• Structural Engineering and Mechanics
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• 제74권2호
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• pp.157-173
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• 2020

In the finite element modelling of long-span cable-stayed bridges, there are a lot of uncertainties brought about by the complex structural configuration, material behaviour, boundary conditions, structural connections, etc. In order to reduce the discrepancies between the theoretical finite element model and the actual static and dynamic behaviour, updating is indispensable after establishment of the finite element model to provide a reliable baseline version for further analysis. Traditional sensitivity-based updating methods cannot support updating based on static and dynamic measurement data at the same time. The finite element model is required in every optimization iteration which limits the efficiency greatly. A convenient but accurate Kriging surrogate model for updating of the finite element model of cable-stayed bridge is proposed. First, a simple cable-stayed bridge is used to verify the method and the updating results of Kriging model are compared with those using the response surface model. Results show that Kriging model has higher accuracy than the response surface model. Then the method is utilized to update the model of a long-span cable-stayed bridge in Hong Kong. The natural frequencies are extracted using various methods from the ambient data collected by the Wind and Structural Health Monitoring System installed on the bridge. The maximum deflection records at two specific locations in the load test form the updating objective function. Finally, the fatigue lives of the structure at two cross sections are calculated with the finite element models before and after updating considering the mean stress effect. Results are compared with those calculated from the strain gauge data for verification.

• Geomechanics and Engineering
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• 제30권2호
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• pp.139-151
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• 2022

The mechanical properties of expansive soil are very unstable, highly sensitive to water, and thus easy to cause major engineering accidents. In this paper, the expansive soil foundation pit project of the East Huada Square in the eastern suburb of Chengdu was studied, the moisture content of the expansive soil was considered as an important factor that affecting the mechanics properties of expansive soil and the stability of the non-equal-length double-row piles in the foundation pit support. Three groups of direct shear tests were carried out and the quantitative relationships between the moisture content and shear strength τ, cohesion c, internal friction angle φ were obtained. The effect of cohesion and internal friction angle on the maximum displacement and the maximum bending moment of piles were analyzed by the finite element software MIDAS/GTS (Geotechnical and Tunnel Analysis System). Results show that the higher the moisture content, the smaller the matrix suction, and the smaller the shear strength; the cohesion and the internal friction angle are exponentially related to the moisture content, and both are negatively correlated. The maximum displacement and the maximum bending moment of the non-equal length double-row piles decrease with the increase of the cohesion and the internal friction angle. When the cohesion is greater than 33 kPa or the internal friction angle is greater than 25.5°, the maximum displacement and maximum bending moment of the piles are relatively small, however, once crossing the points (the corresponding moisture content value is 24.4%), the maximum displacement and the maximum bending moment will increase significantly. Therefore, in order to ensure the stability and safety of the foundation pit support structure of the East Huada Square, the moisture content of the expansive soil should not exceed 24.4%.

• 콘크리트학회논문집
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• 제17권1호
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• pp.43-49
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• 2005

수화열에 의한 콘크리트 구조물 내의 최대온도에는 재료의 열특성, 초기조건, 거푸집, 외부노출면 등이 영향을 미친다. 일반적인 콘크리트 구조물에는 콘크리트와는 전혀 다른 열특성을 갖는 철근이 보강되고 있으나 보통은 철근의 영향을 무시하고 수화열에 관한 해석을 실시하고 있다. 본 연구에서는 보강철근을 직접 고려하여 수화열의 분포 및 온도응력에 미치는 영향에 대해서 유한요소 해석연구를 실시하였다. 해석결과 철근이 구조물 내의 빠른 열 확산과 외부로의 열랑을 방출하는 효과에 기여하고 있음을 확인하였고, 콘크리트 표면의 인장응력을 감소시키는 것 또한 확인하였다. 따라서 정확한 수화열 해석을 위해서는 철근을 고려한 해석이 타당하며, 이를 통해 온도균열 감소와 온도철근량 감소효과를 기대할 수 있다.

