• Computers and Concrete
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• 제22권2호
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• pp.197-207
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• 2018

In the present study, group method of data handling networks (GMDH) are adopted and evaluated for shear strength prediction of both FRP-reinforced concrete members with and without stirrups. Input parameters considered for the GMDH are altogether 12 influential geometrical and mechanical parameters. Two available and very recently collected comprehensive datasets containing 112 and 175 data samples are used to develop new models for two cases with and without shear reinforcement, respectively. The proposed GMDH models are compared with several codes of practice. An artificial neural network (ANN) model and an ANFIS based model are also developed using the same databases to further assessment of GMDH. The accuracy of the developed models is evaluated by statistical error parameters. The results show that the GMDH outperforms other models and successfully can be used as a practical and effective tool for shear strength prediction of members without stirrups ($R^2=0.94$) and with stirrups ($R^2=0.95$). Furthermore, the relative importance and influence of input parameters in the prediction of shear capacity of reinforced concrete members are evaluated through parametric and sensitivity analyses.

• 콘크리트학회논문집
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• 제26권2호
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• pp.109-116
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• 2014

압축강도 160MPa과 길이 15.4 m를 가진 초고강도 섬유보강 콘크리트 분절박스 거더의 휨거동 실험을 수행하였다. 초고강도 섬유보강 콘크리트 분절 박스에 연성거동 특성을 보강하기 위한 강섬유와 종방향철근의 조합 효과를 두종류의 강섬유 혼입률로 제작된 초고강도 분절형 박스거더의 휨거동을 비교함으로써 평가하였다. 강섬유 혼입률이 1%이고 전단철근과 상부플랜지와 복부에 종방향철근으로 보강한 초고강도 콘크리트 박스거더 BF2의 거동은 탄성응력대에서 전단철근 없이 강섬유 혼입률 2%인 초고강도 섬유보강 콘크리트 박스거더와 유사한 연성거동을 보여준다. 그러나 비선형응력대에서는 BF1의 강성이 약간 더 크고 안정적인 연성거동 형태를 보여주고 있다. 초고강도 섬유보강 콘크리트 박스거더의 분절면은 휨파괴 시까지 균열이나 슬립이 발생하지 않았다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.585-590
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• 1999

There is still a lack of knowledge and modelling relating to shear behaviour in reinforced concrete beams. The reason is that shear loading leads to complicated physical mecanisms, such as interlock action, dowel action, etc. Therefore, It is difficult that we make the ideal model of shear behaviour, while Truss model theory has been made good use of shear design because of simplicity and reasonableness. In this study, 6 T-type reinforced concrete beams were designed and made based on the two truss models, i.e, the plasticity truss model and the compatibility truss model, to observe shear strength of concrete and stress distribution of stirrups. 6 beams test pieces were tested with the following testing parameters. 1) specified concrete strength ; 270kg/$\textrm{cm}^2$, 400kg/$\textrm{cm}^2$ 2) with and without the steel fiber.

• 한국구조물진단유지관리공학회 논문집
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• 제2권3호
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• pp.205-211
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• 1998

The purpose of this study is to evaluate shear strengthening effects of R/C beams with carbon fiber sheets. The major variables are shear reinforcement ratios, CFS strengthening ratios and strengthening methods of CFS. Following conclusions can be extracted. The shear capacity of beam strengthened with CFS is about 32~87% higher than that of beams without shear reinforcement. The strengthening effects of patch type is larger than those of strip type. The strain distribution in CFS intersected with shear crack is similar to that in stirrup and larger strain is observed in the middle of the shear span. It can be estimated that shear strength reduction factor ${\alpha}$=0.3 is appropriate for peeling effect of CFS.

• International Journal of Concrete Structures and Materials
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• 제3권1호
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• pp.47-56
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• 2009

The first diagonal cracking and ultimate shear load of reinforced girder made of ultra high performance fiber reinforced concrete (UHPFRC) were investigated in this paper. Eleven girders were tested in which eight girders failed in shear. A simplified formulation for the first diagonal cracking load was proposed. An analytical model to predict the ultimate shear load was formulated based on the two bounds theory. A fiber reinforcing parameter was constituted based on the random assumption of steel fiber uniform distribution. The predicted values were compared with the conventional predictions and the test results. The proposed equation can be used for the first cracking status analysis, while the proposed equations for computing the ultimate shear strength can be used for the ultimate failure status analysis, which can also be utilized for numerical limit analysis of reinforced UHPFRC girder. The established fiber reinforcing theoretical model can also be a reference for micro-mechanics analysis of UHPFRC.

• Steel and Composite Structures
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• 제12권2호
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• pp.149-166
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• 2012

This paper presents an experimental investigation on the performance of 2.5 m long reinforced concrete (RC) T-beams strengthened in shear using epoxy bonded glass fibre fabric. Eighteen (18) full scale, simply supported RC T-beams are tested. Nine beams are used as control beam specimens with three different stirrups spacing without glass fibre reinforced polymer (GFRP) sheet and rest nine beams are strengthened in shear with one, two, and three layers of GFRP sheet in the form of U-jacket around the web of T-beams for each type of stirrup spacing. The objective of this study is to evaluate the effectiveness, the cracking pattern and modes of failure of the GFRP strengthened RC T-beams. The test result indicates that for RC T-beams strengthened in shear with U-jacketed GFRP sheets, increase the load carrying capacity by 10-46%.

