• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.599-606
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• 2014

Since progressive collapse of tall buildings can cause enormous damage, it should be considered during the design phase of tall buildings. The progressive collapse analysis of tall buildings using finite element methods is almost impossible due to the vast amount of computing time. In this paper, applied element method was evaluated as an alternative to the finite element method. Reduced DOFs modeling technique was proposed to enable the progressive collapse analysis of tall buildings. The reduced DOFs model include only the part which is subjected to direct damage from blast load and the structural properties such as mass, transferred load and stiffness of excluded parts are accumulated into the top story of the reduced DOFs model. The proposed modeling technique was applied to the progressive collapse analysis of 20-story RC building using three collapse scenarios. The reduced DOFs model showed similar collapse behavior to the whole model while the computing time was reduced by 30%. The proposed modeling technique can be utilized in the progressive collapse analysis of tall buildings due to abnormal loads.

• Journal of Korean Association for Spatial Structures
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• v.13 no.3
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• pp.83-90
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• 2013

A series of wind tunnel tests were conducted on 7 super-tall buildings with various polygon cross-sections, including triangle, square, pentagon, hexagon, octagon, dodecagon, and circular. The primary purpose of the present study is to investigate the effect of increasing number of sides on aerodynamic characteristics for super-tall buildings. Wind tunnel tests were conducted under the turbulent boundary layers whose power-law exponent is 0.27. Fluctuating wind pressures from more than 200 pressure taps were recorded simultaneously, and time series of overturning moments were calculated considering tributary area of each pressure tap. The results show that the overturning moment coefficients and the spectral values decrease with increasing number of sides, and the largest mean and fluctuating overturning moments were found for the triangular super-tall building, and the largest spectral values were found for the square super-tall building. The analysis should be conducted more in detail, but currently it can be roughly said that there seems to be a little differences in the aerodynamic characteristics for the super-tall buildings whose number of sides is larger than 5 or 6.

• Wind and Structures
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• v.18 no.4
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• pp.443-456
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• 2014

A popular modern architectural form for tall buildings is two (or more) towers which are structurally linked through such features as a shared podium or sky-bridges. The fundamental features of the wind loading and the structural links of such buildings can be studied by measuring load components on the individual unlinked towers along with their correlations. This paper describes application of dual high frequency force balance (DHFFB) in a wind tunnel study of the base wind loading exerted on generic tall twin buildings in close proximity. Light models of two identical generic tall buildings of square plan were mounted on DHFFB and the base wind loading exerted on the buildings was simultaneously acquired. The effects of the relative positions of the buildings on the correlations and coherences involving loading components on each building and on the two buildings were investigated. For some relative positions, the effects of the building proximity on the wind loading were significant and the loading was markedly different from that exerted on single buildings. In addition, the correlations between the loadings on the two buildings were high. These effects have potential to significantly impact, for example, the modally-coupled resonant responses of the buildings to the aerodynamic excitations. The presented results were not meant to be recommended for direct application in wind resistant design of tall twin buildings. They were intended to show that wind loading on tall buildings in close proximity is significantly different from that on single buildings and that it can be conveniently mapped using DHFFB.

• Wind and Structures
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• v.18 no.4
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• pp.423-441
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• 2014

The high frequency base balance (HFBB) technique is a convenient and relatively fast wind tunnel testing technique for predicting wind-induced forces for tall building design. While modern tall building design has seen a number architecturally remarkable buildings constructed recently, the characteristics of those buildings are significantly different to those that were common when the HFBB technique was originally developed. In particular, the prediction of generalized forces for buildings with 3-dimensional mode shapes has a number of inherent uncertainties and challenges that need to be overcome to accurately predict building loads and responses. As an alternative to the more conventional application of general mode shape correction factors, an analysis methodology, referred to as the linear-mode-shape (LMS) method, has been recently developed to allow better estimates of the generalized forces by establishing a new set of centers at which the translational mode shapes are linear. The LMS method was initially evaluated and compared with the methods using mode shape correction factors for a rectangular building, which was wind tunnel tested in isolation in an open terrain for five incident wind angles at $22.5^{\circ}$ increments from $0^{\circ}$ to $90^{\circ}$. The results demonstrated that the LMS method provides more accurate predictions of the wind-induced loads and building responses than the application of mode shape correction factors. The LMS method was subsequently applied to a tall building project in Hong Kong. The building considered in the current study is located in a heavily developed business district and surrounded by tall buildings and mixed terrain. The HFBB results validated the versatility of the LMS method for the structural design of an actual tall building subjected to the varied wind characteristics caused by the surroundings. In comparison, the application of mode shape correction factors in the HFBB analysis did not directly take into account the influence of the site specific characteristics on the actual wind loads, hence their estimates of the building responses have a higher variability.

