Multi-Hazard Assessment of Steel Buildings Retrofitted Using Passive Control Devices

Abstract eng:
The multi-hazard effects on multi-story steel buildings retrofitted either by bracing systems or energy dissipating passive vibration control devices is assessed for its performance under earthquake- and wind-induced forces. The passive vibration control devices used in this investigation include steel bracing, viscous, and viscoelastic dampers. The buildings without and with the passive control devices are modeled as multi-degree of freedom (M-DOF) systems, with the seismic masses lumped at each floor level. The governing differential equations of motion for the uncontrolled and controlled buildings are solved by using Newmark’s time integration approach. The dynamic response quantities are compared, which include the floor acceleration, inter-storey drift, column base shear, and floor displacement, for the existing and retrofitted buildings subjected to earthquake- and wind-induced forces independently. Joint probabilities of failure are determined in terms of probability density function (PDF) and cumulative distribution function (CDF) by conducting fragility analysis to assess the effectiveness of the retrofit scheme against each natural hazard. It is concluded that upon retrofitting the buildings using the passive control devices, the forces attracted during the two hazards depend mainly on their modified dynamic properties, such as modal frequencies and added damping, which in turn affects the response reduction achieved. It is evident that under the wind loads the control systems which are effective in reducing the forces, limiting the large displacement, under the earthquake loads, tend to attract increased forces. Conversely, a flexible system effective in the seismic response control may prove to be ineffective for the wind response control. Thus, a retrofit strategy providing beneficial effects against a hazard may prove to be detrimental for the other, which calls upon careful selection of the retrofit solution and design for a structure considering such multi-hazard scenario.

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