• Title, Summary, Keyword: longitudinal study

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The Reciprocal Relationship between Caregiver Relations and Peer Relations of Children in Out-of-home Care: Longitudinal Study Using Autoregressive Cross-lagged Modeling (가정외보호 아동의 양육자 관계와 교우관계의 상호 영향: 자기회귀교차지연모형을 활용한 종단연구)

  • Kim, Dami;Kang, Hyunah
    • Journal of Child Welfare and Development
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    • v.16 no.2
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    • pp.109-135
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    • 2018
  • The purpose of this study was to analyze the longitudinal causal relationship between caregiver relations and peer relations of children in out-of-home care. We analyzed the three years(2011-2013) of longitudinal data from the Panel Study on Korean Children in Out-of-Home Care. The autoregressive cross-lagged model (ARCL) was used to measure the longitudinal causal relationship between caregiver relations and peer relations. As a result, first, caregiver relations and peer relations showed stability over time. In other words, the results of the measurement at three time points showed that the caregiver relations and peer relations at the previous time had a significant effect on the caregiver relations and peer relations at the later time point. Second, the previous caregiver relations had a significant effect on the subsequent peer relations over time. Third, the previous peer relations had a significant effect on the subsequent caregiver relations over time. This study confirmed the interrelationships of caregiver relations and peer relations of children in care by examining the longitudinal data using the longitudinal analysis method.

An Experimental Study on the Behavior of Reinforced Concrete Multi-Column Piers with Different Longitudinal and Transverse Reinforcement Details (주철근 겹침이음 및 횡철근 상세에 따른 철근콘크리트 다주교각의 거동특성에 관한 실험적 연구)

  • 김재관;김익현;김정한;조대연
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • pp.211-219
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    • 2002
  • This study is performed to investigate the behavior of multi-column piers and to evaluate the seismic performance. In this study, 3 types of scale model piers with 2-column are designed and tested by quasi-static load in both longitudinal and transverse directions. Each type of model consisting of 2 specimens has different reinforcement details in the lap splice of longitudinal bars and amount of transverse reinforcements. This paper reports that the ductility of the model in transverse direction is rather higher than in longitudinal direction because of formation of several plastic hinges and that the ultimate displacement and the energy absorbtion capacity are enhanced by using continuous longitudinal bars instead of lap-splice ones. And it is confirmed that relatively large amount of ductility can be achieved by providing sufficient lap-splice length and transverse reinforcements with end hook even if longitudinal bars are lap spliced in the base of pier.

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The Experimental Study on Seismic Performance of RC Bridge Columns with Longitudinal Steel Lap Splice (겹침이음 상세에 따른 철근콘크리트 교각의 내진성능에 관한 실험적 연구)

  • 석상근;손혁수;정철호;이재훈
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.553-558
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    • 2001
  • Recent destructive seismic events demonstrated the importance of mitigating human casualties and serious property damages in design and construction of structures. The Korean Bridge Design Specifications (1992) adopted seismic design requirements based on the AASHTO specification, and minor modification was made in 2000. The longitudinal steel connection of reinforced concrete bridge column is sometimes practically unavoidable. The longitudinal reinforcement details affect seismic performance such as flexural failure and shear failure. This research aims to develop longitudinal steel connection details with confinement steel by experimental study for seismic performance of reinforced concrete bridge columns. Quasi-static test under three different axial load levels was conducted for 12 spiral column specimens. All the column specimens had the same aspect ratio of 3.5. The column specimens were transversely reinforced with spiral and with five different longitudinal steel connection. The final objective of this study is to suggest appropriate longitudinal reinforcement connection details for the limited ductility design concept and improve construction quality.

