• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.727-732
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• 2022

Applying the calculated cross-sectional reduction due to the corroded rebar investigated in the field to the numerical analysis model, the damage pattern and delamination of concrete in the field showed a tendency relatively similar to the numerical analysis results. It was analyzed that when the expansion pressure due to corrosion of the reinforcing bar is greater than the tensile stress of the concrete, cracks are generated and the concrete cover can be fracture. As a result of this study, the correlation between the corrosion rate of reinforcing bars and the crack occurrence of the concrete cover of the subway box structure was verified based on the numerical analysis and field test results. To prevent rebar corrosion, the corrosion rate can be reduced by applying rust prevention to the reinforcing bar and changing the material. In the case of exposed to a corrosive environment, the tensile strength of the concrete is improved by adjusting the concrete compressive strength to secure durability against the expansion pressure caused by the corroded rebar.

• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.29-34
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• 2006

Elastic modulus, tensile and bond capacities are important factors for developing an effective reinforcing action of a flexural member as a reinforcing material for concrete structures. Reinforcement must have enough bond capacity to prevent the relative slip between concrete and reinforcement. This paper presents an experimental study to clarify the bond capacity of prestressed carbon fiber reinforced polymer(CFRP) rod manufactured by an automatic assembly robot. The bond characteristics of CFRP rods with different pitch of helical wrapping were analyzed experimentally. As the result, all types of CFRP rods show a high initial stiffness and good ductility. The mechanical properties of helical wrapping of the CFRP rods have an important effect on the bond of these rods to concrete after the bond stress reached the yield point. The stress-slip relationship analyzed from the pull-out test of embedded cables within concrete was linear up to maximum bond capacity. The deformation within the range of maximum force seems very low and was reached after approximately 1 mm. The average bond capacity of CF20, CF30 and CF40 was about 12.06 MPa, 12.68 MPa and 12.30 MPa, respectively. It was found that helical wrapping was sufficient to yield bond strengths comparable to that of steel bars.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.173-179
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• 2000

The friction and wear characteristics of brake friction materials reinforced with aramid fiber, carbon fiber, glass fiber, and potassium titanate whiskers were investigated using a pad-on-disk type friction tester. In particular, the morphology of rubbing surfaces was carefully investigated to correlate the friction performance and properties of transfer films. The aramid fiber reinforced specimen showed severe oscillation of friction coefficient at low speed and low applied pressure. The carbon fiber reinforced specimen showing better friction stability exhibited uniform and stable transfer film than any other specimens. The glass fiber reinforced specimen showed unstable friction changes at high speed and high-applied pressure and the non-uniform transfer film was observed in both friction material and rotor surface. The potassium titanate whiskers reinforced specimen showed stable coherent transfer film. The wear test exhibited the potassium titanate whiskers reinforced specimen was lowest in wear amount and glass fiber reinforced specimen showed the severe wear.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.106-114
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• 2006

Uses of geosynthetics as a reinforcing material for earth structures have ever increased due to their excellent economy. fine external appearance. and easy construction. In the current practice of geosynthetics. however, the lacks of the standardized method of evaluating the soil/geosynthetics friction properties and the inconsistency of conventional design methods develop confusion to the civil engineers. The purpose of site monitoring of the retaining wall reinforced by geogrids was to evaluate the applicability of existing design methods to, and performance of. CHAMSTONE wall system. Full scale field performance during and after construction was monitored by incorporating instrumentation including strain gauges on the geogrid and soil pressure cells. The difference of the reinforcing effects of geosynthetics embedded in the soil will be also investigated by comparing of the line and curve types of retaining wall reinforced by geogrids with block type facings.

• Structural Engineering and Mechanics
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• v.64 no.2
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• pp.155-171
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• 2017

This paper presents a proposed method for producing reinforced composite concrete columns reinforced with various types of metallic and non metallic mesh reinforcement. The experimental program includes casting and testing of twelve square columns having the dimensions of $100mm{\times}100mm{\times}1000mm$ under concentric compression loadings. The test samples comprise all designation specimens to make comparative study between conventionally reinforced concrete column and concrete columns reinforced with welded steel mesh, expanded steel mesh, fiber glass mesh and tensar mesh. The main variables are the type of innovative reinforcing materials, metallic or non metallic, the number of layers and volume fraction of reinforcement. The main objective is to evaluate the effectiveness of employing the new innovative materials in reinforcing the composite concrete columns. The results of an experimental investigation to examine the effectiveness of these produced columns are reported and discussed including strength, deformation, cracking, and ductility properties. Non-linear finite element analysis; (NLFEA) was carried out to simulate the behavior of the reinforced concrete composite columns. The numerical model could agree the behavior level of the test results. ANSYS-10.0 Software. Also, parametric study is presented to look at the variables that can mainly affect the mechanical behaviors of the model such as the change of column dimensions. The results proved that new reinforced concrete columns can be developed with high strength, crack resistance, and high ductility properties using the innovative composite materials.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.117-120
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• 2003