• Journal of The Korean Society of Grassland and Forage Science
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• v.43 no.4
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• pp.199-205
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• 2023

Pasture formation and management are crucial to avoid yield reduction. This experiment aimed to examine the effects of tall fescue-centered mixed-seeding combinations on yield and vegetation changes in perennial pastures in the central region for two years, from September 2020 to October 2022. The treatments were arranged in three replications in a randomized block design: control (C), tall fescue-based mixture-1 (T-1), and tall fescue-based mixture-2 (T-2). The tall fescue (TF), orchard grass (OG), perennial ryegrass (PRG), Kentucky bluegrass (KBG), and white clover (WC) were used. The emergency rate of grasses (70.0 to 73.3%) did not differ among mixed seeding combinations. Overwintering rates (81.7 to 83.3%) were similar among treatments. The plant height of grasses was similar at each harvest date, with the highest height (86.2 cm) recorded in the second harvest of the first year, followed by that (58.4 cm) in the third harvest of the first year; it was least (38.9 cm) in the fourth harvest of the second year. There was no significant difference in the dry matter yield of grasses among the mixed seeding combination treatments in the first, third, or fourth harvests of the first year (p>0.05). For second-year grasses, dry matter yield was not significantly different in harvest date among the treatments (p>0.05). Based on mixed seeding ratio, orchard grass showed the highest yield at 70% in the C treatment, followed by tall fescue at 80% and 60% in the T-1 and T-2 treatments, respectively, in the first harvest after seeding. There was no significant difference in feed value between treatments (p>0.05), but a significant difference was observed between the third and fourth harvest (p<0.05). Therefore, it indicated that it is important to create perennial pastures in the central region through mixed seeding combinations centered on tall fescue.

• Journal of The Korean Society of Grassland and Forage Science
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• v.23 no.2
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• pp.121-128
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• 2003

This study was conducted to investigate the effect of tall type mixtures and tall+short type mixtures on dry matter yield, botanical composition and quality. The experimental design includes two mixture types: Tall type mixtures(TM); orchardgrass(Potomac) 40+tall fescue(Fawn) 20+Festulolium braunii (Paulita) 10+perennial ryegrass(Reveille) 10+timothy(Climax) 10+red clover(Kenland) 5+alfalfa(Vernal) 5%) and tall+short type mixtures(TSM); orchardgrass(Potomac) 40+tall fescue(Fawn) 20+Kentucky bluegrass(Newport, turf type) 10+redtop(Barricuda, turf type) 10+perennial ryegrass(Palmer III, turf type) 10+red fescue(Flyer II, turf type) 5+white clover(Regal) 5%. The dry matter(DM) yield was higher obtained in TSM than that of TM, but there was no significant difference between TM and TSM. In the chemical composition, there was no significant difference between TM and TSM, but the content of cellulose, lignin were higher in TM than those in TSM(p<0.05). Also, the content of acid detergent fiber which affected dry matter digestibility was higher in TM than that of TSM. The crude protein dry matter yield was not observed significant difference between TM and TSM, but digestible dry matter(DDM) yield was higher in TSM than that of TM. In botanical composition, tall fescue, alfalfa and orchardgrass were highly maintained in TM but white clover, tall fescue and orchardgrass were highly, and redtop, red fescue were continuously maintained in TSM. In this experiment, DM yields and quality of two mixture types were no difference. However, the tall+short type mixtures(TSM) were more effective in enhancing the dry matter digestibility and DDM yield, and in maintaining the various botanical composition.

