이동하중의 편측재하에 따른 단순교의 충격계수 및 응답계수 변화 분석

홍상현,노화성 한국구조물진단유지관리공학회 2018 한국구조물진단유지관리공학회 논문집 Vol.22 No.6

교량 내하력 추정을 위해 제안된 모델에서는 응답계수를 충격계수 응답스펙트럼을 활용하여 산정하고 있다. 이때 충격계수 응답스펙트럼은 오일러-베르누이 보 모델을 바탕으로 차량이동하중이 교량의 폭 방향으로 중앙부에 재하 된 조건으로 생성된 결과이다. 따라서 중앙부 차량재하가 아닌 편측 이동하중재하 시 충격계수와 응답계수의 변화를 분석해 볼 필요가 있다. 이를 위해 본 연구에서는 폭이 10m인 2차선 단순교를 대상으로 이동하중해석을 실시하여 최대 충격계수와 응답계수 변화를 분석하였다. 수치해석 결과, 중앙부 재하조건 대비 편측 재하 조건 적용 시 최대 정적 및 동적 변위 모두 증가하지만 동적변위 보다 정적변위의 증가량이 더 크기 때문에 충격계수는 오히려 감소하게 된다. 하지만 이러한 차이는 0.5%p 미만으로서 그 영향이 크지 않다. 그리고 응답계수의 경우, 편측 재하조건으로 인해 정적응답계수보다 동적응답계수에서 차이가 더 크게 나타나지만 편측 재하에 따른 오차율의 차이는 0.18%p 정도로 매우 작았다. 즉, 편측 이동하중재하가 응답계수에 미치는 영향은 거의 없으며, 응답계수 산정에 있어서 중앙부 이동하중재하 조건으로 생성된 충격계수 응답스펙트럼을 활용하여도 충분한 예측이 가능하다고 판단된다. The proposed model to predict the bridge load carrying capacity uses the impact response spectrum. The spectrum is based on Euler-Bernoulli beam and the center of the bridge width for the moving load location. Therefore, it is necessary to investigate the eccentric moving load effects on the impact factor and response factor. For this, this study considers 10 m width and two-lane simply supported slab bridges and performs the moving load analysis to investigate the variations of peak impact factor and corresponding response factor. The numerical results show that the eccentric load increases both the static and dynamic displacements, but the impact factor is decreased since the incremental amount of static displacement is bigger than that of dynamic displacement. However, the difference of the impact factors between the center and eccentric loadings is small showing less than 0.5%p. In the response factor, the eccentric loading increases both the static and dynamic response factors, compared to the center loading. The difference of the response factor is only 0.18%p. It shows that the eccentric loading has very small effects on the response factor, thus the impact factor response spectrum which is generated based on the center moving load can be used to determine the response factor.

Resistance Factor Calculations for LRFD of Axially Loaded Driven Piles in Sands

김동욱,정문경,곽기석 대한토목학회 2011 KSCE Journal of Civil Engineering Vol.15 No.7

This paper presents the development of Load and Resistance Factor Design (LRFD) of axially-loaded driven piles in sands. The resistance factors of base and shaft resistances were calculated separately to account for their different uncertainty levels. The ratios of dead-to-live load and ultimate base resistance to limit shaft resistance change the uncertainty levels of total load and total pile capacity, respectively; thus, those ratios should be reflected in the calculation of base and shaft resistance factors. For the development of LRFD for axially-loaded driven piles in sands, the ultimate limit state for an axially-loaded driven pile was established based on the Imperial College Pile (ICP) design method; the uncertainties of loads and resistance were accessed;reliability analyses were performed using the First-order Reliability Method (FORM); and finally, reasonable resistance factors of base and shaft resistances were calculated based on the results of reliability analyses for different target reliability index levels. The load factors used for the calculation of resistance factors are the ones proposed by AASHTO and ASCE/SEI 7-05. From the results of extensible reliability analyses using FORM, the resistance factors for base and shaft resistances were found to be highly dependent on the ratios of the dead-to-live load and the ultimate base resistance to the limit shaft resistance. Resistance factors are proposed for different combinations of these ratios within their possible ranges.

