• Advances in concrete construction
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• v.11 no.3
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• pp.261-270
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• 2021

In this study, a new understanding is presented on the microcracking behavior of high strength concrete (HSC) with steel fiber addition having prior compressive loading history. Microcracking behavior at critical stress (σcr) region, using seven fiber addition volume of 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0% was evaluated, at two aspect ratios (60 and 75). The specimens were loaded up to a specified compressive stress levels (0.70fc-0.96fc), and subsequently subjected to split tensile tests. This was followed by microscopic analyses afterwards. Four compressive stress levels as percentage of fc were selected according to the linearity end point based on stress-time (σ-t) diagram under uniaxial compression. It was seen that pre-compression has an effect on the linearity end point as well as fiber addition where it lies within 85-91% of fc. Tensile strength gain was observed in some cases with respect to the 'maiden' tensile strength as oppose to tensile strength loss due to the fiber addition with teething effect. Aggregate cracking was the dominant failure mode instead of bond cracks due to improved matrix quality. The presence of the steel fiber improved the extensive failure pattern of cracks where it changes from 'macrocracks' to a branched network of microcracks especially at higher fiber dosages. The applied pre-compression resulted in hardening effect, but the cracking process is similar to that in concrete without fiber addition.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.191-196
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• 2002

The bonding strength of the interface between the actual bridge concrete deck and overlay was primarily affected by the shear that depended on the flexural behavior than pure tensile, but the field bonding test measured bonding strength by the pure tensile due to simplicity and field applicability. Therefore, the purpose this study was to evaluate the required direct bond strength for bridge deck overlay using Finite element analysis with the many variavles such as bridge deck types, span length, material properties, lanes, and loading types. The commercial program LUSAS was used in analysis. The analysis results were compared to the value of specification currently used in highway construction site.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.79-86
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• 2012

Though steel reinforcing bars are the most widely used tensile reinforcement, corrosion problems are encountered due to the exposure to aggressive environments. As an alternative material to steel, the fiber reinforced polymers have been used as reinforcement in concrete structures. However, bond strength of FRP rebar is relatively low compared to steel rebar. It has been reported that fibers in matrix can resist crack growth, propagation and finally result in an increase of toughness. In this study, high-strength concrete reinforced with structural fibers was produced to enhance interfacial bond behavior between FRP rebar and concrete matrix. The interfacial bond-behaviors were investigated from a direct pullout test. The test variables were surface conditions of GFRP bars and fiber types. Total of 54 pullout specimens with three different types of bars were cast for bond strength tests. The bond strength-slip responses and resistance of the bond failure were evaluated. The test results showed that the bond strength and toughness increased according to the increased fiber volume.

• Structural Engineering and Mechanics
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• v.40 no.6
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• pp.847-866
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• 2011

The objective of this study was to experimentally investigate the bond-related tension stiffening behavior of flexural reinforced concrete (RC) beams made with lightweight aggregate concrete (LWAC) under various high-cycle fatigue loading conditions. Based on strain measurements of tensile steel in the RC beams, fatigue-induced degradation of tension stiffening effects was evaluated and was, compared to reinforced normal weight concrete (NWC) beams with equal concrete compressive strengths (40 MPa). According to applied load-mean steel strain relationships, the mean steel strain that developed under loading cycles was divided into elastic and plastic strain components. The experimental results showed that, in the high-cycle fatigue regime, the tension stiffening behavior of LWAC beams was different from that of NWC beams; LWAC beams had a lesser reduction in tension stiffening due to a better bond between steel and concrete. This was reflected in the stability of the elastic mean steel strains and in the higher degree of local plasticity that developed at the primary flexural cracks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.73-81
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• 2022

Recently, as the service life of structures increased, the load-carrying capacity of deteriorated reinforced concrete, where corrosion of reinforcing bars occurs due to various causes, is frequently decreased. In order to address this problem, many studies on the bond characteristic of FRP (Fiber Reinforced Polymer) bars with corrosion resistance, light weight and high tensile strength have been conducted, however there are not many studies on the bond characteristic of grid-typed CFRP embedded in concrete. Therefore, in order to evaluate the bond characteristics of grid-typed CFRP and its usability as a substitute for steel rebar, a pull-out test is performed using the longitudinal bond length and transverse grid length of the grid-typed CFRP as variables. Through the pull-out test, the bond load-slip curve of the grid-typed CFRP is derived, and the bond behavior is analyzed. The total bond load equation is proposed as the sum of the bond force of the longitudinal bond length and the shear force of the grid in the transverse direction. Also, expressing the area of the bond load-slip curve as total work, the change in dissipated energy with respect to the slip is analyzed to examine the effect of the tranverse grid on the bond force.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.865-870
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• 2001

This paper propose a new seismic detail for ductility enhancement by interlocking spiral reinforcement in the potential yield regions of a wall. Through the theoretical consideration and experiment program, confinement with interlocking spirals lead the structural walls to ductile behavior. All specimens show stable hysteretic behavior and good energy dissipation capacity. Also the increase of shear strength mainly induces a flexural failure mode. As interlocking spiral are used in lapped splice region, they increase the bond strength and prevent a early tensile failure caused by the loss of bond stresses. Consequently, the confinement with interlocking spirals may result in a lower value of force reductions factor, newly proposed detail will be provide more economical design.

