• Title/Summary/Keyword: Structural Flexibility

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Investigation on wind stability of three-tower cable-stayed-suspension hybrid bridges under skew wind

  • Xin-Jun Zhang;Li Bowen;Nan Zhou
    • Wind and Structures
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    • v.38 no.6
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    • pp.427-443
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    • 2024
  • By using a computational program of three-dimensional aerostatic and aerodynamic stability analysis of long-span bridges under skew wind, the dynamic characteristics and structural stability(including the aerostatic and aerodynamic stability) of a three-tower cable-stayed-suspension hybrid bridge with main span of 1 400 meters are investigated numerically under skew wind, and the skew wind and aerostatic effects on the aerostatic and aerodynamic stability of three-tower cable-stayedsuspension hybrid bridge are ascertained. The results show that the three-tower cable-stayed-suspension hybrid bridge is a longspan structure with greater flexibility, and it is more susceptible to the wind action. The aerostatic instability of three-tower cable-stayed-suspension hybrid bridges is characterized by the coupling of vertical bending and torsion of the girder, and the skew wind does not affect the aerostatic instability mode. The skew wind has positive or negative effects on the aerostatic stability of the bridge, the influence is between -5.38% and 4.64%, and in most cases, it reduces the aerostatic stability of the bridge. With the increase of wind yaw angle, the critical wind speed of aerostatic instability does not vary as the cosine rule as proposed by the skew wind decomposition method, the skew wind decomposition method may overestimate the aerostatic stability, and the maximum overestimation is 16.7%. The flutter critical wind speed fluctuates with the increase of wind yaw angle, and it may reach to the minimum value under the skew wind. The skew wind has limited effect on the aerodynamic stability of three-tower cable-stayed-suspension hybrid bridge, however the aerostatic effect significantly reduces the aerodynamic stability of the bridge under skew wind, the reduction is between 3.66% and 21.86%, with an overall average drop of 11.59%. The combined effect of skew and static winds further reduces the critical flutter wind speed, the decrease is between 7.91% and 19.37%, with an overall average decrease of 11.85%. Therefore, the effects of skew and static winds must be comprehensively considered in the aerostatic and aerodynamic stability analysis of three-tower cable-stayed-suspension hybrid bridges.

The Prediction of Currency Crises through Artificial Neural Network (인공신경망을 이용한 경제 위기 예측)

  • Lee, Hyoung Yong;Park, Jung Min
    • Journal of Intelligence and Information Systems
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    • v.22 no.4
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    • pp.19-43
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    • 2016
  • This study examines the causes of the Asian exchange rate crisis and compares it to the European Monetary System crisis. In 1997, emerging countries in Asia experienced financial crises. Previously in 1992, currencies in the European Monetary System had undergone the same experience. This was followed by Mexico in 1994. The objective of this paper lies in the generation of useful insights from these crises. This research presents a comparison of South Korea, United Kingdom and Mexico, and then compares three different models for prediction. Previous studies of economic crisis focused largely on the manual construction of causal models using linear techniques. However, the weakness of such models stems from the prevalence of nonlinear factors in reality. This paper uses a structural equation model to analyze the causes, followed by a neural network model to circumvent the linear model's weaknesses. The models are examined in the context of predicting exchange rates In this paper, data were quarterly ones, and Consumer Price Index, Gross Domestic Product, Interest Rate, Stock Index, Current Account, Foreign Reserves were independent variables for the prediction. However, time periods of each country's data are different. Lisrel is an emerging method and as such requires a fresh approach to financial crisis prediction model design, along with the flexibility to accommodate unexpected change. This paper indicates the neural network model has the greater prediction performance in Korea, Mexico, and United Kingdom. However, in Korea, the multiple regression shows the better performance. In Mexico, the multiple regression is almost indifferent to the Lisrel. Although Lisrel doesn't show the significant performance, the refined model is expected to show the better result. The structural model in this paper should contain the psychological factor and other invisible areas in the future work. The reason of the low hit ratio is that the alternative model in this paper uses only the financial market data. Thus, we cannot consider the other important part. Korea's hit ratio is lower than that of United Kingdom. So, there must be the other construct that affects the financial market. So does Mexico. However, the United Kingdom's financial market is more influenced and explained by the financial factors than Korea and Mexico.

A Study on Adhesion Characteristics and Physical Properties of Animal Glue Added Genipin (제니핀을 첨가한 아교의 접착 특성과 물성 변화 연구)

  • Lee, Jun Ho;Yu, Ji A;Chung, Yong Jae
    • Journal of Conservation Science
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    • v.34 no.3
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    • pp.157-166
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    • 2018
  • In this study, gelatin binding ability was increased by adding cross linking agent to improve adhesive characteristic of animal glue. Animal glue added genipin measured gel strength and viscosity, the structural analysis, the color retention degree, elution degree, and rupture strength. And the water resistance and ultraviolet light resistance with the addition of genipin were compared. As a result of the study, the gel strength and viscosity increased with the amount of genipin. As a result of the structural analysis, in gelatin, the absorption peak of the triple structure of collagen structurally stabilized was observed. As a result of the color retention degree, the film was observed because of the lowered brightness. The amount of elution glue was increased with addition of genipin at 50C distilled water condition and rupture strength has increased with the amount of genipin. In the water resistance and light fastness, there was no appearance before and after deterioration due to the addition of genipin. Based on the results of this study, it confirmed the adhesive characteristics of animal glue added genipin and examined the experimental method applicable for animal glue. After the addition of genipin, flexibility, re-solving, adhesive force, and curing speed, which are unique characteristics of glue, can be improved without disappearing, so it is expected that it will be applicable to production of animal glue and conservation of cultural heritage when homogeneous glue is secured.

