Overall flexural-shear buckling strength design of built-up radially battened columns

Abstract

The built-up radially battened columns (RBCs) have a promising prospect in public building engineering due to their aesthetical form and good load-bearing capacity. However, their design methods are not covered in the current design specifications because of their distinctive appearance. This paper aims to present the flexural-shear buckling behavior of built-up RBCs and propose its corresponding strength design recommendations. At first, the finite element model (FEM) of the RBC is established, and a lot of examples are calculated in eigenvalue buckling analysis and elastoplastic analysis by using this FEM. Three kinds of possible first-order buckling modes are observed in the elastic buckling analysis, which are flexural-shear buckling, torsional buckling, and local buckling respectively. Only flexural-shear buckling is involved in this study, and torsional buckling will be investigated in a companion paper. Local buckling (of the chord tube wall) can be prevented by a radius-to-thickness ratio limit. It has been proven that shear deformation plays an essential role in determining the flexural-shear buckling of built-up members, thereby a unit shear angle model is established to study the shear stiffness of RBCs when they buckle overall. Then, the prediction equations for elastic flexural-shear buckling load and its corresponding normalized slenderness ratio are derived. The design curves for the ultimate load-bearing capacity of built-up RBCs are also proposed based on the numerous results from elastoplastic FEMs by changing normalized slenderness ratios. Furthermore, the compound buckling of RBCs is considered by employing a FEM that exerted the individual chord initial imperfection (FEM-c), and accordingly, a strength reduction factor caused by compound buckling is proposed. Finally, the design methods for the individual chords and radial-shaped battens are studied. The internal forces in chords and batten plates are derived and the analysis of the local buckling of batten plates is conducted. It is recommended that chords should be regarded as a member under combined compression and bending, and batten plates can be guaranteed to not lose their stability before the RBC reaches their ultimate load-bearing capacity by adopting the ‘isostable criterion’. In conclusion, these results provide a method for accurately and conservatively predicting the strength of RBCs when overall flexural or compound buckling occurs, which will expand the application of RBCs in engineering and make our public buildings more pleasing.