• Computers and Concrete
• /
• 제23권1호
• /
• pp.61-68
• /
• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

• 한국항공우주학회지
• /
• 제47권4호
• /
• pp.256-265
• /
• 2019

본 논문에서는 평직물 CFRP로 제작한 직교 격자 쉘의 굽힘 하중에 의한 점진적 손상 연구를 수행하였다. 직교 격자는 복합재 바닥면과 함께 경화하여 제작하였다. 굽힘을 받는 직교 격자 쉘의 점진적 손상 해석은 Hashin-Rotem 파손 기준과 Matzenmiller-Lubliner-Taylor (MLT) 모델으로 비선형 유한요소법을 이용하여 수행하였다. 또한, 직교 격자 쉘에 대한 3점 굽힘 시험을 수행하였으며, 시험 결과와 해석 결과를 비교하였다. 변형률과 변위에 대한 시험과 해석 결과는 유사하게 나타났다. 손상 영역은 점진적 손상 해석으로 예측하였으며, 육안 검사와 초음파 비파괴 검사를 통해 측정한 결과와 비교하였다.

• Advances in concrete construction
• /
• 제11권5호
• /
• pp.429-445
• /
• 2021

With regard to economic efficiency, composite fix beams are widely used to pass longitudinal shear forces across the interface. The current knowledge of the composite beam load-slip activity and shear capability are restricted to data from measurements of push-off. Modelling and analysis of the composite beams based on Euro-code 4 regarding to shear, bending, and deflection under differing loads were carried out using Finite Element through an efficient computer simulation and the final loading and sections capacity based on the failure modes was analysed. In bending, the section potential was increased by an improvement of the strength in both steel and concrete, but the flexural and compressive resistance growth is very weak (3.2% 3.1% and 3.0%), while the strength of the concrete has increased respectively from 25 N/mm² to 30, 35, and 40 N/mm² compared to the increment of steel strength by 27% and 21% when it was raised from 275 to 355 and 460 N/mm², respectively. It was found that the final flexural load capacity of fix beams was declined with increase in the fix beam span for both three steel strength. The shear capacity of sections was remained unchanged at constant steel strength and different length, but raised with final yield strength increment of steel sections by 29%, and 67% when it was raised from 275 N/mm² to 355 N/mm² and 460 N/mm², respectively.

• 한국지반환경공학회 논문집
• /
• 제12권11호
• /
• pp.23-30
• /
• 2011

본 연구에서는 터널의 상부에 작용하는 토압을 평가하는데 있어서 기존의 Terzaghi 공식이 가지는 문제점을 해결하기 위해 흙의 팽창성(Dilatancy)을 고려하여 Terzaghi 공식을 수정하였다. Terzaghi 공식과 수정식에 대한 수학적 해석결과, 터널의 토압은 수정식이 Terzaghi 공식에 비해 작게 나타났으며 토피고가 커질수록 그 차이는 증가하였다. 터널모형실험 결과와 비교해 본 결과, Terzaghi 공식에 의해 계산된 상부토압은 굴착 전 토압의 약 70%이며, 수정식에 의하면 약 60% 정도로 나타났고, 터널모형실험에 의해 측정된 토압은 약 40% 정도 임을 볼 수 있었다. 또한 유한요소해석을 이용하여 Terzaghi 공식과 수정식에 의해 산정된 터널 상부토압과 전단변형률을 비교해본 결과 수학적 해석결과와 동일하게 수정식이 Terzaghi 공식보다 작게 나타났다.

• Computers and Concrete
• /
• 제30권3호
• /
• pp.175-183
• /
• 2022

To study the working mechanism and size effect of an innovative dovetail UHPC joint originated from the 5th Nanjing Yangtze River Bridge, a large-scale testing subject to negative bending moment was conducted and compared with the previous scaled specimens. The static responses, i.e., the crack pattern, failure mode, ductility and stiffness degradation were analyzed. It was found that the scaled specimens presented similar working stages and working mechanism with the large-scale ones. However, the post-cracking ductility and relative stiffness degradation all decrease with the enlarged length/scale, apart from the relative stiffness after flexural cracking. The slab stiffness at the flexural cracking stage is 90% of the initial stiffness while only 24% of the initial stiffness reserved in the ultimate stage. Finite element model (FEM) was established and compared with the experiments to verify its effectiveness in exploring the working mechanism of the innovative joint. Based on this effective method, a series of FEMs were established to further study the influence of material strength, pre-stressing level and ratio of reinforcement on its deflection-load relationship. It is found that the ratio of reinforcement can significantly improve its load-carrying capacity among the three major-influenced factors.