Influence of Column Base Rigidity on Behavior of Steel Buildings (강구조물 지지부의 강성도가 구조물 거동에 미치는 영향)

  • 권민호;박문호;장준호;박순응
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.1
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    • pp.165-172
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    • 2002
  • Generally, the steel rigid frame has been analyzed using finite element analysis tools. While many efforts have been poured into the understanding and accurate prediction for the nonlinear behavior of the columns and beam-columns connections, the base of the columns are modeled as simply hinged or fixed. However, the base of the steel columns practically is neither fixed not hinged. It behaves as semi-rigid. In this paper, the supports of the columns we modeled as semi-rigid and the importance of such approach in moment-resisting columns is evaluated. Two typical buildings designed by the US specification are modeled and analyzed by the finite element based on stiffness method and flexibility method. The column bases of three-story buildings are modeled as rotational springs with a varying degree of stiffness and strength that simulates the semi-rigidity of the base. Depending on the degree of stiffness and strength, the semi-rigidity varies from the hinged to the fixed. Buildings with semi-rigid column bases behaves similarly to the building with fixed bases. It has been numerically observed through the pushover and nonlinear time history analyses that the decrease of the stiffness of the column base induces the rotational demand on the int air beams. an increase of rotation demands on the first store connections and lead to a soft-story mechanists Due often to the construction and environmental effects, undesired reduction of column base stiffness may cause an increase of rotation demands on the first store connections and lead to a soft-story mechanism.

An application of the A-PDA model and the water supply performance index for the temporal and spatial evaluation of the performance of emergency water supply plans via interconnections (비상시 용수 연계공급 성능의 시·공간적 평가를 위한 A-PDA 모형 및 공급성능지표의 적용)

  • Oak, SueYeun;Kim, SuRi;Jun, Hwandon
    • Journal of Korea Water Resources Association
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    • v.51 no.11
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    • pp.977-987
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    • 2018
  • The purpose of the water distribution system is gradually changing to increase the flexibility for responding to various abnormal situations. In addition, it is essential to improve resilience through preparing emergency plans against water supply failure. The most efficient way is emergency interconnections which supply water from interconnected adjacent blocks. To operate successful interconnections, it is essential to evaluate the supply performance in spatial and temporal aspects. The spatial and temporal aspects are dominated by its interconnected pipes and interconnected reservoirs respectively. In this study, an emergency interconnection scenario where problem occurred in reservoir 1 at 0:00hr in A city, Korea. An Advanced-Pressure Driven Analysis model was used to simulate the volume and inflow volume of the interconnected reservoirs. Based on the hydraulic analysis results, a multi-dimensional evaluation of the supply performance was conducted by applying possible water supply range indicator (PWSRI) and possible water supply temporal indicator (PWSTI) which are based on fuzzy membership functions. As a result, it was possible to evaluate the supply performance on the sides of consumers in spatio-temporal aspects and to review whether established plans mitigate the damage as intended. It is expected to be used for decision making on structural and non-structural emergency plan to improve the performance of an emergency interconnection.

Multilevel Mediation Analysis: Statistical Methods, Analytic Procedure, and a Real Example (다층자료의 매개효과 분석: 통계방법, 분석절차 및 실례)

  • Park, Sun-Mi;Bak, Byung-Gee
    • Science of Emotion and Sensibility
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    • v.19 no.4
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    • pp.95-110
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    • 2016
  • The purpose of this study was to propose a proper method for the multilevel mediation analysis, for which the hierarchical method should be utilized, then MLM (multilevel modeling) approach as a hierarchical method has been popularly utilized until MSEM (multilevel structural equation modeling) approach was not proposed. This purpose was covered by three research questions about statistical methods, analytic procedure, and real example. First, MSEM statistical method was preferred to MLM method for its estimation accuracy and analytic flexibility. Second, the four-step procedures of model building, assumption examination, model comparison, and coefficient testing were proposed for the multilevel mediation analysis. Third, the real data of 2695 students of elementary and secondary schools and 89 teachers were analyzed in the multilevel directions of 221 and 112. Out of these directions of 221, and 112 model, only the coefficient of 221 model was significant at the 95% CI. Mplus programs used for the real example are attached on the Appendix. Based on the results, significance and limitations of this study, were discussed in detail.

