• Steel and Composite Structures
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• v.18 no.1
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• pp.1-28
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• 2015

In this paper, the dynamic response of functionally gradient steel (FGS) composite cylindrical panels in steady-state thermal environments subjected to impulsive loads is investigated for the first time. FGSs composed of graded ferritic and austenitic regions together with bainite and martensite intermediate layers are analyzed. Thermo-mechanical material properties of FGS composites are predicted according to the microhardness profile of FGS composites and approximated with appropriate functions. Based on the three-dimensional theory of thermo-elasticity, the governing equations of motionare derived in spatial and time domains. These equations are solved using the hybrid Fourier series expansion-Galerkin finite element method-Newmark approach for simply supported boundary conditions. The present solution is then applied to the thermo-elastic dynamic analysis of cylindrical panels with three different arrangements of material compositions of FGSs including ${\alpha}{\beta}{\gamma}M{\gamma}$, ${\alpha}{\beta}{\gamma}{\beta}{\alpha}$ and ${\gamma}{\beta}{\alpha}{\beta}{\gamma}$ composites. Benchmark results on the displacement and stress time-histories of FGS cylindrical panels in thermal environments under various pulse loads are presented and discussed in detail. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state of the art of this problem, and provide pertinent results that are instrumental in the design of FGS structures under time-dependent mechanical loadings.

• Journal of the Korean Wood Science and Technology
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• v.25 no.1
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• pp.42-49
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• 1997

The purpose of this study was to investigate the relationships among density, moisture content, and modulus of elasticity in which are important characteristics in physical and mechanical properties of woods. In this study, the dynamic MOE was calculated through the combination with resonance frequency of transverse vibration method and density, and the estimated moisture contents were calculated with two different equations (1, 2) in order to compare with experimental moisture contents. The following results from this study were obtained: 1. According to the regression analysis with two different parameters (E and density), the two regression lines appeared to be straight intersecting at 0.6 density. As another factor, moisture contents in wood also influenced on the analysing regression at the below F.S.P. 2. When considering the relationship between moisture contents and E, the tendency of each moisture content and E showed very similar pattern suggesting that moisture contents in addition to density are very important parameter. 3. When together with moisture contents and density as parameters for multiple regression analysis, coefficiences of determinations are dramatically improved. Interestingly, the coefficiences of determinations are further increased when analysing at the below point of F.S.P. and when analysing higher and lower density separately. In summary, more correct estimation of the dynamic MOE of woods can be possible with only transverse vibration and density in wood. Therefore, with this indirect method, the calculation of MOE in all kinds of woods including timber, live tree and wood products can be feasible resulting in accelerating the efficiency of time and labor.

• Advances in concrete construction
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• v.6 no.4
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• pp.363-373
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• 2018

Portland cement pervious concrete (PCPC) is an effective pavement material to solve or reduce the urban waterlogging problems. The Mechanical properties, the permeability, the abrasion resistance and the frost resistance of PCPC without fine aggregate were investigated. The increase of porosity was achieved by fixing the dosage of coarse aggregate and reducing the amount of cement paste. The results show that the compressive strength and the flexural strength of PCPC decrease with the increase of porosity. The permeability coefficient and the wear loss of PCPC increase with the increase of the porosity. The compressive strength and the flexural strength of PCPC subjected to 25 freeze-thaw cycles are reduced by 13.7%-17.8% and 10.6%-18.3%, respectively. For PCPC subjected to the same freeze-thaw cycles, the mass loss firstly increases and then decreases with the increase of the porosity. The relative dynamic modulus elasticity decreases with the increase of freeze-thaw cycles. And the lower the PCPC porosity is, the more obvious the dynamic modulus elasticity decreases.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.9 no.3
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• pp.17-25
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• 2006

To increase freeze-thaw resistance of porous concrete, this study examined physical properties of polymer by replacing paste used as a binding material with polymer, using unsaturated polyester and epoxy resin, and changing the mixing ratio of polymer. According to the result of this study, when the mixing ratio of resin paste to aggregates was 11 to 16%, voids volume was 33 to 37% and unit weight was about 1620 to 1720kg/$m^3$. In comparison with previous studies using cement paste, voids volume increased by about 7 to 16%, while unit weight decreased by about 100 to 300kg/$m^3$. Compressive strength was 90 to 155kg/$cm^2$ at the age of 7 days, which was 5-40kg/$cm^2$ bigger than porous concrete using cement paste. From a viewpoint of freeze-thaw resistance, it was identified that pluse velocity fell by 0.23km/sec, about 7% of the original velocity, when the cycle of freeze-thaw was repeated 300 times. In spite of 300 repetitions of the cycle, relative dynamic modulus of elasticity was more than 60%, which suggested that its freeze-thaw resistance was more excellent compared with the result that relative dynamic modulus of elasticity of porous concrete using cement paste was 60 % or less under the condition of 80 repetitions of freeze-thaw cycle.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.2
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• pp.104-110
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• 1999

This study was performed to evaluate the properties of permeable polymer concrete with fly ash and CaCO3. The following conclusions are drawn. The static modulusof elasticity is in the range of 1.19 $\times$105 ~1.49$\times$105 kgf/$\textrm{cm}^2$, which is approximately 53 ~56% of that of the normal cement concrete. The oission's number of permeable polymer concrete is in the range of 3.95 ~6.53, which is less than that of the normal cement concrete. The dynamic modulus of elasticity is in the range of 1.29$\times$105 ~1.59$\times$105 kgf/$\textrm{cm}^2$, which is approximately less compared to that of the normal cement of the static modulus . Fly ash 50% and CaCO3 50% filled permeable polymer concrete has showed higher dynamic modulus. The water permeability is in therange of 3.971 ~4.393$\ell$ /$\textrm{cm}^2$/h, and it is largely dependent upon the mix design. These concrete can be used to the structures which need water permeability.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.7
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• pp.47-53
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• 2004

