Experimental and numerical studies of S960 ultra-high strength steel welded I-section columns

The present paper reports a thorough experimental and numerical study of the structural behaviour and resistances of 5960 ultra-high strength steel welded I-section columns failing by flexural buckling about the minor principal axis. A testing programme, including initial geometric imperfection measurements and ten pin-ended column tests, was conducted. The testing programme was accompanied by a numerical modelling programme, where finite element models were firstly developed and validated against the test results, and then employed to perform parametric studies to generate further numerical data. The existing codes in Europe, America and Australia only cover the design of steel structures with nominal material yield stresses less than or equal to 700 MPa (or 690 MPa), and design of 5960 ultra-high strength steel welded I-section columns is therefore out of their application scopes. The obtained test and numerical results were adopted to assess the applicability of the relevant codified design buckling curves for 5700 (or 5690) high strength steel welded I-section columns failing by minor-axis flexural buckling to their 5960 ultra-high strength steel counterparts. The assessment results indicated that the design buckling curves in both the European code and Australian standard yield rather conservative resistance predictions when used for 5960 ultra-high strength steel welded I-section columns failing by minor-axis flexural buckling, while the design buckling curve in American specification results in overall accurate and consistent flexural buckling resistance predictions, though the predicted resistances are marginally conservative for those relatively short 5960 ultra-high strength steel welded I-section columns with member non-dimensional slendernesses from 0.6 to 1.0. Finally, a revised Eurocode design buckling curve was proposed and shown to yield substantially more accurate and consistent resistance predictions for 5960 ultra-high strength steel welded I-section columns failing by minor-axis flexural buckling than the original Eurocode design buckling curve.