Fire resistant design of concrete filled tubular steel columns

Concrete filled tubular (CFT) columns have many attractive features and are being increasingly used in prestigious projects. A design software package (Firesoft) has recently been developed to help make this type of construction more accessible to structural engineers. It is important the design software is thoroughly validated and this paper presents background information to the method adopted in the package. This method is based on the well established cold design method in EN 1994-1-1 for composite columns including CFT columns, but modified to take into account strength and stiffness degradations of steel and concrete at high temperatures. Although this method is not adopted in the fire part of Eurocode 4 (EN 1994-1-2) for composite columns including CFT columns, it has the advantage of using the same method for both cold and fire resistant designs of CFT columns. This paper first presents validation results for the alternative method by comparing Firesoft calculation results against the results of a large number of fire resistance tests on unprotected and externally protected CFT columns under axial compression or combined axial compression and bending moments. A study was then conducted to assess a current design method for externally protected CFT columns. The objective of the study is to propose an interim design method for externally protected CFT columns that use intumescent coating until such time as reliable thermal properties of intumescent coating for CFT applications are available.