• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.49-52
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• 2008

The tensile and bond performance of GFRP rebar are different from those of conventional steel reinforcement. It requires some studies on concrete members reinforced with GFRP reinforcing bars to apply it to concrete structures. GFRP has some advantages such as high specific strength, low weight, non-corrosive nature, and disadvantage of larger deflection due to the lower modulus of elasticity than that of steel. Bridge deck is a preferred structure to apply FRP rebars due to the increase of flexural capacity by arching action. This paper focuses on the behavior of concrete bridge deck reinforced with newly developed GFRP rebar. A total of three real size bridge deck specimens were made and tested. Main variable was reinforcement ratio of GFRP rebar. Static test was performed with the load of DB-24 level until failure. Test results were compared and analyzed with ultimate load, deflection behavior.

• Journal of Ocean Engineering and Technology
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• v.29 no.6
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• pp.454-462
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• 2015

An extended study was conducted on the fracture criterion by Choung et al. (2011; 2012) and Choung and Nam (2013), and the results are presented in two parts. The theoretical background of the fracture and the results of new experimental studies were reported in Part I, and three-dimensional fracture surface formulations and verifications are reported in Part II. How the corrected true stress can be processed from the extrapolated true stress is first introduced. Numerical simulations using the corrected true stress were conducted for pure shear, shear-tension, and pure compression tests. The numerical results perfectly coincided with test results, except for the pure shear simulations, where volume locking appeared to prevent a load reduction. The average stress triaxialities, average normalized lode parameters, and equivalent plastic strain at fracture initiation were extracted from numerical simulations to formulate a new three-dimensional fracture strain surface. A series of extra tests with asymmetric notch specimens was performed to check the validity of the newly developed fracture strain surface. Then, a new user-subroutine was developed to calculate and transfer the two fracture parameters to commercial finite element code. Simulation results based on the user-subroutine were in good agreement with the test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.613-616
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• 2008

This study is about appling non-exposure waterproofing method which combines the Cement Polymer Modified Waterproof Membrane coating and Selfadhesive Rubberized Asphalt sheet to the Roof Structure, Because there are a lot of problems in previous methods. So We had the performance tests using waterproofing method which combines two materials, and we analyzed the results. This study showed us very important results. We had bond strength test and tensile test under high, normal and low temperature, and the results were successful. And we also tested for coping with crack and movement. We found that tested materials were safe in those conditions. I think that Non-Exposure waterproofing method which combines the Cement Polymer Modified Waterproof Membrane coating and Selfadhesive Rubberized Asphalt sheet is available to concrete structure.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1118-1125
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• 2009

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing Bearing Capacity Evaluation method for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 21 kinds of the laboratory model tests with the end restraint conditions of the reinforcement that comprises the constrained and partially constrained (3 types) conditions were conducted. According to result of tests, Terzaghi's bearing capacity method is adequate to calculate bearing capacity in non-stiff material(geotextile, geogrid). But, It can't adequate to stiff material(bamboo net). So, New bearing capacity method suggest surface reinforcement method of very soft ground which Terzaghi's bearing capacity method modify for effect of stiffness.

• Composites Research
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• v.23 no.6
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• pp.61-66
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• 2010

In this paper, the variation of mechanical properties of T800 carbon/epoxy composites according to the forming pressure, which was referred to previous studies on a filament winding process, were investigated. The specimens of all the tests were fabricated by an autoclave de-gassing molding process controlling forming pressure (absolute pressures of 0.1MPa, 0.3MPa, 0.7MPa including vacuum) and water jet cutting after fabricating composite laminates. Various tensile tests were performed for in-plane properties and interlaminar properties were also measured by using Iosipescu test jig. Fiber volume fraction was measured to correlate the property variation and the forming pressure. This properties are expected to be utilized in the design of Type III pressure vessel for hydrogen vehicles which uses the same carbon fiber (T800 carbon fiber) for the filament winding process.

