• 제목/요약/키워드: time of loading

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Fundamental behavior of CFT beam-columns under fire loading

  • Varma, Amit H.;Hong, Sangdo;Choe, Lisa
    • Steel and Composite Structures
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    • 제15권6호
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    • pp.679-703
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    • 2013
  • This paper presents experimental investigations of the fundamental behavior of concrete filled steel tube (CFT) beam-columns under fire loading. A total of thirteen specimens were tested to determine the axial force-moment-curvature-temperature behavior of CFT beam-columns. The experimental approach involved the use of: (a) innovative heating and control equipment to apply thermal loading and (b) digital image correlation with close-range photogrammetry to measure the deformations (e.g., curvature) of the heated region. Each specimen was sequentially subjected to: (i) constant axial loading; (ii) thermal loading in the expected plastic hinge region following the ASTM E119 temperature-time T-t curve; and (iii) monotonically increasing flexural loading. The effects of various parameters on the strength and stiffness of CFT beam-columns were evaluated. The parameters considered were the steel tube width, width-tothickness ratio, concrete strength, maximum surface temperature of the steel tube, and the axial load level on the composite CFT section. The experimental results provide knowledge of the fundamental behavior of composite CFT beam-columns, and can be used to calibrate analytical models or macro finite element models developed for predicting behavior of CFT members and frames under fire loading.

Traffic-load-induced dynamic stress accumulation in subgrade and subsoil using small scale model tests

  • Tang, Lian Sheng;Chen, Hao Kun;Sun, Yin Lei;Zhang, Qing Hua;Liao, Hua Rong
    • Geomechanics and Engineering
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    • 제16권2호
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    • pp.113-124
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    • 2018
  • Under repeated loading, the residual stresses within the subgrade and subsoil can accelerate the deformation of the road structures. In this paper, a series of laboratory cyclic loading model tests and small-scale model tests were conducted to investigate the dynamic stress response within soils under different loading conditions. The experimental results showed that a dynamic stress accumulation effect occurred if the soil showed cumulative deformation: (1) the residual stress increased and accumulated with an increasing number of loading cycles, and (2) the residual stress was superimposed on the stress response of the subsequent loading cycles, inducing a greater peak stress response. There are two conditions that must be met for the dynamic stress accumulation effect to occur. A threshold state exists only if the external load exceeds the cyclic threshold stress. Then, the stress accumulation effect occurs. A higher loading frequency results in a higher rate of increase for the residual stress. In addition to the superposition of the increasing residual stress, soil densification might contribute to the increasing peak stress during cyclic loading. An increase in soil stiffness and a decrease in dissipative energy induce a greater stress transmission within the material.

국내 인공댐호의 물리적 환경인자에 의한 호수특성 고찰에 관한 연구 (Studies on the Phisical Environmental Factor Analysis for Water Quality Management in Man-made Lake of Korea)

  • 김좌관;홍욱희
    • 한국환경과학회지
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    • 제1권2호
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    • pp.49-57
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    • 1992
  • First, We classified man-made lakes in Korea as 4-type lakes, that is, there were River-run lakes, Dendritic lakes, Reservoir-lakes, River-mouth lakes, We studied on the environmental factors of 3-type lakes except River-mouth lakes, compared these lakes with natural lakes in foreign country. Environmental factors were watershed area, lake storage, mean depth, hydraulic retention time. As a results, 3-type lakes in Korea had remarkable differences one another according to above-mentioned environmental factors. First, We recognized that River-run lakes had higher nutrient loading according to having wider watershed area than natural lakes, and had lower algal growth rate according to shorter hydraulic retention time than natural lakes. Dendritic lake had higher nutrient loading than natural lakes, longer retention time than River-run lake. Reservoir-lakes had environmental factors between Dentritic lakes and River-run lakes. Therefore, If this studies had no quantitative results about various factors, We recognized that man-made lakes in korea had different environmental factors as compared with natural lakes, and had clear classification among 3-type lakes.