• Steel and Composite Structures
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• 제30권4호
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• pp.365-382
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• 2019

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.

• 대한의용생체공학회:의공학회지
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• 제43권5호
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• pp.319-330
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• 2022

In this study, the optimal driving frequency was derived through finite element analysis (FEA) to optimize the developed piezoelectric ultrasonic medical devices(PUMD) for bone surgery. The core of the PUMD is the piezoelectric ceramic (PZT), which is a vibrator that generates vibration energy. The piezoelectric ceramic shows the maximum current value with respect to the input voltage at the resonance frequency, which generates the maximum mechanical vibration. In the past, various studies have been conducted related to the analysis of PUMD, but most of the research so far has been limited to free vibration analysis. However, in order to derive the accurate resonant frequency, the initial stress generated by bolt tightening in the bolt-clamped Langevin type transducer (BLT) must be considered. In this study, after designing a PUMD, the driving performance according to the bolt tightening value was analyzed through FEA, and this was experimentally verified. First, the resonance mode and frequency response were confirmed through modal and harmonic analysis at 20-40 kHz, which is known as the optimal driving frequency band of PUMD for bone surgery. In addition, the design of the PUMD was confirmed by checking the mechanical behavior of the tip and the piezoelectric ceramic at the resonant frequency. Consequentially, the characteristic evaluation was performed, and it was confirmed that the resonant frequency result derived through the FEA was reasonable. Through this study, we presented a more rational FEA method than before for BLT transducers. We expect that this will shorten the time and cost of developing a PUMD, and will enable the development of more stable and high-quality products.

• 한국해안·해양공학회논문집
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• 제28권2호
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• pp.92-100
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• 2016

응력집중계수를 이용하여 해상풍력발전기 트라이포드 지지구조물에 대한 신뢰성 해석을 수행하였다. 파랑과 풍하중의 극치분포함수는 POT방법을 사용하여 동적응답을 분석함으로써 추정되었다. 일계신뢰도법을 사용하여 신뢰성해석을 수행하였으며, 한계상태함수는 지지구조물의 이음부에서 발생하는 응력을 기반으로 정의하였다. 보 요소에서 계산된 응력에 응력집중계수를 곱하는 방법과 판 요소를 사용하여 계산하는 두 가지 방법으로 최대응력을 계산하여 신뢰성 해석을 수행하고 결과를 비교 분석하였다.

• Earthquakes and Structures
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• 제17권6호
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• pp.533-543
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• 2019

This paper presents a study on the behavior of an RC bridge under near-field and far-field ground motions. For this purpose, a dynamic nonlinear finite element time history analysis has been conducted. The near-field and far-field records are chosen pairwise from the same events which are fits to the seismic design of the bridge. In order to perform an accurate seismic evaluation, the model has been analyzed under two vertical and horizontal components of ground motions. Parameters of relative displacement, residual displacement, and maximum plastic strain have been considered and compared in terms of near-field and far-field ground motions. In the following, in order to decrease the undesirable effects of near-field ground motions, a viscous damper is suggested and its effects have been studied. In this case, the results show that the near-field ground motions increase maximum relative and residual displacement respectively up to three and twice times. Significant seismic improvements were achieved by using viscous dampers on the bridge model. Somehow under the considered near-field ground motion, parameters of residual and relative displacement decrease dramatically even less than the model without damper under the far-field record of the same ground motion.

• 한국재료학회지
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• 제9권2호
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• pp.181-187
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• 1999

In this study, the effect of residual stress on mechanical strength was investigated with 1 kind of whiteware body and 4 kinds of glazes which are produced in succeeding ceramic art place. Using dipping method, the body was coated for different times in order to manipulate the coating thickness and sintered in the different temperatures ($1200^{\circ}C$, $1250^{\circ}C$, $1300^{\circ}C$, $1350^{\circ}C$) for two thus hours. The sintered bodies were characterized by XRD, EPMA, FEM and UTM in order to study the forming of reaction layer between body and glazes, residual stresses and the effects of residual stresses on mechanical strength of pottery. At $1300{\circ}C$, we obtained maximum density and mechanical strength. By the finite element method, the residual stresses in surface of body were minimum in specific thickness of glazes and the mechanical strength of body in that thickness of glazes showed maximum when the firing temperature was settled.