• 한국건설순환자원학회논문집
• /
• 제10권4호
• /
• pp.402-410
• /
• 2022

본 연구에서는 초고성능 강섬유 보강 콘크리트(UHPC)의 재료특성을 고려하기 위해 해석프로그램 LS-DYNA에 있는 CSC모델의 입력상수값 보정기법을 제안하였다. 1축 압축, 3축 압축, 압력-체적 변형률 곡선, 동적증가계수 등 이전 재료단위 실험 연구결과를 기반으로 입력상수값 보정을 수행하였다. 단일요소 해석결과를 실험결과와 비교하여 보정기법의 검증을 수행하였다. 또한, 유한요소모델을 구축하고 충격 및 폭발해석을 수행하여 UHPC 구조물 해석 수행 시 보정된 CSC 모델의 적용 가능성을 확인해보았다.

• Steel and Composite Structures
• /
• 제44권2호
• /
• pp.199-210
• /
• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.

• Structural Engineering and Mechanics
• /
• 제83권5호
• /
• pp.693-707
• /
• 2022

Bonded joints have proven their performance against conventional joining processes such as welding, riveting and bolting. The single-lap joint is the most widely used to characterize adhesive joints in tensile-shear loadings. However, the high stress concentrations in the adhesive joint due to the non-linearity of the applied loads generate a bending moment in the joint, resulting in high stresses at the adhesive edges. Geometric optimization of the bonded joint to reduce this high stress concentration prompted various researchers to perform geometric modifications of the adhesive and adherends at their free edges. Modifying both edges of the adhesive (spew) and the adherends (bevel) has proven to be an effective solution to reduce stresses at both edges and improve stress transfer at the inner part of the adhesive layer. The majority of research aimed at improving the geometry of the plate and adhesive edges has not considered the effect of temperature and water absorption in evaluating the strength of the joint. The objective of this work is to analyze, by the finite element method, the stress distribution in an adhesive joint between two 2024-T3 aluminum plates. The effects of the adhesive fillet and adherend bevel on the bonded joint stresses were taken into account. On the other hand, degradation of the mechanical properties of the adhesive following its exposure to moisture and temperature was found. The results clearly showed that the modification of the edges of the adhesive and of the bonding agent have an important role in the durability of the bond. Although the modification of the adhesive and bonding edges significantly improves the joint strength, the simultaneous exposure of the joint to temperature and moisture generates high stress concentrations in the adhesive joint that, in most cases, can easily reach the failure point of the material even at low applied stresses.

• 한국지반공학회논문집
• /
• 제23권5호
• /
• pp.63-75
• /
• 2007

Piled raft 기초는 연약지반상에서 과도한 침하와 raft 및 말뚝의 지지력 산정 문제 등으로 적합한 기초는 아닌 것으로 알려져 왔으나 최근 국내외에서 연약지반내 구조물 시공이 증대되면서 연약지반상 piled raft 기초에 대한 관심이 커지고 있다. 이에 본 연구에서는 연약지반에 시공된 piled raft기초의 거동을 분석하였으며 이를 위해 ABAQUS를 이용한 3차원 유한요소 해석을 실시하였다. 해석 시 하중은 등분포하중과 집중하중을 각각 적용하였으며 동일한 조건의 군말뚝과 piled raft 기초 및 다양한 말뚝 배치를 갖는 piled raft 기초를 대상으로 수행하였다. 본 연구결과, 하중형태, 다양한 말뚝 배치 및 근입 깊이에 대한 각각의 침하 및 하중분담특성을 비교, 분석하였으며 이를 통해 연약지반상의 piled raft 기초의 특성을 파악하였다.

• 한국지반공학회논문집
• /
• 제23권8호
• /
• pp.117-127
• /
• 2007

사면안정해석은 지반물성의 불확실성을 포함한 많은 불확실한 요인을 내포하는 지반공학적 문제이다. 본 연구에서는 상업용 유한차분해석 프로그램을 이용하여 확률론적 사면안정해석을 수행할 수 있는 절차를 제시하였다. 이 경우 한계상태함수가 명시적인 형태로 표현되지 않기 때문에 한계상태함수를 근사화하기 위하여 인공신경망기법을 활용한 응답면기법을 이용하였으며 파괴확률을 구하기 위해 일차 및 이차신뢰도법과 Monte Carlo simulation을 이용하였다. 제안된 절차의 적용성을 검토하기 위하여 2층 지반의 사면과 Sugar Creek제방사면에 대한 확률론적 사면안정해석을 수행하였다. 해석결과는 제안된 절차의 적정성과 다른 다양한 지반공학 문제로의 확장 적용의 가능성을 보여준다.