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Extension of the Direct Strength Method to hot-rolled and welded H profile cross-sections Li, Yongzhen Doctoral thesis (2014) The cross-sectional capacity is limited by material yielding on one hand and local buckling on the other hand. Most current metallic structural design codes use the concept of section classification for ... [more ▼] The cross-sectional capacity is limited by material yielding on one hand and local buckling on the other hand. Most current metallic structural design codes use the concept of section classification for determining the section capacity of hot-rolled profiles. In this system, there exists a discontinuity between the classes 2 and 3 under pure bending load condition, while for the class 4, the effective width method (EWM) must be used to account for local buckling phenomenon. With the appearance of the more complex cross-sections, especially for thin-walled steel structures, the calculation using EWM becomes more and more intolerable and complicated. In order to overcome these difficulties when evaluating the cross-section strength, the alternative Direct Strength Method (DSM) approach, developed only for cold-formed thin-walled members, has gained importance over the last few years, and has been adopted by the North American and Australian standards for the design of cold-formed steel structural members recently. This thesis investigates the possibility to extend the DSM method to hot-rolled and welded structural steel members, and the objective is to derive a new formulation that would cover the whole field of section slenderness without section classification system used in Eurocode 3, using the same procedure for the DSM developed for cold-formed thin-walled steel structural members. Hot-rolled and welded H sections are mainly considered in this thesis. The DSM is premised on the assumption that the strength can be predicted from the yield strength to the elastic critical load ratio used in conjunction with a strength curve; i.e. the same concept than the one used in Eurocode 3, in terms of member buckling phenomenon. In the DSM approach applied for cold-formed thin-walled sections, local buckling and distortional buckling modes should be considered. For common hot-rolled or welded sections, only local buckling needs to be considered since distortional buckling does not occur for these sections. All available test results in literature are collected and evaluated with the current methods for calculating the cross-section resistance such as EWM, DSM, and the recent Continuous Strength Method (CSM). A short comparison is made and their domains of applicability are commented. A consistent approach has been adopted to develop numerical models for hot-rolled and welded sections subjected to compression and bending respectively. The FE model was built in FineLg and verified against test results of the “Semi-comp: Plastic member capacity of semi-compact steel sections - a more economic design” project, which was carried out earlier with the objective of improving the utilization of plasticity in rolled and welded sections with medium cross-section slenderness. Measured material and geometric properties, initial geometrical imperfections and residual stresses distributions have been highlighted. Once verified against the test results, the FE models have been used to carry out a parametrical study aimed at providing more FE results and highlighting the local buckling interaction between the webs and the flanges. All the experimental and FE numerical results constitute data base for the derivation of the new DSM curves. On the basis of Winter Formula for plate buckling and the generic DSM strength curve, different formulas are proposed for hot-rolled and welded H cross-sections under axial and bending load respectively. Also the statistical evaluation and safety study is conducted to obtain the safety factor γ_M, which is required for practical design. [less ▲] Detailed reference viewed: 71 (10 ULg)Extension of the DSM to welded H profile cross-sections Rossi, Barbara ; Li, Yongzhen in Research and Applications in Structural Engineering, Mechanics and Computation (2013) The objective of the paper is to assess the accuracy of current Direct Strength Method (DSM) equations applied to steel structural welded H shapes in axial compression. Commercialised hot-rolled H ... [more ▼] The objective of the paper is to assess the accuracy of current Direct Strength Method (DSM) equations applied to steel structural welded H shapes in axial compression. Commercialised hot-rolled H sections covering IPE, HE, HD, HL, HP, W and UB profiles and made of three grades (235MPa, 355MPa and 460MPa) were treated in (Li & Rossi 2012). This analysis focuses on welded sections made of the same three grades, including sections characterized by local buckling with a significant post-buckling reserve. The finite element model is described. Then, the results of a parametric analysis using the finite element model are re-ported. The codified resistances are also compared to the numerical results. For each cross-section, the recently developed analytical expressions provided in (Seif & Schafer 2010) for hot-rolled profiles are used to cal-culate the elastic cross-section local buckling stress. A comparison with CUFSM results is also reported. Then, the possibility to use the concept of DSM for the design of structural welded steel shapes is discussed. [less ▲] Detailed reference viewed: 34 (2 ULg)Finite element model for the extension of the direct strength method to hot-rolled profile cross-sections Li, Yongzhen ; Rossi, Barbara in Proceedings of the 12th Nordic Steel Construction Conference (2012, September 05) Abstract: In the present research, a geometrically and materially nonlinear analysis using the FE method has been conducted to evaluate the resistance of axially compressed hot-rolled H profile cross ... [more ▼] Abstract: In the present research, a geometrically and materially nonlinear analysis using the FE method has been conducted to evaluate the resistance of axially compressed hot-rolled H profile cross-sections. The FE model was firstly duly verified against experimental data and then used to carry a parametric analysis. The goal of the analysis is to propose a new Direct Strength Method (DSM) strength curve intended for calculating the resistance of non-compact and slender hot-rolled H profile cross-sections. [less ▲] Detailed reference viewed: 41 (11 ULg)Prediction of the cross-section