Multi-stripe Dynamic Analysis of Existing RC Buildings Seismically Retrofitted by Base Isolation or Dissipative Bracing Systems Conforming to Italian Code

Base isolation and energy dissipative bracing systems are the most used passive control techniques for seismic retrofitting of existing structures. The main goal of this research is the assessment and the comparison of seismic fragility functions of a case study of existing reinforced concrete (RC) building retrofitted with isolation systems based on double concave curved surface sliders (DCCSS) isolators or with dissipative braces based on hysteretic damper (HD) devices. The alternative retrofit applications have been designed conforming to the Italian seismic code considering equivalent single degree of freedom (SDOF) systems with similar global performances and the same anti-seismic devices overstrength level. Multi-stripe nonlinear time-history analysis has been performed on multi degree of freedom (MDOF) numerical models, considering a set of 20 spectra-compatible earthquakes at 10 increasing intensity measure levels. Seismic fragility analysis of the retrofitted building has been evaluated considering a design (minor) damage state and a collapse damage state. The structure drift and the HDs ductility and DCCSSs displacement have been considered as the main engineering demand parameters (EDPs) for the global and local seismic performances. Results of design damage state highlighted that seismic isolation and energy dissipation systems are almost equivalent, coherently with the design assumptions. Results of collapse damage state show the same safety margin for earthquakes bigger than the design one.