Novel adaptive hysteretic damper for enhanced seismic protection of braced buildings

Traditional bilinear hysteretic dampers (BHDs) are installed in buildings to enhance their seismic performance by increasing the effective stiffness and damping and are usually designed to guarantee the structural safety for severe ultimate limit state seismic events. As a negative consequence, only minimal damping is provided during weak but more frequent serviceability limit state earthquakes since BHDs mainly operate in their elastic regime. This can cause high peak floor accelerations (PFAs) that are detrimental for sensitive non-structural components (NSCs), like electric network, elevators, false ceilings, and computers, whose integrity is crucial in high-technological buildings (e.g. hospitals, and emergency centers). In order to improve this unacceptable situation, a novel adaptive hysteretic damper (AHD) has been developed by the authors. The AHD can modulate its effective damping and stiffness to the intensity (e.g. peak ground acceleration) of the occurring earthquake leading to: (i) reduced PFAs and enhanced NSCs protection for minor earthquakes; (ii) not impaired structural safety under major severe events. In this paper the force-displacement response of the AHD is experimentally assessed and a simple linear equivalent design method for braced buildings implementing this innovative technology is proposed and validated through comparison with non-linear time history analyses. The procedure is then exploited to design the seismic-retrofit intervention of a real case-study hospital and the enhanced seismic performances, compared to those offered by conventional BHDs, are quantified.