### Abstract

Following modern design codes, seismically isolated superstructures are designed to respond in the elastic response range or to exhibit limited inelastic behavior. However, the behavior of seismically isolated structures when the superstructure enters the inelastic response range has not been extensively investigated in the past. This paper aims at answering the following questions: What is the probability that a (code-compliant) seismically isolated structure will yield? Will it develop a ductility demand μ larger than that implied by its design strength reduction factor? The probabilistic investigation of such a behavior is important for two reasons: First, to estimate the conservativism implied by the existing code provisions for seismically isolated structures. Second, to account for the case in which the seismic forces acting on an existing seismically isolated structure could exceed the design forces due to a ground motion stronger than the design ground motion level. The investigation is conducted using a two-degree-of-freedom model of a seismically isolated structure. The hysteretic behavior of the seismic isolation devices and the isolated superstructure is simulated in Matlab and OpenSees using a bilinear elastic-plastic model. The results are obtained by analyzing the responses of the isolated structure to a large number of recorded ground motions. Fragility curves to estimate the probability that the structure enters the inelastic range (μ>1), if it is designed according to the existing American and European code provisions for seismically isolated structures are determined through probabilistic seismic demand analysis (PSDA). The influence of the isolated structure overstrength and the isolation system hardening is discussed. Additional fragility curves are provided for other values of the engineering demand parameter (EDP) that are not allowed in the existing code provisions (e.g. superstructure displacement ductility μ>2). The effects of seismic isolation and superstructure design parameters on the fragility curves is quantified through parametric analysis.

Original language | English |
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Title of host publication | ECCOMAS Congress 2016 - Proceedings of the 7th European Congress on Computational Methods in Applied Sciences and Engineering |

Editors | V. Papadopoulos, G. Stefanou, V. Plevris, M. Papadrakakis |

Publisher | National Technical University of Athens |

Pages | 5574-5584 |

Number of pages | 11 |

Volume | 3 |

ISBN (Electronic) | 9786188284401 |

DOIs | |

Publication status | Published - 1 Jan 2016 |

Event | 7th European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS Congress 2016 - Crete, Greece Duration: 5 Jun 2016 → 10 Jun 2016 |

### Conference

Conference | 7th European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS Congress 2016 |
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Country | Greece |

City | Crete |

Period | 5/06/16 → 10/06/16 |

### Keywords

- Code provisions
- Performance-based design
- Seismic isolation
- Seismic probabilistic risk assessment
- Strength reduction factor

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## Cite this

*ECCOMAS Congress 2016 - Proceedings of the 7th European Congress on Computational Methods in Applied Sciences and Engineering*(Vol. 3, pp. 5574-5584). National Technical University of Athens. https://doi.org/10.7712/100016.2203.10015