training neural networks are acceleration response of simple beam under the various damage states ,which are the inputs. The outputs are the damage locations and extents. Not only the trained damages but also untrained damages are. detected accuratelyintheassessmentstage.