Weigh-in-Motion load effects and statistical approaches for development of live load factors

Arcan Yanik,Christopher Higgins 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.1

The aim of this paper is to simply present live load factor calculation methodology formulation with the addition of a simple new future load projection procedure to previously proposed two methods. For this purpose, Oregon Weigh-in-Motion (WIM) data were used to calculate live load factors by using WIM data. These factors were calculated with two different approaches and by presenting new simple modifications in these methods. A very simple future load projection method is presented in this paper. Using four different WIM sites with different average daily truck traffic (ADTT) volume, and all year data, live load factors were obtained. The live load factors, were proposed as a function of ADTT. ADTT values of these sites correspond to three different levels which are approximately ADTT= 5,000, ADTT = 1,500 and ADTT ≤ 500 cases. WIM data for a full year were used from each site in the calibration procedure. Load effects were projected into the future for the different span lengths considering five-year evaluation period and seventy-five-years design life. The live load factor for ADTT=5,000, AASHTO HS20 loading case and five-year evaluation period was obtained as 1.8. In the second approach, the methodology established in the Manual for Bridge Evaluation (MBE) was used to calibrate the live load factors. It was obtained that the calculated live load factors were smaller than those in the MBE specifications, and smaller than those used in the initial calibration which did not convert to the gross vehicle weight (GVW) into truck type 3S2 defined by AASHTO equivalents.

Determination of Optimal Load-Resistance Factors for Gravitational Loads-Governed Limit State of Korean Bridge Design Code

이해성,송상우,김지현 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.8

This paper presents an optimization scheme to determine the optimal load-resistance factors for a gravitational loads-governed limit state in the Korean Highway Bridge Design Code. The random variables in the limit state function are normalized to the total nominal load effect, and the optimization is formulated using the normalized variables. The objective function is defined as an L2- norm of errors between the design strength obtained by the load-resistance factors and the target strength evaluated by the inverse reliability analysis for the target reliability index. Two different types of optimization, reference and sequential optimizations, are proposed. The former is to determine absolute optimal load-resistance factors, while the latter is proposed to obtain the factors suitable for actual design codes. The reference optimization results in load-resistance factors that yield a more uniform reliability index than the sequential optimization. The reliability levels provided by the proposed load-resistance factors are presented in detail and compared with those obtained by the factors in the Korean Highway Bridge Design Code. It is shown that the factors in the code lead to a much higher reliability index than the target while the optimal load-resistance factors yield a reliability index within ± 5% error bounds to the target reliability index.

