• 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.16 no.1 s.79
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• pp.43-53
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• 2004

The current Korean Concrete Design Code(KCI Code) requires the minimum and maximum content of shear s in order to prevent brittle and noneconomic design. However, the required content of the steel reinforcement In KCI Code is quite different to those of the other design codes such as fib-code, Canadian Code, and Japanese Code. Furthermore, since the evaluation equations of the minimum and maximum shear reinforcement for the current KCI Code were based on the experimental results, the equations can not be used for the RC members beyond the experimental application limits. The concrete tensile strength, shear stress, crack inclination, strain perpendicular to the crack, and shear span ratio are strongly related to the lower and upper limits of shear reinforcement. In this research, an evaluation equation for the minimum content of shear reinforcement is theoretical proposed from the Wavier's three principals of the mechanics of materials.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.253-258
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• 2002

An evaluation equation of the minimum shear reinforcement content for reinforced concrete beams was theoretically proposed. The proposed equation takes into account the effects of compressive strength of concrete, longitudinal reinforcement content and shear span ratio. The proposed equation was compared with the current ACI 318-99 and CSA A23.3-94 codes.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.890-895
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• 2003

The purpose of this experimental study is to investigate the influence of shear span-to-depth ratio on the minimum shear reinforcement ratio of reinforced concrete beams. In this study, 7 reinforced concrete beam specimens were tested. The parameters of experiment are shear span-to-depth ratio(a/d=2.0, 3.0, 4.0) and shear reinforcement ratio($p_v$=0%, 0.183%, and 0.233%). The section of all secimens was 350mm width and 450mm depth. The observed results were compared with the calculated results by the current ACI 318-02 Building Code and the proposed equation. The safety rate of the specimens, L5S2A, L5S3A, L5S4A, and L5S4P specimens were 1.80, 1.25, 1.38, and 1.56 respectively. The test results indicated that the shear behavior of reinforced concrete beams with the minimum shear reinforcement was influenced by the shear span-to-depth ratio.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.823-832
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• 2004

The purpose of this research is to investigate the flexure-shear behavior of bridge columns under seismic loads. Four full scale circular reinforced concrete columns were tested under cyclic lateral load with constant axial load. The selected test variables are aspect ratio(1.825, 2.5, 4.0), transverse steel configuration, and longitudinal steel ratio. Volumetric ratio of transverse hoop of all the columns is 0.0023 in the plastic hinge region. It corresponds to $24\%$ of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by limited ductility concept. The columns showed flexural failure or flexure-shear failure depending on the test variables. Failure behavior and seismic performance are investigated and discussed in this paper.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.86-94
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• 2022

Replacement of FRP rod as steel reinforcement has been attracted significantly to prevent the degradation of the concrete structure due to corrosion. So, the technology development to extend the structure's service life by improving FRP properties has been proceeded worldwide. Accordingly, it is necessary to develop Korea's CFRP rod and CFRP grid, including the manufacturing techniques to improve the properties of high-strength and high-stiffness. Moreover, the research should be conducted to evaluate the structural behavior of the beams using the CFRP rod or grid. This study investigates the flexural and shear behavior of reinforced concrete beam using demonstrated CFRP rod as reinforcement according to the reinforcement ratio and shear span to depth ratio. From the results, when the reinforcement ratio is out of a specific range, it is seemed that the effect on performance improvement of the beam using CFRP rod is cancelled or not significant. Meanwhile, when the CFRP rod was used as reinforcement, the possibility of shear failure occurred, even steel stirrups were installed in the beam with CFRP rod as tensile reinforcement according to the Korean Design Standard. Therefore, when the CFRP rod is used as tensile reinforcement in a beam, it should be prepared that a specific limitation of reinforcement ratio and an investigation against shear failure. Also, the ductility of the beam using the CFRP rod is determined by the deformation energy evaluation method. So, the ductility should be investigated by applying the deformation energy evaluation method that reflects the structural behavior of the beam.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.773-783
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• 2007

A simple unbonded-type shear strengthening technique for reinforced concrete beams using wire rope units is developed. Six two-span continuous T-beams externally strengthened with wire rope units and an unstrengthened control beam were tested. The main variables investigated were the amount and prestressing force of wire rope units. All specimens had the same geometrical dimension and arrangement of internal reinforcement. Influence of the distribution of vertical stresses in beam web owing to the prestressing force of wire rope units on the diagonal shear cracking load and the ultimate shear capacity of beams tested is presented. Based on the current study, it can be concluded that the amount and initial prestress of wire rope should be limited to be above 2.5 times the minimum shear reinforcement ratio specified in ACI 318-05 and below 0.6 times its own tensile strength, respectively, to ensure the enhancement of shear capacity and ductile failure mode of the strengthened beams. A numerical analysis based on the upper-bound theorem is developed to assess the shear capacity of continuous T-beams strengthened with wire rope units. From the comparisons of measured and predicted shear capacities, a better agreement is achieved in the proposed numerical analysis than in empirical equations recommended by ACI 318-05.

• Land and Housing Review
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• v.1 no.1
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• pp.67-73
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• 2010

Method of protruding steel bar embedded in PHC pile for connecting with foundation plate is an intermediate form of fixed and hinged connection and has often been used in architectural structures such as apartment complex. However, mechanical properties of this method have not been proved and its construction process is not simple. In this study, therefore, by analyzing previous research and by considering ratio of steel bar and concrete in PHC pile, which is minimum reinforcement of rebar, the newly optimized method of reinforcing joint of PHC pile and foundation plate is suggested with respect to PHC pile type (PHC 450, PHC 500, and PHC 600). To assess mechanical properties (ultimate tensile and shear strength) of joint of PHC pile and foundation plate, full scale experimental tests are performed. As a result, all cases are satisfied with required design criteria and can be practically applied. Our results indicate that reduction of rebar reinforcement compared to previous method would lead cost saving in PHC pile construction.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.137-147
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• 2012

In the steel-free bridge concrete deck, steel straps are generally used instead of conventional steel rebar while laterally restrained in the perpendicular direction to the traffic in order fir the arching effect of concrete deck. In this paper, the minimum amount of FRP bar is to be suggested based on the structural strength, crack propagation, stress level and others in order to control cracks. As a result of laboratory tests, the structural strength of deck with 0.15 percentage of steel strap showed improved structural strength including ductility. The long-term serviceability of steel strap deck with FRP bar proved to satisfy the requirements and to be structurally stable while showing the amount of crack and residual vertical displacement within the allowable limits after two million cyclic loadings. The structural failure of RC bridge deck is generally caused from the punching shear rather than moment. Therefore, the ultimate load at failure could be estimated using the shear strength formula in the two-way slab based on ACI and AASHTO criteria. However the design criteria tend to underestimate the shear strength since they don't consider the arching effects and nonlinear fracture in bridge deck with lateral confinement. In this paper, an equation to estimate the punching shear strength of steel strap deck is to be developed considering the actual failure geometries and effect of lateral confinement by strap while the results are verified in accordance with laboratory tests.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.445-448
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• 1999

The minimum shear and torsional reinforcement provisions in ACI 318-95 are still empirical. This paper describes the derivation of a rational approach for minimum shear and torsional reinforcement in beams so as to preclude brittle failure in shear and torsion. This is ensured by specifying that the beam's ultimate capacity of shear and torsion should be greater than its cracking shear and torsion. The formula presented herein for computing minimum shear and torsional reinforcement shows the need for modification of current provision for the minimum shear and torsion reinforcement.