Eduardo de Miranda Batista

Compressive Local Buckling of Pultruded GFRP I-Sections: Development and Numerical/Experimental Evaluation of an Explicit Equation

AbstractIn this paper, a simple accurate equation to determine the local buckling critical stress of pultruded GFRP I-sections is developed. To assess the proposed expression, an experimental program comprising cross-sectional geometry measurement, material characterization, and compression tests on stub columns were carried out. Stubs having different flange-width-to-section-depth ratios extracted from 76×76×6.4 and 102×102×6.4-mm sections made with vinyl ester and polyester matrices were tested. The proposed expression is compared with experimental results, as well as results from numerical analyses using the finite-strip method (FSM). Finally, examples are presented and critical stresses are compared to those obtained based on other comparable research and by current design guidelines, demonstrating that the latter lead to conservative results.

Buckling Curve for Cold-Formed Compressed Members

Abstract This paper describes an experimental study of cold-formed compressed members, including local-global buckling interaction for the case of thin-walled profiles. The research was based on a large series of tests that were performed for long columns as well as for stub columns and incorporated the analysis of some buckling curves propositions. The adopted buckling curve definition is based on the design prescriptions of the actual Brazilian code for building steel construction and is valid for stiffened and unstiffened channel profiles. Reliability prediction of the proposed buckling curve was verified for different groups of experimental results, including local-flexural and local-torsional flexural buckling interaction. It presents mainly results for long columns, although an accurate analysis for the case of stub columns has also been performed.

Strengthening a reticulated spherical dome against local instabilities

Abstract The strength capacity of a reticulated spherical dome is generally associated with inelastic buckling of its slender members and more often of the partially restrained connections between members. These instability aspects were focused in the theoretical and experimental work performed to analyze the structural behaviour and to design the strengthening details to upgrade a large steel double-layer reticulated spherical dome. The paper outlines the main steps taken on the extensive stability and safety analyses of the as-built structure. Moreover it reports on the most relevant findings from tests carried out on a full-scale model of a typical substructure module, to investigate the collapse mechanisms displayed by the buckling-prone connections. A proposal is made for the use of a simple and rational expression to estimate the connection strength in the first designing stages. Finally, it is shown how structural upgrading was done by strengthening a few of the semi-rigid connections with specially designed fit-in bolted reinforcement details.

On the stability and strength of steel columns affected by distortional buckling

The results of an investigation concerning the effect of distortional buckling on the behaviour of thin-walled cold-formed steel columns displaying “rack” sections are presented. A parametric study is first performed to study the variation of the critical stress and characteristics of the associated buckling mode with (i) the column length and (ii) the thickness and relative widths of the plates forming the cross-section. In particular, cross-sectional proportions leading to the occurrence of a critical distortional buckling mode are identified. The linear stability results were used to define an experimental test program, which is presently under way and is reported next. The experimental set-up and test procedure are briefly described and the test results are displayed and discussed. These results deal with (i) the observation and characterization of the distortional buckling mode, (ii) the estimation of the postbuckling reserve associated to this mode and (iii) the determination of column ultimate strength values.

Local-global buckling interaction—some recent research results

Abstract Some research results applied to the analysis of thin-walled cold-formed structures are presented. The research focuses on the local-global buckling interaction and deals with steel structures in which cold-formed profiles are used. In this context, three main aspects are discussed: the collapse load of an isolated thin-walled member, its post-critical nonlinear behaviour and the complex behaviour of thin-walled plane-framed structures under local-global mode interactions. All these aspects are interconnected and constitute an ensemble that could contribute to words improving the understanding of structural behaviour and therefore code prescription. Many experimental results for stub columns as well as for long columns were used to check and calibrate the proposed approaches. For the case of plane-framed structures, the outcome of near future experimental tests of braced trussed plane frames are expected to check some FEM computational procedures.

Behaviour and ultimate load estimates for thin-walled trussed plane frames

Abstract The elastic non-linear buckling behaviour and collapse of trussed plane frames having cold-formed steel members are analysed via FEM models. Local buckling interaction at a section level between the thin walls of a member is taken into account through the effective width approach. Interaction between this local and Euler buckling mode is also considered in the analysis. The solution of the resulting non-linear equations is sought by a hybrid numerical scheme that makes use of both incremental-iterative plus secant methods. Large-span thin-walled trusses are analysed and the resulting non-linear behaviour and associated ultimate loads are critically examined in the light of conventional elastic calculations and predictions from existing design codes. Correlations with experimental results for pin-ended columns with slender cross-sections are also presented to back up the results found for trussed plane frames.

Análise computacional do fenômeno de transferência de calor em paredes divisórias do tipo dry wall

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 crosssection 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.

Análise de pórticos planos em situação de incêncio pelo método das rótulas plásticas

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.

Modelling Buckling Interaction

The following six sections deal with the problem of coupled instability. The presentation is mainly addressed to steel structures because of the large application of light construction, which conduct to thin-walled members. In this case two main phenomena are to be considered: torsional behavior and local buckling. The former recommends the knowledge of the Vlasov’s theory of beams and the last is to be taken on the basis of the theory of elastic stability. Additionally, interaction between buckling modes may conduct to coupled behavior with important consequences to the member strength. To accomplish a general overview of the buckling interaction of thin-walled members one must be able to deal with the general theory of the elastic stability, as well as to apply numerical solutions for both linear and nonlinear buckling and include experimental analysis results to obtain more profound comprehension of the problem. Finally, one must consider that practical design rules must incorporate the fundaments of the coupled instability theory.