• Journal of the Korean GEO-environmental Society
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• v.14 no.10
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• pp.17-27
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• 2013

This paper explores stress release induced by unloading in dry sand. A series of model tests were carried out to measure stresses developed in testing sand during loading and those released during unloading for different boundary conditions. It was found that stress in the sand increased linearly with applied load. At the onset of unloading, almost no stress release was observed. Significant stress release took place when the shear stress in the sand induced by unloading exceeded the frictional resistance and caused movement of sand particles. The initiation and the magnitude of stress release depend on the stress condition prior to unloading, the decrease of external load, and also the frictional resistance in sand. A new conceptual stress-release model was next developed based on the model test results by considering the fundamental frictional behavior of granular materials.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.143-155
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• 2008

Ground anchors are classified depending on the kind of stress the grout is subjected to. If the grout material is subjected to tension then it is classified as tension anchor while when the grout material is subjected to compression it is classified as compression anchor. In this study a composite type anchor that possesses both the tension and compression mechanism was developed. For field tests, strain gauges were installed inside the anchor body in soft: soil. From the strain monitoring results, pull-out resistance mechanism that possesses both tension and compression strain was seen.

• Journal of Korean Society of Steel Construction
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• v.21 no.3
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• pp.257-266
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• 2009

The results of the analysis of the structural behavior of diagrid nodes that were subjected to cyclic loads such as wind and earthquakes was not fully understood due to difficulties in considering the welding type. In this study, diagrid nodes were tested to determine their behavior when they are subjected to seismic or wind loads. Five specimens were designed and fabricated. The corresponding test parameters were the welding type for each point and the length of the overlap of the side stiffener and the brace web. Tensile force was applied to one diagrid brace member, and compression force was applied to the other diagrid brace member. Cyclic loading was applied until the failure. The test showed that failures are due to axial stress from axial force and the additional bending moment of the two combined axial forces that have different directions. Tensile failure was observed from the tensile force, and local buckling was observed from the compressive force at the flange of the brace member. In addition, the welding type and the length overlap affected the initial stiffness, the yielding stress, and the energy absorption of the diagrid node.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.737-744
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• 2009

In this study, the flexural behavior of steel fiber reinforced ultra high performance concrete (UHPC) was investigated. It presents experimental results of steel fiber reinforced UHPC with steel fiber content of 2% by volume and steel reinforcement ratio of less than 0.02. This study aims at providing more information about UHPC beams in bending in order to establish a reasonable prediction model for flexural resistance and deflection in structural code in the future. The experimental results show that UHPC is in favor of cracking behavior and ductility of beams, and that the ductility indices range from 6.29 to 10.44, which means high ductility of UHPC. Also, the flexural rigidity of beam whose cast is begun from end of beam is larger than that of beam whose cast is begun from midspan of beam. This result represents that the flexural rigidity is affected by the placing method of UHPC.

• Composites Research
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• v.21 no.3
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• pp.24-30
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• 2008

Durability problems may arise in the concrete, which is one of the major construction materials, used in the construction field. Bridge piers and foundation piles are usually made with concrete and they are exposed to the moisture and hence the durability of the concrete reduced significantly due to oxidization of re-bar and icing of concrete. To mitigate such problems, FRP tube has been developed and the concrete filled FRP tube (CFFT) has been investigated to find the confinement effect which is provided additionally. It was reported that if the concrete is wrapped with FRP, strength and chemical resistance are improved significantly. In order to apply such a member in the construction field, structural behavior and applicable design guideline or design criteria must be thoroughly investigated. In the experimental investigation, the results are compared with the previous research results and the relationship which can predict the ultimate strength and strain is suggested. In addition, some comments found at the compression tests are given briefly.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.311-321
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• 2022

