Ultimate behaviour of steel beams with discrete lateral restraints

• Full-scale experimental study of braced steel beams.
• Parallel numerical study of braced beams.
• Investigation of strength and stiffness requirements of brace.

Through a programme of experiments, numerical modelling and parametric studies, the implications of allowing for strain-hardening in the design of laterally restrained steel beams is investigated with particular emphasis on the performance of the bracing elements. A total of twelve tests were performed on simply supported beams considering two basic scenarios: discrete rigid restraints and discrete elastic restraints of varying stiffness. In the latter case, the forces developed in the restraints were measured and compared to the design forces specified in EN 1993-1-1 (2005). Two different restraint spacings were considered in the tests to give non-dimensional lateral torsional slenderness values of 0.3 and 0.4 for the unrestrained lengths. In all tests, bending resistances in excess of the plastic moment capacity were observed, but for the considered restraint spacings, the resistances often fell short of that predicted by the deformation-based continuous strength method (CSM), which allows for strain-hardening. It was concluded that closer restraint spacing may be required to harness significant benefit from strain-hardening and to develop the full CSM bending resistance, though the forces generated in the restraints were within current code requirements.