Stiffness and loss factor of unbonded, multi-strand beams under flexural deformation

Beam-like structures constructed from many long strands that are constrained rather than bonded together can provide high levels of structural damping through friction between individual strands. This paper describes experimental and numerical studies carried out on square-section metal beams that are aimed at improving understanding of the relationship between construction and performance. The beams used in this study are constructed from lengths of square-section, key steel. The bundle of strands is held together at various compression loads with pre-calibrated clamps. Flexural behaviour of an assembled beam is simulated using standard finite element analysis and simple Coulomb friction at the interfaces. The validity of the assumptions used in the models is confirmed by comparison with three point bend tests on a regular nine strand construction at several different clamp loads. Subsequent numerical studies are used to investigate the effects of increasing the number of strands whilst the overall cross-section of the bundle remains unchanged. It is found that overall stiffness drops and loss factor increases when more strands are used. Interestingly, the energy dissipated by each beam construction is almost the same.