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Integral Abutment Bridge behavior under uncertain thermal and time-dependent load
Kim, WooSeok,Laman, Jeffrey A. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.1
Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.
Tunable functionalization of graphene nanosheets for graphene-organic hybrid photodetectors
Kim, Seong Jun,Song, Wooseok,Kim, Sungho,Kang, Min-A,Myung, Sung,Sook Lee, Sun,Lim, Jongsun,An, Ki-Seok IOP 2016 Nanotechnology Vol.27 No.7
<P>Graphene-organic hybrid thin films are promising candidates for use as advanced transparent electrodes and high-performance photodetectors. In this work, we fabricated hybrid thin film structures consisting of graphene and either tetraphenyl-porphyrin (H<SUB>2</SUB>TPP) or metalloporphyrins such as aluminum (III) tetraphenyl-porphyrin (Al(III)TPP) and zinc tetraphenyl-porphyrin (ZnTPP). The optical and electrical characteristics of ultrathin photodetectors based on the graphene-organic hybrid layers were subsequently evaluated. A hybrid deposition system capable of both thermal evaporation and vapor phase metalation was employed to synthesize the tunable metalloporphyrin-based thin films. As a proof of concept, we successfully fabricated various graphene-based photodetectors via <I>the simple and efficient vapor-phase metalation of porphyrin</I>. This work may facilitate the development of new architectures for flexible graphene-organic devices.</P>
Strengthened and flexible pile-to-pilecap connections for integral abutment bridges
WooSeok Kim,Jaeha Lee,Kyeongjin Kim,Soobong Park,정유석 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.4
Pile-to-pilecap connection performance is important as Integral abutment bridges (IABs) have no expansion joints and their flexible weak-axis oriented supporting piles take the role of the expansion joint. This connection may govern the bridge strength and the performance against various lateral loads. The intention of this study is to identify crack propagation patterns when the pile-to-pilecap connection is subjected to lateral loadings and to propose novel connections for improved performance under lateral loadings. In this study, eight different types of connections were developed and modeled, using Abaqus 6.12 to evaluate performances. Three types were developed by strengthening the connections using rebar or steel tube: (i) PennDOT specification; (ii) Spiral rebar; and (iii) HSS tube. Other types were developed by softening the connections using shape modifications: (i) cylindrical hole; (ii) reduced flange; (iii) removed flange; (iv) extended hole; and (v) slot hole connection types. The connections using the PennDOT specification, HSS tube, and cylindrical hole were shown to be ineffective in the prevention of cracks, resulting in lower structural capacities under the lateral load compared to other types. The other developed connections successfully delayed or arrested the concrete crack initiations and propagations. Among the successful connection types, the spiral rebar connection allowed a relatively larger reaction force, which can damage the superstructure of the IABs. Other softened connections performed better in terms of minimized reaction forces and crack prevention.
Comparative study of integral abutment bridge structural analysis methods
Kim, WooSeok,Laman, Jeffrey A.,Jeong, Yoseok,Ou, Yu-Chen,Roh, Hwasung Canadian Science Publishing 2016 Canadian journal of civil engineering. Revue canad Vol.43 No.4
<P> The primary goal is to accurately predict long-term integral abutment bridge (IAB) responses under thermal loads by applying available numerical modeling techniques developed on the basis of a long-term monitoring of in-service IABs. Considered methodologies are: (1) free expansion; (2) empirical approximate; (3) two-dimensional (2D) static analysis; (4) 2D time-history; (5) three-dimensional (3D) static analysis; and (6) 3D time-history. Specific IAB responses evaluated for the comparison are: girder axial force and moment, pile shear, moment, and displacement. The results indicate that the substructure responses predicted by all six analyses are reasonably comparable. However, the superstructure responses predicted by a 2D analysis are significantly different than predictions by a 3D analysis. Both 2D and 3D static analysis predictions tended to form boundaries for 2D and 3D time-history analysis. Therefore, this study concludes that a 3D time-history analysis is preferred for long-term, superstructure response predictions; all 2D and 3D static and time-history analyses are acceptable for substructure response predictions. </P>
Surface and Internal Reactions of ZnO Nanowires: Etching and Bulk Defect Passivation by H Atoms
Kim, Wooseok,Kwak, Geunjae,Jung, Minbok,Jo, Sam K.,Miller, James B.,Gellman, Andrew J.,Yong, Kijung American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.30
<P>Reactions of ZnO nanowires (NWs) with atomic hydrogen were investigated with temperature-programmed desorption (TPD) mass spectrometry, scanning electron microscopy, and photoluminescence (PL) spectroscopy. During TPD, molecular H<SUB>2</SUB>, H<SUB>2</SUB>O, and atomic Zn desorbed from ZnO NWs pretreated with atomic H at 220 K. Three distinct H<SUB>2</SUB> TPD peaks, two from surface H states and one from a bulk H state, were identified. The TPD assignment of the bulk H state was corroborated by significantly suppressed emission at 564 nm and enhanced emission at 375 nm in PL experiments. Etching of ZnO NWs by atomic H was confirmed by desorption of molecular H<SUB>2</SUB>O and atomic Zn in TPD and by electron microscopic images of H-treated ZnO NWs. A mechanistic model for underlying H/ZnO NW reactions is proposed and discussed.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-30/jp304191m/production/images/medium/jp-2012-04191m_0006.gif'></P>