• Smart Structures and Systems
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• 제29권3호
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• pp.445-455
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• 2022

Steel anchor bolts are installed in concrete using a variety of methods. One of the most common methods of anchor bolt installation is using epoxy resin as an infill material injected into the drilled hole to act as a bonding material between the steel bolt and the surrounding concrete. Typical design standards assume uniform stress distribution along the length of the anchor bolt accompanied with single crack leading to pull-out failure. Experimental evidence has shown that the steel anchor bolts fail owing to the multiple failure patterns, hence these design assumptions are not realistic. In this regard, the presented research work details the analytical model that takes into consideration multiple micro cracks in the infill material induced via impact loading. The impact loading from the Schmidt hammer is used to evaluate the bond condition bond condition of anchor bolt and the epoxy material. The added advantage of the presented analytical model is that it is able to take into account the various type of end conditions of the anchor bolts such as bent or U-shaped anchors. Through sensitivity analysis the optimum stiffness and shear strength properties of the epoxy infill material is achieved, which have shown to achieve lower displacement coupled with reduced damage to the surrounding concrete. The accuracy of the presented model is confirmed by comparing the simulated deformational responses with the experimental evidence. From the comparison it was found that the model was successful in simulating the experimental results. The proposed model can be adopted by professionals interested in predicting and controlling the deformational response of anchor bolts.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.117-122
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• 2001

Recently, epoxy-coated re-bar used to the structure partly and put to practical use step, but not economical and appeared to the defect of deterioration of long term bond strength between concrete. The method for complement the defect of epoxy coated re-bar, study of polymer cement slurry coated re-bar started and basic properties appeared to excellent, but study of bond properties embedded in concrete specimens insufficient until now. This study attempts to examination of using possibility for bond strength of polymer cement slurry coated re-bar between concrete specimens compare to ACI Code and KS Code through pull-out test of 15cm$\times$15cm$\times$15cm specimens with polymer cement slurry coated re-bar as polymer cement ratio 50%, 100%, 150%, coating thickness 250${\mu}{\textrm}{m}$, 440${\mu}{\textrm}{m}$ and curing age. In the results of this study, the bond strength of polymer cement slurry coated re-bar compare to plain re-bar, epoxy coated re-bar decreased St/BA-modified polymer cement slurry coated re-bar, but bond strength of PA-modified polymer cement slurry coated re-bar appeared to excellent results. The bond properties of polymer cement slurry coated re-bar between concrete will be obtain more precise results according to compressive strength change of concrete and re-bar diameter size.

• 대한기계학회논문집A
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• 제24권1호
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• pp.250-258
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• 2000

The reinforcing effects of ductile short-fiber reinforced brittle matrix composites are studied by, measuring flexural strength, fracture toughness and impact energy as functions of fiber volume fraction and length. The parameters of fracture mechanics, K and J are applied to assess fracture toughness and bridging stress. It is found that fracture toughness is greatly, influenced by the bridging stress ill which fiber pull-out is occur. For the reinforcing effects as functions of fiber volume fraction($V_f$ = 1, 2, 3 %) and length(L = 3, 6. 10cm), the flexural strength is maximum at $V_f$ = 1% and both fracture toughness.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1992년도 가을 학술발표회 논문집
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• pp.76-81
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• 1992

Short, randomly disturbed steel fibers in concrete increase tensile strength and ductility of concrete under direct tension. These improvements are results form crack arrest mechanisms of steel fibers in concrete. These mechanisms are theoretically considered in this study and verification on the adequancy of different spacing for predicting tensile strength of SFRC are assessed. Results indicate that better correlation exists between experimental result and the spacing concept which take into account the effect of boundaries as well as vibration on reorientation of steel fibers inside concrete. Also considered is the modeling of stress-crack opening relationships in post-peak region of SFRC under tension which bass its deviation on micromechanics of fiber pull-out. Satisfactoring results are observed between tests results and the prediction of the model.

