Experimental and numerical investigation of concrete-filled stainless steel columns exposed to fire

• Concrete-filled stainless steel columns have excellent fire resistance.
• The presence of pre-load increases the post-fire residual strength.
• Negligible fire damage occurred to circular stainless steel composite columns.
• An imperfection amplitude of L/1500 can be used for finite element analysis.

This paper presents an investigation on concrete-filled stainless steel tubular (CFSST) columns in fire and after fire exposure. A total of 12 specimens were tested, including 6 CFSST columns exposed to fire and another 6 CFSST columns subjected to sequential ambient temperature loading, fire exposure with constant applied load and post-fire loading phases. A photogrammetric method was employed during the test to capture the initial imperfections of the CFSST columns and strain developments of the stainless steel tubes in fire. The main variables explored in the test program include: (a) cross-section type (circular, square); (b) axial load level (0.28–0.48); and (c) presence of reinforcement or not. A three-dimensional finite eõlement (FE) model was developed by introducing the measured initial imperfections and load eccentricities. The comparison of the FE predictions and the tests performed showed a reasonable agreement. To further simplify the FE analysis, the initial geometric imperfection of a column may be simulated in the model as the first buckling mode shape of the column multiplied by an amplification factor. The simplified model was verified by comparison with test results.