• Steel and Composite Structures
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• v.31 no.2
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• pp.133-148
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• 2019

This paper reports on the energy absorption characteristics of a lattice-web reinforced composite sandwich cylinder (LRCSC) which is composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, polyurethane (PU) foam and ceramsite filler. Quasi-static compression experiments on the LRCSC manufactured by a vacuum assisted resin infusion process (VARIP) were performed to demonstrate the feasibility of the proposed cylinders. Compared with the cylinders without lattice webs, a maximum increase in the ultimate elastic load of the lattice-web reinforced cylinders of approximately 928% can be obtained. Moreover, due to the use of ceramsite filler, the energy absorption was increased by 662%. Several numerical simulations using ANSYS/LS-DYNA were conducted to parametrically investigate the effects of the number of longitudinal lattice webs, the number of transverse lattice webs, and the thickness of the transverse lattice web and GFRP face sheet. The effectiveness and feasibility of the numerical model were verified by a series of experimental results. The numerical results demonstrated that a larger number of thicker transverse lattice webs can significantly enhance the ultimate elastic load and initial stiffness. Moreover, the ultimate elastic load and initial stiffness were hardly affected by the number of longitudinal lattice webs.

• Coupled systems mechanics
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• v.10 no.2
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• pp.161-184
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• 2021

Strengthening of reinforced concrete beams with externally bonded fiber reinforced polymer plates/sheets technique has become widespread in the last two decades. Although a great deal of research has been conducted on simply supported RC beams, a few studies have been carried out on continuous beams strengthened with FRP composites. This paper presents a simple uniaxial nonlinear analytical model that is able to accurately estimate the load carrying capacity and the behaviour of damaged RC continuous beams flexural strengthened with externally bonded prestressed composite plates on both of the upper and lower fibers, taking into account the thermal load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e., the damaged concrete beam, the FRP plate and the adhesive layer. The flexural analysis results and analytical predictions for the prestressed composite strengthened damaged RC continuous beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The use of composite materials increased the ultimate load capacity compared with the non strengthened beams. The major objective of the current model is to help engineers' model FRP strengthened RC continuous beams in a simple manner. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the FRP-damaged RC hybrid structures.

• Journal of the Korean Wood Science and Technology
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• v.50 no.6
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• pp.436-447
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• 2022

Lignocellulose nanofibrils (LCNFs) were prepared using a two-step deep eutectic solvent (DES) and enzymatic pretreatment followed by mechanical defibrillation, and we examined the effects of enzymatic pretreatment conditions on different characteristics of the LCNFs thus obtained. The LCNFs yielded using the two-step DES pretreatment (Enz-LCNF) exhibited a well-defibrillated entangled web-like structure with an average fiber diameter ranging from 15.7 to 20.4 nm. Furthermore, we found that the average diameter and filtration time of the Enz-LCNFs decreased with an increase in enzyme concentration and enzymatic treatment time, whereas we detected a concomitant reduction in the tensile strength of the Enz-LCNF sheets. The Enz-LCNFs were characterized by a typical cellulose I structure, thereby indicating that the enzymatic treatment causes very little damage to the crystalline form.

• Composites Research
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• v.22 no.2
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• pp.24-29
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• 2009

This study aims to investigate the residual strength of sandwich composites with Al honeycomb core and carbon fiber face sheets after the quasi-static indentation damage by the experimental investigation. The 3-point bending test and the edge-wise compressive strength test were used to find the mechanical properties, and the quasi-static point load was applied to introduce the simulated damage on the specimen. The damaged specimens were finally assessed by the 3-point bending test and the compressive strength test. The investigation results revealed the residual strength of the damaged specimens due to the quasi-static indentation. The both test results showed that the residual strength of the damaged specimen was decreased according to increases of the damaged depth.

• Composites Research
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• v.31 no.5
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• pp.177-185
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• 2018

Fiber metal laminate (FML) is a type of hybrid composites which consist of metallic and fiber-reinforced plastic sheets. As the FML has a drawback of the delamination that is a failure of the interfacial adhesive layer, the nominal stresses and the energy release rates should be determined to identify the delamination behavior. However, it is difficult to derive the nominal stresses and the energy release rates since the operating temperature of the equipment is restricted. For this reason, the objective of this paper is to predict the mode-I nominal stress and the mode-I energy release rate of the adhesive layer using the inverse analysis based on the Levenberg-Marquardt method. First, the mode-I nominal stress was assumed as the tensile strength of the adhesive layer, and the mode-I energy release rate was obtained from the double cantilever beam test. Next, the finite element method was applied to predict the mode-I delamination behavior. Finally, the mode-I nominal stress and the mode-I energy release rate were predicted by the inverse analysis. In addition, the convergence of the parameters was validated by trying to input two cases of the initial parameters. Consequently, it is noted that the inverse analysis can predict the mode-I delamination behavior, and the two input parameters were converged to similar values.