capacity of hot-rolled profiles using the direct strength method and the continuous strength method Li, Yongzhen ; Rossi, Barbara in Chan, S.L.; Shu, G.P. (Eds.) Proceedings of seventh International Conference on Advances in Steel Structures (2012, April) Material yielding on one hand and local buckling on the other hand limit the cross-section capacity of steel structural members. Current structural design codes use the concept of cross-section ... [more ▼] Material yielding on one hand and local buckling on the other hand limit the cross-section capacity of steel structural members. Current structural design codes use the concept of cross-section classification to determine the cross-section resistance of hot-rolled profiles. In this system, the Effective Width Method (EWM) is employed to account for local buckling effects for slender, class 4, cross-sections. Alternative design methods for treatment of local buckling in metallic cross-sections have been proposed, including the Direct Strength Method (DSM), developed for cold-formed steel structural profiles, and, recently, the Continuous Strength Method (CSM). The DSM is based on the assumption that the strength can be predicted from the ratio of the yield strength to the elastic critical load in conjunction with a strength curve for the entire cross-section. Thus it is essentially an extension of the use of column curves for global buckling, but with application to local buckling instability. The CSM is a deformation-based design approach which is based on a continuous relationship between cross-sectional slenderness and cross-section deformation capacity and a rational exploitation of strain hardening. This paper is focused on the evaluation of the cross-sectional resistance of hot-rolled structural profiles. Test data from literature experimental programmes have been gathered and analysed to compare the predictions from the DSM and CSM design approaches. [less ▲] Detailed reference viewed: 96 (11 ULg)Extension of the Direct strength method to hot-rolled profiles cross-sections Li, Yongzhen ; Rossi, Barbara ; Jaspart, Jean-Pierre in 6th European Conference on Steel and Composite Structures : Eurosteel 2011, Budapest 30 October - 2 September 2011 (2011, September) Current metallic structural design codes use the concept of section classification for determining the section capacity of hot-rolled profiles. In this system, there exists a discontinuity between the ... [more ▼] Current metallic structural design codes use the concept of section classification for determining the section capacity of hot-rolled profiles. In this system, there exists a discontinuity between the classes 2 and 3, while for the class 4, the effective width method (EWM) must be used to account for local buckling phenomenon. In order to overcome the complicate and time consuming EWM for evaluating the strength, the alternative Direct Strength Method (DSM) approach, developed only for cold-formed thin-walled members, has gained importance over the last few years. The DSM is premised on the assumption that the strength can be predicted from the yield strength to the elastic critical load ratio in conjunction with a strength curve. The DSM has been advanced for calculating the strength of compression members over the past decades and in this paper, the extension of DSM to hot-rolled profiles cross-sections is investigated. Firstly, the methods for calculating the cross-section resistance such as EWM, DSM, and the recent Continuous Strength Method (CSM) are reviewed; a short comparison is made and their domains of applicability are commented. Secondly, a numerical model carried out in the frame of this research is described. The model was built in ABAQUS and verified against test results of the “Semi-comp: Plastic member capacity of semi-compact steel sections - a more economic design” project, which was carried out earlier with the objective of improving the utilization of plasticity in rolled and welded sections with medium cross-section slenderness. On the basis of these premises, the final goal of the project is detailed: to derive a new formulation that would cover the whole field of section slenderness (present class 1 to class 4), which can be seen as an extension of the so-called DSM approach. [less ▲] Detailed reference viewed: 99 (23 ULg)Intermittent thermal manipulations of broiler embryos during late incubation and their immediate effect on the embryonic development and hatching process. ; Li, Yongzhen ; et al in Poultry science (2011), 90(6), 1302-12 Intermittent high (+3 degrees C) and low (-3 degrees C) temperature treatments for 4 h on embryonic day (E) 16, E17, and E18 showed differential effects on embryonic metabolism, without influencing ... [more ▼] Intermittent high (+3 degrees C) and low (-3 degrees C) temperature treatments for 4 h on embryonic day (E) 16, E17, and E18 showed differential effects on embryonic metabolism, without influencing embryonic growth or hatchability. Embryos in the high-temperature group shifted to a more anaerobic metabolism, as indicated by a lower partial pressure of O(2) and a higher partial pressure of CO(2) in the air cell, lower blood pH, and higher lactic acid production. Three hours after the end of the high-temperature treatment, a decrease in metabolism was observed, as indicated by the lower partial pressure of CO(2) and higher partial pressure of O(2) in the air cell and increased plasma triglyceride levels. The embryos in the low-temperature group responded by temporarily slowing down their metabolism, especially the metabolism of carbohydrates and lipids, as indicated by altered air cell gases, a higher relative yolk weight, higher plasma triglyceride level, and higher liver glycogen level. Three hours after the end of the temperature treatment, the metabolism of embryos in the low-temperature treatment had increased to the level of the control temperature group. However, for both temperature treatments, during the hatching process, all the shortages and excesses created were restored to control levels, which would explain the lack of change in embryo growth and hatchability and the slight delay in the hatching process. These mild consequences of the intermittent temperature treatment indicate that the different metabolic shifts made by the embryos seem to be efficient in overcoming the challenges of the intermittent high- or low-temperature treatment during late incubation. [less ▲] Detailed reference viewed: 19 (5 ULg) |
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