GNGTS 2015 - Atti del 34° Convegno Nazionale

GNGTS 2015 S essione 2.3 229 resulted in increasing mode shape discrepancy, with respect to the undamaged configuration. On the contrary, FE modes 1 and 2 subjected to damage in the central group 2 highlighted an apparent misleading modification of their modal shapes, with larger modifications deriving from the removal of one cable only, rather than two (Fig. 3b). The reason of this finding is strictly related to the vicinity of the natural frequencies of the two modes in the undamaged configuration. A detailed numerical study carried out by gradually introducing the damage in those cables, highlighted in fact a sort of mode hybridization for FE modes 1 and 2. In Fig. 3c, the so calculated natural frequencies in the 2U-1 and 2U-2 damage configurations are proposed as a function of the damage ratio R d = A cable,DAM / A cable , where A cable,DAM and A cable denote the cross- section area of the damaged and undamaged state. Finally, the effect of damage on the maximum axial forces on the cables was investigated. Some comparative results are collected in Fig. 3d, where the maximum variation of axial force on each group of cables, with respect to the average force values for the undamaged groups of stays, are proposed for the examined damage scenarios. Large sensitivity to damage was found especially when removing one or two cables in the group 2U (in the order of 15% and 32% for the scenarios ‘2U-1’ and ‘2U-2’ respectively), hence emphasizing the importance and usefulness of diagnostic investigations. Fig. 3 – Effect of damage in the cables (FE-DAM model, ABAQUS/Standard). a) Natural frequencies, with ∆ f = 100×( f r (FE-DAM) – f r (FE-OPT) )/ f r (FE-OPT) ; b) EMAmode 0, with progressive damage (2U-1); c) Natural frequencies of EMA modes 0 and 1 with progressive damage. R d = A cable,DAM / A cable ; d) Axial force on the cables, ∆ T = 100×( T r (FE-DAM) – T r (FE-OPT) ) / T r (FE-OPT . )