• Steel and Composite Structures
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• v.35 no.4
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• pp.463-474
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• 2020

In this paper, the influence of adding multi-walled carbon nanotube (MWCNT) on the pull behavior of steel and GFRP bars in ultra-high-performance concrete (UHPC) was examined experimentally and numerically. For numerical analysis, 3D nonlinear finite element modeling (FEM) with the help of ABAQUS software was used. Mechanical properties of the specimens, including Young's modulus, tensile strength and compressive strength, were extracted from the experimental results of the tests performed on standard cube specimens and for different values of weight percent of MWCNTs. In order to consider more realistic assumptions, the bond between concrete and bar was simulated using adhesive surfaces and Cohesive Zone Model (CZM), whose parameters were obtained by calibrating the results of the finite element model with the experimental results of pullout tests. The accuracy of the results of the finite element model was proved with conducting the pullout experimental test which showed high accuracy of the proposed model. Then, the effect of different parameters such as the material of bar, the diameter of the bar, as well as the weight percent of MWCNT on the bond behavior of bar and UHPC were studied. The results suggest that modifying UHPC with MWCNT improves bond strength between concrete and bar. In MWCNT per 0.01 and 0.3 wt% of MWCNT, the maximum pullout strength of steel bar with a diameter of 16 mm increased by 52.5% and 58.7% compared to the control specimen (UHPC without nanoparticle). Also, this increase in GFRP bars with a diameter of 16 mm was 34.3% and 45%.

• Magazine of the Korean Society of Agricultural Engineers
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• v.29 no.4
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• pp.124-131
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• 1987

The aims of this study was to determine the mechanical properties of steel-fiber reinforced concrete under direct tensile loading, and also to insestigate the mechanism fiber reinforcement in order to improve the possible applications of steel-fiber reinforced concrete. In this study the major variables of experimental investigation were fiber conntents, and the lengths and diameters of fibers. The major results obtained are summarized as follows : 1. The strength, elastic modulus and energy absorption capability of steel-fiber reinforced concrete under direct tensile loading were improved as increasing of fiber contents. 2. The direct tensile strength of steel-fiber reinforced concrete was not influenced by the lengths of fiber, but was decreased as increasing of fiber diameters. 3. The direct tensile strength of steel-fiber reinforced concrete was not influenced by the fiber aspect-ratio, but this was because the fiber contents were below the critical value of fiber content. 4. The correlation of direct tensile strength and combined parameter, Vf l/d, was not good. 5. Mutiple cracking and post-crack resistance were investigated at stress-strain curves in direct tensile test. 6. The effect of fiber reinforcement can be influenced by fiber orientation and the bond strength between fiber and matrix. 7. The improvement of mechanical properties of steel-fiber reinforced concrete under direct tensile loading can be theoretically explained by the concept of composite materials.

• Journal of the Korean Ceramic Society
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• v.43 no.7 s.290
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• pp.415-420
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• 2006

The residual stresses in the interface region of the Thermal Barrier Coating (TBC)/Thermally Grown Oxide (TGO)/Bond Coat (BC) were calculated on the TBC-coated superalloy samples using a Finite Element Method (FEM). It was found that the stress distribution of the interface boundary was dependent upon mainly the geometrical shape or its aspect ratio and the thickness of TGO layer, which was formed by growth and swelling behavior of oxide layer. Maximum compressive residual stress in the TBC/TGO interface is higher than that of the TGO/bond coat interface, and the tensile stress had nothing to do with change of an aspect ratio. The compressive residual stresses in the TBC/TGO and TGO/bond coat interface region increased gradually with the TGO growth.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.129-136
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• 2012

Compression splices are required for all compression members in almost all of the floors in high-rise buildings. Therefore, a clear understanding of the behavior of compression splices can provide a rational design of compression splices. Tests of compression splices with bearing only and bond only cases were conducted to investigate the component resistance characteristics of compression splices. Test results showed that the circumferential tensile stresses induced by bearing and bond overlapped at the end of the splice length deterred bond and bearing splices from developing target splicing strength when both normal bond and bearing splices were used. In particular, the bearing strength was more significantly reduced than the bond strength since the bearing relied on the limited area near the end of the splice length. However, the strength of the normal splice was always higher than the strength of the bond only or the bearing only case. Consequently, the study results showed that splice strength in compression cannot be improved by means of removing bond or bearing. In addition, the bond strength in bond only splices was nearly same as the bond strength in tension splices and the strength increase of compression splice is attributed to end bearing only characteristic.