• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.53-58
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• 2003

Carbon fiber sheet has been used to rehabilitate many types of reinforced concrete members with its superior characteristics such as their lightweight, high strength, corrosion resistance, and easy execution. But the failure behavior of reinforced concrete members show a high variation by the bond characteristics between carbon fiber sheet and concrete surface. In this study, a bond stress-slip model, which accounts for changes in bonding behavior between concrete and carbon fiber sheet with some link elements, is proposed. The link elements are used to represent the concrete-carbon fiber sheet interface. To investigate the efficiency of this method, the analytical solutions for the behavior of reinforced concrete beam strengthened with carbon fiber sheet are compared with experimental ones. Results from the proposed model comparatively well agree with the experimental results.

• Computers and Concrete
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• v.16 no.6
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• pp.909-918
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• 2015

This paper presents an experimental study for determining the bond performance of lightweight concretes produced using pumice aggregate coated with colemanite-cement paste. For this purpose, eight hinged beam specimens were produced with four different concrete mixtures. 14 mm deformed bars with $10{\Phi}$ development lengths were selected constant for all test specimens. All the specimens were tested in bending and load-slip values were measured experimentally to determine the effect of colemanite-cement coated pumice aggregate on bond performances of lightweight concretes. Test results showed that, colemanite-cement coated pumice aggregate increases compressive strength and bond performance of the lightweight concretes, considerably.

• Structural Engineering and Mechanics
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• v.7 no.1
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• pp.35-52
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• 1999

Realistic steel-concrete bond/slip relationships proposed in the literature are usually uniaxial. They are based on phenomenological theories of deformation and degradation mechanisms, and various pull-out tests. These relationships are usually implemented using different analytical methods for solving the differential equations of bond along the anchored portion, for particular situations. This paper justifies the concepts, and points out the assumptions underlying the construction and use of uniaxial bond laws. A finite element implementation is proposed using 2-D membrane elements. An application example on an interior beam-column joint illustrates the possibilities of this approach.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.770-773
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• 2004

The full-width, full-depth precast panel system is very efficient for the rehabilitation of deteriorated decks as well as for new bridge construction.. The horizontal bond strength at the interface between the two interconnected elements is of primary importance in order to achieve composite action. The strength of the bond between the two precast members should be high enough to prevent any progressive slip from taking place. However, the case when both of the interconnected elements are precast members bonded by means of grout, is not currently addressed by KBDC or AASHTO. This is the main impetus for this study. A total 43 push-off tests were performed to evaluate the horizontal bond strength and to recommend the best practice for the system. Test parameters included different interface surface conditions, different amount and different types of shear connectors. The presence of the shear keys at the top surface of the beam increased the interface bond capacity tremendously compared to the bond capacity with a different surface conditions.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.155-163
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• 2013

This study investigated the bond characteristics of embedded deformed steel bar in donut type biaxial hollow slabs. The donut type hollow sphere make concrete inner cover formed between steel bar and hollow sphere due to the hollow shape and arrangement. Generally, inner cover was thinner than outer cover, and some part of donut type biaxial hollow slab has smaller inner cover thickness than $2.5d_b$. It was affected to the bond condition of deformed bar. Furthermore, inner cover thickness changes along the longitudinal deformed bar due to hollow shape. Therefore, donut type hollow slab was divided 3 regions according to the hollow shape such as insufficient region, transition region, sufficient region. Pull-out test were performed to find out the effect of bond condition by the region. Main parameters are inner cover thickness, embedded length and bond location. Bond characteristics of donut type biaxial hollow slab were confirmed through comparison of bond stress-slip relationship, maximum bond strength and bond stress distribution of each regions. And the calculation method of bond strength of donut type biaxial hollow slab was suggested based on the test results.

• Journal of the Korea Institute of Building Construction
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• v.15 no.5
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• pp.465-471
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• 2015

This study proposed V-shaped tie bar method as an alternative of internal cross-tie for reinforced concrete columns in order to enhance the constructability and confinement effectiveness of the lateral tie bars. A total of 35 pull-out specimens were prepared with the parameters of concrete compressive strength and bending angle and embedment length of the V-shaped bar to examine the bond stress-slip relationship of the V-shaped tie bar. The bond strength of the V-shaped tie bars with the bending angle not exceeding $60^{\circ}$ was higher than the predictions obtained from the equations of CEB-FIP provision. Considering the constructability and bond behavior of the V-shpaed tie bar, the bending angle and embedment length of such bar can be optimally recommended as $45^{\circ}$ and 6db, respectively, where db is the diameter of the tie bar.

• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.119-126
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• 2009

This paper provides a brief summary of the performance of an innovative slip hardening twisted steel fiber in comparison with other fibers including straight steel smooth fiber, high strength steel hooked fiber, SPECTRA (high molecular weight polyethylene) fiber and PVA fiber. First the pull-out of a single fiber is compared under static loading conditions, and slip rate-sensitivity is evaluated. The unique large slip capacity of T-fiber during pullout is based on its untwisting fiber pullout mechanism, which leads to high equivalent bond strength and composites with high ductility. Due to this large slip capacity a smaller amount of T-fibers is needed to obtain strain hardening tensile behavior of fiber reinforced cementitious composites. Second, the performance of different composites using T-fibers and other fibers subjected to tensile and flexural loadings is described and compared. Third, strain rate effect on the behavior of composites reinforced with different types and amounts of fibers is presented to clarify the potential application of HPFRCC for seismic, impact and blast loadings.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.3
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• pp.153-158
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• 2020

In this study, a numerical approach for evaluating the resisting capacity of a partial concrete-filled steel tube (CFST) column is introduced. By strengthening the plastic hinge part of a traditional reinforced concrete column with a steel tube, a partial CFST shows a similar bending moment capacity as that of a full CFST column but with reduced material cost. To conduct an elaborate numerical analysis of a partial CFST column, an improved bond-slip model is applied to a finite element (FE) model at the interface between the steel tube and in-filled concrete. This numerical model is verified through the results of a double curvature bending-compression test. A parametric study with the proposed numerical model is used to obtain the load moment interaction diagrams for evaluating the resisting capacity based on various dimensions. Finally, the required strengthening length is estimated for each degree of thickness of the steel tube, and the failure mechanism of the partial CFST column based on the dimensions of the steel tube are identified.

• Computers and Concrete
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• v.26 no.2
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• pp.115-125
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• 2020

To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800℃ for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concrete-rebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.381-388
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• 2010

In this study, characteristics of the seismic response of the non-earthquake resistant reinforced concrete (RC) frame were identified. The test building is designed to withstand only gravity loads and not in compliance with modern seismic codes. Smooth bars were utilized for the reinforcement. Members are provided with minimal amount of stirrups to withstand low levels of shear forces and the core concrete is virtually not confined. Columns are slender and more flexible than beams, and beam-column connections were built without stirrups. Through the modeling of an example RC frame, the feasibility of the fiber elementbased 3D nonlinear analysis method was investigated. Since the torsion is governed by the fundamental mode shape of the structure under dynamic loading, pushover analysis cannot predict torsional response accurately. Hence, dynamic response history analysis is a more appropriate analysis method to estimate the response of an asymmetric building. The latter method was shown to be accurate in representing global responses by the comparison of the analytical and experimental results. Analytical models without rigid links provided a good estimation of reduced stiffness and strength of the test structure due to bond-slip, by forming plastic hinges closer to the column ends. However, the absence of a proper model to represent the bond-slip poased the limitations on the current inelastic analysis schemes for the seismic analysis of buildings especially for those with round steel reinforcements. Thus, development of the appropriate bond-slip model is in need to achieve more accurate analysis.