Extension of the Overall Interaction Concept to steel open sections and members

La capacité résistante des sections en I en acier laminées à chaud et soudées est étudiée en profondeur dans cette thèse. La résistance en section influencée par le voilement local ainsi que la résistance d'une barre soumise au flambement sont étudiées. Les normes de dimensionnement actuelles reposent sur le principe de classification des sections et la méthode des largeurs efficaces (E.W.M.), ce qui peut conduire à des prédictions de résistance discontinues et des calculs longs et fastidieux, en particulier dans le cas de sections ouvertes non-symétriques ou soumises à des cas de chargement combinés. En raison de ces lacunes, une méthode de conception plus économique et plus simple, l'Overall Interaction Concept (O.I.C.), a été développé. L'O.I.C., qui repose sur l'interaction résistance-instabilité bien connue avec une définition de l'élancement relatif généralisé, abandonne le concept de classification des sections et l'E.W.M., et traite toutes les géométries de section de manière similaire, pour les sections et les membres, et pour des cas de charge simples ou combinés. Compte tenu de ces avantages, le domaine d'application de l'O.I.C. est ici étendu à la conception de profilés en I en acier laminés à chaud et soudés. L'O.I.C. est élargi au Chapitre 1 pour la conception de profilés en I laminés à chaud et soudés dans des situations de chargement combinées ; Le Chapitre 2 se concentre sur la conception de sections en I mono-symétriques sous des cas de charge simples, et le Chapitre 3 traite de l'application de l'O.I.C. au cas des éléments comprimés influencés par les instabilités couplées locales-globales. Dans chaque chapitre, les détails des modèles numériques ainsi que les résultats de validation sont fournis. Des études paramétriques numériques approfondies par le biais de modèles d'éléments finis validés vis-à-vis de résultats expérimentaux sont menées pour étudier l'influence de différentes nuances d'acier, formes de section et divers cas de charge sur la résistance ultime. Sur la base des résultats des éléments finis, des expressions de conception basées sur l'O.I.C. sont proposées. Les prédictions de résistance de l'Eurocode 3, des normes américaines et de la proposition O.I.C. sont comparés aux résultats numériques de référence. Dans l'ensemble, il est démontré que l'O.I.C. délivre des résistances continues et beaucoup plus précises que celles prédites par les normes existantes. Les propositions faites ici serviront de base au développement d'une approche O.I.C plus générale, pour d'autres formes de sections transversales et divers procédés de fabrication.The resistance capacity of hot-rolled and welded steel I-sections are deeply investigated in this thesis. Both cross-section resistance influenced by local buckling and member resistance influenced by global buckling are considered. Current code-oriented design relies on the traditional cross-section classification system and the Effective Width Method (E.W.M.), which may result in discontinuous resistance predictions and lead to long and tedious design calculation processes, especially when it comes to non-doubly symmetric open sections or to combined loading cases. Due to these shortcomings, a more economic and simple design method, the Overall Interaction Concept (O.I.C.), was developed. The O.I.C., which is based on the well-established resistance-instability interaction with a definition of generalised relative slenderness, abandons the cross-section classification concept and the E.W.M. and deals with all cross-section shapes in a similar way for both sections and members, under simple or combined loading cases. Considering these advantages, an extension of its application scope is expected. The range of application of the O.I.C. in this thesis is extended to cover the design of hot-rolled and welded steel I-sections. The O.I.C. is developed in Chapter 1 for the design of hot-rolled and welded I-sections under combined loading situations; Chapter 2 focuses on an O.I.C.-based design of mono-symmetric I-sections under simple load cases and Chapter 3 discusses the application of the O.I.C. to the resistance of compression members as influenced by local-global coupled instabilities. In each chapter, the details of numerical models as well as validation results are provided. Extensive numerical parametric studies through test-validated finite element models are carried out to investigate the influence of different steel grades, section shapes and various load cases on ultimate resistance. Based on the finite element results, O.I.C. design expressions are proposed. Resistance predictions from Eurocode 3, the American Standards and the proposed O.I.C. approach are compared to the reference numerical results. Overall, it is evidenced that the proposed O.I.C. approach provides more continuous and significantly more accurate resistance predictions than existing design standards. The proposals from this research shall serve as a basis for the derivation of a more general O.I.C. approach to other cross-section shapes and manufacturing processes

Robust approach for variable selection with high dimensional Logitudinal data analysis

