• 한국철도학회논문집
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• 제17권1호
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• pp.52-58
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• 2014

노반 성토체에서 발생하는 소성 변형은 콘크리트 궤도의 안정성과 유지보수에 영향을 미친다. 철도 노반에서의 장기적인 소성 변형은 주로 반복적인 열차 통과로 발생하는 누적된 비탄성적 변형률에 의해 발생한다. 누적 소성 변형의 예측은 궤도의 유지보수와 열차의 안전한 운영을 위해서 중요하다. 본 연구에서는 서로 다른 강화노반 두께를 가진 철도노반에서 발생하는 연직 변위를 계산하였다. 누적 소성 변형률을 계산하기 위한 멱함수의 상수는 삼축 실험과 실대형 재하 실험의 결과로부터 구하였다. 표준 노반 단면에 대한 3차원 유한요소해석 결과로부터 강화노반의 두께를 선정하는 가이드라인을 제시하였다.

• Computers and Concrete
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• 제25권1호
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• pp.67-73
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• 2020

Traditionally used analytical approach to predict the fatigue failure of reinforced concrete (RC) structure is generally conservative and has certain limitations. The nonlinear finite element method (FEM) offers less expensive solution for fatigue analysis with sufficient accuracy. However, the conventional implicit dynamic analysis is very expensive for high level computation. Whereas, an explicit dynamic analysis approach offers a computationally operative modelling to predict true responses of a structural element under periodic loading and might be perfectly matched to accomplish long life fatigue computations. Hence, this study simulates the fatigue behaviour of RC beams with finite element (FE) assemblage presenting a simplified explicit dynamic numerical solution to show computer aided fatigue behaviour of RC beam. A commercial FEM package, ABAQUS has been chosen for this complex modelling. The concrete has been modelled as a 8-node solid element providing competent compression hardening and tension stiffening. The steel reinforcements are simulated as two-node truss elements comprising elasto-plastic stress-strain behaviour. All the possible nonlinearities are duly incorporated. Time domain analysis has been adopted through an automatic Newmark-β time incremental technique. The program consists of twelve RC beams to visualize the real behaviour during fatigue process and to obtain the reliability of the study. Both the numerical and experimental results indicate a redistribution of stresses along the time and damage accumulation of beam which severely affect the serviceability and ultimate capacity of RC beam. The output of the FEM analysis demonstrates good match with the experimental consequences which affirm the efficacy of the computer aided model. The controlled fatigue damage evolution at service fatigue load limits makes the FE model an efficient tool in predicting high cycle fatigue behaviour of RC structures.

• 한국산학기술학회논문지
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• 제20권2호
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• pp.7-13
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• 2019

본 연구에서는 이종경량재료의 마찰교반용접을 모사할 수 있는 유한요소 해석모델을 개발하고, 이를 통해 기초분석과 실용적 적용 가능성에 대해 고찰하였다. Coupled Eulerian Lagrangian 에 기반한 유한요소모델을 구성하였으며, 해석 모델은 외연적 시간적분을 이용하여 열-온도, 변위-응력 물리계로 이루어진 다중 물리계를 복합적으로 계산하며, 용접툴 표면과 피용접 재료 간 마찰, 극심한 소성변형으로 인한 열에너지 발생, 그리고, 밑면을 통한 열에너지 소산 등 열발생원과 열전달 메카니즘이 모두 고려되었다. Al6061T6와 AZ61 판재의 맞대기용접을 고려하였으며, 주요 용접변수인 용접 속도와 용접툴 회전속도를 변화시킨 세 가지 조건에 대해 해석을 실시하였다. 각 해석은 피용접물의 온도분포, 결함의 분포, 소성변형률 분포가 출력이 가능하였다. 구축한 모델을 이용한 해석 결과 알루미늄보다는 마그네슘부에서 더 높은 온도가 발생하였으며, 회전속도가 커질수록 최대 온도가 증가하기보다는 알루미늄쪽으로 높은 온도가 분산되어 가는 경향을 보였다. 또한, 회전속도가 커질수록 피용접물 재료가 위로 올라오는 플래시 결함의 경향 예측이 가능하였으나, 툴 주변 결함 형성예측은 메시가 세밀하지 못하여 정확한 결과를 산출하기에는 부족하다고 볼 수 있다. 본 모델은 마찰교반용접 중 발생 가능한 여러 물리계의 여러 물리적 현상을 실제에 가깝게 반영하고 있으며, 실험적으로 밝히기 어려운 기초 분석에 응용될 수 있으나, 1달이 넘는 해석소요시간을 감안하면 실용적으로 최적의 용접조건 도출에 응용되기는 어렵다고 판단된다.

