• Title/Summary/Keyword: 상대 변형량

Search Result 55, Processing Time 0.033 seconds

Experimental Assessment of Reduction in the Negative Skin Friction Using a Pile with a Member Responding to Ground Deformation (지반 변형 대응 부재를 적용한 말뚝의 부마찰력 저감 성능의 실험적 검증)

  • Shin, Sehee;Lee, Haklin;Woo, Sang Inn
    • Journal of the Korean Geotechnical Society
    • /
    • v.38 no.3
    • /
    • pp.5-16
    • /
    • 2022
  • Ground in extremely cold and hot regions can sink by various environmental factors. Ground settlement can generate the negative skin friction to pile shaft, increase the base load of pile, and cut the stability of the pile. This study proposed a member responding ground deformation which can be inserted inside the pile. The member slightly compresses according to the ground settlement to reduce the negative skin friction. As the member materials, this study considered spring and spring-dashpot. To assess the ability of the member, the present research performed model tests for piles with or without the member within settled ground. In the model tests, the base load, total shaft resistance, and horizontal earth pressure were monitored and analyzed. Experimental results show that the pile with spring member can reduce the negative skin friction under small settlement conditions whereas it acts similar to the pile without the member under large settlement conditions as the spring was no longer compressed. However, the pile with the spring-dashpot member can reduce the negative skin friction continuously upon the ground settlement as the dashpot delays the load transfer to the spring and locates friction force on the unloading path.

Properties of the Super Flowing Concrete Using Crushed Stone Fines (쇄석분을 사용한 초유동콘크리트의 특성에 관한 연구)

  • 이승한;정용욱
    • Journal of the Korea Concrete Institute
    • /
    • v.13 no.5
    • /
    • pp.476-483
    • /
    • 2001
  • 초유동콘크리트는 유동성 증진 및 충전성 향상을 위해 단위분체량을 크게하기 때문에 콘크리트의 고강도화와 수화발열량을 증가시키는 문제점을 가지고 있다. 이에 본 연구는 초유동콘크리트의 강도조절과 수화열 저감을 위해 쇄석분을 이용하여 초유동콘크리트의 강도, 유동성, 내구성능 및 건조수축 특성을 검토하였다. 실험결과 쇄석분은 치환율 10% 증가시마다 무치환시의 압축강도를 약 10~15%씩 감소시키며, 변형계수와 물구속비를 감소시켜 초유동콘크리트의 유동성 향상에 효과적이다. 또한 초유동콘크리트에서 쇄석분 10%치환시 마다 단위시멘트량 감소에 따른 최고 단열온도상승량을 약 4$^{\circ}C$씩 감소시켰다. 반면 건조수축량은 10%치환시 마다 약 5%증가시켰다. 한편 초유동콘크리트의 내구성능은 단위분체량과 유동성향상에 따른 조직의 치밀화로 쇄석분 치환에 관계없이 상대동탄성계수 90%이상으로 우수하게 나타났다. 이와 같이 분체로서 쇄석분 사용은 치환량에 따른 초유동콘크리트의 강도조절이 가능하며 수화발열량을 저감시킬 수 있다. ^ x Super flowing concrete causes high strength and the increase of heat of hydration because of the big unit powder content of concrete to increase flowability and to improve compact of concrete. Therefore, this study investigates the characteristic properties of strength, flowability, durability and drying shrinkage to control strength and to reduce heat of hydration of super flowing concrete using crushed stone fines. According to the experimental results, when crushed stone fines are increased every 10%, 10~15% of compressive strength is decreased and flowability of super flowing concrete is effectively improved due to the decrease of modulus of deformation and confined water ratio. When crushed stone fines are replaced every 10%, 4$^{\circ}C$ of the highest adiabatic temperature rise is decreased by reducing the unit cement. However, 5% of drying shrinkage is increased in the same condition. In the meantime, durability of super flowing concrete is excellent, having over 90 % of good relative dynamic modulus of elasticity due to fineness of formation caused by the increase of the unit powder content and the improvement of flowability, without regard to the replacement of crushed stone fines. Therefore, it can be said that the usage of crushed stone fines can control the strength of super flowing concrete by replacement and reduce heat of hydration.