In the buildings with long spans and high floors, such as logistics warehouses and semiconductor factories, it is difficult to install supporting posts under beams during construction. Therefore, the size of structural members becomes larger inevitably, resulting in a significant increase in construction costs. Accordingly, a prestressed hybrid wide flange (PHWF) beam with hollowed steel webs was developed, which can reduce construction costs by making multiple openings in the web of the steel member embedded in concrete. However, since multiple openings exist and prestress is introduced only into the bottom flange concrete, it is necessary to identify the shear resistance mechanism of the PHWF beam. This study presents experimental shear tests of PHWF beams with hollowed steel webs. Four PHWF beams with cast-in-place (CIP) concrete were fabricated, with key variables being the width and spacing of the steel webs embedded in the concrete and the presence of shear reinforcing bars, and web-shear tests were conducted. The shear behavior of the PHWF beam, including crack patterns, strain behavior of steel webs, and composite action between the prestressed bottom flange and CIP concrete, were measured and analyzed comprehensively. The test results showed that the steel web resists external shear forces through shear deformation when its width is sufficiently large, but as its width decreased, it exerted its shear contribution through normal deformation in a manner similar to that of shear reinforcing bars. In addition, it was found that stirrups placed on the cross section where the steel web does not exist contribute to improving the shear strength and deformation capacity of the member. Based on the shear behavior of the specimens, a straightforward calculation method was proposed to estimate the web-shear strength of PHWF beams with CIP concrete, and it provided a good estimation of the shear strength of PHWF beams, more accurate than the existing code equations.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.29-39
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• 2010

In this study, experimental test and numerical analysis were conducted to investigate the heat transfer characteristics and fiber performance of high strength concrete. The fire characteristics of the high strength concrete that couldn't be obtained through the test due to specific requirements and restrictions were forecast using numerical analysis approach. The outcome from the numerical analysis and the test were compared to verify and improve the reliability of the analysis. A numerical analysis of 80 and 100 MPa high strength concrete cases were carried out to identify the heat transfer characteristics and fire behavior using software, ABACUS (V6.8) From the results of verification experiment, a 25~55% level of beam shrinkage reduction was observed compared to the concrete without Fiber-Cocktail, indicating the improved fire resistance performance, which appeared to be attributable to the function of Fiber-Cocktail that was able to control the heat transfer characteristics and ultimately result in enhancing the fire resistance performance.

• Journal of the Korean Ceramic Society
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• v.55 no.6
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• pp.608-617
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• 2018

The effects of the purity and monoclinic phase of feedstock powder on the thermal durability of thermal barrier coatings (TBC) were investigated through cyclic thermal exposure. Bond and top coats were deposited by high velocity oxygen fuel method using Ni-Co based feedstock powder and air plasma spray method using three kinds of yttria-stabilized zirconia with different purity and monoclinic phase content, respectively. Furnace cyclic thermal fatigue test was performed to investigate the thermal fatigue behavior and thermal durability of TBCs. TBCs with high purity powder showed better sintering resistance and less thickness in the thermally grown oxide layer. The thermal durability was found to strongly depend on the content of monoclinic phase and the porosity in the top coat; the best thermal fatigue behavior and thermal durability were in the TBC prepared with high purity powder without monoclinic phase.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.838-845
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• 2006

Recently construction work in Korea, demands of favorable condition ground had been increased with industrialization acceleration and economic growth. However, because of limited land space, it was so hard to ensure favorable condition grounds that construction work proceeds until soft ground area on plans of road, railroad and industrial complex. In this case, soft ground improvement was required such as a stone column method. Stone column method, making a compaction pile using crushed stone, is a soft ground improvement method. However, stone column method is difficult to apply to the ground which is not mobilized enough lateral confine pressure because no bulging failure resistance. Hence, in present study, evaluates the stone columns reinforced by geogrid for settlement reduction and wide range of application of stone columns. Triaxial compression tests were conducted for evaluation which is about behavior characteristics of stone column on replacement rate. Then, 3-dimensional numerical analysis were conducted for application of stone column reinforced by geogrid as evaluate behavior characteristics and settlement reduction effect of stone column reinforced by geogrid on reinforcing depth change of geogrid.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.1-8
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• 2023

At construction sites, interest in the production of precast materials is increasing due to off-site conditions due to changes in construction site conditions due to increased labor costs and the Act on the Punishment of Serious Accidents. In particular, the precast prestressed hollow slab has a hollow shape in the cross section, so structural performance is secured by reducing weight and controlling deflection through stranded wires. With the application of structural standards, the urgency of securing fire resistance performance is emerging. In this study, a fire-resistance cross section was developed by reducing the concrete filling rate in the cross section and improving the upper and lower flange shapes by optimizing the hollow shape in the cross section of the slab to have the same or better structural performance and economic efficiency compared to the existing hollow slab. The PC hollow slab to which this was applied was subjected to a two-hour fire resistance test using the cross-sectional thickness as a variable, and as a result of the test, fire resistance performance (load bearing capacity, heat shielding property, flame retardance property) was secured. Based on the experimental results, it is determined that fire resistance modeling can be established through numerical analysis simulation, and prediction of fire resistance analysis is possible according to the change of the cross-sectional shape in the future.