Cross-sectional compressive capacity of S1200 ultra-high-strength steel welded I-section stub columns: Testing and design

This article reports an experimental study on the compressive strength and behavior of S1200 ultra-high-strength steel (UHSS) welded I-section stub columns. S1200 UHSS, with a nominal yield strength of 1200 MPa, represents an emerging structural steel grade for which no dedicated design guidelines currently exist. A testing program was first conducted, comprising material coupon tests, residual stress measurements using the sectioning method, and 14 stub column compression tests covering a range of cross-sectional slenderness under fixed-ended boundary conditions. Based on the measured residual stress distributions, a new predictive model is also proposed for S1200 UHSS welded I-sections. The acquired test data were subsequently employed to undertake a design analysis, where the existing steel design provisions of EN 1993-1-12 were examined for their suitability for the design of S1200 UHSS I-sections. All specimens failed by local buckling, and the EN 1993-1-12 Class 3 slenderness limit for flanges is shown to be applicable to S1200 UHSS I-sections. The results indicate that EN 1993-1-12 demonstrates good overall prediction accuracy for S1200 UHSS I-sections, with an overall mean capacity ratio Nu/Nu,EC3 of 1.11; however, its predictions become increasingly conservative for sections with higher cross-sectional slenderness, suggesting that the effective width formulations tend to underestimate the capacity of more slender S1200 UHSS I-sections. Overall, EN 1993-1-12 is shown to provide safe and reasonably accurate capacity predictions for S1200 UHSS welded I-section stub columns.