• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.63-76
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• 2007

The transformed field domain analysis method was developed in this study to investigate the aspects of the stress distribution in overlaid concrete pavement systems under multi-axle vehicle loads. The overlay was assumed to be perfectly bonded or perfectly unbonded to the existing concrete pavement. The loads considered included the dual tired single-axle, tandem-axle, and tridem-axle loads, and the effects of the overlay's thickness, elastic modulus, and Poisson's ratio on the stress distribution were investigated. Details of the analysis method in the transformed field domain to analyze the overlaid pavement was described in this paper and the analysis results were verified by comparing with those obtained using the finite element method. From the analysis, it was found that the maximum tensile stress in the existing slab decreased as the overlay's thickness, elastic modulus, and Poisson's ratio increased, and the bonded overlay showed more significant effects than the unbonded one. The overlay's Poisson's ratio did not much affect the stresses, and the features of the maximum stress reduction in the existing slab due to the increase of the thickness, elastic modulus, and Poisson's ratio of the overlay were investigated. The effects of the number of axles on the stress distribution and the maximum stress were also investigated.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.79-91
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• 2016

Geosynthetic-reinforced and Pile-supported (GRPS) embankment method is widely used to construct structures on soft ground due to restraining residual settlement and their rapid construction. However, effect of cyclic loading has not been established although some countries suggest design methods through many studies. In this paper, cyclic loading tests were conducted to analyze dynamic load transfer characteristics of pile-supported embankment reinforced with geosynthetics. A series of 3 case full scale model tests which were non-reinforced, one-layer-reinforced, two-layer reinforced with geosynthetics were performed on piled embankments. In these series of tests, the height of embankment and pile spacing were selected according to EBGEO (2010) standard in Germany. As a result of the vertical load parts on the pile and on the geosynthetic reinforcement measured separately, cyclic loads transferred by only arching effect decreased with strength geosynthetic-reinforced case. However, final loads on the pile showed no differences among the cases. These results conflict with previous studies that reinforcement with geosynthetics increases transfer load concentrated on piles. In addition, it is observed that the load transferred to pile decreases at the beginning of cycle number due to reduction of arching effected by cyclic loading. Based on these results, transferred mechanism for cyclic load on GRPS system has been presented.

• Design & Manufacturing
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• v.14 no.1
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• pp.49-55
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• 2020

In this study, the fatigue behavior and fatigue life characteristics of PA2200 specimens fabricated by SLS 3D printer were studied. Fatigue tests were performed according to the standard specification (ASTM E468) and fatigue life curves were obtained. In order to perform the fatigue test, mechanical properties were measured according to the test speed of the simple tensile test, and the self-heating temperature of the specimen according to the test speed was measured using an infrared temperature measuring camera in consideration of heat generation due to plastic deformation. There was no significant difference within the set test speed range and the average self-heating temperature was measured at 38.5 ℃. The mechanical strength at the measured temperature showed a relatively small difference from the mechanical strength at room temperature. Fatigue test conditions were established through the preceding experiments, and the loading conditions below the tensile strength at room temperature 23 ℃ were set as the cyclic load. The maximum number of replicates was less than 100,000 cycles, and the fracture behavior of the specimens with the repeated loads showed the characteristics of Racheting. It was confirmed that SLS 3D printing PA2200 material could be applied to the Basquin's S-N diagram for the fatigue life curve of metal materials. SEM images of the fracture surface was obtained to analyze the relationship between the characteristics of the fracture surface and the number of repetitions until failure. Brittle fracture, crazing fracture, grain melting, and porous fracture surface were observed. It was shown that the larger the area of crazing damage, the longer the number of repetitions until fracture.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.30-38
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• 2017

Recently, research on the development of a composite slab system for shorting the construction period by simplifying the process by omitting the form work and the reinforcement placing is underway. The purpose of this study is to evaluate the long-term behavior of a simplified slab system that replaces the form work and tensile reinforcement using structural deck-plate and replaces the temperature reinforcement using steel fiber reinforced concrete. In the conventional composite deck-plate slab method, w.w.f is generally used for crack control by drying shrinkage. But previous research results by various researchers were pointed out it is not effective to control the shrinkage and temperature cracking. In this study, the long-term cracking and structural behavior of steel fiber reinforced deck plate slab specimen with two continuous spans constructed under typical load conditions were evaluated. Experimental results showed that the number and width of long-term cracks decreased remarkably in the simplified slab specimen, and the deflection was also decreased compared with conventional RC slab specimen. However, in the continuous end of the slab where the negative moment is applied, it is analyzed that reinforced details are necessary to control the crack width in the service load and to recover deflection at load removal.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.430-439
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• 2002