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재액상화에 관한 원심모형실험과 수치해석 (Centrifuge Test and Its Numerical Modeling for Reliquefaction)

  • 박성식
    • 한국지반공학회논문집
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    • 제22권12호
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    • pp.89-98
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    • 2006
  • 본 논문에서는 지진이 발생한 지역에서 다시 지진이 발생할 경우에 포화된 사질토 지반의 동적거동에 관한 연구를 수행하였다. 반복 직접단순전단시험을 실시하여 느슨한 모래지반에서 간극수압발생량과 재액상화발생여부의 상관관계를 분석하였다. 최초의 전단하중으로 인하여 지반이 원래 가지고 있던 유효수직응력의 약 90%까지 간극수압이 발생하였을 경우 시간 경과에 따라 과잉간극수압이 전부 소산된 이후 다시 전단하중을 가하였을 때 지반의 액상화에 대한 저항력은 증가하였다. 하지만 최초 진동으로 지반이 완전히 액상화되었을 경우에는 다음에 전달되는 전단하중에는 이전보다도 지반이 더욱 조밀해짐에도 불구하고 액상화 저항력은 증가하지 않았다. 이와 같은 실내시험결과를 진동 중에 발생하는 간극수압 변화와 흙의 강성저하를 고려할 수 있는 유효응력모델인 UBCSAND모델에 적용하였으며, 최초 전단하중에서 발생하는 간극수압비에 따라 구성모델의 액상화 저항력을 결정하였다. 이 구성모델을 이용하여 재액상화현상을 연구한 원심모형실험의 결과를 예측하였으며, 계측치와 서로 비교하였다. 국내에서도 일본과 가까운 남부지역에서는 약한 지진이지만 자주 발생하고 있는 시점에서 이와 같은 유효응력모델을 이용한 재액상화 현상에 관한 연구가 절실히 요구되어진다.

2축 짐벌 구조 적재 장치를 위한 최소제곱법 기반 시스템 식별 (Least Squares Method-Based System Identification for a 2-Axes Gimbal Structure Loading Device)

  • 심예리;진상록
    • 로봇학회논문지
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    • 제17권3호
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    • pp.288-295
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    • 2022
  • This study shows a system identification method of a balancing loading device for a stair climbing delivery robot. The balancing loading device is designed as a 2-axes gimbal structure and is interpreted as two independent pendulum structures for simplifying. The loading device's properties such as mass, moment of inertia, and position of the center of gravity are changeable for luggage. The system identification process of the loading device is required, and the controller should be optimized for the system in real-time. In this study, the system identification method is based on least squares method to estimate the unknown parameters of the loading device's dynamic equation. It estimates the unknown parameters by calculating them that minimize the error function between the real system's motion and the estimated system's motion. This study improves the accuracy of parameter estimation using a null space solution. The null space solution can produce the correct parameters by adjusting the parameter's relative sizes. The proposed system identification method is verified by the simulation to determine how close the estimated unknown parameters are to the real parameters.

The structural performance of axially loaded CFST columns under various loading conditions

  • Huang, Fuyun;Yu, Xinmeng;Chen, Baochun
    • Steel and Composite Structures
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    • 제13권5호
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    • pp.451-471
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    • 2012
  • Concrete filled steel tube (CFST) structures have been used widely in high-rise buildings and bridges due to the efficiency of structurally favourable interaction between the steel tube and the concrete core. In the current design codes only one loading condition in the column members is considered, i.e., the load is applied on the steel tube and concrete core at the same time. However, in engineering practice the tube structures may be subjected to various loading conditions such as loading on the concrete core only, preloading on the steel tube skeleton before filling of concrete core, and so on. In this research, a series of comparative experiments were carried out to study the structural performance of concrete filled circular steel tube columns subject to four concentric loading schemes. Then, a generalized prediction method is developed to evaluate the ultimate load capacity of CFST columns subject to various loading conditions. It is shown that the predictions by the proposed method agree well with test results.