Permeable polymer concrete can be applied to roads, sidewalks, river embankments, drain pipes, conduits, retaining walls, yards, parking lots, plazas, interlocking blocks, etc. This study was to explore a possibility of using blast furnace slag powder and stone dust of industrial by-products as fillers for Eco-permeable polymer concrete. Different mix proportions were tried to find an optimum mix proportion of the Eco­permeable polymer concrete. The tests were carried out at $20{\pm}1^{circ}C$ and $60{\pm}2\%$ relative humidity. At 7 days of curing, unit weight, coefficient of permeability, dynamic modulus of elasticity, compressive, flexural and splitting tensile strengths ranged between $1,821{\~}1,955 kg/m^{3}$, $0.056{\~}0.081\;cm/s$, $114{\times}0^{2}{\~}157{\times}10^{2}\;MPa,\;17.6{\~}24.7\;MPa,\;5.98{\~}7.94\;MPa\;and\;3.43{\~}4.70\;MPa$, respectively. It was concluded that the blast furnace slag powder and stone dust can be used in the Eco-permeable polymer concrete.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.128-134
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• 2005

This study was performed to evaluate the strength and durability properties of recycled concrete containing water - redispersible copolymer powder(WRP) and blast furnace slag powder(BSP) [RCWS]. Material used were cemente, recycled coarse aggregare, natural fine aggregate, water-redispersible copolymer powder, blast-furnace slag powder. Especially, Water-redispersible powder was used for blending with Inorganic binders such as cemente, gypsum and hydrated lime etc. First of all, Mixed ratio method of RCWS made Two Type. One was called type-1 which used to BSP content 5% and WRP(Water-redispersible powder) content 0%, 1%, 2%, 3%, 4%, 5%, 6%. respectively. Another was called Type-2 which used to BSP(blast furnace slag powder)content 10% and WRP(Water-redispersible powder) content 0%, 1%, 2%, 3%, 4%, 5%, 6%. respectively. According to the experimental results of (RCWS), Incase Type-2 at curing age 28days, Compressive strength, pulse velocity and dynamic modulous of elasticity were shown higher than Type-1 and The more WRP content increasing($0%{\sim}6%$) was the lower Compressive strength, Pulse velocity and Dynamic modulous of elasticity. Water absorption ratio was in the range of $3.85%\;{\sim}\;3.23%$, it was almost equal to Type-1, 2 but Increasing the WRP content($0%{\sim}6%$), The water absorption ratio is decreased.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.5
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• pp.51-64
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• 1991

In this paper, an attempt is made to analyze the impulsive stress directly underneath the concentrated impact point for a supported square plate by using the three-dimensional dynamic theory of elasticity and the potential theory of displacement (stress function) on the supposition that the load, F$_{*}$0 sin .omega.t, acted on the central part of it. The results obtained from this study are as follows: 1. The impulsive stress cannot be analyzed directly underneath the acting point of concenrated impact load in privious theories, but can be analyzed by using the three-dimensional dynamic theory of elasticity and the potential theory of displacement. 2. Theorically, with increasing the pulse width of applied load, it was possible to clarify that the amount of stress in the point of concentrated impact load was increased and that of stress per unit impulse was decreased. 3. The numerical inversion of laplace transformation by the use of the F.F.T algorithm contributes the reduction of C.P.U time and the improvement of the accuracy or results. 4. In this paper recommended, it is found that the approximate equation of impact load function P (.tau.) = A.tau. exp (-B.tau.), and P (.tau.) =0.85A exp (-B.tau.) sinC.tau. could actually apply to all impact problem. In compared with the experimental results, the propriety of the analytical method is reasonable.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1999.10c
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• pp.294-300
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• 1999

After researching the physical properties of the concrete included Rice Husk Ash(RHA concrete) and workability of fresh concrete admixed RHA, we have tested durability of RHA-concrete against freeaing and thawing in the winter using rapid freezing and thawing test method(KS F 2456) . There aretwo hypotheses to explain the failure mechanism of a freezing and thawing action. First, the hydraulic pressure in the pores of freezing concrete make an internal stress of concrete structures outbreaking micro crack in the face of concrete, Second, Frost action causing damage to cement paste repeatedly come from soil frost action, freezing water in the capillaries. Initial Relative Dynamic Modulus of Elasticity (DME) was biggest in cae of unit binder weight 600kgf/㎥ and relative dynamic modulus of elasticity increased until 300cycles. In general , initial relative DME was proportional to unit binder weight . Relative DME was decreased in proportion to unit binder weight in the case of 300, 400, 500kgf/㎥ , but relative DME fo the others remained more than 90% until 300 cycles. It was not good effect of intermixed RHA to concrete in case of below unit binder weight 300kgf/㎥ and the resistance of freezing and thawing was not good either.

• Journal of the Korean Applied Science and Technology
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• v.21 no.4
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• pp.300-305
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• 2004

High-solid coatings were prepared by blending of previosly synthesized acrylic resins and hexamethylene diisocyanate-trimer and curing it at room temperature. The characterization of the films of the prepared coatings was performed. The impact resistance, cross-hatch adhesion, $60^{\circ}$specular gloss, and heat resistance of the films proved to be good, and the pencil hardness and drying time proved to be slightly poor. Especially, there was a remarkable improvement in the heat resistance. This improvement may stem from the regular arrangement of ethyl groups introduced into the acrylic resin. As a result of Rigid-body pendulum visco-elasticity measurement, dynamic $T_g$ values of cured films increased with dynamic $T_g$ values.