• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.357-360
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• 2006

In this study, it was proposed a direct tensile testing machine(DTTM) to be simple and to be applied to High Performance Fiber Reinforced Cementitious Composites(HPFRCCs), and it was examined the tensile properties of HPFRCCs by this machine. As a results, it was confirmed that a direct tensile test of HPFRCCs could be certainly carried out DTTM to be developed in this study. Also, tensile strength and yield strength of HPFRCCs were similar regardless of specimens thickness. And, all specimens revealed the stable strain-hardening behavior and multiple cracking in flexible and tensile loads. But, deviation of strain at ultimate tensile strength increased with the increase of specimen thickness.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.597-600
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• 2003

The development and maintenance of a sound bond are an essential requirements of concrete repair and replacement. The bond property of a bonded overlay to its substrate concrete during the lifetime is one of the most important performance requirements which should be quantified. A standard or a verified bond strength measurement method is required at field for screening, selecting materials and quality control for overlay or repair materials. This study compares the nipple pipe direct tensile test, flexural adhesion test, and core pull-off test with their test results. Substantial differences in the failure stresses of three test methods were attributed to their different geometries and loading conditions. From these comparison and investigation, core pull-off test was relatively good because the coefficient of variation values were about 2%. It would be suitable for use in-situ because of its simplicity and accuracy.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.47-52
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• 2024

The demand for FRPs that are corrosion-free and have an excellent tensile strength-to-weight ratio. However, there is a lack of research on the mechanical properties of FRP in the form of rebars, especially the changes in performance due to heating. Therefore, in this paper, 60 tensile and compression specimens of CFRP rebars with a diameter of 12 mm were fabricated and subjected to direct tensile and direct compression tests, and their performance was evaluated according to the heating temperature. It was found that as the heating temperature increases above 300 ℃, the performance decrease becomes larger due to the burning of epoxy. The compressive strength was found to be much lower than the tensile strength, but the modulus of elasticity was found to be the same in tension and compression.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.247-260
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• 2012

In order to reduce the amount of steel reinforcements in TBM tunnel segments, the use of Steel Fiber Reinforced Concrete(SFRC) is being tried. The steel fibers with higher aspect ratio than that used in tunnel shotcrete are preferred to compensate the deficiency in tensile strength of the segments. In this study, the tensile properties of SFRC with aspect ratio of steel fibers equal to 80 were evaluated through flexural test and Double Punch Test. In the results of flexural test, flexural strengths of the SFRC were increased about 30%~150% thanks to bond of steel fibers used to concrete and could be properly predicted by the equation proposed by Oh(2008). There was a great difference in the estimated direct tensile strengths of the SFRC by the equations presented in ACI and RILEM. It was found that the Double Punch Test could be suitable methodology to estimate the direct tensile strength presented in RILEM of the SFRC.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.539-550
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• 2022

A detailed experimental program was conducted to investigate the flexural behavior of ultra high performance concrete (UHPC) beams reinforced with high strength steel (HSS) rebars with a specified yield strength of 600 MPa via direct tensile test and monotonic four-point bending test. First, two sets of direct tensile test specimens, with the same reinforcement ratio but different yield strength of reinforcement, were fabricated and tested. Subsequently, six simply supported beams, including two plain UHPC beams and four reinforced UHPC beams, were prepared and tested under four-point bending load. The results showed that the balanced-reinforced UHPC beams reinforced with HSS rebars could improve the ultimate load-bearing capacity, deformation capacity, ductility properties, etc. more effectively owing to interaction between high strength of HSS rebar and strain-hardening characteristic of UHPC. In addition, the UHPC with steel rebars kept strain compatibility prior to the yielding of the steel rebar, further satisfied the plane-section assumption. Most importantly, the crack pattern of the UHPC beam reinforced with HSS rebars was prone to transform from single main crack failure corresponding to the normal-strength steel, to multiple main cracks failure under the condition of balanced-reinforced failure, which validated by the conclusion of direct tensile tests cooperated with acoustic emission (AE) source locating technique as well.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.323-326
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• 2005

Uniaxial tension test of Glass Fiber Reinforced Polymer (GFRP) bar reinforced concrete prisms was performed. The objective was to investigate the adequate cover thickness of the GFRP rebars. The tension stiffening effect of GFRP bar reinforced concrete was also studied. The test variables included rebar types (conventional steel rebar and two different GFRP rebars) and cover thicknesses (five different cover thicknesses ranging between 1-3db). Normal strength concrete was used. Cracking patterns on concrete surface and cracking loads were careful1y observed during the direct tensile test. The test results indicated that the adequate cover thickness of the GFRP rebars may even be larger than that of the steel rebars and that the cover thickness of 2db commonly specified for the GFRP rebars may not be large enough. The tension stiffening effect of the GFRP rebars was also quantified and documented from the test results.