• International Journal of Concrete Structures and Materials
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• 제4권1호
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• pp.37-43
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• 2010

Theoretical models based on modern interpretations of the morphology and interactions of cement hydration products are developed for prediction of the mechanical properties of hydrated cement paste (hcp). The models are based on the emerging nanostructural vision of calcium silicate hydrate (C-S-H) morphology, and account for the intermolecular interactions between nano-scale calcium C-S-H particles. The models also incorporate the effects of capillary porosity and microcracking within hydrated cement paste. The intrinsic modulus of elasticity and tensile strength of hydrated cement paste are determined based on intermolecular interactions between C-S-H nano-particles. Modeling of fracture toughness indicates that frictional pull-out of the micro-scale calcium hydroxide (CH) platelets makes major contributions to the fracture energy of hcp. A tensile strength model was developed for hcp based on the linear elastic fracture mechanics theories. The predicted theoretical models are in reasonable agreements with empirical models developed based on the experimental performance of hcp.

• Computers and Concrete
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• 제22권4호
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• pp.395-405
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• 2018

In this paper, the performance of post-installed adhesive bonded anchor embedded in concrete is assessed using numerical simulations. This study aims at studying the influence of parameters on the performance of a chemically bonded anchorage system. Non-linear finite element modelling and simulations are carried out by properly using the material properties and phenomenon. Materials parameters such as characteristic length, fracture energy, damage criteria, tension retention and crack width of concrete and interface characteristics are carefully assigned so as to obtain a most realistic behaviour of the chemical anchor system. The peak strength of two different anchor systems obtained from present numerical studies is validated against experimental results. Furthermore, validated numerical models are used to study the load transferring mechanism and damage progression characteristics of various anchors systems where strength of concrete, strength of epoxy, and geometry and disposition of anchors are the parameters. The process of development of strain in concrete adjacent to the anchor and energy dissipated during the course of damage progression are analysed. Results show that the performance of the considered anchorage system is, though a combined effect of material and geometric parameters, but a clear distinction could be made on the parameters to achieve a desired performance based on strength, slip, strain development or dissipated energy. Inspite the increase in anchor capacity with increase in concrete strength, it brings some undesirable performance as well. Furthermore, the pullout capacity of the chemical anchor system increases with a decrease in disparity among the strength of concrete and epoxy.

• 한국구조물진단유지관리공학회 논문집
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• 제18권5호
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• pp.41-50
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• 2014

본 연구에서는 섬유종류에 따른 인발특성과 섬유보강 콘크리트의 휨특성에 대하여 평가하기 위하여, 섬유의 재질 및 형상 다른 후크형 강섬유, 비정질 강섬유 및 폴리아미드 섬유에 대하여 인발시험과 섬유보강 콘크리트 시험체를 제작하여 휨특성을 평가하였다. 그 결과, 후크형 강섬유의 경우 최대인발하중에서 섬유가 매트릭스로부터 인발되었지만, 비정질 강섬유는 섬유와 매트릭스의 부착강도가 섬유자체의 인장강도보다 높아 섬유가 매트릭스로부터 인발되지 않고 파괴되는 현상을 나타내었다, 한편, 폴리아미드 섬유는 연신율에 의해 최대인발 하중까지 변위가 크게 발생하였으며, 최대하중이후에 섬유가 끊어지는 파괴특성을 나타내었다. 섬유보강 콘크리트의 휨특성에 있어서 비정질 강섬유는 매트릭스와의 부착강도가 높고, 섬유의 혼입개체수가 많아 콘크리트의 최대휨강도는 높았지만, 균열발생 이후 섬유가 매트릭스로부터 인발되지 않고 섬유가 파괴되는 것에 의해 응력의 저하가 급격하게 발생하지만, 후크형 강섬유보강 콘크리트는 균열발생 이후 섬유가 인발되면서 응력의 저하가 완만하게 발생하였다. 폴리아미드 섬유보강 콘크리트는 균열발생이후 섬유의 연신률에 의해 응력이 급격하게 저하하는 구간이 발생하였으며, 섬유와 매트릭스의 부착에 의해 재상승하였다가 섬유가 끊어지면서 파괴되었다. 섬유와 매트릭스의 인발특성은 섬유보강 콘크리트의 휨강도 및 변형 능력에 큰 영향을 미치는 것으로 판단된다.