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An Analytical Study on Influence of Longitudinal Stiffeners on Seismic Performance of Circular Steel Columns (수직보강재가 원형강기둥의 이력거동에 미치는 영향에 대한 해석적 연구)

  • Jang, Gab-Chul;Chang, Kyong-Ho
    • Journal of Korean Association for Spatial Structures
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    • v.7 no.1
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    • pp.63-70
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    • 2007
  • To improve the land use of urban, Construction of the circular steel column is required recently. The circular steel columns have a advantage for improving a load carrying rapacity as wall as reducing a effective section area. However, the circular steel columns under service load, such as earthquake, shows a tendency to cause local buckling and large deformation. To prevent these phenomena, use of longitudinal stiffeners is considered. The application of longitudinal stiffeners at the circular steel columns is expected to increase a load carrying capacity, buckling strength and seismic performance of circular steel column. However, increasing the loading carving rapacity of buckling which constructed the longitudinal stiffeners, was not investigated yet. Therefore it needs study on effect of longitudinal stiffener in pipe-section steel pier. In this study, the load rallying capacity of buckling of steel pier was investigated by using elastic-plastic finite element analysis considered geometrical and material non-linearity. Also, this study investigated the effect of longitudinal stiffeners on loading carrying capacity of buckling and the relationship between width and thickness of longitudinal stiffeners. And also, a Influence of longitudinal stiffeners on seismic performance of circular steel columns was investigated by numerical analysis

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Study on midtower longitudinal stiffness of three-tower four-span suspension bridges with steel truss girders

  • Cheng, Jin;Xu, Hang;Xu, Mingsai
    • Structural Engineering and Mechanics
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    • v.73 no.6
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    • pp.641-649
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    • 2020
  • The determination of midtower longitudinal stiffness has become an essential component in the preliminary design of multi-tower suspension bridges. For a specific multi-tower suspension bridge, the midtower longitudinal stiffness must be controlled within a certain range to meet the requirements of sliding resistance coefficient and deflection-to-span ratio. This study presents a numerical method to divide different types of midtower and determine rational range of longitudinal stiffness for rigid midtower. In this method, influence curves of midtower longitudinal stiffness on sliding resistance coefficient and maximum vertical deflection-to-span ratio are first obtained from the finite element analysis. Then, different types of midtower are divided based on the regression analysis of influence curves. Finally, rational range for longitudinal stiffness of rigid midtower is derived. The Oujiang River North Estuary Bridge which is a three-tower four-span suspension bridge with two main spans of 800m under construction in China is selected as the subject of this study. This will be the first three-tower four-span suspension bridge with steel truss girders and concrete midtower in the world. The proposed method provides an effective and feasible tool for engineers to design midtower of multi-tower suspension bridges.

Seismic Performance of RC Bridge Columns with Longitudinal Steel Lap Splice (겹침이음 상세에 따른 철근콘크리트 교각의 내진성능)

  • 이재훈;손혁수;석상근;정철호
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • pp.345-352
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    • 2001
  • Recent destructive seismic events demonstrated the importance of mitigating human casualties and serious property damages in design and construction of structures. The Korean Bridge Design Specifications (1992) adopted seismic design requirements based on the AASHTO specification, and minor modification was made in 2000. The longitudinal steel connection of reinforced concrete bridge column is sometimes practically unavoidable. The longitudinal reinforcement details affect seisimc performance such as flexural failure and shear failure. This research aims to develop longitudinal steel connection details with confinement steel by experimental study for seismic performance of reinforced concrete bridge columns. Quasi-static test under three different axial load levels was conducted for 12 spiral column specimens. All the column specimens had the same aspect ratio of 3.5. The column specimens were transversely reinforced with spiral and with five different longitudinal steel connection. The final objective of this study is to suggest appropriate longitudinal reinforcement connection details for the limited ductility design concept and improve construction quality.

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Web bend-buckling strength of plate girders with two longitudinal web stiffeners

  • Kim, Byung Jun;Park, Yong Myung;Kim, Kyungsik;Choi, Byung H.
    • Structural Engineering and Mechanics
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    • v.69 no.4
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    • pp.383-397
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    • 2019
  • More than one longitudinal web stiffener may be economical in the design of plate girders that have considerably high width-to-thickness ratio of webs. In this study, the bend-buckling strength of relatively deep webs with two horizontal lines of flat plate-shaped single-sided stiffeners was numerically investigated. Linear eigenvalue buckling analyses were conducted for specially selected hypothetical models of stiffened web panels, in which top and bottom junctions of a web with flanges were assumed to have simply supported boundary conditions. Major parameters in the analyses were the locations of two longitudinal stiffeners, stress ratios in the web, slenderness ratios and aspect ratios of web panels. Based on the application of assumptions on the combined locations of the two longitudinal web stiffeners, simplified equations were proposed for the bend-buckling coefficients and compared to the case of one longitudinal stiffener. It was found that bend-buckling coefficients can be doubled by adopting two longitudinal stiffeners instead of one longitudinal stiffener. For practical design purposes, additional equations were proposed for the required bending rigidity of the longitudinal stiffeners arranged in two horizontal lines on a web.

