Proposição de uma curva de flambagem para perfis I soldados formados por chapas cortadas a maçarico

Abstract

This dissertation proposes a new buckling curve that is able to predict flame-cut column strength better than the present NBR 8800. A historical review about the evolution of stability theories is developed, from Euler first works until the modern multiple curve criteria. A investigation of the factors that most influence the column strength is made, emphasizing the residual stresses, resulted from the fabrication process. Due to flame-cutting, flame-cut welded wide-flange shapes have tensile stress at the flange tips, that remains after welding. Flame-cut shapes, therefore, exhibit column strength greater than those manufactured fromuniversal mill plates. However, like ENV 1993-1.1, NBR 8800 has classified all welded wide-flange shapes in the same curves, regardless the manufacturing process. The NBR 8800 curves, therefore, do not permit taking into account the favorable residual stress pattern exhibited by flame-cut shapes. A consistent numerical analysis, which takes into account residual stress and initial imperfection, is performed with a software that allows physical and geometrical nonlinearities using the Finite Element Method. Several maximum strength curves, representing many different combinations of steel grade, size of shapes and buckling axes, are generated by the main software together with pre and posprocessors. A general theory, that was used in the main software development, is presented, based on a consistent Lagrangean formulation, using corrotational technique to obtain the tangent stiffness matrix. Based on the deterministic procedure recommended by SSRC, a statistical analysis is performed, in order to develop the new buckling curve. Several comparisons between the present NBR8800 curves and the new curve, together with numerical examples, are developed, showing that a more reliable and economical design can be achievedwith the new proposed buckling curve.