• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.733-738
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• 2000

This paper was aimed to evaluate the structural performance of flexural members repaired by polymer cement and epoxy mortar at soffit. Main test variables were repair materials, ratio of reinforcement and additional reinforcing bars. Test results shows that the repaired beams could change flexural capacity by materials and additional reinforcing bars. In polymer cement, the section repaired can carry same load, cracking moment and the flexural stiffness of the monolithic beams with same size. In epoxy mortar, all data were greater than the shotcrete. However, note that epoxy mortar may conduct member into brittle failure mode.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1992.10a
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• pp.73-78
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• 1992

It would be much effective that single column type pier is used in concrete slab bridges rather than gravity type pier is used. To determine the longitudinal bonging moment in concrete slab bridges supported by single column type piers, the concept of effective width is applied. By elastic plate theory cooperated with finite element method, the distribution of the longitudinal moment of the slab supported by single column type piers is studied. The main variables are span, width, and thickness of the slab and column section size. Then the analytical results obtained are summarized and analysed to evaluate the maximum longitudinal negative moment by simple beam analysis.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.833-838
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• 1998

This paper is aimed to investigate structural performance of flexural members enlarged with epoxy mortar at soffit. Main test variables are steel ratio and interface treatment method and six test beams are tested to investigate the effect of each test variables on maximum load capacity, load-deflection and moment-curvature relationship, interface behavior and failure mode. Test results show that section enlarged beams can carry almost same load of the monolithic beams with same size and the flexural stiffness and cracking moments are increased about 2.5 times and 50 to 70%of failure moment in comparison with same sized control beam, respectively. However, deflections and curvatures are decreased at the same load and interface fractures are not discovered at the ultimate load.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.797-800
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• 2004

Some test results indicated that the current ASTM grip adapter of GFRP rebar was not successful in developing the design tensile strength of GFRP rebar with reasonable accuracy. It is because the current ASTM grip adapter of GFRP rebar does not take into account the various geometric characteristics of GFRP rebar such as surface treatment, shape of bar cross section, bar deformation as well as physical characteristics such as poisson effect, elastic modulus in the transverse direction and so on. The research reported in this paper is to provide how to proportion an adequate grip adapter to develop design tensile properties of GFRP rebar. The proposed grip adapter is derived from the equilibrium or compatibility equations. From the preliminary test results for rounded GFRP rebar, it was found that the grip adapter with specific size proportioned by proposed method shows the highest tensile strength among them.

• Journal of the Society of Disaster Information
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• v.13 no.3
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• pp.366-375
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• 2017

Internal factors having effects on compressive strength test results of concrete include size, shape, height-diameter ratio(h/d), section processing method, dryness and wetness, etc. of the specimen. As it is difficult to ensure dimensions of core specimen due to rebar cutting from rebar spacing, wall thickness, effects on the structure, etc. when taking core of the concrete structure, correction of dimensions and h/d of the specimen become important for quality control of the concrete. Thus, in order to review effects of specimen size and height-diameter ratio for the concretes with compressive strength within 40~60MPa, this study has experimentally reviewed compressive strength test values by applying correction factors pursuant to KS F 2422 (Method of obtaining and testing drilled cores and sawed beams of concrete), when changing specimen diameter to ${\emptyset}5{\sim}15cm$, and h/d to 2.0~1.25.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.311-321
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• 2022

In the buildings with long spans and high floors, such as logistics warehouses and semiconductor factories, it is difficult to install supporting posts under beams during construction. Therefore, the size of structural members becomes larger inevitably, resulting in a significant increase in construction costs. Accordingly, a prestressed hybrid wide flange (PHWF) beam with hollowed steel webs was developed, which can reduce construction costs by making multiple openings in the web of the steel member embedded in concrete. However, since multiple openings exist and prestress is introduced only into the bottom flange concrete, it is necessary to identify the shear resistance mechanism of the PHWF beam. This study presents experimental shear tests of PHWF beams with hollowed steel webs. Four PHWF beams with cast-in-place (CIP) concrete were fabricated, with key variables being the width and spacing of the steel webs embedded in the concrete and the presence of shear reinforcing bars, and web-shear tests were conducted. The shear behavior of the PHWF beam, including crack patterns, strain behavior of steel webs, and composite action between the prestressed bottom flange and CIP concrete, were measured and analyzed comprehensively. The test results showed that the steel web resists external shear forces through shear deformation when its width is sufficiently large, but as its width decreased, it exerted its shear contribution through normal deformation in a manner similar to that of shear reinforcing bars. In addition, it was found that stirrups placed on the cross section where the steel web does not exist contribute to improving the shear strength and deformation capacity of the member. Based on the shear behavior of the specimens, a straightforward calculation method was proposed to estimate the web-shear strength of PHWF beams with CIP concrete, and it provided a good estimation of the shear strength of PHWF beams, more accurate than the existing code equations.

