• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.213-224
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• 2018

In this study, a series of accelerated creep tests (SIM) was carried out on geosynthetic strip reinforcements with folding grooves having different tensile strengths (15 kN, 25 kN, 35 kN, 50 kN, 70 kN, and 90 kN) to analyze creep characteristics and to assess creep reduction factors. In particular, long-term creep tests were conducted on geosynthetic strip reinforcements with 25 kN tensile strength, which is widely used, to compare and analyze the accelerated creep test results. As a result, the creep reduction factor increased with an increasing design life of reinforcement. In addition, geosynthetic strip reinforcement using the same material and manufacturing method showed similar creep reduction factors at the same design life for different tensile strengths. When both long-term and accelerated creep test data were used, the creep reduction factors from the accelerated test were estimated to be 5.9%~7.1% less than those from the long-term creep test for the design life ranging from 50 to 100 years.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.196-203
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• 2008

Durability of geosynthetics for soil reinforcement is accounted for creep and creep rupture, installation damage and weathering, chemical and biological degradation. Among these, the long-term creep properties have been considered as the most important factors which are directly related to the failure of geosynthetic-reinforced soil(GRS). However, the creep test methods and strain limits are too various to compare the test results with each other. The most widely used test methods are conventional creep test, time-temperature superposition and stepped isothermal method as accelerated creep tests. Recently developed design guidelines recommend that creep-rupture curve be used to determine the creep reduction factor($RF_{CR}$) which is a conservative approach. In this study, the different creep test methods were compared and the creep reduction factors were estimated at different creep strain limits of 10% of total creep strain and creep rupture. In order to minimize the impact of creep strain to the GRS structures, the various creep reduction factors using different creep test methods should be investigated and then the most appropriated one should be selected for incorporating into the design.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.303-314
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• 2010

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 49 kinds of the laboratory model tests were conducted. And the result the study suggested $\beta_s$, the stiffness coefficient to evaluate the stiffness effect of reinforcement materials. Then, it was also found that the stiffness coefficient, $\beta_s$ as the testing constant would be appropriate as high as 1.0, 1.1 and 1.5 for geotextile, geogrid and steel bar, respectively. And It was evaluated that the stiffness effect affecting reinforcement improvement effect would be reduced as the thickness of embeded depth increases and that RFe, the stiffness effect reduction coefficient would have positive correlation with H/B. Finally, it was confirmed that the bearing capacity gained from the method to calculate bearing capacity, which was suggested in the study, would almost correctly estimate the capacity, demonstrating the appropriateness of the proposed bearing capacity calculation method.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1519-1524
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• 2009

Construction of high-speed concrete track embankments over soft ground needs many of the ground improvement techniques. Drains, surcharge loading, and geosynthetic reinforcement, have all been used to solve the settlement and embankment stability issues associated with construction on soft soils. However, when time constraints are critical to the success of the project, another measures should be considered. Especially, since the design criteria of residual settlement is limited as 30mm for concrete track embankment, it is very difficult to satisfy this allowable settlement by using the former construction method. Pile net method consist of vertical columns that are designed to transfer the load of the embankment through the soft compressible soil layer to a firm foundation and one or more layers of geosynthetic reinforcement placed between the top of the columns and the bottom of the embankment. In this paper, three cases with different embankment height and number of geosynthetic reinforcement, were studied through FEM analysis for efficient use of pile net method.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.479-489
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• 2019

The corrosion of reinforcement leads to a gradual decay of structural strength and durability. Several models for crack occurrence prediction and crack width propagation are investigated in this paper. Analytical and experimental models were used to predict the bond strength in the period of corrosion propagation. The manner of flexural strength loss is calculated by application of these models for different scenarios. As a new approach, the variation of the concrete beam neutral axis height has been evaluated, which shows a reduction in the neutral axis height for the scenarios without loss of bond. Alternatively, an increase of the neutral axis height was observed for the scenarios including bond and concrete section loss. The statistical properties of the parameters influencing the strength have been deliberated associated with obtaining the time-dependent bending strength during corrosion propagation, using Monte Carlo (MC) random sampling method. Results showed that the ultimate strain in concrete decreases significantly as a consequence of the bond strength reduction during the corrosion process, when the section reaches to its final limit. Therefore, such sections are likely to show brittle behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.11-18
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• 2012

