• Steel and Composite Structures
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• v.42 no.1
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• pp.1-22
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• 2022

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation reported by the authors on back-to-back built-up CFS unequal angle sections with intermediate stiffeners under axial compression. The load-axial shortening behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated finite element model was then used for the purpose of a parametric study comprising 96 models to investigate the effect of longer to shorter leg ratios, stiffener provided in the longer leg, thicknesses and lengths on axial strength of back-to-back built-up CFS unequal angle sections. Four different thicknesses and seven different lengths (stub to slender columns) with three overall widths to the overall depth (B/D) ratios were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% and 5% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections with and without the stiffener, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3B
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• pp.345-354
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• 2008

In this present study, we made a first attempt to investigate physical transformations of incident waves in surf and swash zone and hydrodynamic phenomena of detached and submerged breakwaters. For an accurate simulation of the complicated wave deformation, Three-Dimensional numerical model with Large Eddy Simulation has been developed recently and expanded properly for the current applications, which is able to simulate an accurate and direct WAve Structure Sandy seabed interaction (hereafter, LES-WASS-3D). LES-WASS-3D has been validated through the comparison with experimental results for limited cases, and has been used for the simulation of wave run-up on sandy beach, mean fluid flows over and around submerged structures and swash zone (alongshore/rip current), and spatial distribution of wave height in wide fluid regions. In addition, a strategy of efficient deployment ($Y/L_i=1.50{\sim}1.75$, $W/L_r=0.50$) of the submerged breakwaters has been discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2A
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• pp.131-143
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• 2009

Under transverse earthquake shaking, arching action of bridge structures develops along the deck between the abutments thus providing the so-called deck resistance. The magnitude of the arching action for bridge structures is dependent on the number of spans, connection condition between deck and abutment or piers, and stiffness ratio between superstructure and substructure. In order to investigate the arching action effects for inelastic seismic responses of PSC Box bridges, seismic responses evaluated by pushover analysis, capacity spectrum analysis and nonlinear time-history analysis are compared for 18 example bridge structures with two types of span numbers (short bridge, SB and long bridge, LB), three types of pier height arrangement (regular, semi-regular and irregular) and three types of connection condition between superstructure and substructure (Type A, B, C). The arching action effects (reducing inelastic displacement and increasing resistance capacity) for short bridge (SB) is more significant than those for long bridge (LB). Semi-regular and irregular bridge structures have more significant arching action than regular bridges.

• Animal Bioscience
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• v.35 no.10
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• pp.1566-1574
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• 2022

Objective: This study investigated the effects of dietary methyl sulfonyl methane (MSM) and selenium (Se) on the laying performance, egg quality, gut health indicators, egg yolk Se content, and antioxidant markers in laying hens. Methods: One hundred ninety-two 73-wk-old laying hens were randomly divided into four groups with eight replicates of six hens each. Four diets were prepared in a 2×2 factorial arrangement with or without MSM and Se. The trial lasted for 12 wk. Results: There were no interaction effects or main effects (p>0.05) on laying performance and egg quality. However, feed intake increased in Se-fed hens (p = 0.051) and decreased in MSM-fed hens (p = 0.067) compared with that of hens in the control group. Dietary MSM increased (p<0.05) the ileal villus height and villus height:crypt ratio in hens compared with those receiving the non-supplemented control diet. Dietary MSM and Se did not affect the percentage of short-chain fatty acids in the ileal contents. Dietary Se enriched the Se content in egg yolk compared with that of the non-supplemented control diet (p<0.05). Dietary Se increased (p<0.05) glutathione peroxidase levels in the liver and serum samples compared to the control diet. The total antioxidant capacity in the liver increased (p<0.05) in laying hens that were fed MSM-supplemented diets than in hens fed the control diet. Dietary MSM significantly increased the relative superoxide dismutase levels in serum samples (p<0.05). Conclusion: Supplementation with either MSM or Se independently improved the antioxidant capacity of laying hens. Furthermore, dietary Se produced Se-enriched eggs, but this effect was neither additive nor synergistic with dietary MSM.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.3
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• pp.27-36
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• 2024

This study established a BIM procedure considering manufacturing errors in the production process, and evaluated the flexural ductility of precast all-lightweight aggregate concrete special shear walls (PLASWs) with spliced sleeve technique. In the production process, the concrete cover thickness of PALSW was on average 1.28 times greater than the cross-sectional details of the specimen modeled with Revit BIM program. In particular, the bending inner radius of the hoop and inner-cross tie were greater than the designed details. Consequently, the confinement effect of core concrete reduced from 64% to 54% due to the manufacturing errors in the transverse reinforcing bars, resulting in a decrease in the ductility of PALSW by approximately 4.91%. Considering these findings, the BIM of PLASW with spliced sleeve technique should compliment the bending inner radius of the transverse reinforcing bars, and the defined brittleness increase coefficient reflecting the decreased core concrete confining pressure in the stress-strain relationship of confined concrete should be evaluated as 1.8.

• The Journal of the Acoustical Society of Korea
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• v.29 no.8
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• pp.497-503
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• 2010

In this paper, evaluation of noise reduction performance of HVAC system for ships by means of HVAC mock-up system is presented. Test is done for six different types of HVAC elements including room unit, silencer, etc. It is found that when diameter of silencer is small and air flow is large, flow noise degrades insertion loss. However, as diameter of silencer becomes larger, the effect of flow noise becomes smaller, and insertion loss up to 25 dB is measured. It is observed that insertion loss of diffuser type room unit is usually between zero and 10 dB, whereas that of the nozzle type room unit can be down to - 15 dB. In addition, it is shown that changing duct arrangement can reduce cabin noise by up to 2 dB, and providing same air flow to each room unit is crucial for generating less noise.