인지부하 측정을 위한 구인의 탐색 및 타당화

류지헌 ( Jee Heon Ryu ),임지현 ( Ji Hyun Yim ) 한국교육정보미디어학회 2009 교육정보미디어연구 Vol.15 No.2

이 연구의 목적은 인지부하 측정을 위한 구인을 도출하는 것이다. 이를 위하여 문헌분석을 통하여 5개의 요인을 도출하였으며, 이를 바탕으로 인지부하 측정설문을 개발하였다. 이 연구에 참여한 연구대상은 대학생 217명이었으며 컴퓨터 기반의 학습활동을 실시한 다음에 인지부하 설문에 응답하도록 하였다. 우선 탐색적 요인분석(KMO=.89, Bartlett 검정=2393.58, p<.01)을 실시하였으며 요인추출 방법은 최대우도법(maximum likelihood method)을 적용하여 모형의 적합도를 평가했다. 또한 요인의 회전을 위해서는 사교회전 방법을 적용하였다. 최종적으로 5요인모형이 적합한 것으로 평가되었으며, 설명된 총분산은 61.45%이었다. 최종적으로 도출된 5요인은 자기 평가(self evaluation), 신체적 노력(physical effort), 정신적 노력(mental effort), 자료 설계(material design), 과제 난이도(task difficulty)였으며, 총 20문항으로 구성되었다. 탐색적 요인분석의 결과에 대한 타당화를 위하여 확인적 요인분석이 실시되었다. 확인적 요인분석의 결과에 따르면 카이검증(x2=330.68, p<.05)과 GFI(=.87)는 수용기준에 미치지 못했으나, CMIN/DF=2.07, IFI=.93, CFI=.93, TLI=.91, RMSEA=.07인 것으로 나타나 적합한 것으로 평가되었다. 또한 각 구인별 측정문항의 개념타당도, 개념신뢰도, 분산추출지수, 문항의 내적 일관성에 대한 검토가 진행되었다. 전체적으로 개념타당도, 개념신뢰도, 문항의 내적 일관성에서는 수용수준에 이른 것으로 평가되었다. 그러나 분산추출지수는 최저기준에 이르지 못했기 때문에 수렴타당도를 형성하지 못한 것으로 나타났다. 이 연구를 통하여 다음과 같은 논의를 제시하였다. 첫째, 인지부하를 위한 고차요인 모형의 형성 가능성에 대한 연구가 필요하다. 둘째, 학습자의 지식수준에 따라서 내재적 인지부하가 변화될 수 있기 때문에 이러한 변화가능성을 반영한 요인모형을 연구할 필요가 있다. 셋째, 학습자의 동기수준이나 정서상태에 따라서 인지할당의 효율성이 달라질 수 있다. 넷째, 학습자의 작업기억 용량에 따라서 인지부하의 효율성이 달라질 수 있기 때문에 작업기억과 인지부하와의 역동적 속성을 반영해야 한다. 다섯째, 인지부하에 대한 연구에서 생리신호와 같은 행동적 특성을 반영한 심층적 연구가 필요하다. The purpose of this study was to identify the measurement constructs of cognitive load theory and validate the factor model derived from the exploratory study. In an effort to meet the purposes literature review was conducted to establish initial factors, and it turned out 5 factors(self-evaluation, physical efforts, mental efforts, material design, and task difficulty). The total numbers of questionnaire items were twenty, which each category contained four items. With the given initial factor model, an exploratory factor analysis was conducted. The extraction method was maximum likelihood method, and oblique technique was applied for the factor rotation. The total explained variance were estimated as 61.45%, and five factor model was selected. Also an confirmative factor analysis was conducted to validate the five factor model. The overall goodness-of-model fit was evaluated as acceptable: CMIN/DF, IFI, CFI, TLI, and RMSEA met with the minimum requirements. Once the model estimation was acceptable, construct validation, composite reliability, variance extraction, and Cronbach`s α were evaluated. All the questionnaires were evaluated to meet the requirement for construct validation, composite reliability, and Cronbach`s α. However, variance extractions of each latent variables did not meet the minimum requirement except for mental effort. This result indicated that the five factor model extracted from this study established constructs, which were acceptable for construct validation, but the factor model could not establish a sound convergent validation to measure the cognitive load. First, this study suggested that constructs of cognitive load may form a higher-oder structure rather than a single factor model. Second, there could be a moderate effect by learner`s knowledge level. Third, motivation aspect should be added to measure cognitive load because affective factor may have an impact on learner`s cognitive load. Fourth, the learner`s working memory capacity (WMC) may affect the cognitive load because the efficiency of cognitive process will be relied on the WMC. Last, behavioral feature such as physiological factor should be included for the further study. In this study, physical effort was extracted one of the constructs of cognitive load.