Deterioration and weakening is advanced in compliance with flowing of time and the change of environment in RC structures. Consequently, strength and serviceability decreases, finally, the life of infrastructure shortens and safety characteristics decreases. Accordingly, in this study, a new method to develop a strengthening method using the vacuum impregnation, which increases durability of the infrastructure occurred the safety reduction due to the performance degradation and increases the life of infrastructure by improving the durability compared to the existing method, was planned. For flexural tests, the maximum strength was a low-end order from high order as follows: (1) vacuum impregnation with 2 fold reinforcement, (2) fiber sheet 2 fold reinforcement, (3) vacuum impregnation with 1 fold reinforcement, (4) fiber sheet 1 fold reinforcement, and (5) nothing. Also, for confirmation results about durability, when the fiber reinforcement is being exposed to the inferior environment, the remaining tensile strength exceeded of 90% or more for all environments. This is because the reinforcement used in this research shows the excellent resistance in severe environment.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.161-167
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• 2014

This paper describes reinforcement method of reinforced earth wall near the abutment. The excessive displacement of a case affected by reduction of bearing capacity due to macro-environment condition like a coast. That is, the front displacement of reinforced earth wall has been happening continuously due to strength reduction of foundation ground. The micro pile is applied to reinforcement method, in order to secure a bearing capacity and global slope stability of reinforced earth wall. The results of numerical analysis confirmed that reinforcement method based on micro pile can secure a stability of structure, while the reconstruction of reinforced earth wall is impossible by construction and macro-environment condition.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1233-1250
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• 2015

The behavior of reinforced concrete (RC) columns made from high strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength transverse reinforcing bars and three with normal-strength transverse reinforcement, were tested under double curvature bending load. The effects of yielding strength and ratio of transverse reinforcement on the cracking patterns, hysteretic response, shear strength, ductility, strength reduction, energy dissipation and strain of reinforcement were studied. The test results indicated that all specimens failed in splitting failure, and specimens with high-strength transverse reinforcement exhibited better seismic performance than those with normal-strength transverse reinforcement. It also demonstrated that the strength of high-strength lateral reinforcing bars was fully utilized at the ultimate displacements. Shear strength formula of short concrete columns, which experienced a splitting failure, was proposed based on the Chinese concrete code. To enhance the applicability of the model, it was corroborated with 47 short concrete columns selected from the literature available. The results indicated that, the proposed method can give better predictions of shear strength for short columns that experienced a splitting failure than other shear strength models of ACI 318 and Chinese concrete codes.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.1
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• pp.21-31
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• 2016

This study investigates the seismic performance of new hollow reinforced concrete (RC) bridge piers with triangular reinforcement details. The developed triangular reinforcement details are economically feasible and rational, and facilitate shorter construction periods. We tested a model of new hollow RC bridge piers with triangular reinforcement details under a constant axial load and a quasi-static, cyclically reversed horizontal load. We used a computer program, Reinforced Concrete Analysis in Higher Evaluation System Technology (RCAHEST), for analysis of RC structures. The used numerical method gives a realistic prediction of seismic performance throughout the loading cycles for several hollow pier specimens investigated. As a result, developed triangular reinforcement details for material quantity reduction was equal to existing reinforcement details in terms of required performance.

• Design & Manufacturing
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• v.12 no.2
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• pp.40-45
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• 2018

Recently, in construction equipment machinery production, development has focused on environmentally-friendly functions to improve existing production capacity. For excavators as well, emphasis has been placed on response to environmental regulations, miniaturization, and noise reduction, while technology is being developed considering cost reduction and safety.Accordingly, the front support, an inner reinforcement part of the excavator, as well as high-strength steel plates to improve safety and reduce weight, are being applied.However, in the case of high-strength materials, Springback occurs in the final formed part due to high residual stress during product forming. Derivation of a forming or product shaping process to reduce springback is needed. Accordingly, regarding the front support, an inner reinforcement part of the excavator, this study derived a method to improve springback and secure shape stiffness through analysis of the springback occurrence rate and springback causes through a forming analysis.As for the results of analyzing the springback occurrence rate of existing products through forming analysis, springback of -22.6 mm < z < 27.35 mm occurred on the z-axis, and it was confirmed that springback occurred due to the stiffness reinforcing bead of the upper and middle parts of the product.To control product residual stress and springback, we confirmed a tendency of springback reduction through local pre-cutting and stiffness reinforcement bead relocation.In the local pre-cutting model, springback was slightly reduced by 5.3% compared with the existing model, an insignificant reduction effect. In the stiffness reinforcement bead relocation model, when an X-shaped stiffness reinforcement bead was added to each corner portion of the product, springback was reduced by at least 80%.The X-shaped bead addition model was selected as the springback reduction model, and the level of stiffness compared to the existing model was confirmed through a structural analysis.The X-shaped bead additional model showed a stress springback of 90% and springback reduction of 7.4% compared with the existing model, indicating that springback and stiffness will be reinforced.