• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.393-401
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• 2021

In this paper, we proposed a numerical model based on moment-curvature, to evaluate the resistance of reinforced concrete (RC) members subjected to blast loading. To consider the direct shear failure mode, we introduced a dimensionless spring element based on the empirical direct shear stress-slip relation. Based on the dynamic increase factor equations for materials, new dynamic increase factor equations were constructed in terms of the curvature rate for the section which could be directly applied to the moment-curvature relation. Additionally, equivalent bending stiffness was introduced in the plastic hinge region to consider the effect of bond-slip. To verify the validity of the proposed model, a comparative study was conducted against the experimental results, and the superiority of this numerical model was confirmed through comparison with the analytical results of the single-degree of freedom model. Pressure-impulse (P-I) diagrams were produced to evaluate the resistance of members against bending failure and direct shear failure, and additional parametric studies were conducted.

• Journal of the Korean Geosynthetics Society
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• v.21 no.2
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• pp.1-9
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• 2022

Recently, the reclamation of public waters has been on a downward trend due to environmental problems, but there is a limitation to evaluating environmental characteristics index uniformly. In this study, the stability of settlement behavior on public waters reclaimed land was analyzed using the experimental test. From the primary consolidation influence factors, the characteristics of the waste lime was similar that of clay in process of consolidation. Assuming that the waste lime landfill is the layer reinforced with thin geosynthetic reinforcement, the settlement was predicted by calculating the amount of increase using the Westergaard method. As a result of predicting settlement with degree of consolidation, it was found that the increase in stress was reduced by 40% when the surface layer of the soft ground was reinforce with geotextiles compared to the case where it was not reinforced. In addition, the consolidation behavior characteristics of clay and waste lime were compared using the correlation between the plasticity index and internal friction angle of waste lime. Since the waste lime in the public process of consolidation, it was predicted that long-term settlement will increase further.

• Clean Technology
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• v.16 no.3
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• pp.182-190
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• 2010

The feasibility of clean technology to minimize the $CO_2$ emission by recycling and reuse the waste materials and energy have been studied for the cement industry. A life cycle assessment (LCA) was performed for an alternative raw material-supply method to use the molted slag as the major raw material in the cement clinker manufacturing. Using this new method, a 60% of $CO_2$ could be reduced that comes out during the decarboxylation from the cement rotary kiln. The energy-efficiency improvement and the alternative energy methods that had been determined in our previous study through the environmental assessment of cement industry were applied to the study for the reduction of $CO_2$ emission. The natural gas, one of the fossil fuels, was also used as the first choice to get the result at the earliest time by the most economic and the most efficient green technology and to switch into the carbon neutral energy consumption pattern.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.77-92
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• 2009

In the present paper, a numerical study was carried out for a reasonable and realistic evaluation of tension loads in piles during deep excavation in Singapore soft soil applying pile-plugged jet grouted slab. Based on 2-dimensional finite element analyses using linear elastic-perfectly plastic soil model obeying Mohr-Coulomb failure criterion, effects of pile-plugged jet grouted slab on the stability during excavation were examined, and a parametric study was also conducted to investigate critical influencing parameters in the estimation of reliable pile tension loads. Finally, based on the Modified Cam-Clay model, pile tension loads were estimated by considering on-going consolidation state of the Singapore clay deposit and the range of critical parameters observed during laboratory tests.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6C
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• pp.377-384
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• 2006

Theoretical and experimental study of the unconfined penetration (UP) test was conducted to suggest a new test method (referred to as IUP, Improved Unconfined Penetration) for determination of the tensile strength of compacted sand-bentonite mixtures. The tensile strength of compacted mixtures can be calculated from limit analysis based on the theory of perfect plasticity. The measurement errors in new test method were reduced by improving the UP device. Preliminary experiment results indicate that the tensile strength increases with increasing the disk size, loading rate and pH level. In addition, the disk diameter with 25.4 mm and the loading rate with 0.5%/min~1%/min are most suitable condition for the IUP test. The reliability of IPU test was verified by through the fact that good agreement between the IUP and conventional split tensile test results is observed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.11-17
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• 2024

A seismic structure is an earthquake-resistant design that dissipates seismic energy by equipping the structure with a device called a damper. As research efforts to reduce earthquake damage continue to rise, technology for isolating vibrations in structures has evolved by altering the materials and shapes of dampers. However, due to the inherent nature of the damper, there are an unescapable restrictions on the extent of plastic deformation that occurs in the material to effectively dissipate energy. Therefore, in this study, we proposed a long-life damper that offers semi-permanently usage and enhances structural performance by applying additional tension which is achieved by utilizing super elastic shape memory alloy (SSMA), a material that self-recovers after deformation. To comprehensively understand the behavior of long-life dampers, finite element analysis was performed considering the design variables such as material, wire diameter, and presence of tension, and response behavior was derived to analyze characteristics such as load resistance, energy dissipation, and residual displacement to determine the performance of long-life dampers in seismic structure. Excellence has been proven from finite element analysis results.