변동하중에서 미소하중의 제거가 균열진전에 미치는 영향 (The Effect on Fatigue Crack Growth due to Omitting Low-amplitude Loads from Variable Amplitude Loading)

  • 심동석;이승호;김정규
    • 동력기계공학회지
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    • 제8권4호
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    • pp.11-16
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    • 2004
  • In this study, to investigate the effects of omitting low-amplitude cycles from a flight-simulation loading, crack growth tests were conducted on 2124-T851 aluminum alloy specimens. Three test spectra were generated by omitting small load ranges as counted by the rain-flow count method. The crack growth test results were compared with the data obtained from the flight-simulation loading. The experimental results show that the ranges equal to or smaller than 5% of the maximum load do not contribute to crack growth behavior because these are below the initial stress intensity factor range. Omitting these from the flight-simulation loading, test time can be reduced by 54%. However, in the case of omitting the load ranges below 15% of the maximum load, crack growth rates decreased, and crack growth curve deviated from the crack growth data under the flight-simulation loading because loading cycles above fatigue fracture toughness were omitted.

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Ge 도핑농도와 수소처리시간 변화가 광섬유격자 형성에 미치는 영향 (The effects of Germanium concentration and Hydrogen loading time on the growth of fiber Bragg grating)

  • 송정환;이종훈;송정태;이경식;이유섭;전찬오;전건익
    • 대한전기학회:학술대회논문집
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    • 대한전기학회 1998년도 추계학술대회 논문집 학회본부 C
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    • pp.993-995
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    • 1998
  • We fabricated fiber gratings with three different Ge-doped fibers exposed to 60atm pressure of Hz gas at 90"C for different times and studied the effects of Ge-doping concentration and $H_2$ loading time on the growth of gratings. According to experiments. the growing effect of hydrogen loading on high Ge-doped fiber was great.

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RTS test study and numerical simulation of mechanical properties of HDR bearings

  • Peng, Tianbo;Wu, Yicheng
    • Earthquakes and Structures
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    • 제13권3호
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    • pp.299-307
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    • 2017
  • High Damping Rubber bearings (HDR bearings) have been used in the seismic design of bridge structures widely in China. In earthquakes, structural natural periods will be extended, seismic energy will be dissipated by this kind of bearing. Previously, cyclic loading method was used mainly for test studies on mechanical properties of HDR bearings, which cannot simulate real seismic responses. In this paper, Real-Time Substructure (RTS) test study on mechanical properties of HDR bearings was conducted and it was found that the loading rate effect was not negligible. Then the influence of peak acceleration of ground motion was studied. At last test results were compared with a numerical simulation in the OpenSees software framework with the Kikuchi model. It is found that the Kikuchi model can simulate real mechanical properties of HDR bearings in earthquakes accurately.

채수빈도를 고려한 소하천의 수질오염부하량 특성 연구 (Variations of Estimated Pollutant Loading from Rural Streams with Sampling Intervals)

  • 강문성;박승우;윤광식
    • 한국농공학회:학술대회논문집
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    • 한국농공학회 1998년도 학술발표회 발표논문집
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    • pp.552-557
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    • 1998
  • Sampling schemes are intended for use in situations where stream-flow data are collected regularly, but concentration data are collected during only a limited number of time periods. Estimating water pollutant loading considering sampling intervals is presented, and for illustrative purposes the criterion is applied to the sampling station HS#3 of the Balan-reservoir watershed which is located at the southwest of Suwon. The stratification is employed uniformly for all sampling strategies in that the strata boundaries are defined using the actual distribution of flow values and the selected nonexceedence probabilities to minimize inaccuracy. Ratio estimator for SS, T-N, and T-P were used in order to calculate the water pollutant loading. A sampling scheme incorporating stratified sampling with real-time of the sampling characteristics is found to give the appropriate estimate of the mass load.

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