• Structural Engineering and Mechanics
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• 제65권5호
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• pp.587-600
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• 2018

Infill panel is the first element of a building subjected to blast loading activating its out-of-plane behavior. If the infill panel does not have enough ductility against the loading, it breaks and gets damaged before load transfer and energy dissipation. As steel infill panel has appropriate ductility before fracture, it can be used as an alternative to typical infill panels under blast loading. Also, it plays a pivotal role in maintaining sensitive main parts against blast loading. Concerning enough ductility of the infill panel out-of-plane behavior, the impact force enters the horizontal diaphragm and is distributed among the lateral elements. This article investigates the behavior of steel infill panels with different thicknesses and stiffeners. In order to precisely study steel infill panels, different ranges of blast loading are used and maximum displacement of steel infill under such various blast loading is studied. In this research, finite element analyses including geometric and material nonlinearities are used for optimization of the steel plate thickness and stiffener arrangement to obtain more efficient design for its better out-of-plane behavior. The results indicate that this type of infill with out-of-plane behavior shows a proper ductility especially in severe blast loadings. In the blasts with high intensity, maximum displacement of infill is more sensitive to change in the thickness of plate rather the change in number of stiffeners such that increasing the number of stiffeners and the plate thickness of infill panel would decrease energy dissipation by 20 and 77% respectively. The ductile behavior of steel infill panels shows that using infill panels with less thickness has more effect on energy dissipation. According to this study, the infill panel with 5 mm thickness works better if the criterion of steel infill panel design is the reduction of transmitted impulse to main structure. For example in steel infill panels with 5 stiffeners and blast loading with the reflected pressure of 375 kPa and duration of 50 milliseconds, the transmitted impulse has decreased from 41206 N.Sec in 20 mm infill to 37898 N.Sec in 5 mm infill panel.

• Geomechanics and Engineering
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• 제23권5호
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• pp.455-466
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• 2020

This paper presents analysis of the interaction between tunnel and Qanat with a particular interest for the optimization of Qanat shape using the discrete element code, PFC2D, and the results will be compared with the FEM results of PLAXIS2D. For these concerns, using software PFC2D based on Discrete Element Method (DEM), a model with dimension of 100m ^⁎ 100 m was prepared. A circular tunnel with dimension of 9 m was situated 20 m below the ground surface. Also one Qanat was situated perpendicularly above the tunnel roof. Distance between Qanat center and ground surface was 8 m. Five different shapes for Qanat were selected i.e., square, semi-circular, vertical ellipse, circular and horizontal ellipse. Confining pressure of 5 MPa was applied to the model. The vertical displacement of balls situated in ground surface was picked up to measure the ground subsidence. Also two measuring circles were situated at the tunnel roof and at the Qanat roof to check the vertical displacements. The properties of the alluvial soil of Tehran city are: γ_dry=19 (KN/㎥), E= 750 (kg/㎠), ν=0.35, c=0.3(kg/㎠), φ=34°. In order to validate the DEM results, a comparison between the numerical results (obtained in this study) and analytical and field monitoring have been done. The PFC2D results are compared with the FEM results. The results shows that when Qanat has rectangular shape, the tensile stress concentration at the Qanat corners has maximum value while it has minimum value for vertical ellipse shape. The ground subsidence for Qanat rectangular shape has maximum value while it has minimum value for ellipse shape of Qanat. The vertical displacements at the tunnel roof for Qanat rectangular shape has maximum value while it has minimum value for ellipse shape of Qanat. Historical shape of Qante approved the finding of this research.