• Journal of the Korean Wood Science and Technology
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• v.49 no.2
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• pp.107-121
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• 2021

The purpose of this study is to optimize the bonding method of the plywood suitable for cross-laminated timber (CLT) with plywood as a core by analyzing the flexural performance and failure mode according to the lamina species, the method of bonding plywood in the longitudinal direction, and whether or not adhesive is applied to the joint. In the case of the Douglas fir lamina layer, the modulus of elasticity decreased by about 11.5% due to longitudinal bonding, and the modulus of rupture increased or decreased according to the adhesive application and bonding method. The optimal conditions were derived as the butt joint without adhesive, half lap joint with adhesive, and butt joint. In the case of the larch lamina layer, the modulus of rupture and the modulus of elasticity decreased by about 15% and 40%, respectively. When using the half lab joint and tongue & groove joint, it is believed that it reduces the load transmitted to the middle layer by primarily preventing the failure on flexure at the joint of the plywood layer. From the results of this study, the larch lamina layer used in the manufacturing process of Ply-lam CLT did not show any difference based on the bonding method. Butt joint and half lap joint bonding method are determined to be suitable when using Douglas fir lamina layer.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.535-547
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• 2012

PSRC column is a concrete encased steel angle column. In the PSRC column, the steel angles placed at the corner of the cross-section resists bending moment and compression load. The lateral re-bars welded to steel angles resist the column shear and the bond between the steel angle and concrete. In the present study, current design procedures in KBC 2009 were applied to the flexure-compression, shear, and bond design of the PSRC composite column. To verify the validity of the design method and failure mode, simply supported 2/3 scaled PSRC and correlated SRC beams were tested under two point loading. The test parameters were the steel angle ratio and lateral bar spacing. The test results showed that the bending, shear, and bond strengths predicted by KBC 2009 correlated well with the test results. The flexural strength of the PSRC specimens was much greater than that of the SRC specimen with the same steel ratio because the steel angles were placed at the corner of the column section. However, when the bond resistance between the steel angle and concrete was not sufficient, brittle failures such as bond failure of the angle, spalling of cover concrete, and the tensile fracture of lateral re-bar occurred before the development of the yield strength of PSRC composite section. Further, if the weldability and toughness of the steel angle were insufficient, the specimen was failed by the fracture of the steel angle at the weld joint between the angle and lateral bars.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.35-49
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• 2020

The lateral bearing capacity of the micropile depends on the installed conditions such as number, installation angle and spacing of the pile. Existing research on micropile has been limited to the evaluation of vertical bearing characteristics and suggestion of effective installation methods, and there are few studies on failure mechanisms such as failure mode. And most of the studies on the lateral bearing capacity of micropile are also on the 1-row micropile. Therefore, in this study, a model test was performed to evaluate the behavior and lateral bearing characteristics of a 2-row micropile when the installed conditions such as the installation length, angle, and spacing of the pile were different. As a result of the model test, when the installation angle is θ > 0° (Not cross installation), the lateral bearing capacity of 2-row micropile depends on the spacing of the piles, and the installation angle θ = +30° was the most effective for increasing the bearing capacity. In addition, when the installation angle is θ < 0° (Overlap installation), it depends on the spacing and angle of the pile, and the condition of installation angle θ = -15° was found to be the most effective for increasing the bearing capacity.

• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.135-144
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• 2007

Recently, fiber-reinforced plastic(FRP) wraps are blown as an effective material for the enhancement and rehabilitation of aged concrete structures. The purpose of this investigation is to experimentally investigate behavior of concrete cylinder wrapped with FRP materials. Experimental parameters include compressive strength of concrete cylinder, FRP material, and confinement ratio. This paper presents the results of experimental studies on the performance of concrete cylinder specimens externally wrapped with aramid, carbon and glass fiber reinforced Polymer sheets. Test specimens were loaded in uniaxial compression. Axial load, axial and lateral strains were investigated to evaluate the stress-strain behavior, ultimate strength ultimate strain etc. Test results showed that the concrete strength and confinement ratio, defined as the ratio of transverse confinement stress and transverse strain were the most influential factors affecting the stress-strain behavior of confined concrete. More FRP layers showed the better confinement by increasing the compressive strength of test cylinders. In case of test cylinders with higher compressive strength, FRP wraps increased the compressive strength but decreased the compressive sham of concrete test cylinders, that resulted in prominent brittle failure mode. The failure of confined concrete was induced by the rupture of FRP material at the stain, being much smaller than the ultimate strain of FRP material.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.225-233
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• 2003