• 한국도로학회논문집
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• 제9권1호
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• pp.1-15
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• 2007

본 연구에서는 시험도로 계측 자료와 유한요소해석 기법을 사용한 구조해석 결과를 비교하여 포장 전반에 걸친 거동을 분석할 수 있는 기반을 마련하는데 목적이 있다. 시험도로와 같이 다양한 하중 재하시험을 통하여 얻은 계측 결과와 유한요소 해석 결과를 비교하여 타당성을 입증할 경우, 향후 포장의 구조해석 및 설계 과정에서 유한요소해석 기법의 다양한 응용이 가능하다. 본 연구에서는 슬래브, 린, 보조기층, 길어깨, 다웰 및 타이바가 모두 포함된 3차원 콘크리트 해석 모형을 개발하여 동일 조건의 시험도로 계측값과 비교분석을 실시하였다. 또한, 다양한 온도 조건에서 구조해석을 수행하여 컬링에 의한 슬래브 거동을 파악하였다. 콘크리트포장에서 얻어진 변형률계의 계측 결과들과 유한요소해석에서 얻어진 예측 변형률사이의 오차를 줄이기 위하여 분석 방식은 실제 상황과 유사하게 모사하도록 구현하였으며, 가능하면 변수들을 실제 상황과 일치하도록 변화시켰다. 온도 변화 등 여러 가지 상황을 현장과 동일하게 만든 결과, 유한요소해석에서 예측한 값들이 현장에서 얻은 계측값에 유사하게 접근하는 것을 확인할 수 있었다. 그러나 린층에서는 해석값이 다소 과다하게 발생하여 추가 연구가 필요할 것으로 판단된다. 또한 실제 컬링을 모사한 구조해석 결과 계측값과 거의 동일하게 나타났으며 영구컬링의 존재도 확인할 수 있었다.

• Earthquakes and Structures
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• 제12권5호
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• pp.501-513
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• 2017

To investigate the seismic performance of Y-shaped eccentrically braced frames fabricated with high-strength steel (Y-HSS-EBFs), a shake table test of a 1:2 scaled three-story Y-HSS-EBF specimen was performed. The input wave for the shake table test was generated by the ground motions of El Centro, Taft, and Lanzhou waves. The dynamic properties, acceleration, displacement, and strain responses were obtained from the test specimen and compared with previous test results. In addition, a finite element model of the test specimen was established using the SAP2000 software. Results from the numerical analysis were compared with the test specimen results. During the shake table test, the specimen exhibited sufficient overall structural stiffness and safety but suffered some localized damage. The lateral stiffness of the structure degenerated during the high seismic intensity earthquake. The maximum elastic and elastoplastic interstory drift of the test specimen for different peak ground accelerations were 1/872 and 1/71, respectively. During the high seismic intensity earthquake, the links of the test specimen entered the plastic stage to dissipate the earthquake energy, while other structural members remained in the elastic stage. The Y-HSS-EBF is a safe, dual system with reliable seismic performance. The numerical analysis results were in useful agreement with the test results. This finding indicated that the finite element model in SAP2000 provided a very accurate prediction of the Y-HSS-EBF structure's behavior during the seismic loadings.

• 한국공작기계학회논문집
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• 제16권5호
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• pp.134-139
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• 2007

This paper presents a computer-based analysis on the thermal shock characteristics of Pb-free solder joints and UBM in flip chip assemblies. Among four types of popular UBM systems, TiW/Cu system with 95.5Sn-3.9Ag-0.6Cu solder joints was chosen for simulation. A simple 3D finite element model was first created only including silicon die, mixture between underfill and solder joints, and substrate. The displacements due to CTE mismatch between silicon die and substrate was then obtained through FE analysis. Finally, the obtained displacements were applied as mechanical loads to the whole 2D FE model and the characteristics of flip chip assemblies were analyzed. In addition, based on the hyperbolic sine law, the accumulated creep strain of Pb-free solder joints was calculated to predict the fatigue life of flip chip assemblies under thermal shock environments. The proposed method for fatigue life prediction will be evaluated through the cross check of the test results in the future work.

