• Title/Summary/Keyword: ACCELERATION

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Derivation of Dynamic Characteristic Values for Multi-degree-of-freedom Frame Structures based on Frequency Response Function(FRF) (주파수응답함수 기반 다자유도 골조 구조물의 동특성치 도출 및 구조모델링 적용 )

  • So-Yeon Kim;Min-Young Kim;Seung-Jae Lee;Kyoung-Kyu Choi
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.27 no.4
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    • pp.1-10
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    • 2023
  • In the seismic design of structures, seismic forces are calculated based on structural models and analysis. In order to accurately address the dynamic characteristics of the actual structure in the structural model, calibration based on actual measurements is required. In this study, a 4-story frame test specimen was manufactured to simulate frame building, accelerometers were attached at each floor, and 1-axis shaking table test was performed. The natural period of the specimen was similar to that of the actual 4 story frame building, and the columns were designed to behave with double-curvature having the infinite stiffness of the horizontal members. To investigate the effects seismic waves characteristics, historical and artificial excitations with various frequencies and acceleration magnitudes were applied. The natural frequencies, damping ratios, and mode shapes were obtained using frequency response functions obtained from dynamic response signals, and the mode vector deviations according to the input seismic waves were verified using the Mode assurance criterion (MAC). In addition, the damping ratios obtained from the vibration tests were applied to the structural model, and the method with refined dynamic characteristics was validated by comparing the analysis results with the experimental data.

Inferring Pedestrian Level of Service for Pathways through Electrodermal Activity Monitoring

  • Lee, Heejung;Hwang, Sungjoo
    • International conference on construction engineering and project management
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    • 2022.06a
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    • pp.1247-1248
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    • 2022
  • Due to rapid urbanization and population growth, it has become crucial to analyze the various volumes and characteristics of pedestrian pathways to understand the capacity and level of service (LOS) for pathways to promote a better walking environment. Different indicators have been developed to measure pedestrian volume. The pedestrian level of service (PLOS), tailored to analyze pedestrian pathways based on the concept of the LOS in transportation in the Highway Capacity Manual, has been widely used. PLOS is a measurement concept used to assess the quality of pedestrian facilities, from grade A (best condition) to grade F (worst condition), based on the flow rate, average speed, occupied space, and other parameters. Since the original PLOS approach has been criticized for producing idealistic results, several modified versions of PLOS have also been developed. One of these modified versions is perceived PLOS, which measures the LOS for pathways by considering pedestrians' awareness levels. However, this method relies on survey-based measurements, making it difficult to continuously deploy the technique to all the pathways. To measure PLOS more quantitatively and continuously, researchers have adopted computer vision technologies to automatically assess pedestrian flows and PLOS from CCTV videos. However, there are drawbacks even with this method because CCTVs cannot be installed everywhere, e.g., in alleyways. Recently, a technique to monitor bio-signals, such as electrodermal activity (EDA), through wearable sensors that can measure physiological responses to external stimuli (e.g., when another pedestrian passes), has gained popularity. It has the potential to continuously measure perceived PLOS. In their previous experiment, the authors of this study found that there were many significant EDA responses in crowded places when other pedestrians acting as external stimuli passed by. Therefore, we hypothesized that the EDA responses would be significantly higher in places where relatively more dynamic objects pass, i.e., in crowded areas with low PLOS levels (e.g., level F). To this end, the authors conducted an experiment to confirm the validity of EDA in inferring the perceived PLOS. The EDA of the subjects was measured and analyzed while watching both the real-world and virtually created videos with different pedestrian volumes in a laboratory environment. The results showed the possibility of inferring the amount of pedestrian volume on the pathways by measuring the physiological reactions of pedestrians. Through further validation, the research outcome is expected to be used for EDA-based continuous measurement of perceived PLOS at the alley level, which will facilitate modifying the existing walking environments, e.g., constructing pathways with appropriate effective width based on pedestrian volume. Future research will examine the validity of the integrated use of EDA and acceleration signals to increase the accuracy of inferring the perceived PLOS by capturing both physiological and behavioral reactions when walking in a crowded area.

