• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.323-331
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• 2012

This paper presents a new strengthening method on concrete column against seismic loads for structural performance tests. An X-bracing using high performance carbon fiber threads called the "Carbon fiber anchor X-bracing system" is used to connect RC frames internally. The carbon fiber sheet is wrapped around the column to fix the top and bottom of the column after Super anchor was installed by drilling hole on the column. The structural performance was evaluated experimentally and analytically. Two types of columns specimens were made; flexure fracture scaled model and shear fracture scaled model. For the performance evaluation, cyclic loading tests were conducted on moment and shear resisting columns with and without X bracing. Test results confirmed that the bracing system installed on RC columns enhanced the strength capacity and provided adequate ductility.

• The Journal of the Convergence on Culture Technology
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• v.5 no.3
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• pp.345-349
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• 2019

In Korea, the mountainous area occupies more than 70% of the whole country, cutting of earth slope that cuts a part of the ground surface is widely used when building infrastructures such as road, railroad, and industrial complex construction. In recent years, regulations on environmental damage have become more strict, and various methods have been developed and applied. Among them, Concrete-Panel Retaining Wall technique is actively applied. Concrete-Panel Retaining Wall is a method to resist horizontal earth pressure by forming a wall by attaching a precast retaining wall to the front of the support material and increasing the shear strength of the disk through reinforcement of the support material. Soil nailing, earth bolt, and ground anchor are used as support material. Among them, ground anchor is a more aggressive reinforcement type that introduces tensile load in advance to the steel wire, and a large concentrated load acts on the front panel. This concentrated load is a factor that creates cracks in the concrete panel and reduces the durability of the retaining wall itself. In this study, steel pipe sleeves and reinforcements were purchased at the anchorage of the panel to prevent cracks, and by applying bumpy shear keys to the end of the panel, the weakness of the individual behavior of the existing grout anchors was improved. The problem of degraded landscape by exposure to front concrete of retaining wall and protrusion of anchorage was solved by the production of natural stone patterns and the construction of sections that do not protrude the anchorage. In order to verify the effectiveness of anti-crack sleeves and reinforcements used in the null, indoor testing and three-dimensional numerical analysis have been performed, and the use of steel pipe sleeves and reinforcements has demonstrated the overall strength increase and crack suppression effect of panels.

• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.531-541
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• 2013

This paper investigated the structural capacity of the CT shear connectors, which is a kind of the perfobond rib and functions as an anchor transferring the tension force in the joint between a composite PHC wall pile and a bottom slab. The direct pull-out test was performed for various specimens. From failure modes and load-displacement curves, it was found that transverse rebars should be placed to holes in a web to restrict pull-out failure of CT shear connectors. The results of additional tests for specimens with transverse rebars and various support lengths indicated that all specimens were failed by the tension failure of PHC pile before pull-out failure of CT shear connector and concrete pull-out failure. Thus, the CT shear connector could endure the tension force between the PHC wall pile and the bottom slab.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.197-206
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• 2004

The ground anchor support system may not be occasionally used because of space limitations in urban excavation sites nearby the existing structures. In this case, soil nailing system with relatively short length of nails could be efficiently adopted as an alternative method. The general soil nailing support system, however, may result in excessive deformations particularly in an excavation zone of the existing weak subsoils. Pretensioning the soil nails then could play important roles to reduce deformations mainly in the upper part of the nailed-soil excavation system as well as to improve local stability. In this study, a newly modified soil nailing technology named as the PSN (Pretension Soil Nailing), is developed to reduce both facing displacements and ground surface settlements in top-down excavation process as well as to increase the global stability. Up to now, the analytical procedure and design technique are proposed to evaluate maximum pretension force and stability of the PSN system. Also, proposed are techniques to determine the required thickness of a shotcrete facing and to estimate probability of a failure against the punching shear, Based on the proposed procedure and technique, effects of the radius of a influence circle and dilatancy angle on the thickness of a shotcrete facing, bonded length and safety factors are analyzed. In addition, effects of the reduction of deformations expected by pretension of the soil nails are examined in detail throughout an illustrative example and the $FLAC^{2D}$ program analysis. And a numerical approach is proposed PSN system using the shear strength reduction technique with the $FLAC^{2D}$ program.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.483-490
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• 2007

Traditional external post-tensioning method using either steel bars or tendons is commonly used as a retrofitting method for concrete bridges. However, the external post-tensioning method has some disadvantages such as stress concentration at anchorages and inefficient load carrying capability regarding live loads. Thermal prestressing method is a newly proposed method for strengthening and rehabilitation of concrete girder bridges. Founded on a simple concept of thermal expansion and contraction of steel, the method is a hybrid method of external post-tensioning and steel plate bonding, combining the merits of two methods. In this paper, basic concepts of the method are presented and an illustrative experiment is introduced. From actual experimental data, the thermal prestressing effect is substantiated and the FEM approach for its analysis is verified.