Reinforced concrete buildings constructed until the late 1970’s in most southern European countries were
designed and constructed without considering earthquake provisions, constituting a significant risk.
Recent major earthquakes around the world have evidenced that this type of existing buildings lacking
appropriate seismic resisting characteristics are very vulnerable. Their retrofit or replacement should be
made in order to reduce vulnerability, and consequent risk, to currently accepted levels. The development
of retrofitting techniques represents a key issue in order to avoid both human casualties and economic losses
in future events. Despite the advantages of a refined non-linear dynamic structural fibre modelling, it must
be admitted that this approach can frequently become elaborated and costly. This fact sustains the
development of less complicated structural models without debasing the essential features of dynamic
response. Thus, it is proposed a simplified methodology for non-linear dynamic analysis of buildings
based on the multi-modal spectral seismic response. It is also proposed an optimisation tool for the
strengthening design of existing buildings