Analysis of pile load distribution and ground behaviour depending on vertical offset between pile tip and tunnel crown in sand through laboratory model test (실내모형시험을 통한 사질토 지반에서 군말뚝과 터널의 수직 이격거리에 따른 하중분포 및 지반거동 분석)

  • Oh, Dong-Wook;Lee, Yong-Joo
    • Journal of Korean Tunnelling and Underground Space Association
    • /
    • v.19 no.3
    • /
    • pp.355-373
    • /
    • 2017
  • Tunnelling in urban areas, it is essential to understand existing structure-tunnel interactive behavior. Serviced structures in the city are supported by pile foundation, since they are certainly effected due to tunnelling. In this research, thus, pile load distribution and ground behavior due to tunnelling below grouped pile were investigated using laboratory model test. Grouped pile foundations were considered as 2, 3 row pile and offsets (between pile tip and tunnel crown: 0.5D, 1.0D and 1.5D for generalization to tunnel diameter, D means tunnel diameter). Soil in the tank for laboratory model test was formed by loose sand (relative density: Dr = 30%) and strain gauges were attached to the pile inner shaft to estimate distribution of axial force. Also, settlements of grouped pile and adjacent ground surface depending on the offsets were measured by LVDT and dial gauge, respectively. Tunnelling-induced deformation of underground was measured by close range photogrammetric technique. Numerical analysis was conducted to analyze and compare with results from laboratory model test and close range photogrammetry. For expression of tunnel excavation, the concept of volume loss was applied in this study, it was 1.5%. As a result from this study, far offset, the smaller reduction of pile axial load and was appeared trend of settlement was similar among them. Particulary, ratio of pile load and settlement reduction were larger when the offset is from 0.5D to 1.0D than from 1.0D to 1.5D.

Correction for Membrane Penetration Effect during Isotropic Unloading and Undrained Cyclic Shear Process (등방제하과정과 반복전단과정에서의 멤브레인 관입량 및 보정식에 대한 실험적 고찰)

  • Kwon, Youngcheul;Bae, Wooseok;Oh, Sewook
    • KSCE Journal of Civil and Environmental Engineering Research
    • /
    • v.26 no.3C
    • /
    • pp.201-207
    • /
    • 2006
  • Soil tests are generally conducted using a membrane to measure a pore water pressure. However, it has also been recognized that the membrane penetrates into the specimen by the change of the confining pressure, and it results in the erroneous measurement in the pore water pressure and the volumetric strain. This study examined the effectiveness of the correction equation of the membrane penetration on the basis of the experimental data acquired during the isotropic unloading and the cyclic shear process using the hollow cylindrical shear test equipment. The results showed that the membrane penetration by the correction equation could be overestimated when the mean effective stress was lower than 20kPa in this study. The limitations originated from the sudden increase near the zero effective stress, and in order to prevent the overestimation in low effective stress condition, the use of the constant a was proposed in this study. Furthermore, the correction equation for the membrane penetration had to be applied carefully when the initial relative density was high and the density changes were occurred by the relocation of the soil particle by the liquefaction.

A Study on Determination of Iodine in Serum, Fresh Milk, and Feed Additive by Inductively Coupled Plasma-Mass Spectrometry (유도결합 플라스마-질량분석법에 의한 혈청, 생우유 및 사료첨가제중 요오드의 분석에 관한 연구)

  • Lee, Won;Park, Kyung-Su;Kim, Sun-Tae;Kim, Young-Man
    • Analytical Science and Technology
    • /
    • v.12 no.6
    • /
    • pp.528-533
    • /
    • 1999
  • The total iodine is determined in serum, fresh milk and feed additive by ICP-MS. The preparation involves only a 25-fold dilution with a diluent by direct nebulization in the plasma. The diluent composition is $NH_4OH$(0.5% v/v)+$CH_3OH$(5% v/v) and the abundance of iodine is measured at m/z=127. The calibration curve was linear over the ranges $0-100{\mu}g/L$ with $R^2=0.99$ for iodine. The detection limit of this method is $0.084{\mu}g/L$ for iodine. The relative error range of milk powder SRM in optimum condition is 2.30%-4.73%. The concentration ranges of iodine in the serum, fresh milk, feed additive were $12.4-40.2{\mu}g/L$, < 0.01-3.11 mg/L, < $10^{-7}-2.60g/kg$ respectively.