Electro-micromechanical techniques were applied using four-probe method for carbon nanotube (CNT) or nanofiber (CNF)/epoxy composites with their content. Carbon black (CB) was used to compare with CNT and CNF. The fracture of carbon fiber was detected by nondestructive acoustic emission (AE) relating to electrical resistivity for double-matrix composites test. Sensing for fiber tension was performed by electro-pullout test under uniform cyclic strain. The sensitivity for fiber damage such as fiber fracture and fiber tension was the highest for CNT/epoxy composites, and in CB case they were the lowest compared with CNT and CNF. Reinforcing effect of CNT obtained from apparent modulus measurement was the highest in the same content. The results obtained from sensing fiber damage were correlated with the morphological observation of nano-scale structure using FE-SEM. The information on fiber damage and matrix deformation and reinforcing effect of carbon nanocomposites could be obtained from electrical resistivity measurement as a new concept of nondestructive evaluation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.31-34
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• 2009

Large outrigger elements tie the concrete core to perimeter columns, significantly increasing the building's lateral stiffness as well as its resistance to overturning due to wind. The outriggers are deep elements, and large tie forces are resisted by top and bottom heavy longitudinal reinforcing and vertical ties. To reduce construction costs, all primary reinforcing bars in outrigger levels are SD500. Further, concrete strengths of 80MPa have been specified for outrigger elements. However, the reductions in the amount of concrete and reinforcement steel are more increased in tall building. With these backgrounds, 80MPa high strength concrete outrigger system using post tension method is developed. Significant economic savings can be made by reducing the element sizes and material content. The developed outrigger system is designed using strut-and-tie models. In addition, four 1/4-scale test specimens were selected from the same prototype structure. The results from the tests are confirmed that the structural behaviors of the developed outrigger member have better capacities than those of a conventional method.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.389-396
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• 2001

This paper presents an analytical prediction of the fatigue behavior of reinforced concrete bridge piers under earthquake. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. In boundary plane at which each member with different thickness is connected, local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. The proposed numerical method for fatigue behavior of reinforced concrete bridge piers under earthquake will be verified by comparison with reliable experimental results.

• Structural Engineering and Mechanics
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• v.37 no.1
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• pp.111-129
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• 2011

This paper presents a nonlinear analysis of reinforced concrete column with lap splice confined by FRP wrapping in the critical hinging zone. The steel stress-slip model derived from the tri-uniform bond stress model presented in the companion paper is included in the nonlinear frame analysis to simulate the response of reinforced concrete columns subjected to cyclic displacement reversals. The nonlinear modeling is based on a fiber discretization of an RC column section. Each fiber is modeled as either nonlinear concrete or steel spring, whose load-deformation characteristics are calculated from the section of fiber and material properties. The steel spring that models the reinforcing bars consists of three sub-springs, i.e., steel bar sub-spring, lap splice spring, and anchorage bond-slip spring connected in series from top to bottom. By combining the steel stress versus slip of the lap splice, the stress-deformation of steel bar and the steel stress-slip of bars anchored into the footing, the nonlinear steel spring model is derived. The analytical responses are found to be close to experimental ones. The analysis without lap splice springs included may result in an erroneous overestimation in the strength and ductility of columns.

• Geomechanics and Engineering
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• v.16 no.5
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• pp.559-567
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• 2018

Technological innovations in sustainable materials for soil improvement have attracted considerable interest due to energy crisis and environmental concerns in recent years. This study presents results of a comprehensive investigation on utilization of nanocarbons in reinforcement of a residual soil mixed with 0, 10 and 20% bentonite. Effects of adding proportionate quantities (0, 0.05, 0.075, 0.1 and 0.2%) of carbon nanotubes and carbon nanofibers to soil samples of different plasticities were evaluated. The investigation revealed that the inclusion of nanocarbons into the soil samples significantly improved unconfined compressive strength, Young's modulus and indirect tensile strength. It was observed that carbon nanofibers showed better performance as compared to carbon nanotubes. The nanosized diameter and high aspect ratio of nanocarbons make it possible to distribute the reinforcing materials on a much smaller scale and bridge the inter-particles voids. As a result, a better 'soil-reinforcing material' interaction is achieved and desired properties of the soil are improved at nanolevel.