Effectiveness of damaged viscoelastic dampers in seismic protection of structures under main shocks and aftershocks

•The fractional derivative models for different performance stages of viscoelastic dampers are employed.•The effectiveness of damaged viscoelastic dampers in protection of structures is numerically examined.•The damaged viscoelastic dampers are still helpful for resisting the rest of main shocks and aftershocks.•The efficacy of damaged viscoelastic dampers is overrated if not considering their reduced performances. It has been demonstrated through uniaxial reversal loading tests that damaged viscoelastic dampers are to some extent still able to possess stiffness and energy dissipation capabilities. Based on past performance test results, some analytical models originating from the fractional derivative method have been provided to account for the design, beyond-design, and residual performances of viscoelastic dampers. In this study, these models are employed for modelling the actual dynamic behavior of supplemental viscoelastic dampers installed at different stages in the numerical model of a practical high-rise steel building. Scenarios of main shocks and subsequent aftershocks are assumed as seismic inputs. The numerical results indicate that, even though viscoelastic dampers suffer damage during main shocks, the damaged dampers are still effective in reducing the structural acceleration and displacement responses compared with the undamped structural responses. It is assumed in the analytical model of viscoelastic dampers that the shear force will be immediately reduced to the beyond-design performance without hardening behavior when suffering damage at the beginning half-cycle. Thus, the damped structural acceleration control performance at that instant, particularly of the floors installed with the damaged dampers, might not be satisfactory but still superior to the undamped structural performance. Although some doubts are clarified in this study, it is emphasized that damaged viscoelastic dampers must still be appropriately repaired or even replaced before the next major earthquake occurs.