• Smart Structures and Systems
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• 제28권6호
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• pp.745-760
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• 2021

Dynamic buckling of structure is one of the failure modes that needs to be considered since it may result in catastrophic failure of the structure in a short period of time. For a thin fiber-reinforced polymer (FRP) plate under compression, buckling is an inherent hazard which will be intensified by the existence of defects like holes, cracks, and delamination. On the other hand, the growth of the delamination is another prime concern for thin FRP plates. In the current paper, reinforcing the plates against buckling is realized by using SMA wires in the form of stitches. A numerical framework is proposed to simulate the dynamic instability emphasizing the effect of the SMA stitches in suppressing delamination growth. The suggested algorithm is more accurate than the other methods when considering the transformation point of the SMA wires and the modeling of the cohesive zone using simple and yet reliable technique. The computational design of the method by producing the line by line orders leads to a simple algorithm for simulating the super-elastic behavior. The Lagoudas constitutive model of the SMA material is implemented in the form of user material subroutines (VUMAT). The normal bilinear spring model is used to reproduce the cohesive zone behavior. The nonlinear finite element formulation is programmed into FORTRAN using the Newmark-beta numerical time-integration approach. The obtained results are compared with the results obtained by the finite element method using ABAQUS/Explicit solver. The obtained results by the proposed algorithm and those by ABAQUS are in good agreement.

• Structural Engineering and Mechanics
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• 제85권2호
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• pp.179-195
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• 2023

The performance of reinforced concrete (RC) beam specimens strengthened using a newly proposed Side Near Surface Mounted (S-NSM) technology was investigated experimentally in this work. In addition, analytical and nonlinear finite element (FE) modeling was exploited to forecast the performance of RC members reinforced with S-NSM utilizing steel bars. Five (one control and four strengthened) RC beams were evaluated for flexural performance under static loading conditions employing four-point bending loads. Experimental variables comprise different S-NSM reinforcement ratios. The constitutive models were applied for simulating the non-linear material characteristics of used concrete, major, and strengthening reinforcements. The failure load and mode, yield and ultimate strengths, deflection, strain, cracking behavior as well as ductility of the beams were evaluated and discussed. To cope with the flexural behavior of the tested beams, a 3D non-linear FE model was simulated. In parametric investigations, the influence of S-NSM reinforcement, the efficacy of the S-NSM procedure, and the structural response ductility are examined. The experimental, numerical, and analytical outcomes show good agreement. The results revealed a significant increase in yield and ultimate strengths as well as improved failure modes.

• Steel and Composite Structures
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• 제44권2호
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• pp.241-254
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• 2022

The cables in a cable-stayed bridge are critical load-carrying parts. The potential damage to cables should be identified early to prevent disasters. In this study, an efficient deep learning model is proposed for the damage identification of cables using both a multi-layer perceptron (MLP) and a graph neural network (GNN). Datasets are first generated using the practical advanced analysis program (PAAP), which is a robust program for modeling and analyzing bridge structures with low computational costs. The model based on the MLP and GNN can capture complex nonlinear correlations between the vibration characteristics in the input data and the cable system damage in the output data. Multiple hidden layers with an activation function are used in the MLP to expand the original input vector of the limited measurement data to obtain a complete output data vector that preserves sufficient information for constructing the graph in the GNN. Using the gated recurrent unit and set2set model, the GNN maps the formed graph feature to the output cable damage through several updating times and provides the damage results to both the classification and regression outputs. The model is fine-tuned with the original input data using Adam optimization for the final objective function. A case study of an actual cable-stayed bridge was considered to evaluate the model performance. The results demonstrate that the proposed model provides high accuracy (over 90%) in classification and satisfactory correlation coefficients (over 0.98) in regression and is a robust approach to obtain effective identification results with a limited quantity of input data.