The development of reinforcing steel is required in reinforced concrete structures. The standard hooks that have been widely used for the tensile development in the beam-column joints tend to create difficulties of construction such as steel congestion as the member cross sections are becoming smaller due to the use of higher strength concrete and higher grade steel. Using the reinforcing bars with end mechanical anchoring device (headed reinforcement) provides potential economies in construction such as reduction in development lengths, simplified details, and improved responses to cyclic loadings. In this paper, the pullout strengths and behaviors of the headed reinforcement were experimentally studied. In 33 pullout tests performed using D25 deformed reinforcing bars, the test parameters were embedment depth, edge distance, head size, and the use of transverse reinforcement. The pullout strengths determined from tests closely agreed with the pullout strengths predicted using the CCD method. The pullout strengths increased with increasing embedment depths nd edge distances. The strengths tend to increase with the use of larger heads. From the experimental program where the effect of the transverse reinforcement was examined, a modification factor to the CCD was suggested to represent the effect of such reinforcement that is installed across the concrete failure plane on the pullout strengths.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.136-143
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• 2006

In this study, recently it is urgently required that demolition waste concrete has to be recycled on the construction because urban development is accelerated and redevelopment project is rapidly expanded, production quantity of construction and demolition waste concrete is being increased. As a results of drying shrinkage test under restrained and unrestrained condition, although workability and mechanical properites of concrete using HQRS were similar to that of concrete using natural sand, there were a great difference in deformation characteristic of dry shrinkage according to replacement ratio of HQRS. And, it makes sure that use of HQRS instead of partial nature sand was effective because drying shrinkage of concrete using 30 volume percentage of HQRS was smaller than that using only natural sand. Therefore, it is the objective of this study to provide the fundamental data about the re-application as an analysis of the drying shrinkage characteristics of concrete using HQRS and it is able to creta a high value-added by using HQRS.

• Journal of the Korea Institute of Building Construction
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• v.22 no.1
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• pp.11-21
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• 2022

Currently, in the domestic construction industry, the free web method has been emerging as a potential solution to the shortage of skilled workers due to the prolonged COVID-19 crisis, as it helps in securing economic feasibility through shortening the construction period and reducing labor costs. To consider one part of the construction method, in this study, the bending behavior according to the load was evaluated for the SY slope-type beam formwork, which was manufactured at a factory, assembled with rebar, brought into the site, and then poured into the site. For the SY Beam standard cross-sectional shape, a cross-sectional dimensional width of 400mm and depth 600mm determined through structural modeling using the MIDAS GEN program were applied. A total of 6 specimens were made with a member length of 5,000mm, 5 specimens and one RC specimen in the comparison group were manufactured in real-size format using the thickness of the steel plate(0.8, 1.0, 1.2mm) as a variable, and bending experiments were performed. In the bending test, the steel plate deck showed high initial stiffness and maximum strength as it yielded, which showed that it sufficiently contributed to the flexural strength. It is judged that additional analysis and experimental studies for 1.05, 1.1, and 1.15mm are needed to derive the appropriate steel plate thickness and the method for calculating the tensile force contribution of the steel plate to secure the manufacturing, construction and economic feasibility of SY Beam in the future.

• Composites Research
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• v.36 no.4
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• pp.246-252
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• 2023

A secondary barrier made of glass fiber reinforced composites has been installed infinitely using automatic bonding machine(ABM) in membrane type LNG cargo containment system (CCS). At the same time, significant thermal stress due to cryogenic heat shrinkage has occurred in the composite on the non-bonding area between the adhesive fixation at both ends. There have been studies from the perspective of structural safety evaluation taking this into account, but none that have analyzed mechanical property taking an prolonged length into account. In this study, 2-parameter Weibull distribution statistical analysis was used to standardize reliable mechanical property for actual length, taking into account the composite's brittle fracture of ceramic material with wide fracture strength dispersion. Related experimental data were obtained by performing uniaxial tensile tests at specific temperatures below cryogenic condition considering LNG environment. As a result, the mechanical strength increased about 1.5 times compared to -20℃ at -70℃ and initial non-linear behavior of fiber stretched was suppressed. As the temperature decreased until the cryogenic, the mechanical strength continued to increase due to cold brittleness. The suggested mechanical property in this study would be employed to secure reliable analysis support material property when assessing the safety of secondary barrier's structures.

