Structural behaviour and design of locally unstable angle sections
- Kim Rasmussen
- Shamim Hossain
Angle sections are used extensively in structural applications because of their simple geometry which facilitates easy connection to adjoining members. Typical examples are webs and chords of beams and struts of transmission towers and like triangulated structures. . Traditionally, angles were hot-rolled and generally fully effective, ie capable of supporting the full yield stress in compression. However, angles are increasingly being manufactured by cold-forming, and cross-sections are becoming increasing slender. It is now common to find standard slender sections in product catalogues of cold-formed angles.
In spite of their simple cross-sectional geometry, angles are notoriously difficult to design because a) the shear centre does not coincide with centroid, b) the section is often bent about an axis parallel to a leg, which is a non-principal axis, and c) for slender angle sections, the local buckling mode is identical to the torsional mode. Recent research has shown that conventional design procedures become excessively conservative for slender angle sections because they account for the torsional (local) mode twice: through the member strength provisions and through the effective width provisions.
Recent research has developed design models for slender angles in compression and combined compression and bending. The models include effective width design procedures as well as an application of the Direct Strength Method to beam-columns.