• Journal of the Korean Wood Science and Technology
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• v.16 no.2
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• pp.79-89
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• 1988

This experiment was carried out to investigate the difference of compositions between petroleum ether extract and its tall oil in Pinus rigida Mill. xylem and to obtain the basic data on effective extraction and its utilization of by-product, resin and fatty acid, when pulp making. After both petroleum ether extract from wood meal and its tall oil in pitch pine were separated to the resin and fatty acid by using DEAE-Sephadex and aluminum oxide column, these were analyzed with gas chromatograph. The results obtained were as follows: 1. Fatty acids contained as ester form in living trees were varied by peroxide of organic solvent in petroleum ehter extraction and cooking chemicals in cooking. 2. Pimaric-type acid was eluted earlier than abietic-type acid in resin acids and the fewer the carbons, the earlier the elution in fatty acids. 3. The retention time of SE-30 column was even smaller than that of OV-101 column but the relative retention time obtained by using methyl pimarate and methyl stearate as internal standard was nearly identical. 4. Both petroleum ether extract and tall oil mainly consisted of resin acids, expecially abietic-type acid. 5. Tall oil had more fatty acid but less resin acid than petroleum ether extract. Also, the content of unidentified materials was increased owing to the isomerization and the shift of double bond position in unsaturated fatty acids by high temperature and cooking chemicals when cooking.

• Journal of Bio-Environment Control
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• v.16 no.1
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• pp.32-39
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• 2007

This study was carried out to find the optimum treatment condition for the improving germination using the plant growth regulators with $GA_3$ and BAP, to Kentucky bluegrass and Tall fescue showing low germination. $GA_3$ treatment was more effective on the germination of Kentucky bluegrass than BAP single treatment or the combination treatment of $GA_3$ and BAP, regardless of their treatment concentration. Seed germinability was 6 days treatment was significantly better than that of 3 days treatment in the experiment for treatment period of the plant growth regulators. When seeds were treated with $1000{\mu}M$ of $GA_3$ for 6 days, on the percent germination was improved as much as between 10% and 38% comparing with the control. In Tall fescue seed, the percent germination was not significantly improved, although it was slightly increased when the plant growth regulators were treated. For the optimum condition, on percent germination was improved as much as 10% comparing with the control of Tall fescue treated with $1000{\mu}M$ of $GA_3$ for 3 days. Percent emergence fur the seeds of Kentucky bluegrass and Tall fescue treated $GA_3$ in the field was improved as much as $8{\sim}9%$ comparing with the control, and mean emergence time $(E_{50})$ was also faster for $1{\sim}2$ days than that of the control. However, dry weight, plant height and root length showed no significant effects, although those were slightly improved more than those of the control.

• Journal of The Korean Society of Grassland and Forage Science
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• v.23 no.3
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• pp.187-192
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• 2003

This study was conducted to investigate dry matter yield and quality of six turf grasses, and thus to apply its result into making mixed species in the mixtures. The six turf grasses were Kentucky bluegrass(Newport), red fescue(Salem), creeping bentgrass(Crenshaw), perennial ryegrass(Palmer Ⅱ), tall fescue(Rebell Jr.) and redtop(Barricuda). This experiment was carried out for 3-years at grassland experimental field of Chungnam National University. The dry matter(DM) yield obtained in tall fescue and redtop was higher than those of the other species(p<0.05). Consideration of crude protein content and dry matter digestibility(DMD), the species of high quality compared to the other species were creeping bentgrass, perennial ryegrass, and Kentucky bluegrass. The crude protein dry matter yield was higher in Kentucky bluegrass and redtop, it was lower in red fescue(p<0.05). On the other hand, digestible dry matter(DDM) yield was higher in tall fescue and redtop, but lower in creeping bentgrass and red fescue(p<0.05). Based on the result mentioned above, therefore, it is suggested that turf grasses such as tall fescue, Kentucky bluegrass and redtop are recommended as species of turf grass which could be used as bottom grasses in mixtures.

• Journal of Korean Association for Spatial Structures
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• v.13 no.1
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• pp.79-86
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• 2013

For most of recent tall buildings, one characteristic is that their building shapes vary with height such as taper and setback, and this implies that the distribution of their structural components may also vary with height. Because of these structural variations, although the sectional shapes of these buildings are symmetric, it is difficult to say whether or not they are structurally symmetric. The acceleration responses of structurally asymmetric tall buildings are larger than those of non-eccentric buildings, thus raising the possibility of problems during strong winds and typhoons. This paper describes wind tunnel tests carried out using building models with height variations and acceleration response analyses, and discusses the resulting response characteristics. For tapered and setback buildings, although the across-wind accelerations are larger than those of a square building, the total root-mean-square accelerations remain small because of smaller along-wind and torsional rms accelerations. And it was found that the effects of statistical couplings between along-wind force and other two forces are negligible.