Vulnerability of RC buildings and risk assessment for Cyprus.

Previous studies on Earthquake Risk Assessment (ERA) for Cyprus (Kythreoti, 2001) concluded that a new Peak Ground Acceleration (PGA) attenuation law needs to be derived based on local data and the vulnerability of the building stock needs to be fully re-examined. Field data from recent seismic activity became available and are used to derive a new PGA attenuation law. However, the damage data proved limited and analytical vulnerability curves were found to be necessary. Previous studies on analytical vulnerability underestimate damage from common brittle modes of failures. A variety of failure modes were simulated by using relatively simple element models, which were calibrated based on experimental data and expert judgment. A modified capacity-spectrum procedure was developed for the estimation of structural response and verified against time-history results. This procedure includes the bilinearisation of softening capacity curves so as to predict the response of structures deteriorating due to a variety of local brittle failure modes. A new damage index indicator was developed based on fundamental period shift and this \vas linked to damage limits. Key design parameters from capacity models were treated probabilistically and analytical vulnerability curves were derived for two building types and three design levels. A rapid increase in damage takes place well before the anticipated flexural failure threshold is observed in 'Pre' and 'Basic' design buildings. This occurs due to the dominance of brittle failure modes. The effect of the hazard spectrum on the vulnerability curves was found to be considerable. In the case of Cyprus, Type 2 spectra (EC-8, 2004) were found to simulate better the earthquake hazard potential. Annual insurance premium allocated for seismic risk in Cyprus is currently set at 0.060.08% of value and this appears to predict the overall risk accurately. However, the use of a single premium for all building types and the entire island leads to underestimation of seismic risk in Pre-seismic buildings. This underestimation is more profound in regions along the southwest coast of the island. The single most important issue for analytical vulnerability assessment is the definition of an appropriate structural model, which requires sophisticated modelling capabilities to simulate brittle failure modes and further work is recommended.

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