Post-fire mechanical properties and buckling strength of cold-formed steel hollow section columns

The mechanical properties and buckling strength of cold-formed steel square hollow section columns after heating and cooling processes were examined by coupon tensile tests and axially loaded compressive and stub-column tests at ambient temperature. The coupon tensile test specimens were made from the steel columns with the small sectional shapes (□-50–50-1.6 and 3.2 mm, respectively). Axially loaded compressive and stub-column tests were performed on these specimens. The specimens were treated by two heating and cooling processes: air cooling in a furnace for the specimens heated from 200 to 800 °C, and quenching with water for those heated from 600 to 800 °C for the coupon tensile test specimens. The test results of the axially loaded compressive and stub-column tests were compared with Eurocode and AS/NZS 4600 design equations. It was confirmed that the yield, tensile strength, and flexural and local buckling strength of cold-formed steel square hollow section columns decrease after the heating and cooling processes. Comparing with the test and calculation results of the Eurocode design equations, it was confirmed that the residual flexural and local buckling strength could be evaluated after the fire by the Eurocode design equations using the yield strength.