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Application of Effective Earthquake Force by the Boundary Reaction Method and a PML for Nonlinear Time-Domain Soil-Structure Interaction Analysis of a Standard Nuclear Power Plant Structure (원전구조물의 비선형 시간영역 SSI 해석을 위한 경계반력법에 의한 유효지진하중과 PML의 적용)

  • Lee, Hyeok Ju;Lim, Jae Sung;Moon, Il Hwan;Kim, Jae Min
    • Journal of the Earthquake Engineering Society of Korea
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    • v.27 no.1
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    • pp.25-35
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    • 2023
  • Considering the non-linear behavior of structure and soil when evaluating a nuclear power plant's seismic safety under a beyond-design basis earthquake is essential. In order to obtain the nonlinear response of a nuclear power plant structure, a time-domain SSI analysis method that considers the nonlinearity of soil and structure and the nonlinear Soil-Structure Interaction (SSI) effect is necessary. The Boundary Reaction Method (BRM) is a time-domain SSI analysis method. The BRM can be applied effectively with a Perfectly Matched Layer (PML), which is an effective energy absorbing boundary condition. The BRM has a characteristic that the magnitude of the response in far-field soil increases as the boundary interface of the effective seismic load moves outward. In addition, the PML has poor absorption performance of low-frequency waves. For this reason, the accuracy of the low-frequency response may be degraded when analyzing the combination of the BRM and the PML. In this study, the accuracy of the analysis response was improved by adjusting the PML input parameters to improve this problem. The accuracy of the response was evaluated by using the analysis response using KIESSI-3D, a frequency domain SSI analysis program, as a reference solution. As a result of the analysis applying the optimal PML parameter, the average error rate of the acceleration response spectrum for 9 degrees of freedom of the structure was 3.40%, which was highly similar to the reference result. In addition, time-domain nonlinear SSI analysis was performed with the soil's nonlinearity to show this study's applicability. As a result of nonlinear SSI analysis, plastic deformation was concentrated in the soil around the foundation. The analysis results found that the analysis method combining BRM and PML can be effectively applied to the seismic response analysis of nuclear power plant structures.

Prediction of Chemical Acceleration Durability Time of Polymer Membrane in Polymer Electrolyte Membrane Fuel Cells (고분자 전해질 연료전지에서 고분자막의 화학적 가속 내구 시간 예측)

  • Sohyeong Oh;Donggeun Yoo;Sunggi Jung;Jihong Jeong;Kwonpil Park
    • Korean Chemical Engineering Research
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    • v.61 no.1
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    • pp.26-31
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    • 2023
  • For durability improvement of polymer electrolyte membrane fuel cell (PEMFC) polymer membrane, accelerated durability evaluation methods that can evaluate durability in a short time have been researched and developed. However, the lifespan of fuel cells for large commercial vehicles such as trucks and buses is more than three times that of passenger cars, and the chemical accelerated stress test (AST) time is also longer, reaching 1,500 hours or more. Therefore, in this study, as a method to evaluate the chemical durability of a membrane within a short time, it was examined whether the durability could be predicted by the pristine membrane characteristics. Hydrogen crossover current density (HCCD) and short resistance (SR) were estimated as initial characteristics, and AST time was predicted through the Fenton experiment, which was possible as an out-of-cell experiment for 3 hours. As the HCCD and fluoride ion emission concentration increased, the AST time tended to be linearly shortened, but there was a deviation (R2 ≒0.65). When the SR decreased, the AST time showed a linear increase, and the accuracy was high (R2 =0.93), so the AST time could be predicted with the initial SR of the membrane.

Analysis of Performance in Fostering the Companies Occupied in Technopark and its Characteristics: Focusing on Growth Path and Type (테크노파크 입주기업 육성의 성과 및 특성 분석: 성장경로 및 유형을 중심으로)

  • Seulbee Lee;Myungjun Oh;Jinhee Bae;Seseon Ryou
    • Journal of the Economic Geographical Society of Korea
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    • v.25 no.4
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    • pp.531-546
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    • 2022
  • This study analyzes the performance and characteristics of the fostering policies for the focusing on growth path and type occupied in the Technoparks. First, the companies occupied in the Technoparks have shown the characteristics of landing on an actual growth phase beyond the start-up and fostering phases, and when considering the possession of a dedicated R&D organization and the portion of highly educated technical personnel having masters and doctorate degrees, these companies have also entailed the characteristics of being a technological innovation company. Second, about 30% of the companies that left the Technoparks secured their own factories and offices after standing alone, indicating that the fostering function after startup in the Technoparks has been performing a significant role on the growth path of start-up companies from a temporal perspective. Third, a majority of the companies occupied in the Technoparks were composed of scale-up companies or preliminary scale-up companies that contained promising innovative growth potential. However, it seems to urgently require the acceleration of innovation because many companies are categorized into a stagnated growth type that demonstrates a high R&D investment but low sales revenue growth.

