Ultimate behaviour of continuous steel beams with discrete lateral restraints

Through a programme of experiments, numerical modelling and parametric studies, the implications of allowing for strain-hardening in the design of laterally restrained continuous steel beams are investigated with particular emphasis on the performance of the bracing elements. A total of six tests were performed on continuous 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) for members containing rotated plastic hinges. 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 predicted by the deformation-based continuous strength method (CSM) were exceeded. Using a standardised numerical model validated against the laboratory test data, a series of parametric studies were conducted; it was concluded that elastic restraints for members containing rotated plastic hinges should be designed to sustain higher forces than required for traditional plastic design if the full CSM collapse load is to be achieved.