• Structural Engineering and Mechanics
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• 제88권1호
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• pp.95-107
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• 2023

In this study, circular thin-walled reinforced high strength concrete-filled steel tube (RHSCFST) stub columns with various tube thicknesses (i.e., 1.8, 2.5 and 3.0mm) and reinforcement ratios (i.e., 0, 1.6%, 2.4% and 3.2%) were fabricated to explore the influence of these factors on the axial compressive behavior of RHSCFST. The obtained test results show that the failure mode of RHSCFST transforms from outward buckling and tearing failure to drum failure with the increasing tube thickness. With the tube thickness and reinforcement ratio increased, the ultimate load-carrying capacity, compressive stiffness and ductility of columns increased, while the lateral strain in the stirrup decreased. Comparisons were also made between test results and the existing codes such as AIJ (2008), BS5400 (2005), ACI (2019) and EC4 (2010). It has been found that the existing codes provide conservative predictions for the ultimate load-carrying capacity of RHSCFST. Therefore, an accurate model for the prediction of the ultimate load-carrying capacity of circular thin-walled RHSCFST considering the steel reinforcement is developed, based on the obtained experimental results. It has been found that the model proposed in this study provides more accurate predictions of the ultimate load-carrying capacity than that from existing design codes.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.579-588
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• 2024

The present paper investigates the curvature ductility of confined reinforced concrete (RC) beams with normal (NSC) and high strength concrete (HSC). For the purpose of predicting the curvature ductility factor, an analytical model was developed based on the equilibrium of internal forces of confined concrete and reinforcement. In this context, the curvatures were calculated at first yielding of tension reinforcement and at ultimate when the confined concrete strain reaches the ultimate value. To best simulate the situation of confined RC beams in flexure, a modified version of an ancient confined concrete model was adopted for this study. In order to show the accuracy of the proposed model, an experimental database was collected from the literature. The statistical comparison between experimental and predicted results showed that the proposed model has a good performance. Then, the data generated from the validated theoretical model were used to train the artificial neural network (ANN) prediction model. The R² values for theoretical and experimental results are equal to 0.98 and 0.95, respectively which proves the high performance of the ANN model. Finally, a parametric study was implemented to analyze the effect of different parameters on the curvature ductility factor using theoretical and ANN models. The results are similar to those extracted from experiments, where the concrete strength, the compression reinforcement ratio, the yield strength, and the volumetric ratio of transverse reinforcement have a positive effect. In contrast, the ratio and the yield strength of tension reinforcement have a negative effect.

• 농업과학연구
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• 제19권1호
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• pp.65-78
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• 1992

본(本) 연구(硏究)는 당진지방(唐津地方)의 해성(海成)실트질 점성토(粘性土)를 채취하여 물리적(物理的) 실험(實驗) 및 삼축압축시험(三軸壓縮試驗)을 실시하고, 그 시험결과로 쌍곡선식(雙曲線式) 매개상수(媒介常數)를 구한 후, 쌍곡선식(雙曲線式) 모형(模型)에 의한 응력일변형관계(應力一變形關係)를 검토하여 점성토(粘性土)의 응력일변형(應力一變形)을 추정하여 다음과 같은 결과(結果)를 얻었다. 1. 건조밀도(乾燥密度) 및 함수비(含水比)의 증가(增加)에 따른 탄성계수(彈性係數)는 건조밀도(乾燥密度)에 비례하고, 함수비(含水比)는 반비례하였다. 2. 쌍곡선식(雙曲線式) 모형(模型)에 가장 많은 영향을 미치는 인자는 적압력(積壓力)과 건조밀도(乾燥密度)이었고, 점착력과 내부마찰각(內部摩擦角)은 이보다 적은 영향(影響)을 타나났다. 3. 통계적(統計的) 방법(方法)의 추정치를 쌍곡선식(雙曲線式)에 의한 추정치와 비교하였으나, 통계적(統計的) 추정치가 쌍곡선식(雙曲線式) 모형(模型)에 의한 추정치보다 낮게 나타났다. 4. 많은 그림과 계산과정(計算過程)을 단순화하여 시간적 노력을 줄이는 실용적(實用的) 전산(電算)프로그램을 작성하였으나, 입력되는 기초정수(基礎定數)의 시험오차(試驗誤差)를 없애는 것이 중요하다.

• 대한조선학회논문집
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• 제48권3호
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• pp.275-280
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• 2011

In the present study, a unified viscoplastic-damage model has been applied in order to describe the mechanical characteristics of fresh water ice such as nonlinear material behavior and volume fraction. The strain softening phenomenon of fresh water ice under quasi-static compressive loading has been evaluated based on unified viscoplastic model. The material degradation such as growth of slip/fraction has quite close relation with material inside damage. The volume fraction phenomenon of fresh water ice has been identified based on volume fraction (nucleation and growth of damage) model. The viscoplastic-damage model has been transformed to the fully implicit formulation and the discretized formulation has been implemented to ABAQUS user defined subroutine (User MATerial: UMAT) for the benefit of application of commercial finite element program. The proposed computational analysis method has been compared to uni-axial compression test of fresh water ice in order to validate the compatibilities, clarities and usefulness.