Abstract This work reports a numerical investigation on the distortional buckling/post-buckling behaviors, ultimate strength and Direct Strength Method (DSM) design of cold-formed steel S-beams, commonly used in industrial rack systems. The analyzed beams are single-span, under uniform bending, exhibiting two different end support conditions and 5 cross-sections dimensions. The post-buckling equilibrium paths and ultimate moments are obtained from shell finite element non-linear analysis through the software ANSYS. The reported results evidenced that current codified DSM distortional curve is unable to provide safely strength predictions for the selected beams.

This paper presents the results of an experimental investigation aiming at determining the mechanical properties of Glass Fiber Reinforced Polymer (GFRP) element produced by the Brazilian industry to classify it for structural applications.. The material samples used in this work were (i) prepared in accordance to ABNT-NBR15708:2011 recommendations, (ii) extracted from web and flange parts of different geometries of one standard H-shaped GFRP single profile, (iii) 2D fiber-reinforced fibrous and (iv) exhibited fibers' orientation on the longitudinal/pultrusion direction. A fairly extensive experimental program was carried out to cover both stiffness and strength structural characteristics of GFRP element, comprising the following mechanical failures modes: (i) direct tension and compression, (ii) two-point flexural bending, (iii) pin-bearing pushed-out and (iv) interlaminar shear deformation. Based on the obtained results, it was possible to conclude that the GFRP element analyzed displays structural classification compatible to E17 class mechanical requirement.

Considering the technical-scientific advances of recent years in the steel construction industry, there is a strong trend for the increasing use of cold-formed steel members in civil construction, due to several advantages such as cost and versatility of fabrication and erection. However, there is need for further study concerning the behavior of this type of steel when subjected to fire conditions. This work deals with the experimental characterization of cold-formed steel at high temperatures. It is recognized that the reduction factors of the mechanical properties applicable to hot-rolled steel members do not remain valid for cold-formed ones. In the case of the European Code, cold-formed members are treated in the same way of hot-rolled or welded thin-walled sections (i.e., class 4), the only differences in relation to the other (class 1, 2 or 3) consisting (i) the definition of the yield strength and (ii) the corresponding reduction factors (shown in Table E.1 of appendix E of EC3-1.2:2005). In this context, coupon tensile tests were carried out according to recommendations proposed by AS 2291:2007 standard for ZAR-345 (ABNT NBR 7008-1:2012) (or ASTM A653-2011- SS50(340)C1, equivalent). The variation of the constitutive relations (stress-strain-temperature curves) was measured for different uniform temperatures, ranging from 20 ºC (ambient) to 100-200-300-400-500-600 ºC. The obtained experimental results indicate a clear distinction with the models proposed by other authors as well as specifications of EC3-1.2:2005.

This paper presents the application of a proposed numerical approach, denoted as SAAFE Program (System for Advanced Analysis for Fire Engineering), developed to provide an inelastic analysis of steel and composite (steel-concrete) 2D semi-rigid framed-structures under fire conditions. The proposed structural model allows an accurate description of the structural non-linear response, with less computational effort when compared to the general FEM formulation. The method, although similar in concept to earlier plastic-hinge approaches, differs with regards to numerical implementation methodology and precision. The proposed plastic-hinge model is formulated in a succinct format based on the following characteristics: (i) a refined plastic lumped formulation with interaction surfaces, (ii) a tangent modulus model which includes both gradual inelastic loss of stiffness and ultimate strength of column members, (iii) a second-order large-displacement formulation, based on the Stability Functions concept, (iv) non-homogeneous temperature distribution over the cross-section, (v) a connection semi-rigid model. Obtained results for connection model calibration examples are compared to reported experimental data, showing reasonable agreement. In addition, results of a proposed case-of-study demonstrate the efficiency and robustness of the SAAFE model to perform inelastic analysis semi-rigid members, outlining the advantage of considering advanced analysis in the current fire-design practice of structures.

Apresenta-se, nesse trabalho, um estudo comparativo sobre as recomendações das normas brasileiras para projeto de edifícios de aço sob condições de incêndio. Avalia-se o comportamento estrutural de uma edificação de 11 andares sob diferentes cenários de exposição ao fogo, levando-se em consideração dois métodos analíticos de dimensionamento: simplificado e avançado. No primeiro, a capacidade da edificação é determinada a partir de expressões simplificadas, formuladas com base na teoria elástica. No segundo, o comportamento não-linear inelástico é simulado por meio de um modelo computacional, programa SAAFE (Sistema de Análise Avançada de Fogo em Estruturas), desenvolvido com base no Método das Rótulas Plásticas. A variação de temperatura, determinada em função do tempo decorrido do incêndio postulado, é levada em consideração nas análises estruturais desenvolvidas. Os resultados obtidos, nesse estudo, contribuem para avaliação de modelos simplificados para análise de estruturas de aço sob condições de incêndio, tendo em vista o atual processo de revisão da ABNT NBR 14323:1999.

This paper presents the results of a comparative study of steel-structured buildings built according to Brazilian standards and their behavior when exposed to fire. An eleven-story building, exposed to different fire conditions was analyzed using both simple and advanced dimensioning analytical methods. The simple approach determines, by means of analytical expressions, the ultimate strength capacity in an elastic domain. The advanced approach uses a numerical tool, Program SAAFE (System for Advanced Analysis of Fire Engineering), developed on the basis of the plastic-hinge theory, which is applied to perform the inelastic analysis of the proposed steel-framed structure under fire conditions. The obtained results are contrasted, taking into account the proposed regulations of the new Brazilian code for steel buildings, making it possible to outline the advantages of considering steel ductility in the current design practice for steel structures under fire conditions.

Apresenta-se, nesse trabalho, um modelo numérico computacional para investigação do comportamento de estruturas metálicas aporticadas em situações de incêndio. A análise é dividida em duas etapas, Térmica e Estrutural, respectivamente associadas à determinação do campo não-uniforme de temperaturas e da resposta estrutural sob ação do fogo. Os limites de resistência estrutural, relacionados com o tempo crítico de resistência ao fogo, são estimados por meio de modelo refinado de rótulas plásticas, permitindo-se considerar, de forma computacionalmente eficiente, os efeitos inelásticos de material e mudança de geometria. Resultados numéricos obtidos pelo modelo implementado, para um edifício de 4 andares, são apresentados e criticamente comparados com aqueles gerados pelo programa SAFIR, permitindo-se concluir sobre a aplicabilidade do modelo proposto.

A numeric computational model is presented in this paper to investigate the behaviour of steel-framed structures under fire conditions. The analysis methodology is divided into two main parts, related to thermo and mechanical evaluations, respectively associated to the determination of nonuniform temperature range and structural response under fire action. The structural limits, related to the ultimate critical resistance time, are evaluated by means of a second-order refined plastic-hinge model, being allowed the consideration of inelastic effects resulting from the material and geometrical changing in configuration, in a computationally efficient way. Numerical results obtained from the implemented model for a 4-story building frame, are presented and critically compared to those from the FEM program SAFIR, determining the applicability of the proposed analysis model.