• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.475-482
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• 2014

This paper presents the experimental results concentrically reinforced concrete tension members and compares cracking behavior of amorphous steel fiber and normal steel fiber reinforced concrete members. Two kind of steel fibers were included as a major experimental parameter together with the six cover thickness to bar diameter ratio ($c/d_b$). The presence of amorphous steel fibers effectively controlled the splitting cracks initation and propagation. In the amorphous steel fiber reinforced specimens, no splitting cracks were observed that becomes higher with cover thickness to bar diameter ratio is 2.0. Crack spacing of the each specimens reinforced with amorphous steel fibers and normal steel fibers becomes larger with the increase in cover thickness, and also measured maximum and average crack spacing are significantly smaller than current design code provision. Based on the measured crack spacings, a relationships for predicting the crack spacing is proposed using the measured average crack spacing in amorphous steel fiber reinforced concrete tension members.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.2
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• pp.150-158
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• 2011

Present study aims to investigate the influence of relative breakwater width W/L (W=width of breakwater, L=wavelength), wave steepness $H_i/gT^2$ (Hi=incident wave height, T=wave period) and relative wave height d/W (d=water depth) on forces in the moorings of horizontal interlaced multi-layered moored floating pipe breakwater (HIMMFPB) model. Studies were conducted on scaled down physical models having three layers of Poly Vinyl Chloride (PVC) pipes, wave steepness $H_i/gT^2$ varying from 0.063 to 0.849, relative width W/L varying from 0.4 to 2.65 and relative spacing S/D=2 (S=horizontal centre-to-centre spacing of pipes, D=diameter of pipes). Peak mooring forces were also measured and data collected is analyzed by plotting non-dimensional graphs depicting variation of $f_s/{\gamma}W^2$ ($f_s$=Sea side Mooring force, ${\gamma}$=specific weight of water) & $f_l/{\gamma}W^2$ ($f_l$=Lee side Mooring force) with $H_i/gT^2$ for d/W varying from 0.082 to 0.276 and also variation of $f_s/{\gamma}W^2$ and $f_l/{\gamma}W^2$ with W/L for $H_i$/d varying from 0.06 to 0.400.

• Wind and Structures
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• v.18 no.5
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• pp.511-528
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• 2014

The characteristics of wake galloping phenomenon for two parallel/unparallel circular cylinders were investigated via wind tunnel tests. The two cylinders were initially deployed in parallel and wake galloping phenomena were observed by varying the center-to-center distance. The effect of an unparallel arrangement of two cylinders was next investigated by fixing the spacing ratio of one side of the cylinders at 5.0D and the other side at 3.0D, in which D represents the diameter of the cylinder. For the unparallel disposition, the 5.0D side showed a small, limited vibration while the 3.0D side produced much larger amplitude of vibration, resulting in a rolling motion. However, the overall amplitude appeared to decrease in unparallel disposition when compared with the amplitude of the 3.0D - 3.0D parallel case. This represents the mitigation effect of wake galloping due to the unparallel disposition between two cylinders. Flow visualization tests with particle image velocimetry were conducted to identify flow fields between two cylinders. The test results demonstrate the existence of a complex interaction of the downstream cylinder with the shear layer generated by the upstream cylinder. When the spacing ratio was large enough, the shear layer was not observed and the downstream cylinder showed only limited random vibration.

• Steel and Composite Structures
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• v.36 no.1
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• pp.103-118
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• 2020

The static behavior of grouped large-headed studs (d = 30 mm) embedded in ultra-high performance concrete (UHPC) was investigated by conducting push-out tests and numerical analysis. In the push-out test, no splitting cracks were found in the UHPC slab, and the shank failure control the shear capacity, indicating the large-headed stud matches well with the mechanical properties of UHPC. Besides, it is found that the shear resistance of the stud embedded in UHPC is 11.4% higher than that embedded in normal strength concrete, indicating that the shear resistance was improved. Regarding the numerical analysis, the parametric study was conducted to investigate the influence of the concrete strength, aspect ratio of stud, stud diameter, and the spacing of stud in the direction of shear force on the shear performance of the large-headed stud. It is found that the stud diameter and stud spacing have an obvious influence on the shear resistance. Based on the test and numerical analysis results, a formula was established to predict the load-slip relationship. The comparison indicates that the predicted results agree well with the test results. To accurately predict the shear resistance of the stud embedded in UHPC, a design equation for shear strength is proposed. The ratio of the calculation results to the test results is 0.99.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.297-300
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• 2006

One of main issues of the FRP-concrete composite member is shear connection between FRP and concrete in order to secure composite behavior of FRP and concrete. To solve this problem, perfobond rib FRP shear connector is introduced for the mechanical shear connection. In this study, experimental study was carried out on the perfobond rib FRP shear connectors in order to develop the effective details of perfobond rib FRP shear connectors. Pull-out test specimens were manufactured with FRP plate with holes embedded in concrete block. Main parameters considered in this study were diameter of holes, ratio of spacing between the centres of holes to the diameter of holes, and thickness of FRP plates. Test results are discussed according to above parameters compared with other empirical expressions for steel perfobond rib connector.

