• KCI Concrete Journal
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• 제12권1호
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• pp.69-77
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• 2000

The reinforced concrete(RC) flexural members strengthened with steel plate/CFS at soffit have initial stresses and strains in reinforcements and concrete caused by the service loads at the time of retrofitting works. These initial residual stresses and strains of strengthened beams may affect the flexural performance of the rehabilitated beams. The objective of this study is to evaluate and verify the effectiveness of rehabilitation by external bonded steel plates and CFS to the tension face of the beams under three conditions of pre-loading. Thirteen beam specimens are tested and analyzed. Main test parameters are pre-loading conditions, strengthening materials and reinforcement ratio of specimens. The effect of test parameters on the strengthened beams is analyzed from the maximum load capacity, load-deflection relationship, state of stress of the materials. crack propagation phase, and failure modes. Both test results and design formulas of ACI Code provisions are compared and evaluated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.129-132
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• 2006

It is generally reported that most of RC beams strengthened with simply bonded FRP composite is failed by FRP debonding. Also, the flexural performance of RC member strengthened with FRP composite can be calculated using the effective strain of FRP. The effective strain as a result of the debonding failure depends on many variables, such as FRP stiffness including the thickness($t_f$) and modulus of elasticity($E_f$), the amount of FRP but the FRP stiffness is reportedly the most influential. The purpose of this paper, therefore, is to examine effects of FRP stiffness on the flexural strengthening of RC beams. 4 different stiffness of CFRP composite including CFRP sheet and laminae were selected. From the tests, it was found that the flexural performance of RC beams strengthened with CFRP composite can be calculated based on the effective strain of the CFRP composite and the effective strain is inversely proportional to the CFRP stiffness.

• Advances in concrete construction
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• 제5권6호
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• pp.625-638
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• 2017

The flexural behavior of Fiber reinforced polymer (FRP) sheets has gained much research interest in the flexural strengthening of reinforced concrete beams. The study on flexure includes various parameters like increase in strength of the member due to the externally bonded (EB) Fiber reinforced polymer, crack patterns, debonding of the fiber from the structure, scaling, convenience of using the fibers, cost effectiveness, etc. The present work aims to study experimentally about the reasons behind the failure due to flexure of an externally bonded FRP concrete beam. In the design of FRP-reinforced concrete structures, deflection control is as critical as much as flexural strength. A numerical model is created using Finite element (FEM) software and the results are compared with that of the experiment.

• Earthquakes and Structures
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• 제12권6호
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• pp.603-617
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• 2017

This paper presents investigation into the behavior of beam-column joints, with the joint region concrete being replaced by steel fiber reinforced concrete (SFRC) and by ultra-high performance concrete (UHPC). A total of ten beam-column joint specimens (BCJ) were tested experimentally to failure under monotonic and cyclic loading, with the beam section being subjected to flexural loading and the column to combined flexural and axial loading. The joint region essentially transferred shear and axial stresses as received from the column. Steel fiber reinforced concrete (SFRC) and ultra-high performance concrete (UHPC) were used as an innovative construction and/or strengthening scheme for some of the BCJ specimens. The reinforced concrete specimens were reinforced with longitudinal steel rebar, 18 mm, and some specimens were reinforced with an additional two ties in the joint region. The results showed that using SFRC and UHPC as a replacement concrete for the BCJ improved the joint shear strength and the load carrying capacity of the hybrid specimens. The mode of failure was also converted from a non-desirable joint shear failure to a preferred beam flexural failure. The effect of the ties in the SFRC and UHPC joint regions could not be observed due to the beam flexural failure. Several models were used in estimating the joint shear strength for different BCJ specimens. The results showed that the existing models yielded wide-ranging values. A new concept to take into account the influence of column axial load on the shear strength of beam-column joints is also presented, which demonstrates that the recommended values for concrete tensile strength for determination of joint shear strength need to be amended for joints subject to moderate to high axial loads. Furthermore, finite element model (FEM) simulation to predict the behaviour of the hybrid BCJ specimens was also carried out in an ABAQUS environment. The result of the FEM modelling showed good agreement with experimental results.

• 콘크리트학회논문집
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• 제22권6호
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• pp.777-786
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• 2010

이 연구에서는 강섬유로 보강된 초고성능 콘크리트(UHPC)를 적용한 대형 크기의 프리스트레스트 콘크리트 거더의 정적하중재하실험을 통하여 휨거동 특성을 파악하고자 하였다. 이 연구결과는 추후 UHPC를 적용한 프리스트레스트 콘크리트 거더의 처짐산정 및 휨강도 산정 모델링에 주요한 기초적인 실험결과를 제공한다. 휨 하중하에서의 프리스트레스트 콘크리트 T-거더의 거동을 파악하기 위하여 강섬유를 혼입하였다. 강섬유는 원형단면의 직선형상이며, 콘크리트에서 2%의 부피비를 나타낸다. 거더는 압축강도 150~190 MPa의 UHPC를 이용하여 제작하였으며, 프리스트레스트 거더의 휨내력을 파악하고자 하였다. 실험결과는 강섬유 보강 UHPC가 거더의 균열제어 및 연성거동에 효과적임을 나타낸다. 강섬유 보강 UHPC를 적용한 프리스트레스트 거더의 파괴는 인장균열에서의 가교 역할(bridging effect)을 하는 강섬유의 뽐힘(pullout)과 더불어 발생한다. 강섬유의 뽑힘과 더불어 단면의 인장강도 손실이 발생하며, 이는 거더의 휨파괴를 유발한다. 또한, 도입 프리스트레스량이 거더의 휨강도에 영향을 미치는 것으로 나타난다.

