Seismic Performance Enhancement of Reinforced-Concrete High-Rise Buildings Using Nonlinear Viscous Dampers

Earthquake resilience remains a major challenge for reinforced-concrete (RC) high-rise buildings, especially in regions of high seismic hazard where many structures predate modern design codes. This thesis investigates the use of nonlinear viscous dampers as a retrofit strategy to improve the seismic performance of a 16-storey RC building located in Latakia, Syria, a city in a moderate-to-high hazard zone. The research combines linear Response Spectrum Analysis (RSA) and nonlinear Time-History Analysis (THA) in accordance with Eurocode 8. Seismic input was defined through code-based spectra and suites of seven spectrally matched accelerograms for two performance levels: Damage Limitation (DL, 50-year return period, PGA = 0.10 g) and Life Safety (LS, 475-year return period, PGA = 0.35 g). The retrofit was designed following the systematic Five-Step Procedure, targeting an equivalent damping ratio of 40%. Two placement strategies were evaluated: Stiffness-Proportional Damping (SPD), where dampers were distributed by storey stiffness, and Mass-Proportional Damping (MPD), where dampers were connected to infinitely stiff columns simulating rigid anchorage. Results show that SPD reduced base shear by 50–70% at LS and up to 90% at DL, while also lowering displacements and interstorey drifts. With the same devices reconfigured as MPD, performance improved further, achieving approximately 65% base shear reduction at LS, 91% at DL, and over 85% reduction in roof displacement. The study concludes that viscous dampers are an effective and code-compliant retrofit for RC high-rise buildings, substantially enhancing seismic resilience. Both SPD and MPD delivered strong improvements, with MPD proving superior in efficiency. These findings highlight viscous dampers as a sustainable strategy for reducing seismic risk, improving serviceability, and safeguarding communities in earthquake-prone areas.