• 한국농공학회지
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• 제44권2호
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• pp.117-126
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• 2002

Concrete containing discontinuous discrete steel fiber in a normal concrete is called steel fiber reinforced concrete(SFRC). Tensile as well as flexural strengths of concrete could be substantially increased by introducing closely spaced fibers which delay the onset of tension cracks and increase the tension strength of cracks. However, many properties of SFRC have not been investigated, especially properties on repeated loadings. Thus, the purposes of this dissertation is to study the flexural fatigue characteristics of SFRC considering cumulative damage. A series of experimental tests such as compressive strength, splitting tensile strength, flexural strength, flexural fatigue, and two steps stress level fatigue were conducted to clarify the basic properties and fatigue-related properties of SFRC. The main experimental variables were steel fiber fraction (0, 0.4, 0.7, 1, 1.5%), aspect ratio (60, 83). The principal results obtained through this study are as follows: The results of flexural fatigue tests showed that the flexural fatigue life of SFRC is approxmately 65% of ultimate strength, while that of plain is less than 58%. Especially, the behavior of flexural fatigue life shows excellent performance at 1.0% of steel-fiber volume fraction. The cumulative damage test of high-low two stress levels is within the value of 0.6 ∼ 1.1, while that of low-high stress steps is within the value of 2.4 ∼ 4.0.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.261-264
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• 2006

Deformability of RC members in shear after flexural yielding is limited and controlled by governing failure modes and material strength. Shear strength of members in D-regions has been explained by a direct load path (direct strut or arch action) and indirect load path (fan action or truss action). Indirect load path including truss action and fan action rely on bond along tension ties. Generally, superposition of two actions results in total shear strength when shear failure modes control. The ultimate deformation depends on controlling failure modes and thereby, their force transfer patterns. Proposed models are capable of explaining of limited deformability of RC members in D-regions.

• Structural Monitoring and Maintenance
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• 제9권4호
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• pp.337-357
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• 2022

The objective of this study is to present a data-driven machine learning (ML) framework for predicting ultimate shear strength and failure modes of reinforced concrete ledge beams. Experimental tests were collected on these beams with different loading, geometric and material properties. The database was analyzed using different ML algorithms including decision trees, discriminant analysis, support vector machine, logistic regression, nearest neighbors, naïve bayes, ensemble and artificial neural networks to identify the governing and critical parameters of reinforced concrete ledge beams. The results showed that ML framework can effectively identify the failure mode of these beams either web shear failure, flexural failure or ledge failure. ML framework can also derive equations for predicting the ultimate shear strength for each failure mode. A comparison of the ultimate shear strength of ledge failure was conducted between the experimental results and the results from the proposed equations and the design equations used by international codes. These comparisons indicated that the proposed ML equations predict the ultimate shear strength of reinforced concrete ledge beams better than the design equations of AASHTO LRFD-2020 or PCI-2020.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.309-312
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• 2008

본 연구는 강선 부식이 PSC보 휨강도에 미치는 영향을 알아보기 위해 실내실험을 수행하였다. 긴장력을 달리하여 길이 4m인 PSC보부재 5개를 제작하였으며, 그 중 2개의 부재는 덕트 내부에 있는 PS강재를 노출시킨 상태에서 부식촉진장치를 이용해 인위적으로 PS강재를 부식시켰다. 실험부재의 파괴시까지 정적하중을 재하하면서 철근과 콘크리트의 변형률, 중앙부의 처짐량 변화를 측정하였으며 또한 음향센서를 콘크리트 표면에 부착하여 PS강선의 파단횟수 및 파단시기 등을 계측하였다. 실험 결과, PS강재가 부식된 부재는 PS강재의 단면 감소를 고려해 계산한 휨강도 이론값보다 작은 실험값이 나왔다. 또한 휨 파괴 이전에 PS강재가 조기에 파단되는 현상이 관찰되었으며, 결과적으로 휨강도가 급격히 감소됨을 확인할 수 있었다. 부식된 PS강재를 포함하고 있는 PSC보의 휨강도 평가시 일방향 육안관찰에 의한 PS강재의 단면적을 산정하는 것은 매우 어려운 일이며, 연성거동을 위한 유효 PS강재의 단면적을 판단하는 것은 매우 복잡한 일이라 판단된다.

• Computers and Concrete
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• 제18권6호
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• pp.1213-1234
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• 2016

This paper describes a deformation-based strut-and-tie model for the flexural members at post-yield state. Boundary deformation conditions by flexural post-yield response are chosen in terms of the flexural bar strains as the main factor influenced on the shear strength. The main purpose of the proposed model is to predict the shear capacities of the flexural members associated with the given flexural deformation conditions. To verify the proposed strut-and-tie model, the estimated shear strengths depending on the flexural deformation are compared with the experimental results. The experimental data are in good agreement with the values obtained by the proposed model.

