• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.45-53
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• 2015

In general, RC columns are reinforced by spiral or tied steel and a strength of confined concrete is more increased than this of unconfined concrete. And strength and ductility of column are increased by a confinement effect. A confinement effect is affected by concrete strength, spacing, volume and strength of confinement steel. Many researchers suggested various confinement models which reflected these parameters by many experimental results. In this study, a load-strain relationship is evaluated by a confinement model in EC2, and it is compared with Mander model, Saatchioglu-Razvi model and Cusson et al. model. As results, it is appeared that a confinement model in EC2 is able to apply all kinds of concrete strength and a consistency in sectional analysis can be secured using material models in EC2. In parameter studies using material models in EC2, a confinement effect is more affected by a confinement steel than a concrete strength.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.591-602
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• 2015

In this paper, cyclic loading test was performed to evaluate the seismic performance of the steel coupling beam and RC shear wall. The test parameter was reinforcement detail of the shear wall. For the shear wall which was designed in accordance with the current design codes, a premature bearing failure occurred at the face of the wall. On the other hand, the bearing failure of walls was prevented due to the new type of reinforcement details. Test results indicated that the vertical reinforcements were more affected to the shear strength of the coupled shear wall than the horizontal reinforcement. Based on the failure mode, concrete stress distribution above and below flanges of the embedded steel beam was proposed. Assuming proposed concrete stress distribution, load resistance was predicted and it was agree well with test data.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.1-8
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• 2020

This study presents a shear strength estimation model, in which the shear failure of a reinforced concrete (RC) member is assumed to be governed by the flexure-shear mechanism. Two shear demand curves and corresponding potential capacity curves for cracked tension and uncracked compression zones are derived, for which the bond mechanism developed between reinforcing bars and surrounding concrete is considered in flexural analysis. The shear crack concentration factor is also addressed to consider the so-called size effect induced in large RC members. In addition,unlike exising methods, a new formulation was addressed to consider the interaction between the shear contributions of concrete and stirrup. To verify the proposed method, an extensive shear database was established, and it appeared that the proposed method can capture the shear strengths of the collected test specimens regardless of their material properties, geometrical features, presence of stirrups, and bond characteristics.

• International Journal of Highway Engineering
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• v.8 no.1 s.27
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• pp.119-130
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• 2006

The behavior of continuously reinforced concrete pavement (CRCP) and the effect of the steel ratio on the behavior under moving wheel loads were investigated in this study. The CRCP sections having different steel ratios of 0.6, 0.7, and 0.8% were considered to evaluate the load transfer efficiency (LTE) at transverse cracks and to investigate the strains in CRCP when the system is subjected to moving vehicle loads. The LTEs were obtained by conducting the falling weight deflectometer (FWD) tests and the tests were performed at three different times of a day to find the curling effect due to the daily temperature changes in CRCP. The strains in the concrete slab and the bond braker layer of the CRCP system under moving vehicle loads were obtained using the embedded strain gages. The results of this study show that the LTEs at transverse cracks are very high and not affected by the time of testing and the steel ratio. The strains in CRCP under vehicle loads become smaller as the vehicle speed increases or as the wandering distance increases; however, the strains are not clearly affected by the steel ratio.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.579-588
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• 2006

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.934-941
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• 2002

It is important to consider the effect of member size when estimating the ultimate strength of a concrete flexural member because the strength always decreases with an increase of member size. In this study, the size effect of a reinforced concrete (RC) beam was experimentally investigated. For this purpose, a series of beam specimens subjected to four-point loading were tested. More specifically, three different effective depth (d$\approx$15, 30, and 60 cm) reinforced concrete beams were tested to investigate the size effect. The shear-span to depth ratio (a/d=3) and thickness (20 cm) of the specimens were kept constant where the size effect in out-of-plane direction is not considered. The test results are curve fitted using least square method (LSM) to obtain parameters for the modified size effect law (MSEL). The analysis results show that the flexural compressive strength and the ultimate strain decrease as the specimen size increases. In the future study, since $\beta_1$ value suggested by design code and ultimate strain change with specimen size variation, a more detailed analysis should be performed. Finally, parameters for MSEL are also suggested.

• Journal of the Korea Concrete Institute
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• v.28 no.6
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• pp.655-663
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• 2016

The present study shows the moment-average curvature relationship and effective inertia moment of RC beams obtained from the nonlinear analysis based on the parabola-rectangular stress-strain curve defined in EC-2 code. The variables examined are concrete strength and steel ratio, and moment-average curvature relationship and effective inertia moment obtained are compared with those of the current KCI provisions. As the results of the comparison, the followings could be said: Since the KCI provisions(the Branson method) were originally derived based on the experimental data ranged from 2.2 to 4 of $M/M_{cr}$ and 1.3 to 3.5 of $I_{ut}/I_{cr}$, thereby within these ranges the inertia moments obtained from the nonlinear analysis are closely agreed with those predicted by the Branson method. However, beyond those range the remarkable difference could be found between the two results. In particular, for beams having low steel ratio the inertia moment resulted from the nonlinear analysis are significantly smaller than those obtained from the KCI(Branson) method. This result may imply that the deflection of lightly reinforced members, such as slabs in buildings, becomes much larger than those calculated according to the current design provisions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.319-328
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• 2011

This paper introduces the construction of Strut-Tie model based on the Evolutionary Structural Optimization(ESO) method. Differently from conventional ESO method which uses plane stress elements, the introduced approach adopts the use of truss elements with the fact that the optimum topology of structures by ESO method is open a truss-like structure. Several examples are provided to demonstrate the capability of the proposed method in finding the best Strut-Tie models. In advance, it is shown that the introduced method is supported through the correlation studies between two-dimensional plane stress analysis and Strut-Tie models, and can be used effectively in practice, especially in shear design of complex reinforced concrete members where no previous experience is available.

• Magazine of the Korea Concrete Institute
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• v.7 no.6
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• pp.197-208
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• 1995

The prestressed concrete continuous members with unbonded tendons were investigated while comparing the experimental data with the analytical results. The comparison was carried out with the program TAPS which can take into account the unbonded tendon effects. The subjects that were interested included the load-deflection response, the design equations for the tendon stress at failure, the effects of bonded reinforcements, the effects of span-depth ratio, the effects of loading type. In this paper, contiriuous prestressed concrete members with unbonded ten dons were investigated. Of twelve tests with continuous members, six were two-span beams and six were three span one-way slats. Analytical results were compared favorably with experimental data and disclosed that the tendon stress at flexural failure is the function of the amount of bonded reinforcements, the loading types and patterns, and the tendon profile.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.261-267
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• 2001

The objective of this experimental study is to find the allowable level of axial load to give the proper flexural ductility according to the yield strength of lateral ties, and the distribution and amount of longitudinal bars used in confined high-strength concrete columns. Twelve concrete columns with a 20 cm square section and 80 cm high were tested under hi-axial loads. It was observed that the ductility tends to be improved at the axial loads not less than 0.4f$\_$ck/A$\_$g/. The utilization of high-strength ties in accordance with the ACI 318-99 can cause the brittle failure due to the wide tie spacing. Under the high level of axial loads not less than 0.4f$\_$ck/A$\_$g/. it is necessary for the buckling prevention of the longitudinal bars and the proper ductility improvement to use the high-strength ties with the consideration of the volumetric ratio and confinement type of the lateral ties, and the distribution of the longitudinal bars.