Even though a lot of advanced researches on analysis, design, and performance evaluation of reinforced concrete (RC) under seismic action have been carried out, there has been only a few study on seismic analysis of underground RC structures surrounding soil medium. Since the underground RC structures interact with surrounding soil medium, a path-dependent soil model which can predict the soil response is necessary for analyzing behavior of the structure inside soil medium. The behavior of interfacial zone between the RC structure and the surrounding medium should be also considered for more accurate seismic analysis of the RC structure. In this paper, an averaged constitutive model of concrete and reinforcing bars for RC structure and path-dependent Ohsaki's model for soil are applied, and an elasto-plastic interface model having thickness is proposed for seismic analysis of underground RC structures. A finite element analysis technique is developed by applying aforementioned constitutive equations and is verified by predicting both static and dynamic behaviors of RC structures. Then, failure mechanisms of underground RC structure under seismic action are numerically derived through seismic analysis of underground RC station structure under different seismic forces. Finally, the changes of failure mode and the damage level of the structures are also analytically derived for different design cases of underground RC structures.

• Journal of the Korean Wood Science and Technology
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• v.36 no.3
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• pp.1-8
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• 2008

The lateral strength test of bending type was done to investigate the lateral capacity of the double bolt connection of domestic larix glulam according to bolt spacing. In the shear specimen, which is bolted connection in the inserted plate type, the hole of bolt was made, changing the diameter of bolt (12 mm and 16 mm), the number of bolt (single bolt : control and double bolt), the direction of bolt row (in parallel to grain : Type-A and in perpendicular to grain : Type-B) and the bolt spacing (Type-A : 4 d and 7 d and Type-B : 3 d and 5 d). Lateral capacity and failure mode of bolt connection were compared according to conditions. In prototype design (KBCS, 2000), the reduction factor of the allowable shear resistance that the bolt spacing is reduced was calculated. The results were as follows. 1) Bearing stress per bolt in the single and double bolt connection of Type-A was directly proportional to bolt diameter and bolt spacing. Bearing stress of Type-B decreased as bolt diameter was increased, and decreased by 2~10% when bolt diameter was increased. 2) In the single bolt connection and the double bolt connection of Type-A, the splitted failure was formed in the edge direction. When the bolt spacing was 3 d in Type-B, bolt was yielded more in the part of tension than in the part of compression, and the splitted failure started at the bolt in the part of tension. In the 5 d spacing specimen, the bolt in the part of tension was yielded similarly to bolt in the part of compression, and the splitted failure started in the part of compression. 3) In the prototype design, the reduction factor was calculated by non-dimensionizing the yielding load in the standard of bolt spacing (Type A : 7 d and Type B : 5 d). In 12 mm bolt connection, the reduction factor of bolt spacing 4 d (type-A) and single bolt connection was 0.87 and 0.55, respectively, and the reduction factor of bolt spacing 3 d (Type-B) and single bolt connection was 0.91 and 0.55, respectively. In 16 mm bolt connection, the reduction factor of bolt spacing 4 d (type-A) and single bolt connection was 0.96 and 0.76, respectively, and the reduction factor of bolt spacing 3 d (Type-B) and single bolt connection was 0.91 and 0.77, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.449-455
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• 2016

This study is a part of research to develop a steel-concrete hybrid girder using ultra high-performance concrete with a compressive strength of 80 MPa. To this end, the Eurocode design formula for the shear resistance developed in a concrete-to-concrete interface was examined for the interface between concrete layers of different strengths. To examine the effect of the surface roughness on the shear resistance, a push-out test was conducted on specimens while considering the parameters of the Eurocode design equation. The actual behavior was evaluated with respect to the compressive strength of the concrete, the reinforcement ratio of the shear rebar, and the interfacial surface condition. The specimen with a rough interface shows 20-50% higher shear strength than that estimated by the design equation. In the case of failure mode, abrupt failure tends to occur at the interface of the concrete layer for the specimen with a low reinforcement ratio. It is expected that the shear strength of the concrete layer will increase according to the strength differential in the concrete layers.

