Abstract The Direct Strength Method (DSM) is a well-known formulation presented in the Brazilian standard ABNT NBR 14762:2010, that estimates the strength capacity of cold-formed steel (CFS) members. However, this formulation requires the elastic critical buckling loads as point of departure, regarding local (L), distortional (D) and global (G) modes, which can be obtained by (i) elastic buckling analysis or (ii) available direct equations. The present study is dedicated to the development of a computer program, FStr Computer Application, with graphical user interface (GUI), in order to make the buckling analysis easier and approachable for both research activities and engineering design of thin-walled structures with arbitrary cross-sections (sections combining closed cells with open branches). The proposed application uses the Finite Strip Method (FSM), mainly focused on a simple and accessible GUI, which was implemented in the MATLAB App Designer. Validation of the FStr was performed with the help of examples of open and closed cross-sections and comparison with the results of acknowledged computer programs, such as CUFSM and GBTul, based respectively on FSM and GBT (Generalized Beam Theory), as well as analytical procedures for the case of the global buckling modes. Both, the critical buckling loads expressed by the computed signature curve and the correspondent critical buckling modes are compared, confirming the adequate performance of the proposed computational tool. As future research, the authors plan updates for the FStr Computer Application, including the computation of the buckling modal participation and the automatic strength predictions, based on the DSM-based design prescriptions.

Abstract Steel and concrete floor systems are widely applied for buildings and provide excellent structural response, optimized material consumption, reduced beam height, and improved bending strength and stiffness capacity. In recent years, many experimental investigations concerned with new alternatives addressed to efficient interaction between steel and concrete structures have been reported. In this context, the present study aims at investigating the behavior of a structural composite floor system composed of light cold-formed steel trusses and a partially pre-cast concrete slab, as well as developing an innovative solution for shear connectors. The referred to shear connector consists of Thin-Walled Perfobond (TWP) ribs, composed of 1.25mm thick cold-formed plates crossed by 4.2 mm reinforcing steel bars and connected to the truss chord by self-drilling screws. Preliminary results, based on experimental full-scale testing, indicate that the performance of the composite truss is adequate in terms of ultimate load and deformation capacity. Additionally, the investigation showed that traditional analytical solution is in good agreement with experimental results.

Abstract Buckling mode interaction in cold-formed steel (CFS) members must be considered for the structural design, which may lead to a significant reduction of the structural strength, usually recognized as erosion of the limit load. So far, the distortional-global (DG) buckling interaction is not covered by codes, e.g. Brazilian code NBR 14762:2010. The present investigation is aimed at the DG interaction of CFS lipped channel (LC) columns, which is the most usual section. The methodology evolves a parametric analysis, over a single LC column under DG buckling interaction. First, a study of initial geometric imperfection (IGI) sensibility is performed, with the purpose of understanding the influence of the IGI on the column’s behavior. Moreover, the parametric analysis is extended to a set of yielding stress and column lengths, to understand the ultimate load under different types of DG buckling interaction natures. Conclusions on this research have been shown that the actual global buckling equation from the Direct Strength Method is already suitable to cover the DG buckling interaction for the case of lipped channel columns.

Abstract This article reports the results of experimental tests conducted on built-up cold-formed steel (CFS) stub columns, composed of double lipped channel members connected with self-drilling screws, which will be applied as the chord members of laced columns. These experiments aim to quantify the effect of four distinct web fastener layouts on the composite action, including the ultimate strength, buckling modes and collapse mechanism for built-up CFS members. The tested stub columns are of 480mm length, double 88x86x40x42x12mm lipped channel cross-section and 0.8mm thickness. The built-up CFS lipped channel members were analyzed with help of the Generalized Beam Theory in order to identify their buckling loads and modes. The Direct Strength Method (DSM) was adopted to obtain the analytical strength of the built-up members, to be compared with the experimental results. The axially compressed built-up members displayed local and distortional buckling, negligible composite behavior and minor effect of number and distribution of the screws. The results indicate (i) inefficient behavior of the self-drilling screws for composite condition purposes and (ii) the DSM rules for non-composite CFS are able to estimate the ultimate strength of this type of built-up lipped channel section.

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.

O presente trabalho visa a fornecer uma contribuição ao estudo dos perfis formados a frio sob altas temperaturas, em conseqüência da deflagração de um incêndio. Especificamente, abordam-se assuntos inerentes ao fenômeno da transferência de calor em paredes do tipo steel frame - dry wall com ou sem isolamento térmico na cavidade. Para tanto, propõem-se modelos computacionais capazes de fornecer, com certa precisão, o valor de temperatura em qualquer ponto do sistema estudado. Dessa forma, é possível, então, traçar configurações de distribuição de temperatura (uniforme ou não-uniforme) na seção transversal dos montantes que constituem o painel, fornecendo subsídios para análise de estabilidade e pós-flambagem dos elementos estruturais em questão. As simulações numéricas de transferência de calor são efetuadas com auxílio dos programas computacionais ABAQUS e SAFIR, ambos baseados no método dos elementos finitos.

The present work aims to give a contribution to the study of cold-formed steel members under fire condition. Specifically, the heat transfer in light steel framed walls with or without thermal insulation was studied. For this, computational models are applied to obtain, with acceptable precision, the values of temperature in any position of the structural system. In this way, it will be possible to describe the temperature distribution (uniform or non-uniform) over the cross-section of the studs that constitute the panel, giving subsidies for stability and pos-buckling analyses of the structural members. The numerical simulations of heat transfer are developed with the aid of computational programs ABAQUS and SAFIR, both based on the finite element method.

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.