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In cold-formed steel members under tension and connected with bolts, the resistance capacity of the net section should be calculated, taking into account the shear lag phenomenon. This is done through the net section reduction coefficient, Ct. Different Standards show different equations for Ct. In this work, experimental laboratory data of cold-formed steel angles from the authors are used for the evaluation of the accuracy of the predictions of the net section capacity of members under tension. Such predictions are given by the equations of AISI, Eurocode-3, Brazilian standard NBR 14762, and also by a predictive equation previously proposed by the authors. The paper shows how each equation predicts the tension member resistance capacity in front of the experimental data. Most of the equations in the design standards have good predictions when more sections of the steel angles are connected. The results show that the AISI standard presented the best resistance capacity prediction and lower standard deviations of the output response upon uncertainty.

This paper presents an investigation of the disproportionate collapse of multi-store steel buildings in a natural fire situation due to the progressive failure of their columns. For this purpose, it is intended to evaluate the effects of the redistribution of stress and vertical displacements of columns with the evolution of the temperature addressing, also, the impacts of the localized faults of these structural elements. In addition, another objective of this paper is the development of a practical analysis approach, which is called by successive approximations. As a methodology, advanced computational techniques were developed to predict the structural behavior of the building as the temperature reduces the strength and stiffness of its structural elements. For the parametric study, the overall response of the building was investigated through fire simulations in many columns. The results showed that the phenomenon of redistribution of stresses that occur during the heating period is essentially due to the reduction in the modulus of elasticity of the steel. In addition, the study pointed out that the use of advanced computational techniques through the use of successive approximations technique is an excellent alternative to study the progressive collapse of buildings subject to high temperatures.

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