A Study on Watertightness Improvement of Hybrid Method Using Polyvinyl Acetate(PVAc) (폴리비닐아세테이트(PVAc)를 이용한 복합공법의 수밀성능 향상에 관한 연구)

  • Ryou, Jae Suk;Song, Il Hyun;Lee, Yong Soo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.4
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    • pp.18-24
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    • 2012
  • In this study, hybrid method using polyvinyl acetate (PVAc) which has a strong adhesion and flexibility in which acrylic copolymer chemical-reaction reacts with cement, and is eco-friendly, is to improve the watertightness. The hybrid method is applied applied primarily waterproof stuff comprising silicate system and secondary mortar mixed with PVAc on the concrete surface. And then, in order to evaluate the performance, the properties of bond strength and amount of water absorption were measured. Based on the above experiments, mock-up specimens for field application were fabricated, and then the properties were evaluated as laboratory experiments. As the results, specimens cast from hybrid method using PVAc showed the best results on watertightness and bond strength. And also, with respect to experiment of mock-up specimens, the properties were in agreement with laboratory results. Especially, it could know that PVAc has strengthening effect from the results of the compressive strength. Due to outstanding results of carbonation depth and resistance to chloride ion penetration, it may be applied in weak areas such as underground and marine structures.

A Study on the Eco-Friendly Durable Pre-Painting for Concrete Structure (콘크리트 구조물의 친환경 내구성 도장에 관한 기초 연구)

  • Jo, Byung Wan;Choi, Ji Sun;Lee, Seong Won
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.2
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    • pp.110-116
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    • 2013
  • A concrete structure has become bigger and higher because of development of construction technology and a change in construction environment. Also it tends to focus on repairing, reinforcement and exterior in harmony with environment for structure maintenance and performance improvement. The research is about eco friendly durable painting applicable to concrete structure using civil and architecture. it purpose to improve external beauties and durable problems due to flexibility by variation of temperature, adhesion of exterior wall, crack and delamination in existing organic and mineral painting. For those problems, we made a eco friendly pre-paint that is made with preliminary treatment mixture as a highly enriched waterproof agent and adhesive increasing agent in preprocessing mixture. Then we performed an experiment on durability of prevention neutralization of concrete, durability abrasion, hiding power, adhesion, temperature resistance and resistance to chemical attack. The result of an experiment shows that hiding power is over 0.96 in standard test, durability abrasion test got higher value 1mg than water paint 75mg and tensile strength is 6 times higher than standard waterproof specification.

Multiscale Virtual Testing Machines of Concrete and Other Composite Materials: A Review (콘크리트 및 복합재료용 멀티스케일 가상 시험기계에 관한 소고)

  • Haile, Bezawit F.;Park, S.M.;Yang, B.J.;Lee, H.K.
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.4
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    • pp.173-181
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    • 2018
  • Recently composite materials have dominated most engineering fields, owing to their better performance, increased durability and flexibility to be customized and designed for a specific required property. This has given them unprecedented superiority over conventional materials. With the help of the ever increasing computational capabilities of computers, researchers have been trying to develop accurate material models for the complex and integrated properties of these composites. This has led to advances in virtual testing of composite materials as a supplement or a possible replacement of laboratory experiments to predict the properties and responses of composite materials and structures. This paper presents a review on the complex multi-scale modelling framework of the virtual testing machines, which involve computational mechanics at various length-scales starting with nano-mechanics and ending in structure level computational mechanics, with a homogenization technique used to link the different length scales. In addition, the paper presents the features of some of the biggest integrated virtual testing machines developed for study of concrete, including a multiscale modeling scheme for the simulation of the constitutive properties of nanocomposites. Finally, the current challenges and future development potentials for virtual test machines are discussed.

A Study on the Field Application of the Measurement Technique for Static Displacement of Bridge Using Ambient Vibration (상시 진동을 이용한 교량 정적 처짐 산정 기술의 현장 적용성 연구)

  • Sang-Hyuk Oh;Dae-Joong Moon;Kwang-Myong Lee
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.11 no.4
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    • pp.355-363
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    • 2023
  • In safety assessment of a aged bridge, dynamic characteristics and displacement are directly related to the rigidity of the structural system, especially displacement is the most important factor as the physical quantity that the bridge user can directly detect. However, in order to measure the displacement of the bridge, it is difficult to install displacement sensors at the bottom of the bridge and conduct traffic blocking and loading tests, resulting in increased costs or impossible measurements depending on the bridge's environment. In this study, a method of measuring the displacement of a bridge using only accelerometers without installing displacement sensors and ambient vibration without a loading test was proposed. For the analysis of bridge dynamic characteristics and displacement using ambient vibration, the mode shape and natural frequency of the bridge were extracted using a TDD technique known to enable quick analysis with simple calculations, and the unit load displacement of the bridge was analyzed through flexibility analysis to calculate static displacement. To verify this proposed technology, an on-site test was conducted on C Bridge, and the results were compared with the measured values of the loading test and the structural analysis data. As a result, it was confirmed that the mode shape and natural frequency were 0.42 to 1.13 % error ratio, and the maximum displacement at the main span was 3.58 % error ratio. Therefore, the proposed technology can be used as a basis data for indirectly determine the safety of the bridge by comparing the amount of displacement compared to the design and analysis values by estimating the displacement of the bridge that could not be measured due to the difficulty of installing displacement sensors.