• Structural Engineering and Mechanics
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• v.91 no.3
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• pp.263-277
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• 2024

The primary aim of this study is to introduce an innovative configuration for stirrup hooks in reinforced concrete beams and analyze the impact of factors such as stirrup spacing, placement, and hook lengths on the structural performance of reinforced concrete beam elements. A total of 18 specimens were produced and subjected to reversed cyclic loading, with two specimens serving as reference specimens and the remaining 16 specimens utilizing a specifically developed stirrup hook configuration. The experiment used reinforced concrete beams scaled down to half their original size. These beams were built with a shear span-to-depth ratio of 3 (a/d=3). The experimental samples were divided into two distinct groups. The first group comprises nine test specimens that consider the contribution of concrete to shear strength, while the second group consists of nine test specimens that do not consider this contribution. The preparation of reference beam specimens for both groups involved the utilization of standard hooks. The stirrup hooks in the test specimens are configured with a 90-degree angle positioned at the midpoint of the bottom section of the beam. The criteria considered in this study included the distance between hooks, hook angle, stirrup spacing, hook orientation, and hook length. In the experimental group examining the contribution of concrete on shear strength, it was noted that the stirrup hooks of both the R1 reference specimen and specific test specimens displayed indications of opening. However, when the contribution of concrete on shear strength was not considered, it was observed that none of the stirrup hooks proposed in the R0 reference specimen and test specimens showed any indications of opening. Neglecting the contribution of concrete in the assessment of shear strength yielded more favorable outcomes regarding structural robustness. The study found that the strength values obtained using the suggested alternative stirrup hook were similar to those of the reference specimens. Furthermore, all the test specimens successfully achieved the desired strengths.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.12
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• pp.6542-6549
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• 2013

In highly elevated piers and long span beams, a hollow section is often used to reduce the self-weight and increase the flexural rigidity of members. Numerical analysis was conducted to obtain the moment-curvature curves and curvature ductility factor for the RC hollow section beams under a range of hollow portion sizes and reinforcement conditions in the upper flange and web. The curvature ductility factor was constantly maintained until the hollow portion size($b_i/b_o/h_i/h_o$) was less than or equal to 0.5. The curvature ductility factor decreased sharply if ($b_i/b_o/h_i/h_o$) was 0.7 or more. The curvature ductility factor of the beam decreased if reinforcement was provided in the web of the RC hollow section beam. To obtain the same level of the ductility factor as the singly reinforced section, the reinforcement should be provided in the upper flange as much as the web reinforcement.

• Fire Science and Engineering
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• v.25 no.5
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• pp.85-92
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• 2011

Along the fire resisting capacity of high strength concrete has been brought up as a social issue, and the Ministry of Land also had notified the control standard about it, the researches for improving the fire resisting capacity have been considerably activated these days. In this study, we performed a research for developing a high strength concrete, contains the fiber cocktail, which is a hybrid of polypropylene fiber as organic matter, and steel fiber. As we analyzed the temperature of the steel part during the fire test with 100 MPa high strength concrete, there was a tendency that the lower temperature comes out with the larger cross section, and the $600{\times}600mm$, $800{\times}800mm$ cross sectioned can secure the fire resistance capability, so the $600{\times}600mm$ is deducted as the optimal size if we consider the double economic feasibility. As well, among them the best qualified $600{\times}600mm$ shapes, the fiber cocktail hybrid of $1.5kg/m^3$ PP fiber and $40kg/m^3$ of steel, comes out the best ratio.

• Structural Engineering and Mechanics
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• v.50 no.3
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• pp.287-304
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• 2014

A computer based iterative numerical procedure has been developed to analyse reinforced high strength concrete columns subjected to horizontal wave loads and eccentric vertical load by taking the material, geometrical and wave load non-linearity into account. The behaviour of the column has been assumed, to be represented by Moment-Thrust-Curvature relationship of the column cross-section. The formulated computer program predicts horizontal load versus deflection behaviour of a column up to failure. The developed numerical model has been applied to analyse several column specimens of various slenderness, structural properties and axial load ratios, tested by other researchers. The predicted values are having a better agreement with experimental results. A simplified user friendly hydrodynamic load model has been developed based on Morison equation supplemented with a wave slap term to predict the high frequency non-linear impulsive hydrodynamic loads arising from steep waves, known as ringing loads. A computer program has been formulated based on the model to obtain the wave loads and non-dimensional wave load coefficients for all discretised nodes, along the length of column from instantaneous free water surface to bottom of the column at mud level. The columns of same size and material properties but having different slenderness ratio are analysed by the developed numerical procedure for the simulated wave loads under various vertical thrust. This paper discusses the results obtained in detail and effect of slenderness in resisting wave loads under various vertical thrust.