• Structural Engineering and Mechanics
• /
• v.5 no.6
• /
• pp.803-815
• /
• 1997

It is well understood that concentrated forces applied in the plane of a beam or panel (such as a wall or slab) lead to splitting forces developing within a disturbed region forming beyond the bearing zone. In a linearly elastic material the length of the disturbed region is approximately equal to the depth of the member. In concrete structures, however, the length of the disturbed region is a function of the orthotropic properties of the concrete-steel composite. In the detailing of steel reinforcement within the disturbed regions two limit states must be satisfied; strength and serviceability (in this case the serviceability requirement being acceptable crack widths). If the design requires large redistribution of stresses, the member may perform poorly at service and/or overload. In this paper the results of a plane stress finite element investigation of concentrated loads on reinforced concrete panels are presented. Two cases are examined (i) panels loaded concentrically, and (ii) panels loaded eccentrically. The numerical investigation suggests that the bursting force distribution is substantially different from that calculated using elastic design methods currently used in some codes of practice. The optimum solution for a uniformly reinforced bursting region was found to be with the reinforcement distributed from approximately 0.2 times the effective depth of the member ($0.2D_e$) to between $1.2D_e$ and $1.6D_e$. Strut and tie models based on the finite element analyses are proposed herein.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.3 no.3
• /
• pp.161-167
• /
• 1991

This paper presents the results of some measurement of the fluctuating velocity field in the turbulent boundary layer disturbed by a triangular prism and discusses the discovery of the disturbed boundary layer. A prism of height 8mm was used for experiments. The streamwise location of the prism was fixed at 1200mm downstream from the leading edge and the space between the prism center and the wall was set at three different values, 6, 15 and 33.5mm. The results show that the near-wall region of the disturbed boundary layer recovers original state much more quickly than the outer region. In the case h=6mm the recovery is faster than the other cases. Moreover, it was found that peak of fluctuating velocities moves outwards somewhat rapidly with increasing ${\times}$ mainly due to the turbulent diffusion of the fluctuating velocity.

• Journal of Ecology and Environment
• /
• v.32 no.1
• /
• pp.13-18
• /
• 2009

This study was conducted to investigate ectomycorrhizal (ECM) diversity on Pinus densiflora seedlings in a disturbed pine forest. Pine seedlings less than one year old were collected from disturbed and undisturbed sites in the Mt. Songni region. The belowground ECM fungal communities colonizing P. densiflora seedlings were studied using morphotyping and DNA sequencing. The relative abundance of ECM root tips was significantly higher in the undisturbed sites than in the disturbed sites, and the ECM species diversity was lower in the disturbed sites than in the undisturbed sites. In addition, the ECM community composition was significantly different in the disturbed and undisturbed forest sites.

• Journal of The Korean Astronomical Society
• /
• v.27 no.2
• /
• pp.147-158
• /
• 1994

We have obtained high angular resolution maps toward a molecular cloud associated with an HII region S287 and studied mainly kinematics of the cloud. The mapped region is 1.5 square degrees of the cloud in the transitions of $^{12}CO\;and\;^{13}CO\;J=1-0$. We have obtained a large range of mass, $1.3\times10^4M_\bigodot$, to $7.2{\times}10^4M_{\bigodot}$ using three different techniques. The S287 molecular cloud shows a very disturbed feature: velocity field of the cloud is very complicated, and shows several arcs. It is likely that the southern part of cloud is being disrupted by the residing HII region S287 as well as external perturbing sources. In addition to an HII region, five bipolar outflows are also disturbing the molecular gas significantly. The large virial mass and the very disturbed morphology may reflect the fact that the cloud is not gravitationally bound system, as in the case of nearby giant molecular cloud (GMC) G216-2.5. The several arc structure and the filamentary features are possibly driven by external strong stellar winds, and these external perturbing sources may be driving the second generation of star-forming activities on the edges of the S287 molecular cloud.

• Korean Journal of Environment and Ecology
• /
• v.10 no.2
• /
• pp.171-183
• /
• 1997

Diversity, abundance, species distributions and distributions of two strategists (specialist and geceralist) of butterflies were investigated monthly from June 1996 to Oct. 1996 by line transect method in the Chunbul-dong valley from park gate to Yangpok Sanjang. The butterfly faunas of the eight regions in Kwangwon province, Gyunggi proavince and Pusan were also studied by the same method to assess diversity and abundance of butterfly community in the study region. The 18 butterfly species in 7 families were found in this study and the 48 butterfly species in 7 families were distributed in the study area from thes study and the other researches. The 30 butterfly species reported in the other studies were not found in this study and Kaniska canace L. of them would be to decrease in density. In the study area, the common species were Artogeia melete M., Neptis sappho P. and Libythea celtis F.. The representative Korean common butterflies such as Artogeia rapae L., Colias erate E. and Papillio xuthus L. were rare. The PCA(Principal Component Analysis) ordinations indicate that habitat disturbance by human would be major factor for butterfly community and species distribution. Difference was not found in diversity according to habitat disturbance. Abundance, however, was higher in the disturbed region than the undisturbed region. Compared with the other regions, abundance was greatly lower and diversity was slightly lower than that of the other regions. Two strategists exhibited different distribution patterns. Generalists were found more commonly in the disturbed region and widely distributed in both of the disturbed region and the undisturbed region than specialists.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.7 no.1
• /
• pp.10-18
• /
• 2004

