Search for Improved Steel Cold-Formed Lipped Channel Beams

Resumo

Cold-formed steel (CFS) members are light-weight structural elements with high strength-weight ratio,
usually applied in many industrial applications. The CFS sections are frequently classified as thin-walled
structures, which means high sensitivity to buckling behavior associated to the buckling modes: local, distortional
and global. In order to improve the structural capacity of the CFS members, one may design thin-walled sections
including intermediate stiffeners, providing quite improved structural behavior. The main purpose of the
investigation is the development of a search procedure for stiffened lipped channel beams, performing the highest
critical buckling moment and flexural strength. For this, the point of departure is a 600 mm width and 1.0 mm
thick steel sheet, originated from a steel coil, which will be designed to produce lipped channel CFS with the
following possibilities of intermediate stiffeners: (i) type of stiffener; (ii) number of stiffeners in a single element;
(iii) stiffeners distribution in the flanges and the web; (iv) stiffener dimensions. As all the CFS’s candidates will
be created from the same initial coil (600 x1.0 mm), all will have the same cross-section area and weight. In this
condition, the search process is restricted to the geometric organization of the cross-section dimensions and choice
of the stiffeners geometry, dimensions and distribution, in order to display the most efficient section for simple
bending loading (in the major axis). After the generation of the possible CFS’s, the corresponding beam members
were submitted to elastic buckling analysis with the help of the finite strip method computational program
CUFSM, for the determination of the critical buckling bending moment. The obtained results are applied for the
calculation of the flexural strength of the beams, on the basis of the Direct Strength Method (DSM) rules included
in the Brazilian standard NBR 14762:2010. A shell FEM model was implemented via Ansys computational
package, in order to confirm the accuracy of the DSM results in terms of the beam strength. Finally, it was
concluded that (i) the presence of intermediate stiffeners may bring remarkable structural performance
improvement (up to 60% in some cases) and (ii) that the combination of the FSM and the DSM proved to be an
optimal tool for determining the most efficient geometry for a CFS cross section from any steel coil indicated as
input data.