• Journal of Industrial Technology
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• v.23 no.A
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• pp.149-156
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• 2003

The development and maintenance of a sound bond are essential requirements of concrete repair and replacement. The bond property of a overlay to its substrate concrete during the lifetime is one of the most important performance requirements which should be quantified. A standard or a verified bond strength measurement method is required at field for screening, selecting materials and quality control for overlay or repair materials, but no test method has been adopted as a standard. In this study, a concrete pull off bond strength measurement method for field application is proposed and evaluated. This study compares the splitting tensile test, slant shear test, nipple pipe direct tensile test, flexural adhesion test, briquette tensile test, jumbo nail pull-out test and core pull-off test with their test procedures. From these comparison and investigation, core pull-off test is selected as a main topic of this study because of it's suitability for in situ testing, simplicities in field application and clearness at interface boundary condition. Thus, the proposed core pull off test is evaluated to be the most appropriate method for field application in a simple manner. The fracture surface and fracture mode could be easily determined by visual observation of failure surface of the field specimen. The core pull off test was found to be sensitive to surface condition and latex contents at latex modified concrete.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.23-28
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• 2003

The effect of the welding speeds on the weld bead shape, microstructure, and mechanical properties in type 304 austenitic stainless steels was investigated by microscopic test, Erichsen test and tensile test. In this study welds were produced using autogeneous Direct Current Straight Polarity (DCSP) and pulsed current GTA welding. This study shows the ferrite content, ductility, tensile strength and elongation of high speed welds are decreased with increasing welding speed. The high speed welds exhibits satisfactory tensile strength, though the ductility is not good as that of the base metal.

• Transactions of Materials Processing
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• v.12 no.5
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• pp.504-512
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• 2003

The plastic strain ratios(R-values) of low carbon steel sheets were determined by the automatic strain measurement method using two extensometers, the indirect photo method for the same tensile specimen during tensile test and the indirect method for the specimen after tensile test. The experimental results showed that the measured plastic strain ratios from the automatic strain measurement method using two extensometers coincided with those from the indirect photo method and the indirect method for all tensile specimens. In addition, the strain dependence of plastic strain ratios could be continuously recorded and the anisotropy of the strength coefficient, K, and strain hardening exponent, n, could be automatically calculated in three directions by computer through the use of two extensometers. The experimental results showed that the strain dependence of R-value was related to the anisotropy of strain hardening exponent in low carbon steel sheets.

• KCI Concrete Journal
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• v.12 no.2
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• pp.85-93
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• 2000

Potentially significant mechanical improvements in tension can be achieved by the incorporation of randomly distributed, short discrete fibers in concrete. The improvements due to the incorporation fibers significantly influence the composite stress - strain ($\sigma$-$\varepsilon$) characteristics. In general incorporating fibers in a plain concrete has relatively small effect on its precracking behavior. It, however, alters its post-cracking behavior quite significantly, resulting in greatly improved ductility, crack controls, and energy absorption capacity (or toughness). Therefore, a thorough understanding the complete tensile stress - strain ($\sigma$-$\varepsilon$) response of fiber reinforced concrete is necessary for proper analysis while using structural components made with fiber reinforced concrete. Direct tensile stress applied to a specimen is in principle the simplest configuration for determining the tensile response of concrete. However, problems associated with testing brittle materials in tension include (i) the problem related to gripping of the specimen and (ii) the problem of ensuring centric loading. Routinely, indirect tension tests for plain concrete, flexural and split-cylinder tests, have been used as simpler alternatives to direct uniaxial tension test. They are assumed to suitable for fiber reinforced concrete since typically such composites comprise 98% by volume of plain concrete. Clearly since the post-cracking characteristics are significantly influenced by the reinforcing parameters and interface characteristics, it would be fundamentally incorrect to use indirect tensile tests for determining the tensile properties of fiber reinforced concrete. The present investigation represents a systematic look at the failure and toughening mechanisms and macroscopic stress - strain ($\sigma$-$\varepsilon$) characteristics of fiber reinforced concrete in the uniaxial tension test. Results from an experimental parametric study involving used fiber quantity, type, and mechanical properties in the uniaxial tension test are presented and discussed.