The design method for composite frames of steel and concrete given in Part 5 of the Bridge Code uses effective column lengths based on elastic theory, which is strictly not applicable at ultimate loads. Details are given of tests on eight composite columns, elastically restrained about one or both axes, in a purpose-designed rig of capacity 2MN, in which axial load is applied through crossed knife-edges. The ultimate loads, deflections and end moments were found to agree well with computed values. The design method of BS 5400: Part 5 is shown to be satisfactory for these columns, for both the serviceability and the ultimate limit states.
R.P. Johnson and I.M. May