• Steel and Composite Structures
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• 제43권2호
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• pp.165-183
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• 2022

Most transportation departments have recognized and developed procedures to address the ever-increasing weights of trucks traveling on bridges in a service today. Transportation agencies also recognize the issues with overheight vehicles' collisions with bridges, but few stakeholders have definitive countermeasures. Bridges are becoming more vulnerable to collisions from overheight vehicles. The exact response under lateral impact force is difficult to predict. In this paper, nonlinear impact analysis shows that the degree of deformation recorded through the modeling of the unprotected vehicle-girder model provides realistic results compared to the observation from the US-61 bridge overheight vehicle impact. The predicted displacements are 0.229 m, 0.161 m, and 0.271 m in the girder bottom flange (lateral), bottom flange (vertical), and web (lateral) deformations, respectively, due to a truck traveling at 112.65 km/h. With such large deformations, the integrity of an impacted bridge becomes jeopardized, which in most cases requires closing the bridge for safety reasons and a need for rehabilitation. We proposed different sacrificial cushion systems to dissipate the energy of an overheight vehicle impact. The goal was to design and tune a suitable energy absorbing system that can protect the bridge and possibly reduce stresses in the overheight vehicle, minimizing the consequences of an impact. A material representing a Sorbothane high impact rubber was chosen and modeled in ANSYS. Out of three sacrificial schemes, a sandwich system is the best in protecting both the bridge and the overheight vehicle. The mitigation system reduced the lateral deflection in the bottom flange by 89%. The system decreased the stresses in the bridge girder and the top portion of the vehicle by 82% and 25%, respectively. The results reveal the capability of the proposed sacrificial system as an effective mitigation system.

• Steel and Composite Structures
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• 제47권2호
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• pp.167-184
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• 2023

In this study, a new recentering friction device (RFD) to retrofit steel moment frame structures is introduced. The device provides both self-centering and energy dissipation capabilities for the retrofitted structure. A hybrid performance-based seismic design procedure considering multiple limit states is proposed for designing the device and the retrofitted structure. The design of the RFD is achieved by modifying the conventional performance-based seismic design (PBSD) procedure using computational intelligence techniques, namely, genetic algorithm (GA) and artificial neural network (ANN). Numerous nonlinear time-history response analyses (NLTHAs) are conducted on multi-degree of freedom (MDOF) and single-degree of freedom (SDOF) systems to train and validate the ANN to achieve high prediction accuracy. The proposed procedure and the new RFD are assessed using 2D and 3D models globally and locally. Globally, the effectiveness of the proposed device is assessed by conducting NLTHAs to check the maximum inter-story drift ratio (MIDR). Seismic fragilities of the retrofitted models are investigated by constructing fragility curves of the models for different limit states. After that, seismic life cycle cost (LCC) is estimated for the models with and without the retrofit. Locally, the stress concentration at the contact point of the RFD and the existing steel frame is checked being within acceptable limits using finite element modeling (FEM). The RFD showed its effectiveness in minimizing MIDR and eliminating residual drift for low to mid-rise steel frames models tested. GA and ANN proved to be crucial integrated parts in the modified PBSD to achieve the required seismic performance at different limit states with reasonable computational cost. ANN showed a very high prediction accuracy for transformation between MDOF and SDOF systems. Also, the proposed retrofit showed its efficiency in enhancing the seismic fragility and reducing the LCC significantly compared to the un-retrofitted models.

• 한국시뮬레이션학회논문지
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• 제19권4호
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• pp.199-208
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• 2010

모델링 시뮬레이션에서 전술객체의 위치는 시공간 위치 정보(Time, Space and Position Information, TSPI)로 표현된다. 미 국방성에서 시험, 훈련, 평가 시스템을 연동하기 위해 개발한 TENA(Test and Training Enabling Architecture)의 TSPI 객체 모델을 참고하여 시공간 위치 정보의 형태 및 정보 기록 소요를 도출하였다. 전술 데이터 링크(Tactical Data Link, TDL) 중 가장 정교한 링크 16(Link-16)의 PPLI(Precise Participant Location and Identification) 메시지를 통해 시공간 위치 정보의 교환 방식에 대해 알아보았다. 객체 위치 모의 및 추적을 위한 필터링 알고리즘으로 선형 시스템을 위한 칼만 필터 및 비선형 시스템을 위한 확장형 칼만 필터와 unscented 칼만 필터를 소개한다. 운동 방정식을 이용하여 탄도 미사일의 궤적을 모델링 한 후에, unscented 칼만 필터로 추정한 탄도 미사일의 궤적 추적 성능을 시뮬레이션 하였다.

