• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.1-9
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• 2017

Spiral reinforcement in a circular column plays an effective role in the ductile behavior of a column through position fixing and buckling restraining of the longitudinal reinforcement, and confining core-concrete. Each country has suggested the minimum volumetric ratio of spiral reinforcement in order to secure the ductility of concrete columns. The minimum volumetric ratio of spiral reinforcement suggested by ACI 318-14 and the national concrete structure design standard was developed based on the theory of Richard et al. (1928); furthermore it has been used until now. However, their theory cannot consider the effects of high strength concrete and high strength reinforcement, and arrangement condition of the spiral reinforcement. In this study, a modified minimum volumetric ratio equation is suggested, which is required to improve the ductility of reinforced concrete circular columns and to recover their stress. The modified minimum volumetric ratio equation suggested here considers the effect of the compressive strength of concrete, the yield strength of spiral reinforcement, the cross sectional area of columns, the pitch of spiral reinforcements and the diameter of spiral reinforcement. In this paper, the validity of the minimum volumetric ratios from ACI 318-14 and this study was investigated and compared based on the results of uniaxial compression experiment for specimens in which the material strength and the spiral reinforcements ratio were used as variables. In the end of the study, the modification method for the suggested equation was examined.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.830-842
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• 2002

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.33-40
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• 2016

The KCI-12 and ACI 318-14 design codes limit the maximum yield strength of shear reinforcement to prevent concrete compressive crushing before the yielding of shear reinforcement. The maximum yield strength of shear reinforcement is limited to 420 MPa in the ACI 318-14 design code, while limited to 500 MPa in the KCI-12 design code. A total of eight post-tensioning prestressed concrete beams with high strength shear reinforcement were tested to observe the shear behavior of PSC beams and the applicability of the high strength reinforcement was thus assessed. In the all PSC beam specimens that used stirrups greater than maximum yield strength of shear reinforcement required by the ACI 318-14 design code, the shear reinforcement reached their yield strains. The observed shear strength of tested eight PSC beams was greater than the calculated ones by the KCI-12 design codes. In addition, the diagonal crack width of all specimens at the service load was smaller than the crack width required by the ACI 224 committee. The experimental and analytical results indicate that the limitation on the yield strength of shear reinforcement in the ACI 318-14 design code is somewhat under-estimated and needs to be increased for high strength concrete. Also the application of high strength materials to PSC is available with respect to strength and serviceability.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.795-803
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• 2004

To prevent the shear failure that occurs abruptly with no sufficient warning, the minimum amount of shear reinforcement should be provided to reinforced concrete(RC) beams. The minimum amount of shear reinforcement of RC beams is influenced by not only compressive strength of concrete but also shear span-to-depth ratio and ratio of tensile longitudinal reinforcement. In this paper, 14 RC beams were tested in order to observe the influences of shear span-to-depth ratio, ratio of tensile longitudinal reinforcement, and compressive strength of concrete. The test results indicated that the rate of shear strength to the diagonal cracking strength of RC beams with the same amount of shear reinforcement increased as the ratio of tensile longitudinal reinforcement increased, while it decreased as the shear span-to-depth ratio increased. The observed test results were compared with the calculated results by the current ACI 318-02 Building Code and the proposed equation.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.883-891
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• 2002

The chloride penetration in concrete structures is influenced by many factors such as types of cement and admixture proportion. Therefore, the effects of these factors on chloride diffusion must be correctly considered. The conventional diffusion analysis also neglected the existence of reinforcing bar in concrete structures. The purpose of the present paper is therefore to investigate the effect of reinforcing bar on the chloride diffusion in concrete structures. For this purpose, a comprehensive finite element analyses have been conducted to obtain chloride penetration profile. The results indicate that the chlorides are accumulated in front of a reinforcing bar and that the accumulation is much larger for the case of large diameter bars. The higher accumulation of chloride at bar location causes much faster corrosion of reinforcing steel. It can be concluded from the present study that the effects of reinforcing bars must be considered in chloride diffusion analysis for more realistic prediction of durable life of concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.78-83
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• 2010

This paper discusses the surface roughness of corroded reinforcement rebar in reinforced concrete structures focusing on the quantitative measurement technique for rebar corrosion. Reinforcement rebar was corroded using accelerated corrosion induced method and corrosion rates were 0%, 1%, 2%, 3%, 5%, and 10% of mass losses. Using 3-dimensional scanner each surface profile of reinforcement rebar was established, and surface roughness was measured. Through tests and analyses of corroded reinforcement rebar, the following topics were particularly discussed: measurement of surface roughness, relationship between area and surface roughness, relationship between surface roughness and bond performance. As a result, surface roughness of corroded rebar was found to be very effective to bond strength until 2% of corrosion rate. It was also discussed how to relate surface roughness of corroded rebar to bond strength of reinforced concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.180-188
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• 2011

Recently a number of researches about mechanical splice have been studied to apply on a large diameter reinforcing steel bars of spliced sleeves. In this study the structural performance of large diameter reinforcing bars with spliced sleeves was evaluated. For the application of nuclear power plant structures, two different types of existing splices with #11, 14, 18 rebars were fabricated and static and dynamic test were performed on the basis of ASME SEC III DIV.2CC-4330.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.95-102
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• 2017

This paper describes the experimental results for the structural performance of full-scale coupling beams with different reinforcement layout (diagonal and horizontal). For the reinforcements of the coupling beams, high-strength steel bars(SD500 and SD600) were used in order to improve workability and economic feasibility. The rigid steel frames and linked joints were used to maintain the clear span length (distance between both shear walls) of the coupling beam during the cyclic loading. Experimental results indicated that the diagonally reinforced coupling beam specimen could exhibit more ductile behavior compared to horizontally reinforced specimen. ACI318-14 code is applicable to design of coupling beam with diagonally reinforcement, however, that is overestimating the strength of horizontally reinforced coupling beam. It is remarkable that effective elastic stiffness values of both reinforcement details coupling beam significantly lees than ASCE 41-13.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.982-988
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• 2002

Current design equations for shear strength of reinforced concrete columns generally overestimate the shear strength contribution by the circular transverse reinforcement. This is due to the simplification of the discrete distribution of the reinforcement to the continuous one and the imprudent application of the classical truss model to the circular section, which is different in shear-resisting mechanism from the rectangular section. This study presents a rational model for the prediction of shear strength contribution by the circular transverse reinforcement considering the starting location of a diagonal crack, the number of transverse reinforcing bars crossing the main crack and the geometrical strength component of the transverse resistance. It was found that, for lower amount transverse reinforcement, the crack starting point and the number of crack crossing bars greatly influence the shear-resisting capacity. Proposed model leads to a reliable design equation which is derived using a linear regression method and is in good agreement with the lower bound of exact strength curve.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.3
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• pp.39-48
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• 2010

Improved seismic performances of RC bridges can be attained by sufficient ductilities of piers, which can be obtained by providing sufficient lateral confinements to the plastic hinge regions of piers. The cross sectional shape and the amount of lateral reinforcements are key parameters in the determination of effective confinements. Even though identical amounts of lateral reinforcement are provided, the effective confinement differs due to different spacing, arrangements, hook details and so on. Unlike circular sections in which confinement is exerted by mere hoop reinforcements, cross-ties are arranged in square or rectangular sections to enhance the effective confinements. The stress-strain relationship of confined concrete is varied by how to consider these cross-ties. In this study, the stress-strain relationships of confined concrete with cross-ties are investigated experimentally and their mechanical characteristics are estimated by comparison with other empirical equations.