• Computers and Concrete
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• 제21권3호
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• pp.299-310
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• 2018

When reinforced concrete structures are subjected to strong seismic forces, their beam-column connections are very susceptible to be damaged during the earthquake event. Consequently, structural designers try to fit an important quantity of steel reinforcement inside the connection, complicating its construction without a clear justification for this. The aim of this work is to evaluate -and demonstrate- numerically how the quantity and the array of the internal steel reinforcement influences on the nonlinear response of the RC beam-column connection. For this, two specimens (extracted from an experimental test of 12 RC beam-column connections reported in literature) were modeled in the Finite Element code FEAP considering different stirrup's arrays. The nonlinear response of the RC beam-column connection is evaluated taking into account the nonlinear thermodynamic behavior of each component: a damage model is used for concrete; a classical plasticity model is adopted for steel reinforcement; the steel-concrete bonding is considered perfect without degradation. At the end, the experimental responses obtained in the tests are compared to the numerical results, as well as the distribution of shear stresses and damage inside the concrete core of the beam-column connection, which are analyzed for a low and high state of confinement.

• Earthquakes and Structures
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• 제24권2호
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• pp.97-109
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• 2023

This experimental study investigates the effectiveness of applying carbon fiber reinforced polymer (CFRP) jackets for the retrofit of short reinforced concrete (RC) columns with inadequate transverse reinforcement and stirrup spacing to longitudinal rebar diameter equal to 12. RC columns scaled at 1/3, with round and square section, were subjected to axial compression up to failure. A damage scale is introduced for the assessment of the damage severity, which focusses on the extent of buckling of the longitudinal rebars. The damaged specimens were subsequently repaired with unidirectional CFRP jackets without any treatment of the buckled reinforcing bars and were finally re-tested to failure. Test results indicate that CFRP jackets may be effectively applied to rehabilitate RC columns (a) with inadequate transverse reinforcement constructed according to older practices so as to meet modern code requirements, and (b) with moderately buckled bars without the need of previously repairing the reinforcement bars, an application technique which may considerably facilitate the retrofit of earthquake damaged RC columns. Factors for the estimation of the reduced mechanical properties of the repaired specimens compared to the respective values for intact CFRP-jacketed specimens, in relation to the level of damage prior to retrofit, are proposed both for the compressive strength and the average modulus of elasticity. It was determined that the compressive strength of the retrofitted CFRP-jacketed columns is reduced by 90% to 65%, while the average modulus of elasticity is lower by 60% to 25% in respect to similar undamaged columns jacketed with the same layers of CFRP.

• 콘크리트학회논문집
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• 제22권2호
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• pp.199-208
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• 2010

FRP bar를 철근 대체제로 활용하기 위해서는 설계 기준의 확립이 시급하나 국내에서는 이 소재에 대한 기초 연구가 부족한 상황이다. 그러므로 2차에 걸쳐 전단보강이 없는 18개의 FRP RC와 4개의 기존 RC 실험체의 거동을 관찰하였다. 1차 실험은 휨 파괴 거동과 사용성 항목의 계측 자료 수집을 목적으로 시작되었다. 휨파괴를 유도하기 위하여 전단배근을 강화하는 대신 그로 인한 거동의 불확실성을 배제하기 위하여 전단지간비만을 조정하여 휨파괴를 유도하고, 전단배근을 사용하지 않기로 하였다. 실험 결과 거의 모든 실험체는 전단파괴 되었으며 실험계획에 적용한 ACI 440.1R과 CSA S806의 전단 강도식이 실제와 큰 편차가 있음을 확인하였다. 1차 실험의 결과를 근거로 2차 실험에서는 전단파괴거동을 집중적으로 관찰하였다. 표준 실험체의 제원은 길이 3,300 mm폭 ${\times}$ 800 mm ${\times}$ 유효깊이 200 mm, 순지간 2,800 mm, 전단지간 1,200 mm로 전단지간비는 6.0이며, 단순지지 조건으로 4점 재하실험을 수행하였다. 검토 변수에는 콘크리트 압축강도, 보강근의 종류 및 탄성계수, 전단지간비, 유효보강비, 다발 배근의 영향, 피복두께의 영향이 포함된다.

• 콘크리트학회논문집
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• 제29권1호
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• pp.53-64
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• 2017

강섬유 보강 초고성능 콘크리트(UHPFRC)는 높은 압축강도 뿐 아니라 강섬유 보강에 의한 뛰어난 응력분산효과로 인해 높은 인장강도를 가지며, 미세균열의 확장을 통해 균열 후에도 경화거동을 하여 구조부재가 안정적으로 외력에 저항하도록 한다. 본 연구에서는 UHPFRC 재료 인장강도를 정의함에 있어 노치가 있는 휨실험과 직접인장실험을 비교하여 실험법 및 결과 분석의 장단점을 알아보았다. I-형 보의 전단부재실험은 복부의 면내전단거동을 알아보기 위하여 전단 경간비, 유효높이, 재료인장강도를 변수로 계획하였다. 실험결과를 통해 전단보강근이 없는 UHPFRC I형 보의 균열발생 이후 전단거동의 응력 재분배효과를 정량적으로 판단하고, 균열 후 거동을 기존 전단 강도식이 잘 반영하고 있는지 검토하였다. 전단철근 보강이 없는 UHPFRC 전단부재의 경우 파괴모드는 사인장 파괴로 동일하였고, 이러한 파괴모드를 가지는 부재는 전단 경간비와 유효높이에 크게 영향을 받게 되어 부재 설계 시 이러한 변수에 대한 고려가 필요한 것으로 나타났다.