• East Asian mathematical journal
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• v.40 no.2
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• pp.183-207
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• 2024

This study is a case study that considered fractional senses and fraction operation abilities for 107 gifted students in elementary school classes. In order to find out the fractional sense, in the first question comparing the sizes of fractions 2/3 and 4/5, the students showed a variety of strategies, but the utilization rate of strategies excluding reduction to a common denominator did not exceed 50%. The second question can be solved by using the first question. It is a problem of finding two fractions by selecting four from six numbers 1, 3, 4, 5, 6, and 7 to create two fractions of which sum does not exceed 1. The percentage of correct answers to this question was about 27% (29 out of 107). Only 5 out of 29 students found answers using the first question, and the rest of the students sought answers through trial and error in various calculations. It shows that the item arrangement method from a deductive perspective has no significant effect on elementary school students. The percentage of correct answers was about 27% in the questions to find out the fraction operation ability-the question of drawing a 4/3 bar using a given 3/8-sized bar and 30.7% (23 out of 75) of the students who had wrong answers showed insufficient splitting operation. In addition, it has been shown that the operation of partitioning and iterating to form numerical senses and fractional concepts related to the fractions of the students has no significant impact.

• Journal of Wind Energy
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• v.14 no.2
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• pp.26-33
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• 2023

In this study, the global response characteristics of floater and mooring for floating offshore wind turbine with a detachable mooring system are performed. Global motion and structural response result extracted from the coupled motion analysis of 10MW DTU floating offshore wind turbine with detachable mooring system modeled by high-order boundary element model and finite element mesh, were used to study the characteristics of tension on mooring lines subjected to three different types of ocean loads. Breaking limit of mooring line characterized by wind, current and wave load has a major effect on the distribution of mooring tension found in time domain analysis. Based on the numerical results of coupled motion analysis, governing equation for calculating the motion response of a floater under ocean loads, and excitation force and surge motion and tension respectively are presented using excursion curve. It is found that the response of floater is reliable and accurate for calculating the tension distributions along the mooring lines under complex loadings. This means that the minimun breaking limit of mooring system satisfied a design criteria at ultimate ocean environmental loading condtions.

• Steel and Composite Structures
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• v.50 no.6
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• pp.659-674
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• 2024

Casting Ultra High-Performance Concrete (UHPC) on an orthotropic steel deck and forming a composite action by connectors could improve the steel deck fatigue performance. This study presents the mechanical performance of a proposed post-combination connection between UHPC and steel, which had a low constraint effect on UHPC shrinkage. A total of 10 push-out tests were conducted for static and fatigue performance investigations. And the test results were compared with evaluation methods in codes to verify the latter's applicability. Meanwhile, nonlinear simulation and parametric works with material damage plasticity models were also conducted for the static and fatigue failure mechanism understanding. The static and fatigue test results both showed that fractures at stud roots and surrounding local UHPC crushes were the main failure appearances. Compared with normally arranged studs, group arrangement could result in reductions of static stud shear stiffness, strength, and fatigue lives, which were about 18%, 12%, and 27%, respectively. Compared with the test results, stud shear capacity and fatigue lives evaluations based on the codes of AASHTO, Eurocode 4, JSCE and JTG D64 could be applicable in general while the safety redundancies tended to be smaller or even insufficient for group studs. The analysis results showed that arranging studs in groups caused obviously uneven strain distributions. The severer stress concentration and larger strain ranges caused the static and fatigue performance degradations of group studs. The research outcome provides a very important basis for establishing a design method of connections in the novel post-combination steel-UHPC composite deck.

• FLOWER RESEARCH JOURNAL
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• v.19 no.2
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• pp.89-95
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• 2011

This study was conducted to improve commercial quality of cut spray chrysanthemums 'Charming Eye' and 'Pink Pride' bred in Korea by foliar application of daminozide, suppressing excessive elongation of peduncle caused by high temperature in greenhouse. Applications were made at two floral-bud-developmental stages and concentrations used were 0, 500, 1000, and $2000mg{\cdot}L^{-1}$. As for 'Charming Eye', cut flower length, peduncle diameter, stem diameter, flower bud diameter, and the number of flower buds did not show any significant difference among all treatments including control. However, the suppressing effect of peduncle elongation, widening angle of flower cluster arrangement on apical part, and increasing parallel flower buds in stage I showed better than those in stage II regardless of daminozide concentration. As for 'Pink Pride', cut flower length, peduncle diameter, and stem diameter did not show any significant difference among all treatments including control but angle of flower cluster on apical part increased compared to control as daminozide was sprayed at stage I and II except $2,000mg{\cdot}L^{-1}$ daminozide-sprayed at stage II. The number of flower buds and flower bud diameter showed the greatest increment through $1,000mg{\cdot}L^{-1}$ daminozide-sprayed at stage I and did the least values as sprayed with $2,000mg{\cdot}L^{-1}$ daminozide at stage II. Daminozide also gradually reduced peduncle length in a concentration-dependant manner but elongation of peduncle foliar-sprayed at stage I showed the more suppressing effect than that at stage II. Increasing the number of parallel flower buds showed the best results when sprayed with $2,000mg{\cdot}L^{-1}$ at stage I. In conclusion, we recommended that foliar spraying with $500-1,000mg{\cdot}L^{-1}$ daminozide at stage I and foliar spraying with $1,000-2,000mg{\cdot}L^{-1}$ daminozide at stage I improved cut flower quality of 'Channing Eye' and 'Pink Pride', respectively.