Seminar - Derrick Yap - Interaction of local and distortional buckling of cold-formed high strength steel
Wednesday, October 20, 2004, 1.10 - 1.50 pm
Civil Engineering Lecture Room 3
Cold-formed steel structures are steel structures that are made by bending flat sheets of steel at ambient temperature into shapes, while hot-rolled steel are formed at elevated temperatures. Cold-formed sections are usually bent by either roll-forming or brake pressing. With developing technology, cold-formed members are being fabricated with higher yield stress materials. With the use of higher strength steels comes a reduction in thickness, which leads to the development of highly stiffened sections with more folds and stiffeners. This would inevitably lead to complex design problems for the treatment of structural instabilities.
In compression, cold-formed members exhibit the modes of instabilities, namely local, distortional and flexural or flexural-torsional buckling. With a highly stiffened section, a more accurate solution is required for the treatment of local buckling, distortional buckling and the interaction between them. The interaction of modes is not well documented in current literature as thicker sections are often being used. However with the reduction in thickness, sections are now prone to local and distortional buckling and the interaction between them. Hence there is a need to recognize this mode interaction and to accurately account for it in mathematical models.
With the complexity of modern section shapes, a simplified design method has been developed based on 'whole section' analysis called the Direct Strength Method (DSM). The Direct Strength Method proves a much simpler approach compared to the elemental method of calculating effective widths by the Effective Width Method (EWM). However both DSM and EWM do not account for the interaction of local and distortional buckling modes. Therefore a design method is required for structural designers to account for these mode interactions.
The seminar will describe preliminary investigation of sections with concurrent buckling modes including local and multiple distortional modes. Development of the sections for testing will be described. These sections are quite innovative and different from any investigated previously.