Nonlinear FE analysis of the ultimate behavior of steel castellated beams

A numerical model is developed to predict the behavior of castellated beams with hexagonal and octagonal openings up to failure. The numerical model takes into account both material and geometric nonlinearities. To initiate buckling, an initial small out-of-plane geometric imperfection, obtained from an eigenvalues buckling analysis, was imposed to the model. Results of experimental data obtained from previous works have shown that the model is able to predict, with good accuracy, the ultimate load and to some extent the mode of failure. A parametric study is then realized to assess the cross-section classification given in the Annex N and to compare between the ultimate load behavior of castellated beams with hexagonal and octagonal openings when subjected to flexure and shear force. The numerical results have been compared with those obtained with the design method presented in ENV1993-1-1 Annex N.

► The behavior of castellated beams is modeled up to failure.
► A parametric study is performed.
► Castellated beams of class 3 and 4 are subjected to web-post buckling.
► Webs with intermediate plates are more susceptible to buckling.
► Intermediate plates should be used only for beams of class 2.