The installation of dampers close to cable anchorages is a common approach for stay-cable vibration mitigation. Inspired by the force-deformation relationship produced by actively controlled dampers, passive negative-stiffness dampers (NSDs) were proposed for stay cables in the past to achieve excellent vibration-control performance. However, a systematic comparison between passive NSDs and active control in cable vibration mitigation has rarely been reported in literature. This paper systematically compares vibration mitigation performances of a passive NSD to the performance of two active control methods, linear quadratic regulator (LQR) and output feedback control. The comparison indicates that a passive NSD can offer a stay cable with a high damping level comparable to that of LQR control. However, passive NSD will also decrease the modal frequencies of a stay cable, whereas LQR will increase the frequencies slightly. The dynamic response results also indicate that the active LQR control offers slightly better control performance than the passive NSD in various loading cases. The superiority of the LQR control over the passive NSD can be explained through an output feedback control approach. It is noteworthy that the NSD is regarded as more practical and reliable because it offers protection by completely passive means without the need for the feedback and actuation that are required in active control.
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