This paper presents the latest developments concerning the numerical modeling of steel-concrete composite beams using GBT-based (beam) finite elements. In particular, it is shown that GBT makes it possible to assess, accurately and with computational efficiency, the buckling (bifurcation) behavior of steel-concrete composite beams subjected to negative (hogging) bending. Two relevant buckling phenomena are considered, namely (ⅰ) local buckling of the web (plate-like), possibly involving the torsional rotation of the compression flange, and (ⅱ) distortional buckling, combining a lateral displacement/rotation of the lower flange with cross-section transverse bending. The determination of the buckling loads is performed in two stages: (ⅰ) a pre-buckling analysis is first carried out, accounting for shear lag and concrete cracking effects, and (ⅱ) an eigenvalue buckling analysis is performed next, on the basis of the calculated pre-buckling stresses, allowing for cross-section distortion and plate bending. Several numerical examples are presented, illustrating the application of the proposed GBT-based finite element and providing clear evidence of its capabilities and potential.
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