• Structural Engineering and Mechanics
• /
• 제5권6호
• /
• 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.

• 설비공학논문집
• /
• 제3권3호
• /
• 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
• /
• 제32권1호
• /
• 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.

• 천문학회지
• /
• 제27권2호
• /
• 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.

• 한국환경생태학회지
• /
• 제10권2호
• /
• pp.171-183
• /
• 1997

설악산 매표소에서 양폭산장에 이르는 천불동계곡지역의 나비군집의 특성을 구명하기 위하여, 1996년 6월부터 10월까지 월별로 나비의 종구성, 다양도와 풍부도 및 생존전략별 분포특성 등을 선조사법으로 조사하였다. 다양도와 풍부도의 평가를 위해 강원도와 경기도 및 부산 등지의 8개 지역에서 동일한 방법으로 조사한 결과를 비교하였다. 조사결과 7과 18종이 발견되었다. 과거기록을 포함하여 천불동계곡지역에서 서식이 확인된 나비류는 7과 48종이었다. 기분포종 44종 중 30종은 미발견되었고, 미발견종 중 청띠신서난비는 밀도감소 가능성이 있는 것으로 추정되었다. 출현종 중 큰줄흰나비, 애기세줄나비 및 뿔나비는 천불동계곡지역의 보통종이었고, 우리나라의 대표적인 보통종들인 배추흰나비, 노랑나비, 호랑나비는 희귀하였다. PGA(Principal Component Analysis)좌표분석 결과 나비군집의 종구성과 종별분포를 결정하는 주요인은 인간간섭으로 추정되었다. 다양도는 간섭지역과 비간섭지역에서 차이가 없었고 풍부도는 간섭지역이 더 높게 나타났다. 비교지역들에 비해서는 천불동계곡지역의 나비군집은 풍부도는 현저시 낮게, 다양도는 약간 낮게 나타났다. 생존 전략별로 다소 다른 분포특성이 나타났는데, 비전문가(generalist)는 전문가(specialist)에 비해 간섭지역에 출현하는 종이 많았고, 간섭지역과 비간섭지역에 널리 분포하는 종이 많았다.

• 한국환경복원기술학회지
• /
• 제7권1호
• /
• 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.

• 한국환경생태학회지
• /
• 제10권1호
• /
• pp.87-102
• /
• 1996

한반도 난대기후대의 식생구조를 연구하기 위하여 남해안 도서지방의 상록활엽수림 지역에 52개 조사구를 설치하였다. 난대상록활엽수림은 지리적 격리와 인위적 교란에 의해 지역간 식생구조가 매우 상이하였다. 조사지의 식생들은 대체적으로 자연적 식생천이가 이루어진 상록활엽수림 집단, 장기간 훼손되었거나 관리되어온 상록활엽수림 집단, 그리고 상록활엽수종으로 천이되고 있는 조림식생 집단으로 구분되었다. 52개 조사구에서 80% 이상의 상재도를 보인 수종은 후박나무, 사스레피나무, 마삭줄, 생달나무, 광나무 등이었다. 난대기후대의 극상군락이라고 추정되는 육박나무군락은 주도와 애도에 잔존하고 있었다. 과거 교란이 있었던 해안지역에서는 구실잣밤나무로 이차천이가 예상된다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1996년도 춘계학술대회 논문집
• /
• 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
• /
• 제77권2호
• /
• 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
• /
• 제28권6호
• /
• 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.