  • PDF

Joint Quality Control of MPEG-2 Video Programs for Digital Broadcasting Services (디지털 방송 서비스를 위한 MPEG-2 비디오 프로그램들의 결합 화질 제어)

  • 홍성훈;김성대
    • Journal of Broadcast Engineering
    • /
    • v.3 no.1
    • /
    • pp.69-84
    • /
    • 1998
  • In digital broadcasting, services such as digital satellite TV, cable TV and digital terrestrial TV, several video programs are compressed by MPEG-2, and then simultaneously transmitted over a conventional CBR (Constant Bit Rate) broadcasting channel. In this paper, we propose a joint quality control scheme to be able to accurately control the relative picture quality among the video programs, which is achieved by simdt;,nL'Ously controlling the video encoders to generate the VBR (Variable Bit Rate) compressed video streams. Our quality control scheme can prevent the video buffer overflow and underflow by total target bit allocation process, and also exactly control the relative picture quality in terms of PSNR (Peak Signal to Noise Ratio) between some programs requiring higher picture quality and others by rate-distortion modification. Furthermore we present a rate-distortion estimation method for MPEG-2 video, which is base of our joint quality control, and verify its performance by experiments. The most attractive features of this estimation method are as follows: 1) computational complexity is low because main operation for the estimation is to calculate the histogram of OCT coefficients into quantizer; 2) estimation results are very accurate enough to be applied to the practical MPEG-2 video coding applications. Simulation results show that the proposed joint quality control scheme accurately controls the relative picture quality among the video progran1s transmitted over a single channel as well as provides more consistent and higher picture quality than independent coding scheme that encodes each program independently.

  • PDF

Damage Assessment of Adjacent Structures due to Tunnel Excavation in Urban Areas (II) - Focused on the Variations of Building Stiffness Ratio - (도심지 터널 굴착에 따른 인접구조물의 손상평가에 관한 연구 (II) - 지상 건물의 강성비 변화를 중심으로 -)

  • 김창용;배규진;문현구;박치현;오명렬
    • Journal of the Korean Geotechnical Society
    • /
    • v.15 no.5
    • /
    • pp.81-98
    • /
    • 1999
  • The influence of tunnelling on buildings has become an important issue in urban areas. The problem is an interactive one: not only do tunnelling settlements affect existing structures, but existing structures affect tunnel-induced soil movements. In order to examine the constraint of surface settlement and the degradation of building damage parameters, 3-dimensional elasto-plastic finite element analyses are peformed. Also, in this paper, the results of the parametric studies for the variations of the damage parameters due to the ground movements are presented by utilizing 2-dimensional elasto-plastic finite element models, totally 162 models. The width of a structure, its bending and axial stiffness, its position relative to the tunnel and the depth of tunnel are considered. The interaction is shown by reference to commonly-used building damage parameters, namely angular distortion, deflection ratio, maximum building settlements, maximum differential settlements and horizontal strain. By introducing relative stiffness parameters which combine the bending and axial stiffness of the structure with its width and stiffness of soil, design curves are established. These give a guide as to the likely modification of the greenfield settlement trough caused by a surface structure. They can be used to give initial estimates of likely building damage.