발생부하원단위와 수치표고모형을 이용한 하천유역 오염부하량 산정

양홍모,김혁,Yang, Hong-Mo,Kim, Hyuk 한국조경학회 2001 韓國造景學會誌 Vol.29 No.1

The purpose of this study is to compare calculated pollutant loadings using pollutant load unit factors and vector type coverage, and expected mean concentration(EMC) and raster type of digital elevation model(DEM). This study is also focusing on comparison of the advantages and the disadvantages of the two methods, and seeking for a method of calculation of pollutant loadings using DEM. Estimation of pollutant inputs using pollutant load unit factors has limitations in identifying seasonal variations of pollutant loadings. Seasonal changes of runoffs should be considered in the calculation of pollutant loadings from catchments into reservoirs. Evaluation of pollutant inputs using runoff-coefficient and EMC can overcome these drawbacks. Proper EMC and runoff-coefficient values for the Koeup stream catchments of the Koheung estuarine lake were drawn from review of related papers. Arc/Info was employed to establish database of spatial and attribute data of point and non-point pollutant sources and characteristics of the catchments. ArcView was used to calculate point and non-point pollutant loadings. Pollutant loads estimated with either unit factors-coverages, i.e., pollutant load unit factors and vector coverages f point sources and land use, or EMC and digital elevation mode(DEM) were compared with stream monitoring loads. We have found that some differences were shown between monitoring results and estimated loads by Unit Factors-Coverage and EMC-DEM. Monthly variations of pollutant loads evaluated with EMC-DEM were similar to those with monitoring result. The method using EMC-DEM can calculate accumulated flows and pollutant loads and can be utilized to identify stream networks. A future research on correcting the difference between vector type stream using flow direction grid and digitalizing vector type should be conducted in order to obtain more exact calculation of pollutant loadings.

극한상태의 정재하시험결과를 이용한 타입말뚝의 안전율 적용성 평가

기완서 ( Wan Seo Ki ),박노환 ( Noh Hwan Park ),김선학 ( Sun Hak Kim ) 대한지질공학회 2009 지질공학 Vol.19 No.4

본 연구는 국내·외의 사질지반에 시공된 타입말뚝에 대해 파괴가 현저하게 나타날 때까지 재하한 정재하시험 실측값을 이용하여 극한하중·항복하중·침하량기준의 각각 판정법으로 극한하중을 추정하였다. 추정된 극한하중을 실측된 파괴하중으로 정규화하고 말뚝특성에 따라 판정법별 비교·분석 하였다. 또한 극한하중 추정시 적합한 판정법을 검토하고 허용하중 결정시 안전율을 재평가하여 다음과 같은 결론을 얻었다. 극한하중 판정법으로 구한 극한하중은 Chin 방법에 의해 해석된 값이 실측값 보다 과대평가하는 경향을 나타냈으며 B. Hansen 80%기준과 Stability Plot 방법이 실측치와 거의 일치하여 가장 신뢰성이 있는 방법으로 판단되었다. 허용하중 산정시 극한하중 판정법에 의해 구한 파괴하중에 적용해야 할 안전율을 구조물기초설계기준에 적용된 안전율을 기준으로 환산하면 B. Hansen 90% 방법을 제외하고 3.0보다 큰 값이 적용되어야 할 것으로 판단되었으며 항복하중 판정법들의 경우 기준안전율 2.0보다 큰 값이 적용되어야 할 것으로 판단되었다. 침하량 기준에 의해 구한 하중에 적용해야 할 안전율을 극한하중에 대한 안전율 3.0을 기준으로 환산해 보면, 전침하량 기준 및 순침하량 기준은 3.0보다 작은 값이 적용되어야 할 것으로 판단되었다. This study estimated ultimate load by the determination methods based on ultimate load, yield load and settlement using experimental data from static load tests that applied load to driven piles used in sandy grounds at home and overseas until failure appeared markedly. Estimated ultimate load was normalized with actually measured failure load, and was compared among the determination methods according to the characteristics of pile. In addition, I have identified to the determination methods suitable for estimating ultimate load, and reevaluated the safety factor when determining allowable load. From the results of this study were drawn conclusions as follows. Among ultimate loads estimated by the ultimate-load-based determination methods, the value interpreted by Chin`s method tended to overestimate actual measurements, and B. Hansen 80% standard and the stability plot method were considered most reliable as their results were closest to actual measurements. According to the results of this study, in calculating the allowable load, if the safety factor to be applied to failing load obtained by the method of determining extreme load is converted to the safety factor applied to the Standards for Structure Foundation Design, a value larger than 3.0 should be applied except the B. Hansen 90% method, and a value larger than 2.0 should be applied in the methods of determining yield load. In addition, if the safety factor to be applied to load obtained by the settlement standard is converted based on safety factor 3.0 for extreme load, a value smaller than 3.0 should be applied to the total settlement standard and the net settlement standard.