This paper proposes a new robust smooth-threshold estimating equation to select important variables and automatically estimate parameters for high dimensional longitudinal data. A novel working correlation matrix is proposed to capture correlations within the same subject. The proposed procedure works well when the number of covariates p increases as the number of subjects n increases. The proposed estimates are competitive with the estimates obtained with the true correlation structure, especially when the data are contaminated. Moreover, the proposed method is robust against outliers in the response variables and/or covariates. Furthermore, the oracle properties for robust smooth-threshold estimating equations under "large n, diverging p" are established under some regularity conditions. Extensive simulation studies and a yeast cell cycle data are used to evaluate the performance of the proposed method, and results show that our proposed method is competitive with existing robust variable selection procedures.Comment: 32 pages, 7 tables, 5 figure

Multidimensional Meaning, Existing Problems and Optimization Path for the Management of Coaches in Chinese University Basketball League

A well-managed level of competition and training by coaches is an essential catalyst for the achievement of talent development goals in the Chinese University Basketball League. This study compares the multi-dimensional meaning of the management of coaches in the Chinese College Basketball League, and analyses the existing management problems based on the SMART principle, the 4P model of human resource management, and the GROW model, to propose feasible measures to optimize the management of coaches. This research aims to provide a theoretical reference and practical basis for the improvement of the management and to provide a driving force for the realization of the long-term goal of talent training in the Chinese University Basketball League

Thoughts and Targeted Initiatives for the Nurturing of Youth Football Reserve Talents in China

In order to strengthen the foundation for the cultivation of Chinese youth football reserve talents, a systematic review of the current ideas on the development of Chinese youth football reserve talents is conducted, and based on this, a targeted response is derived from it. The study concludes that the cultivation of Chinese youth football reserve talents should be based on the country and the world in a hierarchical and directional manner, with emphasis on the integration of the excellent Chinese traditional culture at the primary school level and the absorption of outstanding foreign achievements and experience at the secondary school level, and the promotion of three types of policy tools, namely the supply side, the demand side and the environment side, to form a protective synergy for the cultivation of youth football reserve talents, so as to build an effective and long-term development strategy that will benefit the present and the future. The aim is to speed up the construction of a reserve pool of Chinese youth football talents, improve the international competitiveness and influence of Chinese football, and contribute to the early realisation of the Chinese football dream

Physical, physiological demands and movement profiles of elite men’s field hockey games

The aim of this study was to investigate physical demands, physiological demands, and movement profiles of different positions across four quarters in professional men’s field hockey games. Eighteen professional male field hockey players participated in the study, and data were collected in eleven official matches. Players wore global positioning system units and heart rate monitors to collect physical, physiological, and movement profile data. Defenders had significantly higher absolute total distance covered, player load, acceleration and deceleration count, and forward-backward initial movement analysis (IMA) count, but lower high speed running distance, compared with midfielders and forwards (p<.05). However, when using relative metrics (normalised by playing time), defenders had the lowest physical and physiological outputs, and forwards had the highest (p<.05). Total distance covered per minute, high-speed running distance per minute, player load per minute, acceleration and deceleration count per minute, and repeated high-intensity efforts per minute were all significantly higher in quarter 1 than in other three quarters (p<.05). The percentages of linear running and non-linear dynamic movement duration decreased quarter by quarter. Modified training impulse per minute reached its peak in quarter 2 (p<.05). It was concluded that defenders had the highest volume in terms of the game demands due to their high playing minutes; however, they had the lowest relative volume compared with the other two positions. Forwards had the highest linear running intensity, while midfielders were required to perform more multi-directional, non-linear movements. Quarter 1 was the most active quarter and players became fatigued in quarter 2. IMA counts were not sensitive to fatigue compared to movement profile and modified training impulse variables

Facile synthesis of CdS nanocrystals using thioglycolic acid as a sulfur source and stabilizer in aqueous solution

A novel method has been developed for the synthesis of CdS nanocrystals (NCs) using thioglycolic acid (TGA) as a sulfur source and stabilizer with the presence of hydrogen peroxide in an aqueous medium. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The results indicate that the product was of zinc-blend crystal structure in a sphere-like shape. The room-temperature luminescence spectra revealed that the emission peak of CdS NCs prepared in relatively short refluxing times (10-120 min) could be tuned from 518 nm to 610 nm, and the photoluminescence quantum yield of the as-prepared CdS NCs could reach as high as 12.6%. In addition, the mechanism of the CdS nanocrystals formation was preliminarily discussed.KEY WORDS: Chemical synthesis, CdS, Nanostructures, Optical properties, Photoluminescence spectroscopy Bull. Chem. Soc. Ethiop. 2011, 25(3), 393-398