Proposição de formulação da rigidez rotacional de vigas mistas com perfil celular para determinação do momento crítico elástico à flambagem lateral com distorção

Abstract

Continuous and semi-continuous steel and concrete composite beams have been presented as an interesting option for rationalization and optimization of structural systems, since they have better moment distribution. Additionally, when cellular steel profiles are used in composite beams the results with regard to economy can be more promising. At the hogging moment region, close to the supports, though, for continuous and semi-continuous composite beams, a portion of the steel profile is subject to compressive forces, what may cause a global instability limit state called lateral-torsional buckling (LTB). The Brazilian Standard ABNT NBR 8800:2008 provides an approximate procedure for the verification of this limit state with which the critical elastic moment can be obtained from the rotational stiffness of the composite beams, but this procedure is restricted to composite beams with full web profiles. In this work, an equation was analytically deduced for the computation of the rotational stiffness of the cellular profile web and subsequently verified through numerical simulations carried out using ANSYS. This showed the efficiency of the developed equation. A parametric analysis was implemented for the evaluation of the influence of the cellular profile geometric parameters at the computed value of the rotational stiffness of its web. The proposed formulation for rotational stiffness of cellular profile composite beams utilizes the equation deduced for this research in the computation of the web stiffness and the equation from ABNT NBR 8800:2008 in the computation of the rotational stiffness of the slab. From this, the value of the rotational stiffness is determined based on the expression of the stiffness of springs serially connected. Finally, the critical moment for LTB computation, prescribed by ABNT NBR 8800:2008, is extended to cellular steel profile composite beams in numerical examples with the necessary modifications in the geometric properties and in the rotational stiffness.