무효전력 민감도와 부하지속곡선을 활용한 적정 부하역률의 효과적인 산정 기법에 관한 연구

이병하(Byung Ha Lee),황승호(Sung-Ho Hwang) 대한전기학회 2012 전기학회논문지 Vol.61 No.12

In this paper, a methodology to use load duration curve and the reactive power factor sensitivity of generation cost is proposed for analyzing the effects of load power factor effectively. A great deal of cases of power systems are classified into several patterns according to the characteristics using load duration curve, and the overall effects of load power factor are assessed by integrating the analysis results of load power factor in all the patterns. The reactive power sensitivity of generation cost and the integrated costs such as generation cost, investment cost, voltage variation penalty cost and CO2 emission cost are used for determining an appropriate load power factor. A systematic procedure for effective analysis of load power factor is presented. It is shown through the application to the practical power system of KEPCO(Korea Electric Power Corporation)that the effects of load power factor can be analyzed effectively using load duration curve and reactive power factor sensitivity.

A Study on Effective Enhancement of Load Power Factor Using the Load Power Factor Sensitivity of Generation Cost

Lee Byung Ha,Kim Jung-Hoon The Korean Institute of Electrical Engineers 2005 KIEE International Transactions on Power Engineeri Vol.a5 No.3

Various problems such as increase of power loss and voltage instability may often occur in the case of low load power factor. The demand of reactive power increases continuously with the growth of active power and restructuring of electric power companies makes the comprehensive management of reactive power a troublesome problem, so that the systematic control of load power factor is required. In this paper, the load power factor sensitivity of generation cost is derived and it is used for effectively determining the locations of reactive power compensation devices and for enhancing the load power factor appropriately. In addition, voltage variation penalty cost is introduced and integrated costs including voltage variation penalty cost are used for determining the value of load power factor from the point of view of economic investment and voltage regulation. It is shown through application to a large-scale power system that the load power factor can be enhanced effectively using the load power factor sensitivity and the integrated cost.

신뢰성 해석에 의한 지역특성 활하중계수

김상진,박현수 濟州大學校 海洋硏究所 2004 해양과환경연구소 연구논문집 Vol.28 No.2

This study determines the site-specific live load factors using the reliability analysis and reviews the appropriateness of the live load factor of the AASHTO LRFD bridge design specifications. The Rackwitz and Fiessler method is used for the reliability analysis. The analysis is performed for the reinforced concrete T-girder bridges. The spans, spacings, and depths of bridge girders are considered as main design variables of the reinforced concrete T-girder bridges. Statistical characteristics of the resistance of the T-girder bridges and those of the dead load are obtained from the literature survey. The statistical characteristics of the site-specific live loads are estimated from the data of the truck axle weights and axle spacings measured in Michigan. The results of the site-specific live load factors were varied from 1.2 to 3.5. The decisive element for the determination of the live load factors is found to be the bias factors of the live load. If the design provisions are satisfied, the change of the spacing and depth of the girders has little influence on the reliability of the bridges. The results show that the live load factors of the AASHTO LRFD bridge design specifications cannot accommodate the live load variations for various sites.