• Steel and Composite Structures
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• 제30권6호
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• pp.591-601
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• 2019

This research study investigates experimentally and analytically the axial compressive behaviour of Concrete Filled Fiber Reinforced Polymer Tube (CFFT) columns with and without Fiber Reinforced Polymer (FRP) bars. The experimental program comprises five circular columns of 204-206 mm outer diameter and 800-812 mm height. All columns were tested under concentric axial compressive loads. It was found that CFFT columns with and without FRP bars achieved higher peak axial compressive loads and corresponding axial deformations than conventional steel reinforced concrete (RC) column. The contribution of FRP bars was about 12.1% of the axial compressive loads carried by CFFT columns reinforced with FRP bars. Axial load-axial deformation ($P-{\delta}$) curves of CFFT columns were analytically constructed, which mapped well with the experimental $P-{\delta}$ curves. Also, an equation was proposed to predict the axial compressive load capacity of CFFT columns with and without FRP bars, which adequately considers the contributions of the circumferential confinement provided by FRP tubes and lower ultimate strength of FRP bars in compression than in tension.

• KCI Concrete Journal
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• 제13권2호
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• pp.19-25
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• 2001

A simple expression to predict bond strength of reinforcing bars with rib deformation to the surrounding is derived for the case of splitting bond failure. Finite element analysis is used to model the confining behavior of concrete cover. The roles of the interfacial properties, specifically, the friction coefficient, cohesion, the relative rib area and the rib face angle are examined. Values of bond strength obtained using the analytical model are in good agreement with the bond test results from the previous studies. The analytical model provides insight into interfacial bond mechanisms and the effects of the key variables on the bond strength of deformed bars to concrete. Based on the comparison between the analytical results and the test results, the values of cohesion, coefficient of friction, and the effective rib face angle are proposed.

• Earthquakes and Structures
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• 제9권4호
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• pp.699-718
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• 2015

The effect of reinforcing concrete members with high strength steel bars with yield strength up to 600 MPa on the overall seismic behavior of concrete moment frames was studied experimentally and numerically. Three geometrically identical plane frame models with two bays and two stories, where one frame model was reinforced with hot rolled bars (HRB) with a nominal yield strength of 335 MPa and the other two by high strength steel bars with a nominal yield strength of 600 MPa, were tested under simulated earthquake action considering different axial load ratios to investigate the hysteretic behavior, ductility, strength and stiffness degradation, energy dissipation and plastic deformation characteristics. Test results indicate that utilizing high strength reinforcement can improve the structural resilience, reduce residual deformation and achieve favorable distribution pattern of plastic hinges on beams and columns. The frame models reinforced with normal and high strength steel bars have comparable overall deformation capacity. Compared with the frame model subjected to a low axial load ratio, the ones under a higher axial load ratio exhibit more plump hysteretic loops. The proved reliable finite element analysis software DIANA was used for the numerical simulation of the tests. The analytical results agree well with the experimental results.

• 한국수소및신에너지학회논문집
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• 제14권3호
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• pp.207-216
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• 2003

By using the electrochemical method, the relation between the deformation and the geometrical shape, and the effect of cold work on hydrogen absorption-desorption cycling in palladium were investigated, In order to study this problem, four kinds of the Pd specimens used were plates and bars as cold worked and annealed states. As results, it is found that the deformation of thickness direction in the palladium plates increased whereas other lateral directions decreased. But the palladium bars showed the same deformation ratio in all directions because of uniform distribution of the $\beta$ phase. Grains in the plate specimens were greatly deformed after hydrogenation cycling whereas grains in the bar specimens were pulverized. Also, deterioration of the hydrogen absorption rate of the bar specimen was larger than the plate specimen. And the effect of cold work on hydrogen absorption capacity was relatively small.

• Structural Engineering and Mechanics
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• 제15권1호
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• pp.71-81
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• 2003

The governing differential equation for buckling of a one-step bar with the effect of shear deformation is established and its exact solution is obtained. Then, the exact solution is used to derive the eigenvalue equation of a multi-step bar. The new exact approach combining the transfer matrix method and the closed form solution of one step bar is presented. The proposed methods is convenient for solving the entire and partial buckling of one-step and multi-step bars with various end conditions, with or without shear deformation effect, subjected to concentrated axial loads. A numerical example is given explaining the proposed procedure and investigating the effect of shear deformation on the critical buckling force of a multi-step bar.

