• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.957-960
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• 2000

The purpose of this study was performed to estimate the influence of compressive strength of the concrete according to change test specimens of concrete were investigated by measurements of slump, air content and compressive strength. As a result, according to moved test specimens, the compressive strength, fiexed test specimens effected on Concrete compressive strength, test specimens than moved test specimens, increased 4∼10% fixed test specimens, 2∼9% moved test specimens.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.773-778
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• 1998

For imaging of concrete specimens using radar, the principles of radar, microwave, and the electromagnetic properties of concrete are discussed. Experimental data obtained from radar measurement of concrete specimens with no steel bars at three different frequency bandwidths of 2~3.4 GHz, 3.4~5.8 GHz and 8~12 GHz are processed to determine the thickness of the specimens. A signal processing scheme has been implemented to visualize the concrete specimens. The purpose of this study is to determine particular frequency range appropriate for measuring the thickness of concrete specimens using radar.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.799-802
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• 2001

For imaging of concrete specimens using radar, principles of radar and signal processing are discussed. Experimental data obtained from radar measurement of two different concrete specimens at two different frequency bandwidths of 2~3.4 GHz, 3.4~5.8 GHz and these two frequencies are combined to show better imaging. A signal processing scheme has been implemented to visualize the concrete specimens. Through combined frequency, imaging results of concrete specimens were improved.

• Computers and Concrete
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• v.19 no.1
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• pp.33-39
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• 2017

In this study, two types of aggregate were used for making self-compacting concrete. Standard cubic specimens were exposed to different temperatures. Seventy-two standard cylindrical specimens ($150{\times}300mm$) and Seventy-two cubic specimens (150 mm) were tested. Compressive strengths of the manufactured specimens at $23^{\circ}C$ were about 33 MPa to 40 MPa. The variable parameters among the self-compacting concrete specimens were of sand stone type. The specimens were exposed to 23, 100, 200, 400, 600, and $800^{\circ}C$ and their mechanical specifications were controlled. The heated specimens were subjected to the unconfined compression test with a quasi-static loading rate. The corresponding stress-strain curves and modulus of elasticity were compared. The results showed that, at higher temperatures, Scoria aggregate showed less sensitivity than ordinary aggregate. The concrete made with Scoria aggregate exhibited less strain. The heated self-compacting concrete had similar slopes before and after the peak. In fact, increasing heat produced gradual symmetrical stress-strain diagram span.

• Computers and Concrete
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• v.20 no.1
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• pp.57-63
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• 2017

A coupled experimental-numerical study on shear fracture in concrete specimens with different geometries is carried out. The crack initiation, propagation and final breakage of concrete specimens are experimentally studied under compression loading. The load-strain and the strength of the specimens are experimentally measured, indicating decreasing effects of the shear behavior on the failure load of the specimen. The effects of specimen geometries on the shear fracturing path in the concrete specimens are also investigate. Numerical models using an indirect boundary element method are made to evaluate the crack propagation paths of concrete specimens. These numerical results are compared with the performed experiments and are validated experimentally.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.119-123
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• 1993

Axial load-strain relationships of confined concrete with spiral reinforcement were investigated. The main variables were compressive strength of concrete, spacing of hoop reinforcement, and specimen height of plain concrete. The program included tests of eleven confined specimens, and twelve plain specimens, but for all specimens no longitudinal reinforcement was provided. Load-strain curves of confined and plain concrete specimens are reporeted.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.521-524
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• 1999

Twelve column specimens were tested in compression, six were slab-column specimens and six were isolated column specimens. The slab column specimens were first tested to punching shear failure before the columns of the specimens were loaded axially. The effects of confinement from the surrounding slab on the axial capacity of the columns was investigated. Other parameters investigated were the placement of fiber-reinforced concrete in the slab and the concentration of flexural reinforcement in the column vicinity.

• 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 Concrete Institute
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• v.12 no.6
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• pp.99-108
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• 2000

The size effect on axial compressive strength in notched concrete specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimens under compression were discussed. In this study, experiments of axial compressive failure, which is one of the two failure modes, was carried out by using cylindrical specimens. Adequate notch length was taken from the experimental result of strength variation based on the notch length. And, by taking various sizes of specimens the size effect on axial compressive strength of concrete was investigated. Also, model equations were suggested by modified size effect law (MSEL). The test results show that size effect appears conspicuously for all series of specimens. Additionally, the effect of initial notch length on axial compressive strength was also apparent.

• Advances in concrete construction
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• v.9 no.6
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• pp.597-610
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• 2020

Stress-strain models of fibre reinforced polymer (FRP) confined concrete have been widely investigated; however, the existing load which is always supported by structures during the retrofitting phase, namely 'preload', has been neglected. Thus, preload effects should be clarified, providing insightful information for FRP retrofitting of structures with preload conditions. Towards this aim, experiments were performed for 27 cylinder concrete specimens with the diameter 150 mm and the height 300 mm. Three specimens were used to test the compressive strength of concrete to compute the preloads 20%, 30% and 40% of the average strength of these specimens. Other 24 specimens were divided into 2 groups; each group included 4 subgroups. Four subgroups were subjected to the above preloads and no preload, and were then wrapped by 2 FRP layers. Similar designation is applied to group 2, but wrapped by 3 FRP layers. All specimens were tested under axial compression to failure. Explosive failure is found to be the characteristic of specimens wrapped by FRP. Experimental results indicated that the preload decreases 12-13% the elastic and second stiffness of concrete specimens wrapped by 2 FRP layers. The stiffness reduction can be mitigated by the increase of FRP layers. Preload negligibly reduces the ultimate force and unclearly affects the ultimate displacement probably due to complicated cracks developed in concrete. A mechanism of preload effects is presented in the paper. Finally, to take into account preload effects, a modification of the widely used model of un-preload FRP confined concrete is proposed and the modified model demonstrated with a reasonable accuracy.