The urban ecosystem, unlike the natural ecosystem, has been affected by the urban environment, so the existences of normal creatures have been threatened and eventually the stability has declined to consist of those that have adapted to such. Therefore, by creating a list of such organisms, their number of variety can be found out and their ecological distinction can be understood. Because flora is known to be an ecological index reflecting region's effects of human and societal environments, weather, and climates, it is a useful method of finding out the ecological position and distinctiveness of that region. The study site is part of watershed at Yangjae Stream, Kahngnam-ku, Seoul. In this study, the difference of flora in each land use type are investigated by plant identification. The purpose of this study is to evaluate the city's plant surviving environment, and eventually to contribute to the restoration of urban green spaces by finding out the plants which are appropriate for the corresponding environment. After doing the study, it was found that the urban forest is the most stable urban ecosystem while the urban park is seriously disturbed, and ecologically unstable. The urban stream is also disturbed continuously.

• Korean Journal of Environment and Ecology
• /
• v.10 no.1
• /
• pp.87-102
• /
• 1996

To study vegetational structure of the Korean warm temperate region fifty two plots were surveyed in evergreen broad-leaved forests of southern islands. The vegetational structures among sites were dissimilar in virtue of geographical isolation and artificial disturbance. The surveyed plots were generally classified into three groups; the first, the group in which plant succession has proceeded naturally, the second, the group which was disturbed and managed for a long time, the third, the group which was afforested and has been succeeded into evergreen broad-leaved forest. The species with constancy over 80% in fifty two plots were Machilus thunbergii, Eurya japonica, Trachelospermum asiaticum var. intermidium, Cinnamomum japonicum, and Ligustrum japonicum. The community of Lozoste lancifolia, which is assumed to be a climax community of the Korean warm temperate region, remains in Chudo and Aedo. The secondary succession of seashore forest which were disturbed in the past will be done into Castanopsis cuspidata var. sieboldii

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1996.05a
• /
• pp.137-141
• /
• 1996

This paper deals with the prebreakdown phenomena of $SF_{6}$ gap stressed by non-oscillating and oscillating impulse voltages in a strong inhomogeneous field disturbed by a fred needle shaped-protrusion on the earth-side electrode. The breakdown voltage-time characteristics were measured for both positive and negative polarities and over the gas pressure range of 0.1∼0.5 MPa, and the temporal developments of the 77breakdown were observed by a shunt of 50 n. The dependence of the leader stopping time on the gas pressure were obtained. The local field enhancement due to the space charges, which is produced by the streamer corona, has influence with the electrical breakdown of the test gap. The test streamer corona is oxy a necessary condition for the electrical breakdown and the subsequent ionization activities launch the leader at the local field region.

• Structural Engineering and Mechanics
• /
• v.77 no.2
• /
• pp.273-291
• /
• 2021

The strut-and-tie method (STM) has been widely accepted and used as a rational approach for the design of disturbed regions ('D' regions) of reinforced concrete members such as in corbels and deep beams, where traditional flexure theory does not apply. This paper evaluates the applicability of the equilibrium based STM in strength predictions of deep beams (with rectangular and circular cross-section) and corbels using the available experiments in literature. STM is found to give fairly good results for corbel and deep beams. The failure modes of these deep members are also studied, and an optimum amount of distribution reinforcement is suggested to eliminate the premature diagonal splitting failure. A comparison with existing empirical and semi empirical methods also show that STM gives more reliable results. The nonlinear finite element analysis (NLFEA) of 50 deep beams and 20 corbels could capture the complete behaviour of deep members including crack pattern, failure load and failure load accurately.

• Computers and Concrete
• /
• v.28 no.6
• /
• pp.621-634
• /
• 2021

For the reliable strut-and-tie model (STM) design of disturbed regions of concrete members, structural designers must accurately determine the strength of concrete struts to check the strength conditions of a selected STM el and the anchorage of reinforcing bars in nodal zones. In this study, the author proposed a consistent numerical method for strut strength, applicable to all two-dimensional STMs. The proposed method includes the effects of a biaxial stress state associated with tensile strains in reinforcing bars crossing a strut, deviation angle between strut orientation and compressive principal stress flow, and degree of confinement provided by reinforcement. The author examined the method's validity through the STM prediction of the ultimate strengths of 517 reinforced concrete (RC) deep beams, 24 RC panels, and 258 RC corbels, all tested to failure.