The seismic vulnerability associated with existing buildings, constructeduntil the late 1970’s, in urban areas in most southern European countries,with moderate to high seismic risk, is of extreme importance. In thatperiod, reinforced concrete buildings were designed and constructedwithout considering earthquake provisions, constituting a significantrisk. Recent major earthquakes around the world have evidenced thatthis type of existing buildings lacking appropriate seismic resistingcharacteristics are very vulnerable. Their retrofit should be made inorder to reduce vulnerability, and consequent risk, to currently accepted levels. Despite the evident advantages of a refined non-linear dynamicstructural fibre modelling, it must be admitted that this approach canfrequently become elaborated and costly. Simplified non-linear staticmodels considering just one DOF (such the Capacity Spectrum Method)are frequently not able to assess accurately irregular structural systems.These facts sustain the development of less complicated structuralmodels without debasing the essential features of dynamic response.It is demonstrated a recently proposed simplified methodology for nonlineardynamic analysis of buildings based on the multi-modal spectralseismic response, and an optimisation tool for the strengthening designof existing buildings.
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