• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.449-452
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• 2004

The lap splice lengths of deformed steel reinforcing bars and GFRP bars with two different to surface type were experimentally compared using beam specimens. The purpose was to evaluate the length required of the GFRP bar to develop strength equivalent to the conventional steel reinforcing bar. The main test variable was the lap splice length. Two different GFRP bar surfaces were tested: (1) spiral-type GFRP bars and (2) sand coated GFRP bars. For the conventional steel bars (SD400 grade), strength over 400 MPa in tension was reached using the lap splice length of $30d_b$. Splice failure was observed in the specimen with the lap splice length of $20d_b$. For the spiral-type and sand coated GFRP bars, the tensile strength developed in the GFRP bars decreased with decreasing splice lengths. Development of the cracks on beam surfaces was clearly visible for the beams reinforced with the GFRP bars. Mid-span deflections, however, were significantly smaller than the comparable beams with conventional steel bars indicating potential ductility problem.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.127-130
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• 2011

The duplex waterproofing construction method has been investigated to improve various problems (how to fix the sheet, breaking, air/water pocket, and cracks caused by different materials) of the existing rooftop exposed waterproofing construction method. By using fiber sheet, Net PE fabric, and thixotropy urethane with high viscosity, the waterproofing construction method is to glue the ground and waterproof course by circular dot. The method is also to construct the waterproof course with high hardness by using waterproof membrane coatings in upper hybrid system. By gluing the ground and the waterproof course by circular dot, the study is expected to be useful to minimize the simultaneous breaking in the waterproof course as tensile stress is buffer in case of the ground crackling. Also, since the waterproofing construction method is good at moving and emitting vapor from the ground, it is considered to be effective to minimize any damages caused by air/water pocket and get loose of the waterproof course.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.84-92
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• 2012

Anchorage zone in prestressed concrete cable stayed bridges is very important area due to the more accurate analysis is needed to estimate the behavior. In the study, since the cable anchorage zone in the prestressed concrete cable-stayed bridge is subject to a large amount of concentrated tendon forces, it shows very complicated stress distributions and causes a serious local cracks. Accordingly, It is necessary to investigate the parameters of affecting the stress properties, such as the cable inclination, the position of anchor plate, the modeling method and the three dimensional effect. The tensile stress distribution of anchorage zone is compared to the actual design condition by varing the stiffness of spring element in the local modeling and an appropriate position of anchor plate is determined. These results would be elementary data to the stress state of anchorage zone and more efficient design.

• International Journal of Highway Engineering
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• v.16 no.1
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• pp.31-39
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• 2014

PURPOSES : Surface treatment material for pavement preventive maintenance should be inspected field applicability. This study(Part II) aimed to checkup coating characteristics and performance analysis using lab and field tests. The hydrophobic - low viscosity filling material for pavement preventive maintenance is presented in Part I, which is a series of companion study. METHODS : Relative comparison between general asphalt mixtures and surface treatment asphalt mixtures are analyzed and measured for the field application such as indirect tensile strength ratio(TSR), abrasion resistance, crack propagation resistance, temperature resistance, coating thickness, permeability resistance and skid resistance in terms of british pendulum number(BPN). RESULTS : It is found that TSR, crack propagation resistance and permeability resistance is increased as against uncoated asphalt specimen. Abrasion resistance and temperature resistance is secured from the initial coating thickness point of view, which is about 0.2~0.3mm. Skid resistance on the surface treatment pavement is satisfied with the BPN criteria of national highway because of exposed aggregate and crack sill induced pavement deterioration and damage cracks. CONCLUSIONS : The hydrophobic - low viscosity surface treatment material for pavement preventive maintenance is validated on field applicability evaluation based on quantitative analysis of coating thickness and performance analysis using lab and field tests.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.27-31
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• 2013

Magnesium alloy is used on parts of aircraft and electronic equipment because of the highest specific strength among the common metal materials. Recently, studies about appling magnesium alloy sheet to automotive bodies are on the increase rapidly. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Magnesium alloy has low boiling point, so getting sound bead shape is difficult when appling varies welding processes. Resistance spot welding is also particular about setting optimum welding conditions because of spatter generation, pores and cracks occurrence in nugget. And life of electrodes is very short because of alloying with copper that main material of electrodes. This requires frequent dressing and replacement of electrodes and decrease in productivity of resistance spot welding on magnesium alloy. Therefore in this study, for effective analysis of changes in tensile shear load and nugget size during electrode life test, evaluate detail characteristics of resistance spot welding on magnesium alloy sheet using dome type electrode.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.5
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• pp.462-465
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• 2004

After 6 month of using, cracking of gas exhaustion bag cage of Type 304 stainless steel wire for Al melting reverberatory furnace was founded in welds. Analysis of crack causes in the wire were tested by electrochemical method, SEM images of structure and analysis of composition. Resulted from the test, it could be observed that cracks in the welds were a accelerated by formed polythionic acid on surface of bag cage in sensitized region of HAZ, tensile stress and using environment.