• Journal of the Korean Society of Marine Environment & Safety
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• v.16 no.1
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• pp.125-133
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• 2010

Researches and studies which have been conducted so far on external confinement of long span concrete columns have mainly concentrated on concentric loading. But, long span bridge concrete columns over the sea are mainly subjected to concentrated axial load, and at the same time lange amount of moment by eccentric load. This paper experimentally investigates the performance of externally confined high-strength concrete columns subjected to loading mechanism and evaluates the effectiveness of two confinement materials carbon fibre and high performance glass fibre. Twelve short columns with the same dimensions were cast and tested Six columns were reinforced with hoop bars, the remaining six columns were reinforced with spiral bars and wrapped with three layers of carbon failure and high performance glass FRP sheets. Test variables considered were the shape of internal reinforcement and strengthening materials according to loading location. The experimental results showed that eccentric load could obviously lower down the maximum failure load of FRP-confined concrete columns, compared with the columns under concentric load. And compared with the carbon FRP-confined reinforced concrete columns, high performance glass FRP-confined columns displayed a higher load capacity and ductility, when tested both concentrically and eccentrically.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.239-247
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• 2008

Use of both carbon fiber (CF) and glass fiber (GF) at the same time to strengthen existing flexural members was exploited. Using a proper volumetric GF / CF ratio, the CF can rupture first followed by subsequent rupture of GF at higher stress and strain showing a pseudo-ductile behavior. A theoretical study indicated that the ratio is 4.62 : 1 and higher where the pseudoductile effect can be shown. Flexural tests of plain concrete beams strengthened using fibers were first carried out. Hybrid FRP sheet using 8.8 : 1 ratio was then fabricated and the sheet was used to strengthen reinforced concrete beams. The RC beams strengthened using 1-ply and 2-ply hybrid sheets both revealed increased strength over a non-strengthened beam and ductile flexural behavior. A comparable beam strengthened using CF also showed increased strength but with limited ductility.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.317-327
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• 2012

The average specific cake resistance, the most important indicator for cake filtration and solid-liquid separation, is measured by filtration experiment. But the exact value is difficult to measure because of the other influences such as sedimentation during filtration. This study, a little more stable method named filtration-permeation is proposed for measuring average specific cake resistance. The filtration-permeation is composed of permeation of particle eliminated water through pre-formed cake by filtration. Using 1 wt% calcium carbonate suspension, the filtration-permeation experiments were performed for 8 kinds of filter media at the conditions of 0.5 atm and 0.2 atm, 1 and 3 sheets of filter media. At each specific condition, three to five times filtration-permeation were accomplished. As a result, stable permeation speed is measured. According to this experimental result, the characteristics of permeation and the effect of sedimentation are analyzed with Ruth's equation. The one way analysis of variance (one way ANOVA) is applied to the average specific cake resistances of filtration and permeation obtained with the selected three kinds of filter media. The average specific cake resistances between 0.5 atm and 0.2 atm by filtration do not distinguished, but those by permeation is perfectly distinguished. The experimental results during permeation have a very narrow distribution than that measured during filtration. The analysis of filtration experiments, it was verified that the resistance of filter medium by traditional method is of no significance. Finally, the migration of small particles through the medium composed of fiber glass at low pressure was studied.

• Earthquakes and Structures
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• v.5 no.6
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• pp.703-731
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• 2013

In order to verify the applicability of buckling restrained braces (BRB's) and fiber reinforced polymer (FRP) sheets to the seismic strengthening of a low-rise RC building having the irregularities of a soft/weak story and torsion at the ground story, a series of earthquake simulation tests were conducted on a 1:5 scale RC building model before, and after, the strengthening, and these test results are compared and analyzed, to check the effectiveness of the strengthening. Based on the investigations, the following conclusions are made: (1) The BRB's revealed significant slips at the joint with the existing RC beam, up-lifts of columns from RC foundations and displacements due to the flexibility of foundations, and final failure due to the buckling and fracture of base joint angles. The lateral stiffness appeared to be, thereby, as low as one seventh of the intended value, which led to a large yield displacement and, therefore, the BRB's could not dissipate seismic input energy as desired within the range of anticipated displacements. (2) Although the strengthened model did not behave as desired, great enhancement in earthquake resistance was achieved through an approximate 50% increase in the lateral resistance of the wall, due to the axial constraint by the peripheral BRB frames. Finally, (3) whereas in the original model, base torsion was resisted by both the inner core walls and the peripheral frames, the strengthened model resisted most of the base torsion with the peripheral frames, after yielding of the inner core walls, and represented dual values of torsion stiffness, depending on the yielding of core walls.

• Membrane and Water Treatment
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• v.9 no.5
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• pp.327-334
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• 2018

The nano/micro composites with highly porous surface area have attracted of great interest, particularly the synthesis of porous and thin film sheets of high performance. In this paper, an easy method of cost-effective synthesis of thin film ceramic fiber membranes based on Hydroxyapatite, and activated carbon by turned into studied to be applied within the service-facilitated the transport of radioactive waste such as $^{90}Sr$, $^{137}Cs$ and $^{60}Co$) as activated product of radioisotopes from ETRR-2 research reactor and dissolved in 3M $HNO_3$, across a thin flat-sheet supported liquid membrane (TFSSLM). Radionuclides are transported from alkaline pH values. The presence of sodium salts in the aqueous media improves in $HNO_3$, the lowering of permeability because the initial $HNO_3$ concentration is improved. The study some parameters on the thin sheet ceramic supported liquid membrane. EDTA as stripping phase concentration, time of extraction and temperature were studied. The study of maximum permeability of radioisotopes for all parameters. The pertraction of a radioactive waste solution from nitrate medium were examined at the optimized conditions. Under the optimum experimental 98.6-99.9% of $^{90}Sr$, 79.65-80.3% of $^{137}Cs$ and $^{60}Co$ 45.5-55.5% in 90-110 min with were extracted in 10-30 min, respectively. The process of diffusion in liquid membranes is governed by the chemical diffusion process.