• 응용통계연구
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• 제36권4호
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• pp.295-307
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• 2023

HAR 모형은 간단한 선형 모형으로 실현 변동성의 장기기억성을 비교적 잘 설명할 수 있어 널리 쓰이고 있다. 하지만, 실현 변동성은 조건부 이분산성, 레버리지 효과, 변동성 집중 등과 같은 복잡한 특징을 보이고 있기에 단순 HAR 모형을 확장할 필요가 있다. 따라서 본 연구는 조건부 이분산성을 설명하는 GARCH 모형에 임계값에 따라 계수가 달라지는 비선형 모형인 임계 HAR 모형(THAR-GARCH)을 제안하고 그 추정 방법 및 예측 성능에 대해서 살펴보고자 한다. 보다 구체적으로 오차항의 등분산 가정을 벗어났기 때문에 모형의 계수를 추정하기 위해서 반복적인 가중최소제곱추정법을 제안하고 모의실험을 통해 일치성을 보였다. 또한 전세계 21개의 주요 주가 지수의 실현 변동성에 대한 예측 오차를 비교함으로써 제안한 GARCH 오차를 가지는 임계 HAR 모형이 일반적으로 더 우수한 예측력을 보임을 확인하였다.

• 한국지반공학회논문집
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• 제24권1호
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• pp.61-70
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• 2008

지표면 침하량, 침하 기울기 그리고 터널주변의 지반 변위에 대한 관리와 예측은 도심지 저토피 터널의 설계와 시공에서 주요한 인자가 된다. 저토피 터널에서의 굴착에 따른 변형 해석은 터널 측벽부에서 지표부까지 발달하는 전단대의 변형특성을 파악하는 것이 중요하다. 본 연구는 2차원 실내 터널 모형실험과 전단 탄성계수 및 강도 정수의 저하를 고려한 변형률 연화모델 해석을 통하여 미고결 저토피 터널에서의 굴착으로 인한 변형 거동 특성을 규명해 보았다. 변형률 연화모델을 이용한 수치해석과 모형 터널 실험과의 비교에서 지표면 침하, 천단침하 그리고 전단대의 발달형태에서 부합되는 결과가 나타났다. 본 연구에서 변형률 연화모델은 저토피 터널의 비선형 변형해석에 대하여 적용성이 있음을 알 수 있었다.

• 대한토목학회논문집
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• 제43권3호
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• pp.287-295
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• 2023

교량은 지진에 의해 붕괴가 일어나면 많은 수의 인명피해와 재산피해가 발생할 수 있어 정확한 지진거동 예측과 대비가 필요하다. 특히, 교각은 교량의 지진거동에 있어서 지배적인 역할을 한다. 또한, 교각의 겹침이음 길이 부족과 같은 설계적인 문제가 있다면 지진에 대한 위험성이 더욱 증대하게 된다. 본 연구에서는 교각에서 겹침이음 특성을 분석하기 위해, 겹침이음 길이가 부족한 교각의 수치해석 모델을 정의하고 실험데이터를 통해 검증하였다. 제시된 교각 모델을 일반적으로 사용되는 RC 슬래브 교량에 적용하였다. 교각의 비선형 정적해석을 수행하여 겹침이음에 따른 성능점 변화를 평가하였다. 또한, 지진취약도 곡선을 산정하여 교각의 겹침이음 길이에 따른 지진취약도 비교분석을 수행하였다.

• Earthquakes and Structures
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• 제22권5호
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• pp.503-515
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• 2022

This paper presents the development of seismic fragility curves for a precast reinforced concrete bridge instrumented with a structural health monitoring (SHM) system. The bridge is located near an active seismic fault in the Dominican Republic (DR) and provides the only access to several local communities in the aftermath of a potential damaging earthquake; moreover, the sample bridge was designed with outdated building codes and uses structural detailing not adequate for structures in seismic regions. The bridge was instrumented with an SHM system to extract information about its state of structural integrity and estimate its seismic performance. The data obtained from the SHM system is integrated with structural models to develop a set of fragility curves to be used as a quantitative measure of the expected damage; the fragility curves provide an estimate of the probability that the structure will exceed different damage limit states as a function of an earthquake intensity measure. To obtain the fragility curves a digital twin of the bridge is developed combining a computational finite element model and the information extracted from the SHM system. The digital twin is used as a response prediction tool that minimizes modeling uncertainty, significantly improving the predicting capability of the model and the accuracy of the fragility curves. The digital twin was used to perform a nonlinear incremental dynamic analysis (IDA) with selected ground motions that are consistent with the seismic fault and site characteristics. The fragility curves show that for the maximum expected acceleration (with a 2% probability of exceedance in 50 years) the structure has a 62% probability of undergoing extensive damage. This is the first study presenting fragility curves for civil infrastructure in the DR and the proposed methodology can be extended to other structures to support disaster mitigation and post-disaster decision-making strategies.