• Journal of the Korean Wood Science and Technology
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• v.19 no.1
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• pp.31-63
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• 1991

It was proved that in conventional kiln drying of disks piling position in the kiln exerted a great influence on drying rates, and the larger the variation of disk diameter, the more undulating drying rates of disks. While in vacuum drying disks there was no influence on drying rates. By the end-wrapping treatments and the radial direction of disks tangential surface stresses in the core of disks were slightly compressive in three species. In control disks the drying stresses distributed into one step-style that compressive stresses in the pith side of 6cm from pith were larger than those in the bark side, while in the disks end-wrapped with Korean paper the drying stresses distributed uniformly, because flow rates of free water in disks had no difference between heart-and sap-wood by obstruction of evaporating water from surface of disks by end-wrapping with Korean paper. And end-wrapping with Korean paper considerably restrained those. Tangential differential shrinkage stresses developed the maximum tensile stress near the bark and with approaching the pith the stresses gradually reduced and changed into compressive stresses in near the pith. At the end of vacuum drying the maximum tangential tensile stresses of disks end-wrapped with Korean paper were smaller than those of control disks, and critical moisture contents causing the V-shaped crack of disks end-wrapped with Korean paper were lower than those of control disks because of the set by obstruction of evaporating water of end-wrapping with Korean paper. In the experiment of vacuum drying stress distribution the disks end-wrapped with Korean paper or aluminum foil in three species were free from V-shaped cracks and control disks were defected very slightly by V-shaped cracks. And also disks end-wrapped with Korean paper were free from heart checks in Alnus japonica and Juglans sinensis, and heart checks were occurred very slightly in others. Especially, not to speak of disks end-wrapped with Korean paper, vacuum drying of disks end-wrapped with aluminum foil prevented effectively drying defects, moreover drying times could be shortened, that is. Ginkgo biloba, Alnus japonica, and Juglans sinensis disks could be dried from green to in-use moisture content in 110 hours, 272 hours, and 407 hours, respectively.

• Journal of the Korean Wood Science and Technology
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• v.38 no.4
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• pp.323-332
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• 2010

Petroleum-based adhesive resins have extensively been used for the production of wood panels. However, it is necessary to develop environmentally friendly adhesive resins due to the increase of manufacturing cost and the environmental issue, such as the emission of volatile organic compounds, of the pertroleum-based adhesive resins. This study was conducted to formulate environmentally friendly adhesive resins using by rapeseed flour (RSF), which is the by-product of bio-diesel produced from rapeseed, for replacing petroleum-based adhesives with them. To formulate RSF-based adhesive resins, RSF was hydrolyzed in de-ionized water, 1% and 3% sodium hydroxide solutions. As a crosslinking agent, PF prepolymers were prepared with 1.8, 2.1 and 2.4 mol formaldehyde and 1 mol phenol (1.8-, 2.1- and 2.4-PF), and then mixed with RSF hydrolyzates to complete the formulation of RSF-based adhesive resins. The RSF-based adhesive resins were applied to fabricate 3-ply plywood panels. The solid content of RSF-based adhesive resins were ranged from 26.08% to 36.12% depending on the hydrolysis condition of RSF and PF prepolymer type with a high viscosity. The tensile shear strength and wood failure of plywood fabricated with RSF-based adhesive resins exceeded a minimum requirement of KS standard for ordinary plywood regardless of the hydrolysis condition of RSF and PF prepolymer type. Formaldehyde emissions of the plywood panels fabricated with 1.8-PF and RSF hydrolyzates were lower than that of E0 specified in the KS standard. Based on the results, RSF might be used as a raw material of environmentally friendly adhesives for the production of plywood panels, but further researches - the increase of solid content of RSF-based adhesives for reducing press time and the microscopic observation of plywood specimen for identifying the relationship between tensile shear strength and the penetration of adhesives into wood structure - are required to commercialize the RSF-based adhesives.