• Journal of Bio-Environment Control
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• v.30 no.4
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• pp.287-294
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• 2021

In order to expand facility agriculture and reduce greenhouse construction costs in reclaimed land, a greenhouse foundation method that satisfies economic feasibility and structural safety at the same time is required. As an alternative, the allowable bearing capacity and settlement were reviewed when the DCM(Deep cement mixing) method was applied among the soft ground reinforcement methods. To examine the applicability of the greenhouse foundation, the allowable bearing capacity and settlement were calculated by applying the theory of Terzaghi, Meyerhof, Hansen, and Schmertmann. In case of the diameter of 800mm and the width and length of the foundation of 4m, the allowable bearing capacity was 179kN/m² and the settlement was 7.25mm, which satisfies the required bearing capacity and settlement standards. The calculation results were verified through FEM(Finite element method) analysis using the Mohr-Coulomb material model. The allowable bearing capacity was 169kN/m² and the settlement was 2.52mm. The bearing capacity showed an error of 5.6% compared to calculated value, and the settlement showed and error of 65.4%. Through theoretical calculations and FEM analysis, it was confirmed that the allowable bearing capacity and settlement satisfies the design criteria as a greenhouse foundation when the width and length of the foundation were 4m. Based on the verified design values, it is expected to be able to present the foundation design criteria for greenhouses through empirical tests such as bearing capacity tests and long-term settlement monitoring.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.565-575
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• 2009

In recent years, there have been numerous explosion-related accidents due to military and terrorist activities. Such incidents caused not only damages to structures but also human casualties, especially in urban areas. To protect structures and save human lives against explosion accidents, better understanding of the explosion effect on structures is needed. In an explosion, the blast load is applied to concrete structures as an impulsive load of extremely short duration with very high pressure and heat. Generally, concrete is known to have a relatively high blast resistance compared to other construction materials. However, normal strength concrete structures require higher strength to improve their resistance against impact and blast loads. Therefore, a new material with high-energy absorption capacity and high resistance to damage is needed for blast resistance design. Recently, Ultra High Strength Concrete(UHSC) and Reactive Powder Concrete(RPC) have been actively developed to significantly improve concrete strength. UHSC and RPC, can improve concrete strength, reduce member size and weight, and improve workability. High strength concrete are used to improve earthquake resistance and increase height and bridge span. Also, UHSC and RPC, can be implemented for blast resistance design of infrastructure susceptible to terror or impact such as 9.11 terror attack. Therefore, in this study, the blast tests are performed to investigate the behavior of UHSC and RPC slabs under blast loading. Blast wave characteristics including incident and reflected pressures as well as maximum and residual displacements and strains in steel and concrete surface are measured. Also, blast damages and failure modes were recorded for each specimen. From these tests, UHSC and RPC have shown to better blast explosions resistance compare to normal strength concrete.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.4
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• pp.564-572
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• 2015

Nutritional compositions, volatile compounds, and sensory attributes of Cynanchi wilfordii Radix were analyzed in order to examine its practical utilization as a food resource. In the proximate analysis, protein and lipid contents were shown to be 14.6 and 5.0 mg/100 g, respectively, in C. wilfordii Radix. Potassium was the most predominant mineral (809 mg/100 g), as determined by inductively coupled plasma-optical emission spectrometry in parallel with microwave acid digestion. Total phenolic content was found to be 410 mg/100 g. Further, arginine and linoleic acid were the most abundant amino acid and fatty acid of C. wilfordii Radix, respectively. To examine its functional properties, classical 2,2-diphenyl-1-picrylhydrazyl (DPPH) analysis was performed. As a result, the concentration of C. wilfordii Radix required to scavenge 50% of DPPH radicals was 1.16 mg of dried material. Lastly, in olfactory and sensory tests, ${\beta}$-eudesmol (woody odor) was the major flavor compound responsible for the bitter taste and sensory attributes of C. wilfordii Radix. Taken altogether, the above results provide important preliminary results for utilization of C. wilfordii Radix as a food resource.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.139-146
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• 2009

Experimental study was performed to evaluate the long-term behavior of CFRP (carbon fiber reinforced polymer) strips under sustained loads including prestressing force in strengthening RC members with post-tensioned CFRP strips. Two types of CFRP strip such as unidirectional CFRP strip and hybrid CFRP strip which is composed of carbon fiber and steel plate were considered. Also two types of loading scheme were included in this study. Direct sustained loading test had been carried out to estimate the creep deformation and relaxation of CFRP strips including slip deformation at both mechanical anchorages for over 700 days. Also, flexural sustained loading test had been conducted to estimate the initial prestress losses on clamping the CFRP strips at jacking anchorages for over 90 days. From the sustained loading tests, it was observed that stress losses of unidirectional CFRP strips due to the creep deformation and relaxation of material itself and slip deformation at mechanical anchorage were ignorable. On the other hand, significant stress losses caused by the yielding of steel embedded in CFRP strips were found in case of hybrid CFRP strips due to the initial jacking force over steel yielding stress. Also, initial prestress losses during setting of CFRP strips on mechanical anchorage were about 10% of intial jacking force, which must be considered in the design.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.199-207
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• 2009