A Study on the Prevention of Liquefaction Damage of the Sheet File Method Applicable to the Foundation of Existing Structures Using the 1-G Shaking Table Experiment (1-G 진동대 실험을 이용한 기존 구조물 기초에 적용 가능한 시트파일 공법의 액상화 피해 방지에 관한 연구)

  • Jongchan Yoon;Suwon Son;Junhyeok Park;Junseong Moon;Jinman Kim
    • Journal of the Korean GEO-environmental Society
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    • v.24 no.7
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    • pp.5-14
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    • 2023
  • Recently, earthquakes have occurred frequently in worldwide. These earthquakes cause various forms of natural and physical damage. In particular, liquefaction in which the ground shows liquid-like behavior causes great damage to the structure. Accordingly, various liquefaction damage reduction methods are being studied and developed. Therefore, in this study, a method of reducing liquefaction damage in the event of an earthquake applicable to existing structures was studied using the sheet pile method. The 1-G Shaking table test was performed and the ground was constructed with Jumunjin standard sand. A two-story model structure was produced by applying the similitude law, and the input wave applied a sine wave with an acceleration level of 0.6 g and a frequency of 10 Hz. The effect of reducing structure damage according to various embedded depth ratio was analyzed. As a result of the study, the structure settlement when the ground is reinforced by applying the sheet pile method is decreased by about 71% compared to when the ground is not reinforced, and the EDR with minimum settlement is "1". In addition, as the embedded depth ratio is increased, the calculation of the pore water pressure in the ground tends to be delayed due to the sheet pile. Based on these results, the relationship with structural settlement according to the embedded depth ratio is proposed as a relational equation with the graph. The results of this study are expected to be used as basic data in developing sheet pile methods applicable to existing structures in the future.

Evaluation of Dynamic Group Pile Effect in Sand by 1 g Shaking Table Tests (1g 진동대 실험을 이용한 사질토 지반에서의 동적 군말뚝 효과 분석)

  • Yang, Eui-Kyu;Choi, Jung-In;Han, Jin-Tae;Kim, Myoung-Mo
    • Journal of the Korean Geotechnical Society
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    • v.26 no.8
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    • pp.77-88
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    • 2010
  • In this study, 1 g shaking table group pile tests were performed for various conditions of subgrade and pile spacing. The pile spacing was changed from three to seven times of pile diameters. It could be confirmed that the dynamic p-y curves for the group pile observed as the results of a series of shaking table tests show difference according to the pile spacing, the pile location within the pile group, the relative density of subgrade and the excess pore pressure during earthquake. The dynamic p-multipliers were calculated by comparing the dynamic p-y backbone curves of a single pile suggested by Yang (2009) and dynamic p-y curves for the group pile. Dynamic p-multiplier values overall increase as the relative density of subgrade and amplitude of input acceleration increase. The dynamic group pile effect was neglected, if the pile spacing was seven times as large as pile diameters. It was found that the exisiting p-multiplier values suggested by various researchers for the static and dynamic loading, and the values recommended by globally used specifications show difference with the test results by up to 0.7 (approximately 70%). Therefore, the dynamic p-multipliers were newly suggested according to the pile spacing and the relative density of subgrade using the test results.

Estimation of Settlement on the Crest of CFRD Subjected to Earthquake Loading Using Sensitivity Analysis (민감도분석을 통한 지진하중을 받는 CFRD 정상부 침하량 예측)