• Structural Engineering and Mechanics
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• v.10 no.6
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• pp.589-601
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• 2000

A simplified analysis procedure utilizing the strut-tie modeling technique is developed to take a close look into the post-elastic deformation capacity of beam-column connections in ductile reinforced concrete frame structures. Particular emphasis is given to the effect of concrete strength decay and quantity and arrangement of joint shear steel. For this a fan-shaped crack pattern is postulated through the joints. A series of hypothetical rigid nodes are assumed through which struts, ties and boundaries are connected to each other. The equilibrium consideration enables all forces in struts, ties and boundaries to be related through the nodes. The boundary condition surrounding the joints is obtained by the mechanism analysis of the frame structures. In order to avoid a complexity from the indeterminacy of the truss model, it is assumed that all shear steel yielded. It is noted from the previous research that the capacity of struts is limited by the principal tensile strain of the joint panel for which the strain of the transverse diagonal is taken. The post-yield deformation of joint steel is taken to be the only source of the joint shear deformation beyond the elastic range. Both deformations are related by the energy consideration. The analysis is then performed by iteration for a given shear strain. The analysis results indicate that concentrating most of the joint steel near the center of the joint along with higher strength concrete may enhance the post-elastic joint performance.

• Computers and Concrete
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• v.16 no.2
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• pp.209-222
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• 2015

This paper presents results of biaxial compressive tests and strength criterion on two replacement percentages of recycled coarse aggregate (RPRCA) by mass for plain structural recycled aggregate concrete (RAC) at all kinds of stress ratios. The failure mode characteristic of specimens and the direction of the cracks were observed and described. The two principally static strengths in the corresponding stress state were measured. The influence of the stress ratios on the biaxial strengths of RAC was also analyzed. The experimental results showed that the ratios of the biaxial compressive strength ${\sigma}_{3f}$ to the corresponding uniaxial compressive strength $f_c$ for the two RAC are higher than that of the conventional concrete (CC), and dependent on the replacement percentages of recycled coarse aggregate, stress states and stress ratios; however, the differences of tensile-compressive ratios for the two RAC and CC are smaller. On this basis, a new failure criterion with the stress ratios is proposed for plain RAC under biaxial compressive stress states. It provides the experimental and theoretical foundations for strength analysis of RAC structures subject to complex loads.

• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.1-7
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• 2018

The Continuous Ship Unloader (CSU) is an equipment that unloads freight from the ship docked in the port to the land. And the design target life time is designed to be 30 to 50 years, and it is classified as a semi-permanent large facility. However, cracks may occur due to structural defects, abnormal loads, and corrosion, and fatigue failure may occur before the design life is reached. In this study, we predicted the remaining life time of the main component of the CSU considering crack. And also proposed inspection cycle for maintenance of CSU based on the results of the remaining life time prediction. For this purpose, the structure, operational stresses of the CSU were analyzed and main members were selected. And tensile tests and fatigue crack propagation tests were performed with SM490YA and SM570TMC, which are used as main materials for CSU.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.10
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• pp.3-10
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• 2018

Hybrid Prestressed Precast Concrete System (HPPC system) is a newly developed frame system that can improve the performance of precast concrete (PC) joints by post-tensioning. In particular, the details proposed in this study can reduce the lifting weight of the PC members and eliminate problems caused by cracks in the joints that occur under service loads. This study performed an evaluation on the negative moment performance of full-scaled HPPC girders. The test specimens were cast with or without slabs, with bonded or unbonded tendons, and had different post-tensioned lengths in tensile section. The test results showed that the specimens with slabs had significantly higher stiffness and strength than those without slabs. There were no differences in the flexural behavior between those with bonded or unbonded tendons, and between those with short or long post-tensioned lengths in the negative moment region.