Evaluation and considerations about fundamental periods of damaged reinforced concrete buildings

The aim of this paper is an empirical estimation of the fundamental period of reinforced concrete buildings and its variation due to structural and non-structural damage. The 2009, L’Aquila earthquake has highlighted the mismatch between experimental data and code provisions value not only for undamaged buildings but also for the damaged ones. The April 6th, 2009 L’Aquila earthquake provided the first opportunity in Italy to estimate the fundamental period of reinforced concrete (RC) buildings after a strong seismic sequence. 68 buildings with different characteristics, such as age, height and damage level, have been investigated by performing ambient vibration measurements which provided their fundamental translational period. Four different damage levels were considered according with the definitions by EMS 98 (European Macroseismic Scale), trying to regroup the estimated fundamental periods versus building heights according to damage. The fundamental period of RC buildings estimated for low damage level, is equal to previous relationship obtained in Italy and Europe for undamaged buildings, well below code provisions. When damage levels get higher, the fundamental periods increase, but again with values much lower than those provided by codes. Finally, the authors suggest a possible update of the code formula for the simplified estimation of the fundamental period of vibration for RC existing buildings, taking into account also the inelastic behaviour