• Structural Engineering and Mechanics
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• 제7권4호
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• pp.413-432
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• 1999

A macro-element model is developed to account for shear deformation and bond slip of reinforcement bars in the beam-column joint region of reinforced concrete structures. The joint region is idealized by two springs in series, one representing shear deformation and the other representing bond slip. The softened truss model theory is adopted to establish the shear force-shear deformation relationship and to determine the shear capacity of the joint. A detailed model for the bond slip of the reinforcing bars at the beam-column interface is presented. The proposed macro-element model of the joint is validated using available experimental data on beam-column connections representing exterior joints in ductile and nonductile frames.

• 콘크리트학회논문집
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• 제15권1호
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• pp.17-24
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• 2003

지진하중을 받는 철근콘크리트구조의 취성파괴의 원인은 철근과 콘크리트사이의 급속한 부착손상에 의해 발생되는 국부 부착-슬립이다. 본 연구는 반복하중하에서 부착손상에 대한 철근의 마디높이의 효과를 평가하는 것이다. 큰 상대마디면적을 가진 가공된 철근을 사용하여 부착 시험체를 제작하였다. 또 다른 변수로서 연직방향 철근에 의해 횡구속 철근량의 정도가 고려되었다. 실험결과로부터 에너지 소산력의 크기가 산정되고 여러 변수들에 대해서 비교되었다. 실험결과로서, 하중의 반복이 증가함에 따라 부착강도와 부착강성은 현저히 감소함을 알 수 있다. 횡구속량이 크고 상대마디면적이 큰 철근에서 단조하중시에 비해서 반복하중시의 부착강도의 감소가 줄어들고 국부부착저하를 지연시키는데 효과가 있음을 알 수 있다. 에너지 소산량 또한 횡구속량과 마디상대면적이 증가함에 따라 증가한다. 그러나, 마디가 매우 높은 철근의 부착실험에서 높은 강성 때문에 부착이 적은 슬립에서 손상을 입는다는 것을 알 수 있다. 본 연구는 반복하중하에서 부착저하기구를 이해하고 높은 상대마디면적을 가진 새로운 이형철근의 개발에 유용할 것이다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1990년도 가을 학술발표회 논문집
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• pp.79-82
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• 1990

The results of a large-scale study to determine the effects of epoxy coating on the bond strength between deformed reinforcement and concrete are descrebed. Tests include beam-end specimens containing No. 5(16mm), No. 6 (19mm), No. 8(25mm), No. 11(32mm) bars with average coating thicknesses ranging from 3 to 17 mils(0.08-0.43mm). Three deformation patterns are evaluated. Specimens with covers of 1, 2, and 3 bar deameters are studied. Both top-cast and bottom-cast bars are tested. Epoxy coatings are found to significantly reduce bond strength. The severity of that reduction is a function of deformation pattern, bar size, and coating thickness. Design recommendations based on these observations differ from the modifications to the 1989 ACI Building Code.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.209-212
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• 2006

Bond between reinforcing bar and surrounding concrete is supposed to transfer load safely in the process of design of reinforced concrete structures. The effects of defomation properties on bond of reinforcing bars to concrete are studied. Beam-end tests are used to investigate the effects of machining of bars in addition to rib angle and relative rib area. The test results show that bond strength of machined bars were higher than the conventional bars produced in factory. Higher rib height bars with rib angle $30^{\circ}{\sim}60^{\circ}$ showed higher bond strength than lower rib height bars with low angle.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.171-174
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• 2005

In this study, new moment-resisting precast concrete beam-column joint is proposed for moderate seismic regions. It has the connection reinforcing bars, penetrated the joint and lap-spliced with the bottom bars of precast U-beam. To evaluate the performance for noncontact lapped splice, analytical works were conducted. Major variables for FEM analysis are the length of lap, the diameter of connection reinforcing bars, and the distance between lapped bars. The results of this study show thar the these variables has much influence on strength and deformation of lapped joint.