  • PDF

Study on Nucleation and Evolution Process of Ge Nano-islands on Si(001) Using Atomic Force Microscopy (AFM을 이용한 Si (001) 표면에 Ge 나노점의 형성과 성장과정에 관한 연구)

  • Park, J.S.;Lee, S.H.;Choia, M.S.;Song, D.S.;Leec, S.S.;Kwak, D.W.;Kim, D.H.;Yang, W.C.
    • Journal of the Korean Vacuum Society
    • /
    • v.17 no.3
    • /
    • pp.226-233
    • /
    • 2008
  • The nucleation and evolution process of Ge nano-islands on Si(001) surfaces grown by chemical vapor deposition have been explored using atomic force microscopy (AFM). The Ge nano-islands are grown by exposing the substrates to a mixture of gasses GeH4 and H2 at pressure of 0.1-0.5Torr and temperatures of $600-650^{\circ}C$. The effect of growth conditions such as temperature, Ge thickness, annealing time on the shape, size, number density, and surface distribution was investigated. For Ge deposition greater than ${\sim}5$ monolayer (ML) with a growth rate of ${\sim}0.1ML/sec$ at $600^{\circ}C$, we observed island nucleation on the surface indicating the transition from strained layer to island structure. Further deposition of Ge led to shape transition from initial pyramid and hut to dome and superdome structure. The lateral average size of the islands increased from ${\sim}20nm$ to ${\sim}310nm$ while the number density decreased from $4{\times}10^{18}$ to $5{\times}10^8cm^{-2}$ during the shape transition process. In contrast, for the samples grown at a relatively higher temperature of $650^{\circ}C$ the morphology of the islands showed that the dome shape is dominant over the pyramid shape. The further deposition of Ge led to transition from the dome to the superdome shape. The evolution of shape, size, and surface distribution is related to energy minimization of the islands and surface diffusion of Ge adatoms. In particular, we found that the initially nucleated islands did not grow through long-range interaction between whole islands on the surface but via local interaction between the neighbor islands by investigation of the inter-islands distance.

An experimental study on the ground movement around a square pipe by its penetration for trenchless construction in sandy ground (사각형 강관을 이용한 비개착 시공에 따른 지반거동의 분석: 모래지반에 대한 모형 토조실험)

  • Choi, Soon-Wook;Park, Young-Taek;Chang, Soo-Ho;Bae, Gyu-Jin;Lee, Ki Taek;Baek, Yong Ki
    • Journal of Korean Tunnelling and Underground Space Association
    • /
    • v.14 no.5
    • /
    • pp.485-501
    • /
    • 2012
  • This study aims to experimentally investigate ground settlement and ground movement around the square pipe by its penetration in sandy ground. A series of laboratory model tests were carried out with a small-scale auger equipment for penetration of a square pipe as well as a newly designed test box with a sand raining equipment. From the experiments, it is shown that a square pipe induces ground movement evenly around it in a low overburden condition. However, as the overburden becomes higher, ground movement by a square pipe is concentrated mainly above it. Especially, horizontal strain above the square pipe was mainly dominated by its penetration. In addition, sand surface movement is the smallest in case of the dimensionless penetration rate equal to 0.2. When its penetration rate of the square pipe is fixed, the rotation speed of auger controls surface movement whether it is settlement or heaving. Therefore, the selection of an optimal dimensionless rate for the square pipe is a key design factor to minimize ground settlement in a trenchless construction.

Poly(arylene ether ketone) block copolymer prepared through sulfonation process for polymer electrolyte membrane fuel cell (술폰화 공정을 통해 제조한 고분자 전해질형 연료전지용 폴리(아릴렌 이서 케톤) 블록 코폴리머)

  • Jang, Hyeri;Nahm, Keesuk;Yoo, Dongjin
    • Journal of Energy Engineering
    • /
    • v.25 no.3
    • /
    • pp.66-72
    • /
    • 2016
  • In this study, a sulfonated poly(arylene ether ketone) block copolymer was prepared from hydrophilic oligomer and hydrophobic oligomer. The structure of the prepared membrane was characterized by $^1H$-NMR, FT-IR and GPC. The $M_w$(weight-average molecular weights) of the polymer was $209,700g\;mol^{-1}$ and the molecular weight distribution($M_w/M_n$) of 1.25 was obtained. The prepared membrane showed excellent thermal stability with gradual weight loss up to $200^{\circ}C$. The proton conductivity of SPAEK block copolymer reached the maximum of $9.0mS\;cm^{-1}$ at $90^{\circ}C$ under 100% relative humidity (RH). From the observed results, it is necessary to do more aggressive attempt to study the possibility of application as an ion-conductive composite electrolyte.