  • Ha, Ik-Soo
    • Journal of the Korean Geotechnical Society
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    • v.23 no.1
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    • pp.39-49
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    • 2007
  • In this study, quantitative sensitivity analysis on rockfill material influencing the dam crest settlement of CFRD (Concrete-Faced Rockfill Dam) subjected to earthquake loading was carried out. The purpose of this study is to indicate the most important input parameter from the results of sensitivity analysis, to show the quantitative variation of settlement at the crest of CFR type dam during earthquake with this input parameter, and to recommend the approximate estimation method of the settlement on the crest of CFRD subjected to earthquake loading. The statistic characteristics of rockfill parameters which were obtained from large triaxial tests were evaluated. The total 108 dynamic numerical analyses (2 input earthquake, 2 magnitudes for each earthquake, 27 rockfill material property combinations) on CFRD were conducted. The global sensitivity analysis was carried out using the results of numerical analysis. From the sensitivity analysis, It was found that the crest settlement of the CFRD subjected to earthquake was absolutely affected by the shear modulus of rockfill material irrespective of the input earthquakes and the magnitude of input acceleration. On the contrary, it was found that the effect of cohesion and friction angle of rockfill was negligible. From the results of sensitivity analysis and numerical analysis, the approximate estimation method of the settlement on the crest of CFRD subjected to earthquake loading was recommended on condition that the rockfill shear modulus and simple dam information was known.

Comparison of 1-g and Centrifuge Model Tests for Similitude Laws (상사법칙 검증을 위한 1-g 모형실험과 원심모형실험의 비교 연구)

  • Kim Sung-Ryul;Hwang Jae-Ik;Kim Myoung-Mo;Ko Hon-Yim
    • Journal of the Korean Geotechnical Society
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    • v.22 no.5
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    • pp.59-67
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    • 2006
  • The centrifuge and 1-g shaking table tests were performed simultaneously to compare the dynamic behaviors of loose sands of the same geotechnical properties. The prototype soils were 10 m thick liquefiable loose sands. The geometric scaling factors were 20 for 1-g and 40 for centrifuge tests. The excess pore pressure, surface settlement, and acceleration in the soil were measured at the same locations in the 1-g and centrifuge tests. The total excess pore pressure from development to dissipation was measured. In the centrifuge test, viscous fluid was used as the pore water to eliminate the time scaling difference between dynamic time and dissipation time. In the 1-g tests, the steady state concept was applied to determine the unit weight of the model soil, and two different time scaling factors were applied for the dynamic time and the dissipation time. It is concluded that the 1-g tests can simulate the excess pore pressure of the prototype soil if the permeability of the model soil is small enough to prevent dissipation of excess pore pressure during shaking and the dissipation time scaling factor is properly determined.

Reliability of mortar filling layer void length in in-service ballastless track-bridge system of HSR

  • Binbin He;Sheng Wen;Yulin Feng;Lizhong Jiang;Wangbao Zhou
    • Steel and Composite Structures
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    • v.47 no.1
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    • pp.91-102
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    • 2023
  • To study the evaluation standard and control limit of mortar filling layer void length, in this paper, the train sub-model was developed by MATLAB and the track-bridge sub-model considering the mortar filling layer void was established by ANSYS. The two sub-models were assembled into a train-track-bridge coupling dynamic model through the wheel-rail contact relationship, and the validity was corroborated by the coupling dynamic model with the literature model. Considering the randomness of fastening stiffness, mortar elastic modulus, length of mortar filling layer void, and pier settlement, the test points were designed by the Box-Behnken method based on Design-Expert software. The coupled dynamic model was calculated, and the support vector regression (SVR) nonlinear mapping model of the wheel-rail system was established. The learning, prediction, and verification were carried out. Finally, the reliable probability of the amplification coefficient distribution of the response index of the train and structure in different ranges was obtained based on the SVR nonlinear mapping model and Latin hypercube sampling method. The limit of the length of the mortar filling layer void was, thus, obtained. The results show that the SVR nonlinear mapping model developed in this paper has a high fitting accuracy of 0.993, and the computational efficiency is significantly improved by 99.86%. It can be used to calculate the dynamic response of the wheel-rail system. The length of the mortar filling layer void significantly affects the wheel-rail vertical force, wheel weight load reduction ratio, rail vertical displacement, and track plate vertical displacement. The dynamic response of the track structure has a more significant effect on the limit value of the length of the mortar filling layer void than the dynamic response of the vehicle, and the rail vertical displacement is the most obvious. At 250 km/h - 350 km/h train running speed, the limit values of grade I, II, and III of the lengths of the mortar filling layer void are 3.932 m, 4.337 m, and 4.766 m, respectively. The results can provide some reference for the long-term service performance reliability of the ballastless track-bridge system of HRS.