Fire resistant design of concrete filled tubular steel columns

Concrete filled tubular (CFT) columns have many attractivefeatures and are being increasingly used in prestigious projects.A design software package (Firesoft) has recently beendeveloped to help make this type of construction moreaccessible to structural engineers. It is important the designsoftware is thoroughly validated and this paper presentsbackground information to the method adopted in thepackage. This method is based on the well established colddesign method in EN 1994-1-1 for composite columns includingCFT columns, but modified to take into account strength andstiffness degradations of steel and concrete at hightemperatures. Although this method is not adopted in the firepart of Eurocode 4 (EN 1994-1-2) for composite columnsincluding CFT columns, it has the advantage of using the samemethod for both cold and fire resistant designs of CFT columns.This paper first presents validation results for the alternativemethod by comparing Firesoft calculation results against theresults of a large number of fire resistance tests on unprotectedand externally protected CFT columns under axial compressionor combined axial compression and bending moments. A studywas then conducted to assess a current design method forexternally protected CFT columns. The objective of the study isto propose an interim design method for externally protectedCFT columns that use intumescent coating until such time asreliable thermal properties of intumescent coating for CFTapplications are available.