Design of steel beams with discrete lateral restraints

Discrete lateral restraints offer an effective means of stabilising beams against lateral-torsional buckling. Design expressions for simply-supported beams braced regularly along their span with elastic restraints, based on analytically-derived formulae, are presented herein. These include the minimum restraint stiffness required to force the beam to buckle in between the restraint nodes and the forces induced in the restraints, along with a brief treatment of the critical moment of the beam. It is demonstrated that there is close agreement between the values obtained from the design formulae and their original analytical counterparts. These are also compared with the results from design formulae based on analogous column behaviour, an approach commonly used in design codes. It is found that the column rules used by design codes return values that, when compared with the results of the current analysis, are overly conservative for cases where the restraints are positioned at the compression flange of the beam but unsafe for restraints positioned at the shear centre.

► Expressions for key features of discretely-braced beams have been found analytically.
► Close approximations are provided by newly-formulated design rules.
► A procedure has been developed to optimise brace stiffness and strength.
► Existing rules are found to be conservative or unsafe, depending on restraint height.