• Journal of the Korean Chemical Society
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• v.39 no.8
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• pp.627-634
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• 1995

Layered double hydroxides ($Mg-Al-CO_3$ systems, LDH), which are hydrotalcite-like anionic clay minerals, having different $Mg^{2+}\;to\;Al^{3+}$ ratio were synthesized by coprecipitation method. The subsequent products were characterized by the following methods; elemental analysis, X-ray powder diffraction, thermal analysis (DSC and TGA), FT-IR and $^{27}$Al-MAS NMR. X-ray powder patterns showed that the products formed were layered structure materials. Two heat absorption peaks were observed around 20 ∼280$^{\circ}C$ (surface water and interlayer water) and 280∼500$^{\circ}C$ (water from lattice hydroxide and carbon dioxide from interlayer carbonate) in DSC diagrams, and they were quantitatively analyzed by TGA diagrams (in case LDH4 16.2% and 28.6% respectively). FT-IR spectra indicate that the interlayer carbonate ions occupied symmetrical sites between two adjacent layers in a parallel direction. $^{27}$Al-MAS NMR spectra show only single resonance (8.6 ppm) of the octahedrally coordinated aluminum similar magnesium. When LDH4 was calcined at 560$^{\circ}C$ for 3 hours in air, its layered structure was destroyed giving a mixed metal oxide. However it readily became rehydrated in aqueous chromate solution to its original structure.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.51-62
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• 2007

Recently, the pavement distresses in the bridge deck have seriously affected the durability of bridge deck and driver's safety. The existing asphalt materials have the limitations in reducing the pavement distresses of brides deck. To protect the bridge deck and withstand the high deflection, it is necessary to develop the asphalt materials with good fatigue resistance for bridge deck pavement. The asphalt binder combined with SBS and two other admixtures has been developed for improving the resistance to fatigue cracking, productivity, and workability for bridge deck pavement. Based on the various binder test results, the developed binder is found to be PG 70-34 indicating very higher resistance against fatigue cracking. Fatigue testing, wheel tracking testing, and moisture susceptibility testing have been conducted to evaluate the performance of asphalt mixtures developed in this study. Laboratory test results show that the developed asphalt material has three times higher fatigue lives than the typical modified asphalt mixture. Full scale accelerated testing was also performed on the typical asphalt mixture and newly developed asphalt mixture to evaluate the full scale performance of asphalt mixtures. Test results indicate that the length of cracking on the new materials is only 38% of the typical material at the 250,000 load repetitions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1227-1240
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• 2014

Abandoned mines often cause environmental problems, such as alteration of landscape, metal contamination, and landslides due to a heavy rainfall. Geotechnical and rheological tests were performed on waste materials corrected from Imgi waste rock dump, located in Busan Metropolitan City. Debris flow mobility was examined with the help of 1-D BING model which was often simulated in both subaerial and subaqueous environments. To determine flow curve, we used a vane-penetrated rheometer. The shear stress (${\tau}$)-shear rate (${\dot{\gamma}}$) and viscosity(${\eta}$)-shear rate (${\dot{\gamma}}$) relationships were plotted using a shear stress control mode. Well-known rheological models, such as Bingham, bilinear, Herschel-Bulkley, Power-law, and Papanastasiou concepts, were compared to the rheological data. From the test results, we found that the tested waste materials exhibited a typical shear shinning behavior in ${\tau}$-${\dot{\gamma}}$ and and ${\eta}$-${\dot{\gamma}}$ plots, but the Bingham behavior is often observed when the water contents increased. The test results show that experimental data are in good agreement with rheological models in the post-failure stage during shearing. Based on the rheological properties (i.e., Bingham yield stress and viscosity as a function of the volumetric concentration of sediment) of waste materials, initial flowing shape (5 m, 10 m, and 15 m) and yield stress (100 Pa, 200 Pa, 300 Pa, and 500 Pa) were input to simulate the debris flow motion. As a result, the runout distance and front velocity of debris flow are in inverse propositional to yield stress. In particular, when the yield stress is less than 500 Pa, most of failed masses can flow into the stream, resulting in a water contamination.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.713-718
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• 2009

Advanced industries-IT, BT, NT and ET are rapidly developing in 21 century. And the cement industry is becoming the principal factor in air pollution because of the creation of $CO_2$ during manufacturing. Also, the cement industry will be faced with a crisis due to the exhaustion of natural resources. In this study, nano cement by Bottom-up method of a chemical synthesis was developed. The generation of $CO_2$ during the plasticization process of cement manufacturing was avoided. The purpose was to produce building materials that have both high strength and durability as the high value-added growth engine industry of the 21 century. The nano cement was developed using hydrothermal synthesis. This is a method of mixing after ripening, by manufacturing the high density gel and low gel, which does not require special test equipment or pressure conditions to produce. Particle size, SEM, EDX, and porosity tests were conducted. This study investigated the compressive strength of concrete with various compositions. Specimens were tested for compressive strength at 3, 7, 14 and 28 days. The medium-sized (50% by weight) cement particles created by chemical synthesis were less than 168 nm. The compressive strength of the mortar prepared using this cement was 53.9 MPa. But it was judged that succeeding study will be necessary for development of nano building materials with high ability and economical analysis.