• Structural Engineering and Mechanics
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• v.54 no.3
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• pp.501-520
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• 2015

Presence of torsional loadings can significantly affect the flow of internal forces and deformation capacity of reinforced concrete (RC) columns. It increases the possibility of brittle shear failure leading to catastrophic collapse of structural members. This necessitates accurate prediction of the torsional behaviour of RC members for their safe design. However, a review of previously published studies indicates that the torsional behaviour of RC members has not been studied in as much depth as the behaviour under flexure and shear in spite of its frequent occurrence in bridge columns. Very few analytical models are available to predict the response of RC members under torsional loads. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. The present study shows that STM prediction is not sufficiently accurate particularly in the post cracking region when compared to test results. An improved analytical model for RC square columns subjected to torsion with and without axial compression is developed. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensile strength of concrete is the main reason behind the discrepancies in the STM predictions. The existing STM is extended in this paper to include the effect of tension stiffening for better prediction of behaviour of square RC columns under torsion. Three different tension stiffening models comprising a linear, a quadratic and an exponential relationship have been considered in this study. The predictions of these models are validated through comparison with test data on local and global behaviour. It was observed that tension stiffening has significant influence on torsional behaviour of square RC members. The exponential and parabolic tension stiffening models were found to yield the most accurate predictions.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.343-351
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• 2018

Brazilian disc test is one of the most widely used experiments in the literature of geo-mechanics. In this work, the pre-holed concrete Brazilian disc specimens are numerically modelled by a two-dimensional discrete element approach. The cracks initiations, propagations and coalescences in the numerically simulated Brazilian discs (each containing a single cylindrical hole and or multiple holes) are studied. The pre-holed Brazilian discs are numerically tested under Brazilian test conditions. The single-holed Brazilian discs with different ratios of the diameter of the holes to that of the disc radius are modelled first. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured and the crack propagation mechanism around the wall of the ring is investigated. The crack propagation and coalescence mechanisms are also studied for the case of multi-holes' concrete Brazilian discs. The numerical and experimental results show that the breaking mechanism of the pre-holed disc specimens is mainly due to the initiation of the radially induced tensile cracks which are growth from the surface of the central hole. Radially cracks propagated toward the direction of diametrical loading. It has been observed that for the case of disc specimens with multiple holes under diametrical compressive loading, the breaking process of the modelled specimens may occur due to the simultaneous cracks propagation and cracks coalescence phenomena. These results also show that as the hole diameter and the number of the holes increases both the failure stress and the crack initiation stress decreases. The experimental results already exist in the literature are quit agree with the proposed numerical simulation results which validates this simulation procedure.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.113-123
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• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcements and the ratio of shear rebars. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. The increase of plastic deformation after yielding transforms the shear transfer by arch action into by truss action. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The strain distribution model of shear reinforcements and flexural reinforcements based on test results is presented. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. The flexural-shear failure mechanism determines the ultimate state of RC coupling beams. It is expected that this model can be applied to displacement-based design methods.

• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.685-692
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• 2020

In this study, the experimental and analytical study were performed on the location of longitudinal cracks in the middle of underground box structures. The location where the longitudinal cracking occurred was investigated that the overlapping joint of the rebar and the section of maximum tensile stress generated. Using the finite element analysis, the strength reduction ratio of the rebar was estimated by lack of overlap joint length. As the result of adequacy investigation for the length of the overlap joint presented in the design criteria, it was analytically proved that the lack of the overlap joint length could be cause the decreasing cross-sectional force and concrete cracking. As the result of this study, the adequacy of the overlapping criterion in the current design criteria was confirmed based on the finite element analysis and actual field case. In the case of overlapping joints installed in inappropriate position, it was considered that a long term crack control would be need to ensure the sufficient safety factor for the designed cross-sectional force.

• Corrosion Science and Technology
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• v.2 no.6
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• pp.283-288
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• 2003

The cathodic protection method is being widely used in marine structural steel, however a high tensile steel like RE 36 steel for marine structural steel is easy to get hydrogen embrittlement due to over protection during cathodic protection as well as preferential corrosion of HAZ(Heating Affected Zone) part. In this paper, corrosion resistance and mechanical properties such as elongation and hydrogen embrittlement were investigated with not only in terms of electrochemical view but also SSRT(Slow Strain Rate Test) method with applied constant cathodic potential, analysis of SEM fractography in case of both As-welded and PWHT(Post-Weld Heat Treatment) of $550^{\circ}C$. The best effect for corrosion resistance was apparently indicated at PWHT of $550^{\circ}C$ and elongation was increased with PWHT of $550^{\circ}C$ than that of As-welded condition. On the other hand. Elongation was decreased with applied potential shifting to low potential direction which may be caused by hydrogen embrittlement, however the susceptibility of hydrogen embrittlement was decreased with PWHT of $550^{\circ}C$ than that of As-welded condition and Q.C(quasi cleavage) fracture mode was also observed significantly according to increasing of susceptibility of hydrogen embrittlement. Eventually it is suggested that an optimum cathodic protection potential range not causing hydrogen embrittlernent is from -770 mV(SCE) to -850 mV(SCE) in As-welded condition while is from -770 mV(SCE) to -875 mV(SCE) in PWHT of $550^{\circ}C$.