• 콘크리트학회지
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• 제11권2호
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• pp.157-165
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• 1999

콘크리트 휨부재의 극한강도를 예측할 떼에는 부재의 크기효과는 고려하지 않는 것이 일반적이다. 그러나 콘크리트는 여러 형태의 하중에 대하여 부재의 크기가 증가함에 따라 강도가 감소하는 크기효과를 항상 나타낸다. 따라서 본 논문에서는 휨압축 부재에 대한 실험을 수행하여 크기효과를 검토하고자 한다. 이를 위하여 축 압축력과 휨모멘트를 동시에 받는 일련의 C형 공시체에 대한 실험을 수행하였다. 공시체의 크기는 3가지 였으며 콘크리트의 압축강도는 528 kg/$cm^2$로 하였다. 실험결과로부터 부재의 크기가 증가함에 따라 파괴시의 휨압축 강도가 감소하는 크기효과가 존재하며, 실린더 공시체의 축압축 강도보다 강도감소 현상이 더욱 분명함을 알 수 있었다. 최종적으로 실험자료에 대한 회귀분석을 수행하여 이를 예측할 수 있는 모델식을 제안하였다.

• 한국강구조학회 논문집
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• 제18권3호
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• pp.339-347
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• 2006

2거더 철도교량의 사용성, 특히 부모멘트 영역의 휨강성을 증대시키기 위해서 이중합성단면이 제안되었다. 이 논문에서는 제안된 이중합성구조를 갖는 5m-5m의 연속 2거더 교량 모델에 대한 실험적 연구를 수행하였다. 교량 모델에 대한 실험적 연구를 통해서 유효폭,전단연결부, 이중합성단면의 극한강도에 대한 설계 고려사항을 연구하였다. 하부 콘크리트 바다판의 전단열결부는 완전합성 거동을 나타내어 제안된 경험식의 타당성을 검증하였다. 이중합성단면의 휨거동을 통해서 하부 콘크리트 슬래브의 유효폭은 압축을 받는 콘크리트 슬래브의 유효폭으로 계산될 수 있다. 교량모델의 극한 휨 강도 평가에서 이중합성단면의 완전소성해석이 타당함을 밝혔다. 실험결 과에 근거한 설계사항들이 제안되었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.202-205
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• 2003

The purpose of this experimental study is to understand the flexural Behavior of structural deck plate continuous slabs (power deck plate slabs). The main variables considered in this test are thickness of the slab and the deck plate. Five specimens that have length of 600cm and width of 60cm were manufactured. Test results indicated that the ultimate flexural strength of power deck plate slabs was conservative compared to ACI flexural provisions. But, suitable arrangement of bar of top reinforcement is needed for crack control.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.405-411
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• 1998

An iterative numerical computational algorithm is presented to design a plate of shell element subjected to membrane and flexural forces. Based on equilibrium consideration, equations for capacities of top and bottom reinforcements in two orthogonal directions have been derived. The amount of reinforcement is determined locally, i. e., for each sampling point, from the equilibrium between applied and internal forces. One case of design is performed for a hyperbolic paraboloid saddle shell (originally used by Lin and Scordelis) to check the design strength against a consistent design load, therefore, to verify the adequacy of design practice for reinforced concrete shells. Based on nonlinear analyses performed, the analytically calculated ultimate load exceeded the design ultimate load from 14-43% for an analysis with relatively low to high tension stiffening, ${\gamma}$ =5~20 cases. For these cases, the design method gives a lower bound on the ultimate load with respect to Lower bound theorem. This shows the adequacy of the current practice at least for this saddle shell case studied. To generalize the conclusion many more designs-analyses are performed with different shell configurations.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.421-426
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• 2003

For the replacement of deteriorated concrete decks or wider-span slab, composite slab could be very attactive due to higher stiffness and strength. Based on the previous research, a modified I-beam composite hollow slab was suggested. In order to investigate the static flexural behavior of the proposed composite slab and to suggest its flexural design method, experiments were performed. Judging from the tests, a composite slab with I-beam having a semi-circle hole showed better structural performance. The effect of web details on the flexural stiffness was negligible. Flexural stiffness, ultimate strength, and ductility of the composite slabs were significantly greater than the RC slab due to composite action. While the failure of the RC slab was punching shear failure, the composite hollow slab showed flexural cracking and failure by yielding of the I-beams and crushing of concrete. Therefore, the current one-way design concept is appropriate for the design of I-beam composite hollow slab.