• Wind and Structures
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• v.29 no.1
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• pp.55-64
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• 2019

The effect of vortex impingement on the fluid dynamics around a cylinder submerged in the wake of another of different diameters is numerically investigated at a Reynolds number Re = 200. While the diameter (D) of the downstream cylinder is fixed, impinging vortices are produced from the upstream cylinder diameter (d) varied as d/D = 0.24, 0.4, 0.6, 0.8 and 1.0, with a spacing ratio L=5.5d, where L is the distance between the center of the upstream cylinder to the front stagnation point of the downstream cylinder. Two-dimensional simulations are carried out using the finite volume method. Fluid forces acting on the two cylinders are correlated with impinging vortices, vortex shedding, and wake structure. Different facets of wake formation, wake structure, and flow separation and their connections to fluid forces are discussed.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.165-168
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• 2008

A numerical analysis was conducted to predict the heat transfer characteristics of a solar receiver which is subject to very high heat fluxes and temperatures for solar thermal applications. The concentration ratio of the solar receiver ranges 1000 and the concentrated heat is required to be transported to a certain distance for specific applications. This study deals with a solar receiver according to internal geometry variation incorporating high-temperature heat pipe. The isothermal characteristics in the receiver section is of major concern. The diameter of the solar thermal receiver was 120 mm and the length was 400 mm and the angle of receiver end wall set $90^{\circ},\;60^{\circ},\;45^{\circ},\;30^{\circ}$. And the diameter of the heat pipe was 12.7 mm, 48 axial channels of the same dimensions were attached to the outer wall of the receiver with even spacing in the circumferential direction. The channels are changed to high-temperature sodium heat pipes. Commercial softwares were employed to deal with the radiative heat transfer inside the receiver cavity and the convection heat transfer along the channels. The numerical results are compared and analyzed from the view point of high-temperature solar receiver.

• Journal of Forest and Environmental Science
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• v.39 no.1
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• pp.20-26
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• 2023

Cow pea (Vigna unguiculata) was intercropped with Ziziphus spina-christi as summer forage in two consecutive seasons of 2017 and 2018. The aims to find out suitable agroforestry practice for saline soils of Khartoum State. And to investigate effect of tree spacing on forage biomass yield under semi -irrigated systems. Completely randomized block design with 3 replicates was conducted for this trial. Thus Z.spina-christi that fixed at 4×4 m was intercropped with cowpea at 1 m and 1.5 m spacing from trees trunk. Tree growth parameters were measured in terms of tree height, tree collar diameter, tree crown diameter and fruit yield per tree. While crop were parameters were determined in terms of plant height, number of plant, forage biomass yield per ha and land equivalent ratio. Soil profile of 1×1 m and 1.5 m depth was excavated and its features were described beside its chemical and physical properties were analyzed for 0-10 cm, 0-30 cm, and 30-60 cm and 60-100 cm layers. The results revealed that soil pH, CaCO₃, SAR, ESP, and EC ds/m were increased by increasing soil depths. Meanwhile tree growth in terms of tree height was significant in the first season 2017 when compared with tree collar diameter and tree crown diameter. Also significant differences were recorded for tree growth when compared with sole trees in the second season in 2018. Tree fruit showed marked variations between the two seasons, but it was higher under intercropping particularly at ZS2. Crop plant height was highly significant under sole cropping than intercropping in first season in 2017. In contrast forage biomass yield was significant under intercropping in ZS1 and ZS2 treatments. Land equivalent ratio was advantageous under this agroforestry system particularly under ZS2. Thus it recorded 5 and 9 for ZS2 in the two consecutive seasons respectively. Therefore, it is feasible to introduce this agroforestry system under such arid lands to provide summer forage yield of highly nutritive value and low cost for animals feed as well as to increase farmers' income and to halt desertification and to sequester carbon.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.46-55
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• 2016

Three small scale hollow circular reinforced concrete columns(4.5 aspect ratio) were tested under cyclic lateral load with constant axial load. Diameter of section is 400 mm, hollow diameter is 200 mm. The selected test variable are transverse steel ratio. Volumetric ratio of spirals of all the columns is 0.302~0.604% in the plastic hinge region. It corresponds to 45.9~91.8% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The final objectives of this study are to provide quantitative reference data and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, steel fracture, etc. In this paper, describes mainly failure behavior, strength degradation behaviour, displacement ductility of circular reinforced concrete bridge columns with respect to test variables.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.7 s.250
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• pp.773-778
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• 2006

High-aspect-ratio nano-hair or nano-pillar arrays have great potential in a variety of applications. In this study, we present a simple and cost-effective replication method of high-aspect-ratio polymer nano-hair arrays. Highly ordered nano-porous AAO (anodic aluminum oxide) template was utilized as a reusable nano-mold insert. The AAO nano-mold insert fabricated by the two-step anodization process in this study had close- packed straight nano-pores, which enabled us to replicate densely arranged nano-hairs. The diameter, depth and pore spacing of the nano-pores in the fabricated AAO nano-mold insert were about 200nm, $1{\mu}m$ and 450nm, respectively. For the replication of polymer nano-hair arrays, a UV nano embossing process was applied as a mass production method. The UV nano embossing machine was developed by our group for the purpose of replicating nano-structures by means of non-transparent nano-mold inserts. Densely arranged high-aspect-ratio nano-hair arrays have been successfully manufactured by means of the UV nano embossing process with the AAO nano-mold insert under the optimum processing condition.