• Journal of the Korea Concrete Institute
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• v.11 no.5
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• pp.3-10
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• 1999

Earthquake resistant R/C frame structures are generally designed to prevent the columns from plastic hinging. R/C columns under higher axial load or strong earthquake showed a brittle behavior due to the deterioration of strength and stiffness degradation. An experimental study was conducted to examine the behavior and to find the relationship between amounts of lateral reinforcements and compressive strength of ten R/C column specimens subjected to reversed cyclic lateral load and higher axial load. Test results are follows : An increase in the amount of lateral reinforcement results in a significant improvement in both ductility and energy dissipation capacities of columns. R/C columns with sub-tie provide the improved ductility capacity than those with closely spaced lateral reinforcement only. While the load resisting capacity of the high strength R/C columns is higher than the normal strength concrete columns under both an identical ratio of lateral reinforcement, however the ductility capacity of high strength R/C columns is decreased considerably. Therefore, the amounts of lateral reinforcement must be designed carefully to secure the sufficient ductility and economic design of HSC columns under higher axial load.

• Structural Engineering and Mechanics
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• v.58 no.1
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• pp.1-19
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• 2016

Recently, the high-strength concrete is increasingly used in the construction of reinforced concrete structures due to its benefits, but this use is influenced negatively on the local ductility of structural elements. The objective of this study is the prediction of a new approach to evaluate the curvature ductility factor of high strength concrete beams according to Eurocode 2. After the presentation of the Constitutive laws of materials and the evaluation method of curvature ductility according to the Eurocode 2, we conduct a parametric study on the factors influencing the curvature ductility of inflected sections. The calibrating of the obtained results allows predicting a very simple approach for estimating the curvature ductility factor. The proposed formula allows to calculate the curvature ductility factor of high strength concrete beams directly according to the concrete strength $f_{ck}$, the yield strength of steel $f_{yk}$ and the ratio of tension and compression reinforcements ${\rho}$ and ${\rho}^{\prime}$ respectively, this proposed formula is validated by theoretical and experimental results of different researchers.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.481-482
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• 2010

There is disagreement among researchers in many areas of FRP RC design code except flexural. So a new efficient and reliable shear strength equation which show a high accuracy and a consistent variation in predicting failure modes and shear strength was proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.533-536
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• 1999

The primary purpose of this study is to investigate experimentally the effect of steel fiber reinforcement on the total energy dissipation capacity of R/C flexural members and to make a contribution to the construction of 40~60 story R/C high rise building by developing the new materials and reinforcing details which can improve the seismic performance of high-strength R/C beam-column joints. Experimental research was carried out on 4 type specimen under cyclic loading. Main variables are steel fiber reinforcement, intermediate reinforcements and yield strength of rebars. From the test results, steel fiber reinforcement can improve the ductility of R/C flexural members.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.215-230
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• 2012

An experimental research on the possibility of using high-strength concrete with the design strength of 60 MPa and high-tension rebar with the yielding strength of 600 MPa instead of conventional reinforced concrete segment to reduce its production cost was performed. Full-scale bending tests on both conventional and high-strength reinforced concrete segments were carried out to compare their mechanical and structural behaviors of the segments under flexural action. From the experiments, it was shown that the failure load of high-strength reinforced concrete segment was approximately 30% higher than that of the conventional segment even though reinforcements in high-strength segment were reduced by 26%. The test result showed that the bearing capacity of high-strength segment highly increased by high-strength concrete and high-tension rebar. It also verified the high possibility of high-strength reinforced concrete segment as a technical alternative to reduce the production cost of segments in a shield tunnel.

