Impact of cable sag on the efficiency of an inertial mass damper in controlling stay cable vibrations

摘要

Passive negative stiffness dampers (NSDs) that possess superior energy dissipation abilities, have been proved to be more efficient than commonly adopted passive viscous dampers in controlling stay cable vibrations. Recently, inertial mass dampers (IMDs) have attracted extensive attentions since their properties are similar to NSDs. It has been theoretically predicted that superior supplemental damping can be generated for a taut cable with an AVID. This paper aims to theoretically investigate the impact of the cable sag on the efficiency of an AVID in controlling stay cable vibrations, and experimentally validate superior vibration mitigation performance of the AVID. Both the numerical and asymptotic solutions were obtained for an inclined sag cable with an AVID installed close to the cable end. Based on the asymptotic solution, the cable attainable maximum modal damping ratio and the corresponding optimal damping coefficient of the AVID were derived for a given inertial mass. An electromagnetic AVID (EIMD) with adjustable inertial mass was developed to investigate the effects of inertial mass and cable sag on the vibration mitigation performance of two model cables with different sags through series of first modal free vibration tests. The results show that the sag generally reduces the attainable first modal damping ratio of the cable with a passive viscous damper, while tends to increase the cable maximum attainable modal damping ratio provided by the AVID. The cable sag also decreases the optimum damping coefficient of the AVID when the inertial mass is less than its optimal value. The theoretically predicted first modal damping ratio of the cable with an AVID, taking into account the sag generally, agrees well with that identified from experimental results, while it will be significantly overestimated with a taut-cable model, especially for the cable with large sag.