• 콘크리트학회논문집
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• 제22권1호
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• pp.123-130
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• 2010

순환골재 콘크리트와 철근의 부착 거동 규명은 철근콘크리트 구조물에 순환골재를 적용하기 위해서 매우 중요한 요소이다. 이에 따라 이 연구에서는 콘크리트와 철근 상호간의 부착 거동을 평가하기 압축인발 실험을 수행하였다. 실험에 사용된 변수는 설계압축강도(21, 27, 40 MPa), 순환 굵은골재 치환율(0, 30, 60, 100%) 및 철근의 배근방향 및 위치(상단근, 하단근)로 하였다. 이 연구를 통하여 얻어진 실험 결과를 종합해 보면, V형 시험체의 경우 순환골재 치환율에 관계없이 상호 유사한 값을 나타내고 있으며 H형 시험체의 경우는 철근의 배근 위치에 영향을 받는 것으로 나타났으나 일부 HT형 시험체를 제외하고는 대부분 CEB-FIP 및 ACI 408 기준식에 의한 계산 값을 상회하는 것으로 나타나 재생골재 사용에 따른 성능 저하는 크지 않은 것으로 판단된다. HT형 시험체의 경우 순환골재 치환율 증가에 따라 골재 침하 현상이 크게 발생되며 불리딩 및 레이턴스에 의한 부착면적의 감소로 최대 부착응력이 다른 시험체에 비하여 낮게 나타났다. 전술한 바에 의하면 현행 규준에서 정하는 상부철근의 높이인 300 mm 이하(높이 225 mm)에서도 부착강도의 저하가 발생하며 이에 따라 현재 규준에서 제안하는 철근 위치 보정계수 1.3의 값의 수정과 신뢰성 확보가 필요할 것으로 판단된다.

• 대한기계학회논문집A
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• 제24권2호
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• pp.438-448
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• 2000

Mechanical press joining technique has been used in sheet metal joining processes because of its simple process and possibility of joining dissimiliar metals, such as steel and aluminum. The static and cyclic behavior of single overlap AI-alloy and steel(SPCC) joints has been investigate. Relationships were developed to estimate the strength of the joint taking into consideration base metal strength properties and the geometry of the joint. Fatigue test results have shown that fatigue resistance of the SPCC mechanical press joints is almost equal to that of the spot weld at the life of $10^6$ cycles. Also, the dissimilar material jointed specimen with upper SPCC plate and button diameter corresponding to the nugget diameter of the spot welded specimen has almost same strength as the same material jointed specimen and as the spot welded specimen.

• 한국안전학회지
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• 제30권3호
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• pp.1-6
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• 2015

Self-piercing riveting (SPR) is receiving more recognition as a possible and effective solution for joining automotive body panels and structures, particularly for aluminum parts and dissimilar parts. In this study, static strength and fatigue tests were conducted using coach-peel and cross-tension specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. For the static experiment results, the fracture modes are classified into pull-out fracture due to influence of plastic deformation of joining area. During the fatigue tests for the coach-peel and cross-tension specimens with Al-5052, interface failure mode occurred on the top substrate close to the rivet head in the most cycle region. There were relationship between applied load amplitude $P_{amp}$ and life time of cycle N, $P_{amp}=715.5{\times}N^{-0.166}$ and $P_{amp}=1967.3{\times}N^{-0.162}$ were for the coach-peel and cross- tension specimens, respectively. The finite element analysis results for specimens were adopted for the parameters of fatigue lifetime prediction. The relation between SWT fatigue parameter and number of cycles was found to be $SWT=192.8N_f^{-0.44}$.