Dissipative Exoskeletons for Seismic Enhancement of RC Frame Structures

This thesis investigates the use of structural exoskeletons for seismic retrofitting of existing RC buildings, defining and classifying exoskeleton systems based on stiffness and load-transfer behaviour. It examines various dissipative exoskeletons with fluid-viscous dampers, including 2D and 3D configurations, façade-parallel or orthogonal solutions, and systems with dissipative bracing (SPD) or dissipative connections (MPD). The study presents a detailed structural analysis of the undamped RC building, evaluating and comparing the seismic response using the Equivalent Lateral Force (ELF) method, the Response Spectrum Analysis (RSA), and the nonlinear Time–History Analysis (THA) with seven ground motions selected to be compatible with the design response spectrum. This comparison provides a reliable baseline for understanding the dynamic behaviour of the existing structure. Nonlinear time–history analyses were performed in SAP2000 for three configurations: the original undamped structure, a retrofitted system with a 3D dissipative tower and inter-storey diagonal dampers providing stiffness-proportional damping (SPD), and a retrofitted system with a 3D dissipative tower and dissipative links providing mass-proportional damping (MPD). Linear viscous dampers were designed for a target response reduction factor eta = 0.40. The SPD system reduced internal forces, top-storey displacement, and acceleration by about 50%, 70%, and 48%, respectively, while the MPD system achieved much greater reductions of up to 89%, 97%, and 88%. These results demonstrate that the MPD system is significantly more effective than the SPD system for seismic response control and performance-based retrofitting of existing RC structures. The results confirm that the MPD system is considerably more effective than the SPD system in controlling seismic response, making it a highly efficient solution for performance-based seismic retrofitting of existing RC structures.