• Clinical and Experimental Pediatrics
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• v.48 no.1
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• pp.68-74
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• 2005

Purpose : There is growing use of continuous renal replacement therapy(CRRT) for pediatric patients, but reports about the use and outcome of CRRT in children is rare in Korea. We report our experiences of CRRT in critically ill pediatric patients. Methods : We reviewed the medical records of 23 pediatric patients who underwent CRRT at Asan Medical Center between May 2001 and May 2004. We evaluated underlying diseases, clinical features, treatment courses, CRRT modalities and outcomes. Results : Ages ranged from three days to 16 years with a median of five years. Patients weighed 2.4 to 63.9 kg(median 23.0 kg; 10 patients ${\leq}20kg$). The underlying diseases were malignancy(nine cases), multiple organ dysfunction syndrome(five cases), hyperammonemia(four cases), acute renal failure associated with liver failure(three cases), dilated cardiomyopathy(one case) and congenital nephrotic syndrome(one case). Pediatric Risk of Mortality(PRISM) III score was $17.6{\pm}7.6$ and the mean number of failing organs was $3.0{\pm}1.7$. Duration of CRRT was one to 27 days(median : nine days). Eleven patients(47.8%) survived. Chronic renal failure developed in two cases, intracranial hemorrhage in one case, and chylothorax in one case among the survivors. PRISM III score and the number of vasopressor before the start of CRRT was significantly lower in the survivors($12.7{\pm}4.2$ and $0.9{\pm}1.1$) compared with nonsurvivors($22.1{\pm}7.8$ and $2.4{\pm}1.4$)(P<0.05). Conclusion : CRRT driven in venovenous mode is an effective and safe method of renal support for critically-ill infants and children to control fluid balance and metabolic derangement. Survival is affected by PRISM III score and the number of vasopressors at the initiation of CRRT.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.345-351
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• 2017

This study evaluated the effectiveness of V-shaped ties as an alternative to the supplementary crossties specified in ACI 318-14 on the flexural ductility of reinforced concrete columns. From column specimens tested under constant axial loads and reversed cyclic lateral loads, the mode of failure and lateral load-lateral displacement relationship were measured according to the variation of the applied axial load levels. After the columns reached the peak lateral load capacity, the $90^{\circ}$ hooks of the crossties gradually opened, which eventually caused premature buckling of the longitudinal reinforcement and severe crushing of the core concrete, whereas no V-ties were extracted from the core concrete until the column failure. As a result, the cumulative work damage indicators up to 80% of the peak lateral load for V-tie columns under the axial load level of 0.2, 0.4, and 0.55 was as much as 2.4, 2.3, and 5.2 times higher, respectively, than those of the companion crosstie columns. The superiority of the V-ties to the conventional crossties in enhancing the flexural ductility of columns became more prominent as the axial load level increases.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.763-771
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• 2007

Over the last few decades, many researches have been conducted in order to find solution to the problem of corrosion in steel reinforced concrete. As a result, methods such as the use of stainless steel bars, epoxy coatings, and concrete additives, etc., have been tried. While effective in some situations, such remedies may still be unable to completely eliminate the problems of steel corrosion. Fiber reinforced polymer (FRP) elements are appealing as reinforcement due to some material properties such as high tensile strength, low density, and noncorrosive. However, due to the generally lower modulus of elasticity of FRP in comparison with the steel and the linear behavior of FRP, certain aspects of the structural behavior of RC members reinforced with FRP may be substantially different from similar elements reinforced with steel reinforcement. This paper presents the flexural behavior of one-way concrete slabs reinforced with FRP bars. They were simply supported and tested in the laboratory under static loading conditions to investigate their crack pattern and width, deflections, strains and mode of failure. The experimental results shows that behavior of the FRP reinforced slabs was bilinearly elastic until failure. Also, the results show that the FRP overreinforced concrete beams in this study can be safe for design in terms of deformability.