Seismic Vulnerability Assessment of Retrofitted Steel Structures with Fractional Viscoelastic Dampers Considering Uncertainty Variables

Using viscoelastic (VE) dampers is one of the most effective tools for seismic retrofitting of steel structures. The results of many experimental studies demonstrated that using fractional derivative terms for modelling viscoelastic dampers offers an acceptable level of accuracy. Unlike viscous dampers the damping force is not linearly dependent to velocity and it is also highly affected by excitation frequency and ambient temperature. For this reason, solving the dynamic equation and calculating the seismic response of the structures equipped with VE dampers have many complexities. In this paper, the responses of a viscoelastically damped structure are calculated and the seismic performance of the building is evaluated while considering the effects ambient temperature as well as the inherent uncertainties related to ground motion excitation. The proposed relationships were used to calculate the structural responses and assess the seismic performance of a 5-story steel structure retrofitted with fractional viscoelastic dampers. The maximum relative displacement of the controlled structural at the operation, design, and maximum considered expected hazard levels were compared to those of the initial structure (without damper). Furthermore, fragility curves were used to compare responses and exceedance probabilities of performance limit states. The results show great improvement in structural seismic performance related to the reduction of both structural responses and exceedance probabilities of limit states. The effect of temperature changes in results has been also demonstrated.