• 대한토목학회논문집
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• 제11권1호
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• pp.69-78
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• 1991

본 연구은 단조하중을 받는 철근콘크리트 휨부재의 처짐을 해석하기 위한 것으로서, 콘크리트는 직교이방성재료로 모형화하고, 이력거동과 균열거동을 추적하기 위하여 등가일축변형율과 균열변형율을 이용하며, 철근은 탄소성재료로 모형화하고, 항복조건으로는 von Mises기준을 적용한다. 단조하중을 받는 철근콘크리트 휨부재의 변위거동을 해석하기 위하여 4절점 등매개요소와 트러스요소의 유한요소정식과 중분-반복기법을 적용한 유한요소 프로그램을 도출하고, 단조하중을 받는 과소 철근콘크리트 보에 대한 실험결과와 본 연구의 해석결과를 비교하여 개발된 모형과 해석프로그램의 타당성을 검증한다.

• 콘크리트학회논문집
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• 제17권5호
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• pp.835-842
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• 2005

This paper presents an experimental investigation of bond-strengthening hooks as a new method to increase bond strength along flexural reinforcing bars in reinforced concrete (RC) beams and columns. The RC members, which consisted of 1,300 MPa-class spirals as shear reinforcement, often suffered from bond splitting failure. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Twelve specimens with varied amounts and sizes of the hooks were prepared to verify the strengthening effectiveness under monotonic and cyclic loading conditions. The test result indicated that the hooks increased the bond strength along the flexural bars although the strengthening effectiveness was limited by effective reinforcement ratio $P_{be}$. This limit is determined by size of stress-transmitting zones of concrete around anchors of the hooks. Anchors of the hooks are recommended to be longer than twelve times the hook diameter and inserted deeper than a quarter of the member depth (D/4). Proposed design equations provide modest estimates of the shear strengths.

• 한국해양공학회지
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• 제26권1호
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• pp.1-8
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• 2012

To correctly estimate ice load and ice resistance for a ship's hull, it is essential to understand the material properties of sea ice during ice field trials and to use the proper experimental procedure for gathering ice strength data. The first Korean-made icebreaking research vessel (IBRV), ARAON, had her second sea ice trial in the Arctic Ocean during July and August of 2010. This paper describes the test procedures used to properly obtain sea ice strength data, which provides the basic information on the ship's performance in an ice-covered sea and can be used to estimate the correct ice load and ice resistance on the IBRV ARAON. The data gathered from three sea ice field trials during the Arctic voyage of the ARAON includes the ice compressive strength, flexural strength, and failure strain of sea ice. This paper analyzes the gathered sea ice data in comparison with data from the first voyage of the ARAON during her Antarctic Sea ice trial in January 2010.

• 한국구조물진단유지관리공학회 논문집
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• 제4권4호
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• pp.201-210
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• 2000

The Rehabilitation and repair of structurally deteriorated reinforced concrete structure become more necessary as time goes by. The goal of this study is that provide the data about flexural retrofitted effect of RC beam strengthened by Steel Plate. In order to provide the data, 6 specimens were manufactured and divided with standard specimen and damaged degree A, B, C. Division of damaged A, B, C is based on deflection and degree of crack. In the determination of deflection and degree of crack, we loaded standard specimen to failure under two-point bending to find yielding load and failure load, and then we found deflections and degree of crack that correspond to 75%, 100%, 105% of the yielding load of standard specimen respectively. When we are compared with standard specimen and strengthened specimens, we founded from the experimental results that flexural capacity of structurally damaged beam strengthened by Steel Plate incremented highly, ductility was decreased, and energy absorbtion capacity was almost same.

• Steel and Composite Structures
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• 제20권3호
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• pp.487-500
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• 2016

In order to investigate the flexural bearing capacity of panel zone of diaphragm-through joint between concrete filled square steel tubular column and steel beam, four specimens were tested under static tension loads to study the mechanical properties and bearing capacity of diaphragm-through joints with a failure mode of panel zone. Finite element models of these specimens were developed to simulate the test and compare the predicted failure modes, load-displacement curves and bearing capacities with the experimentally observed. It was found that the tensile load from the steel beam flange is mainly shared by the square steel tube and the diaphragm. The diaphragm plastic zone appears along the cross-section lines enclosed by the square steel tube and the influence of steel beam web on the plastic zone of the steel tube is significant and cannot be neglected. Computational models of yield lines on square steel tube and diaphragm are established based on the distribution pattern of the plastic zone, and an analytical method for the evaluation of the bearing capacity of the joint is proposed. The theoretical results and the experimental data are compared and found in good agreement.