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Couto C.,University of Aveiro | Vila Real P.,University of Aveiro | Lopes N.,University of Aveiro | Zhao B.,Cticm Center Technique Industriel Of La Construction Metallique
Journal of Constructional Steel Research | Year: 2015

In this work, the resistance of slender I-shaped cross-sections, where local buckling has a predominant role in the ultimate capacity, is investigated at elevated temperatures. A numerical study considering several cross-sections submitted to compression or bending about the major-axis is performed using a finite element analysis software. The results are compared with the existing formulae available in Part 1.2 of Eurocode 3 showing that they need to be improved. For Class 3 cross-sections, it is observed that the existing rules lead to unsafe results because local buckling occurs at elevated temperatures prior to the development of the elastic bending resistance or the gross cross-section compression resistance. For Class 4 cross-sections, the results show that these rules are not adequate because it is recommended for the design yield strength of steel the use of the 0.2% proof strength even if the cross-section has plates not prone to local buckling. A new methodology to account for the local buckling in steel I-sections at elevated temperatures is presented based on the expressions previously developed by the authors to calculate the effective width of thin plates at elevated temperatures. According to this new methodology, an effective cross-section is calculated for Class 3 and Class 4 cross-sections and the yield strength at 2% total strain is used for Class 4 cross-sections as recommended by Eurocode 3 for the other section classes. Finally, it is demonstrated that this methodology leads to good results when compared against numerical and experimental results. © 2015 Elsevier Ltd. Source


Couto C.,University of Aveiro | Vila Real P.,University of Aveiro | Lopes N.,University of Aveiro | Zhao B.,Cticm Center Technique Industriel Of La Construction Metallique
Thin-Walled Structures | Year: 2014

The local buckling of thin steel plates exposed to fire is investigated using a finite element model. The reduction of strength and stiffness that occurs at elevated temperatures needs to be taken into account in the design, as it increases the susceptibility to local buckling of the plates thus affecting their load carrying capacity. The obtained results show that the current existing design method of Eurocode 3 to take into consideration the local buckling in the calculation of the ultimate strength of steel thin plates at elevated temperatures needs to be improved. These methods are based on the same principles as for normal temperature but using for the design yield strength of steel, at elevated temperatures, the 0.2% proof strength of the steel instead of its strength at 2% total strain as for the cases where the local buckling is not limiting the ultimate strength of the plates. This consideration, however, leads to an inconsistency if cross-sections are composed simultaneous of plates susceptible and not to local buckling. To address this issue, new expressions for calculating the effective width of internal compressed elements (webs) and outstand elements (flanges) are proposed, which have been derived from the actual expressions of the Part 1.5 of the Eurocode 3 and validated against numerical results. It is also demonstrated that it is not necessary to use for the yield stress at elevated temperatures the 0.2% proof strength of the steel instead of the yield stress at 2% total strain, given that the necessary allowances are considered in these new expressions, thus leading to a more economic design. © 2014 Elsevier Ltd. Source


Couto C.,University of Aveiro | Vila Real P.,University of Aveiro | Lopes N.,University of Aveiro | Zhao B.,Cticm Center Technique Industriel Of La Construction Metallique
Journal of Constructional Steel Research | Year: 2016

The behaviour of laterally restrained steel beam-columns with slender cross-sections (Class 4) where local buckling occurs under fire situation is numerically investigated. Although recommendations are given in Eurocode to address the local buckling for the case of fire, few studies address its influence at elevated temperatures, and more particularly its influence on the load bearing capacity of laterally restrained beam-columns, which represents an unknown safety level for the Eurocode procedures. As a primary objective of this study, the level of accuracy and safety of simplified methods of Eurocode 3 is studied based on extensive numerical investigation of several member lengths, different bending moment distributions and load ratios for various cross-sections and considering different heating temperatures. Local and global geometrical imperfections as well as residual stresses have been included in the numerical simulations. It is concluded that the Eurocode procedures lack consistency and the capacity of laterally restrained beams-columns is overestimated in many cases due to local buckling. Therefore, modifications to the current design methodology are proposed in this study leading to better estimation of the overall capacity of the laterally restrained beam-columns in case of fire, and finally, improved safety and consistency is achieved. © 2016 Elsevier Ltd. All rights reserved. Source


Couto C.,University of Aveiro | Vila Real P.,University of Aveiro | Lopes N.,University of Aveiro | Zhao B.,Cticm Center Technique Industriel Of La Construction Metallique
Engineering Structures | Year: 2016

An extensive numerical study is performed to investigate the lateral-torsional buckling of steel beams with slender cross sections for the case of fire. The influence of local buckling is analysed, and the numerical results are compared to the simplified design methods of Part 1-2 of Eurocode 3 for the case of beams with Class 1 and 2 cross sections. The actual provisions of Eurocode 3 Part 1-2 are demonstrated to be unreliable. A parametric study is carried out to investigate the influence of several parameters on the resistance of laterally unrestrained steel beams with slender cross sections for the case of fire: the effective section factor, temperature, steel grade, depth-to-width ratio (h/b) and residual stresses. Based on the parametric study, a proposal for a new design curve is made for beams with slender cross sections for the case of fire, taking into account the influence of local buckling by grouping the response of beams into different ranges of effective section factors. The capacity predicted by the simplified methods using the proposed design curve leads to an improved yet safe design method compared to the results of the finite element analysis. © 2015 Elsevier Ltd. Source


Galea Y.,Cticm Center Technique Industriel Of La Construction Metallique | Martin P.-O.,Cticm Center Technique Industriel Of La Construction Metallique
Journal of Constructional Steel Research | Year: 2010

The design of longitudinally stiffened plates under direct stresses according to Eurocode 3 Part 1.5 implies the calculation of the global critical buckling stress σ c r, p, a specific stress, which is difficult to define and assess. After analysing and clarifying this concept, and on the assumption that the global mode corresponding to this stress is associated with the buckling of the stiffeners in the elastic continuum of the plate, this article proposes a general method for assessment of σ c r, p based on the use of a software which calculates the critical buckling stress of plates. This software, EBPlate, has been developed by the authors, is free of charge and can be downloaded from the internet. © 2010 Elsevier Ltd. All rights reserved. Source

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