Many researches on electromagnetic (EM) properties like dielectric constant and conductivity are performed since they can be characterized in nonmetallic cement-based material such as mortar and concrete. However, they are much affected by the moisture so that the behaviors of EM properties are to be clearly understood. In this paper, measurements for saturation and EM properties are performed for cement mortar specimens with five different water to cement (W/C) ratios including basic tests like compressive strength and porosity measurement. Every saturated specimens are exposed to room condition and the changes in EM properties caused by decreasing saturation are analyzed. In the saturated condition, higher measurement of EM properties are evaluated in the specimens with higher porosity, however this relationship is adversely changed with drying process. Since the pores without filled water causes the decreases in EM properties, the measurements show stable and linear increment with the lower W/C ratios. Furthermore, the increasing ratios of EM measurements with W/C ratio are shown with saturation and the relationships between them are derived through regression analysis.

• Geophysics and Geophysical Exploration
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• v.13 no.1
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• pp.102-108
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• 2010

The internal structure of a river embankment must be delineated as part of investigations to evaluate its safety. Geophysical methods can be most effective means for that purpose, if they are used together with geotechnical methods such as the cone penetration test (CPT) and drilling. Since the dyke body and subsoil in general consist of material with a wide range of grain size, the properties and stratification of the soil must be accurately estimated to predict the mechanical stability and water infiltration in the river embankment. The strength and water content of the levee soil are also parameters required for such prediction. These parameters are usually estimated from CPT data, drilled core samples and laboratory tests. In this study we attempt to utilise geophysical data to estimate these parameters more effectively for very long river embankments. S-wave velocity and resistivity of the levee soils obtained with geophysical surveys are used to classify the soils. The classification is based on a physical soil model, called the unconsolidated sand model. Using this model, a soil profile along the river embankment is constructed from S-wave velocity and resistivity profiles. The soil profile thus obtained has been verified by geotechnical logs, which proves its usefulness for investigation of a river embankment.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.3
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• pp.23-33
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• 2012

Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.391-398
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• 2012

This paper presents the shear capacities of biaxial hollow slab with donut type hollow sphere. Recently, various types of slab systems which can reduce self-weight of slabs have been studied for increasing constructions of taller and larger building structures. A biaxial hollow slab system is widely known as one of the effective slab system, which can reduce self-weight of slab. According to previous studies, the hollow slab has low shear strength, compared to solid slab. Also, the shear capacities of biaxial hollow slab are influenced by the shapes and materials of hollow spheres. However, the current code does not provide a clear computation method for the shear strength of hollow slab. To verify the shear capacities of this hollow slab, one-way shear tests were performed. Four test specimens were used for test parameters. One was conventional RC slab and others were hollow slabs. The test parameters included two different shapes and materials of plastic balls. The shape parameters were donut and non-donut forms and the material parameters were general plastic and glass fiber plastic. The results showed that the shear strengths varied depending on hollow shapes and materials used in the slab.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.10-19
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• 2013

Recently, researches related to precast modular construction have been actively conducted for nuclear power plant, LNG gas tank, and small-medium PCCV as well as bridges and buildings. In this study, the precast panel cast with steel mesh reinforced mortar (SRM) which is similar reinforced ferrocement was developed for efficient precast construction, construction time reduction, and easy transportation. Mortar mixture with high strength and flowability was obtained from various case studies using silica fume and GGBS. Also, $1,200{\times}600{\times}150mm$ SRM and reinforced concrete (RC) panels were manufactured with reinforcing ratio of 2% and 4%. To verify structural performance of the SRM specimen, the basic material tests, free shrinkage test, and 3-point flexural test with a line loading were carried out. From the test results, it was determined that SRM specimens showed outstanding flexural capacity and ductility. However, the 4% reinforced SRM specimens must consider shear reinforcing to be used as a precast modular member.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.112-118
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• 2011

The recycled asphalt concrete has gotten increasing attention due to the environmental issues. The volume of reclaimed asphalt has increased significantly for last few years because of city remodeling, pavement maintenance, utility excavation, and road widening. Considering the value of reclaimed asphalt, it is rather used for the recycled asphalt concrete than it is used for fill and cover up material instead of soil. This research will be a supplements incomplete issues from existing research results and suggests the quality control guideline for recycled asphalt concrete and upcoming laws. As the first step of research, the trial construction of RAP(Recycled Asphalt Pavement) performed in expressway construction sites. These trial construction sites have been checked every years. And another construction sites studied and selected for more deeper performance check of RAP. For this checks, we used automatic pavement survey equipment and computerized analysis tools. Also, DSR(Dynamic Shear Rheometer) was used for the fatigue life calculation of binder blends(RAP and virgin binder). As a consequence of this research, the application of recycled asphalt provides good enough quality for highway construction. The preceeding literatures reviewed shows that the asphalt rejuvenator are used in many countries but that type of chemical agent are not used in Korea. By using the data of trial construction and mix design in Chongwon-Sangju construction lane, the surface and base courses consisted with the 10% and 30% rap mix asphalt section maintains good performance for up to 7 years. Through the performance check and laboratory tests(DSR), the quality control and mixture's low temperature prevention are the important factor and chemical agent necessary for increasing the fatigue life of RAP binder.