Back to the Future: leaving archaic composite column design rules behind

Brian Preston
General Manager UK Office
Magnetek, Bedford

Column composite codes worldwide are renown for having a large number of limitations placed on the material strengths and geometric properties that can be designed for. A significant portion of these limitations however are based on empirical procedures that were obtained more than 50 years ago. With the recent focus on trying to push design standards further to achieve taller and more architecturally open structures, it has become imperative to revisit the origins of the code limitations and how they impact on current designs.

This presentation focuses on the history of the design process found unanimously within the global composite codes for column design, with specific attention being given to the geometric restrictions imposed. Reviewing the evolution of both the equations for strength and geometric limits, a study is presented on not just the future but also the relevance of the current design methodology moving forward. Specific recommendations are made for liberalizing current restrictions, and the research underpinning these recommendations is briefly summarised.

To complement the theory, a case study is presented on two innovative towers in Sydney, Australia that have utilized concrete filled tubular columns with geometries that fall outside of the limitations imposed by all the international design standards. This case study gives a review of the process that was adopted for the design of a series of slender, thin-walled composite columns. By highlighting the specific deviations from the design codes, a clear trend in the areas that should be revised becomes apparent. This case study further validates the need for a revision of current composite codes.