Structural Response and Residual Capacity of S700 High-Strength Steel CHS Columns after Exposure to Elevated Temperatures

The structural behavior and residual capacity of S700 high-strength steel circular hollow section (CHS) columns after exposure to elevated temperatures were studied through testing and numerical modeling. The testing program was conducted on 10 S700 high-strength steel CHS columns and comprised heating and cooling of the specimens as well as postfire material testing, measurements of initial geometric imperfections, and pin-ended column tests. Numerical simulations were subsequently performed, where finite element models were built and validated with reference to the experimental results and afterward used to conduct parametric studies to obtain further numerical data. Given that there are no specific provisions for the design of steel structures after exposure to elevated temperatures, the relevant room-temperature design buckling curves were evaluated, using postfire material properties, for their applicability to S700 high-strength steel CHS columns after exposure to elevated temperatures, based on the experimental and numerical data. The evaluation results indicated that the buckling curves prescribed in the American specification and Australian standard lead to accurate and consistent residual capacity predictions for S700 high-strength steel CHS columns after exposure to elevated temperatures, while the Eurocode buckling curve yields conservative predictions of residual capacity. A revised Eurocode buckling curve was then proposed, and resulted in a higher level of accuracy than its original counterpart.