• Computers and Concrete
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• v.4 no.3
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• pp.187-206
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• 2007

A rational three-dimensional nonlinear finite element model is described and implemented for evaluating the behavior of high strength concrete slabs under transverse load. The concrete was idealized by using twenty-nodded isoparametric brick elements with embedded reinforcements. The concrete material modeling allows for normal (NSC) and high strength concrete (HSC), which was calibrated based on experimental data. The behavior of concrete in compression is simulated by an elastoplastic work-hardening model, and in tension a suitable post-cracking model based on tension stiffening and shear retention models are employed. The nonlinear equations have been solved using the incremental iterative technique based on the modified Newton-Raphson method. The FE formulation and material modeling is implemented into a finite element code in order to carry out the numerical study and to predict the behavior up to ultimate conditions of various slabs under transverse loads. The validity of the theoretical formulations and the program used was verified through comparison with available experimental data, and the agreement has proven to be very good. A parametric study has been also carried out to investigate the influence of different material and geometric properties on the behavior of HSC slabs. Influencing factors, such as concrete strength, steel ratio, aspect ratio, and support conditions on the load-deflection characteristics, concrete and steel stresses and strains were investigated.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.404-417
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• 2016

The purpose of this study is to examine the extent to which the deterioration in strength of high strength concrete of 60MPa replaced by a large amount of recycled coarse aggregates (more than 60% to 100% of replacement ratio) could be recovered with steel fiber reinforcement through material compressive strength test and shear failure test on short and middle beams and then to offer useful data for aggregate supply system of a sustainable resource circulation type. This study first examined the results of previous related tests. The results of the material compressive strength tests confirmed that when using a combination of steel fiber reinforcements of volumn ratio 0.75% and high quality recycled coarse aggregates with an water absorption rate within 2.0%, the strength characteristics of high strength concrete of 60MPa level were not only restored to the strength level of concrete made with natural aggregates, but also showed superior ductility. And the shear failure tests on short and middle beams using recycled coarse aggregates more than 60% with shear span to depth ratio (a/d) of 2 and 4 controlled by shear forces mainly confirmed that effects of superior shear strength increase and ductile behavior characteristics were showed by steel fiber reinforcements.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.603-613
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• 2015

In current design codes, minimum shear reinforcement is required for reinforced concrete flexural members, and the use of steel fiber reinforced concrete is permitted to replace the minimum shear reinforcements. In the present study, to estimate the effects of shear reinforcements and fibers on shear strength, simply supported beams were tested under transverse loading. The test results showed that the shear strength was significantly increased by the use of fibers. Particularly, the effect of fiber reinforced concrete was pronounced when high-strength concrete was used. The performance of fiber reinforced concrete for minimum shear reinforcement was evaluated using results of the present study and existing tests.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.533-539
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• 2008

An high frequency induction hardening technology of vehicle body press-formed of thin sheet steel has been developed to increase the strength of vehicle body parts locally by high frequency induction heating, thereby eliminating the need for reinforcements. And this technique for increasing the tensile strength of sheet steel was practically applied to the front floor cross member and center pillar reinforcement of a passenger car. The side impact behavior has been investigated when induction hardening technology is applied to the conventional low-carbon steel and weight reduction of an automotive body is expected. In this paper, basic experiments were performed for the hat-shaped specimen under high frequency induction heating process. Martensitic transformation was found in the heating zone through microscopic observation which showed higher hardness. In addition, the hardness and strength of the center-pillar specimen made of boron steel increased remarkably by high frequency induction heating.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1619-1629
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• 1995

The Al/Al$_{2}$O$_{3}$ SiC and Al/Al$_{2}$O$_{3}$/C hybrid metal matrix composites (MMCs) were fabricated by squeeze infiltration method. Uniform distribution of reinforcements were found in the microstructure of metal matrix composites. Mechanical tests were carried out under various test conditions to clearly identify mechanical behavior of MMCs, and the wear mechanism of Al/Al$_{2}$O$_{3}$/(SiC or C) hybrid metal matrix composites were investigated. The tensile strength and hardness of hybrid composites was resulted in increasing compared with those of the unreinforced matrix alloy. Wear resistance was strongly dependent upon kinds of fiber, volume fraction and sliding speed. The wear resistance of metal matrix composites was remarkably improved by the addition of reinforcements. Especially, the wear resistance of the hybrid composites of carbon fibers was more effective than in the composites reinforced with alumina and SiC whiskers of reinforcements. This was due to the effect of carbon fiber on the solid lubrication. Wear mechanisms of hybrid composites were suggested from wear surface analyses. The major wear mechanism of hybrid composites was the abrasive wear at low to intermediate sliding speed, and the melting wear at intermediate to high sliding speed.