An Experimental Study on Behavior of Field Splice Joints of Longitudinal Rib in Orthotropic Steel Decks (강상판 종리브 현장연결부의 실험적 거동 특성)

  • Choi, Dong Ho;Choi, Hang Yong
    • Journal of Korean Society of Steel Construction
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    • v.13 no.6
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    • pp.621-629
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    • 2001
  • This study consists of static and fatigue tests to evaluate the behavior on the field splice joint of longitudinal rib in orthotropic steel deck specimens. Specifically, static and influence surface tests are performed for the stress distribution at the scallop area and high-strength bolt connection of longitudinal rib to examine the existence of handhole cover plate and the effect of eccentric loads. The ultimate strength of the field splice joint of longitudinal rib is obtained. In fatigue tests, cracks are observed at the scallop in the lower level test and the catastrophic failure of longitudinal rib is occurred following the failure of handhole cover plate in the higher level test. This study gives a basis for the better understanding of the field splice joint of longitudinal rib.

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The Analytical Study on the Cause of Fatigue Damage and the Improvement of Fatigue Performance for Orthotropic Steel Deck (강바닥판 피로손상 원인규명 및 피로성능 개선에 관한 해석적 연구)

  • Kyung Kab-Soo;Shin Dong-Ho;Kim Kyo-Hoon
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.647-654
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    • 2006
  • In orthotropic steel decks, it is likely to have defects due to fatigue damages because most of structural joints(the connection of longitudinal rib and transverse rib, the connection of deck plate and longitudinal rib) are connected by welds. However. orthotropic steel decks have many advantages. such as light weight and reduction of construction time. in comparison with concrete decks. Therefore. they are mostly used in long-span bridges and urban highway bridges. This study consists of the cause identication of fatigue damage and the suggestion of rational thickness on deck plate about the connection of deck plate and longitudinal rib. The results are as follows: fatigue damage cause at the connection of deck plate and longitudinal rib is local deformation in deck plate. And, rational thickness of deck plate is 16mm thickness.

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Experimental Study on Hydrofoil Arrangement and Longitudinal Moment Characteristics for Navigation Safety of High Speed Craft (고속선 운항 안정성을 위한 수중익 배치 및 종모멘트 특성에 관한 실험적 연구)

  • Park, Hwa-Pyeong;Kim, Sang-Hyun;Lim, Geun-Nam
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.4
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    • pp.443-450
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    • 2014
  • In this study, we have discussed about the effect of hydrofoil arrangement and longitudinal moment characteristic on longitudinal motion stability of fully-submerged hydrofoil by the experiment of tandem hydrofoil model. First of all, tandem hydrofoil model that has canard wing arrangement has been made and characteristics of lift force and drag force by performing the lift force and drag force measuring experiment has also been estimated. Besides, tandem hydrofoil model's wing arrangement which has the initial stability and self stability of longitudinal motion has also been determined. In longitudinal stability experiment of tandem hydrofoil model, the motion characteristic of pitch and heave and the longitudinal stability of foil borne condition by variation of self stability of longitudinal moment and longitudinal distance are estimated. The result from the experiment and it's important conclusion can be described as below; Increase the self stability for longitudinal moment, the higher self stability for pitch motions in a constant pitch angles. By increasing the self stability for longitudinal moment, the range of fluctuation of pitch motion and heave motion for pitch angle also will change relatively small and longitudinal stability is excellent. Lastly, when the lift force of hydrofoil is remain constants, we can conclude that securing the enough self stability for longitudinal moment is essential for stable foil borne condition of tandem hydrofoil.