La risposta sismica in superficie nella valutazione ed adeguamento di edifici esistenti in c.a.: aspetti metodologici ed applicativi

The coming into force of the “Technical Standards for Construction” (D.M. 14 January 2008) in Italy and the experience acquired after the seismic events of Abruzzo (2009) and Emilia (2012) favoured the increasing interest of the professionals’ community to the procedures focused on refined evaluations of seismic actions to be used both in the design of new structures and in the assessment and retrofitting of existing ones. The evaluation of the design seismic loads is based on probabilistic estimate of the seismic input on rock coming from the seismogenic framework of the studied zone and the possible local amplification effects. From a rigorous seismological point of view, although both these aspects are well described in literature and considered within the national and international normative context, their full application in the engineering field needs further close examinations, specifically for what concerns the estimation of local amplification effects. After a brief technical and normative overview, this work describes some methodological aspects addressed to the use of the seismic response studies applied to the evaluation and the retrofitting of existing structures. In particular, the case-study of an existing RC building designed for gravity loads only is considered to compare the results obtained from a local seismic response spectrum approach and a simplified approach based on the classification of ground types. In addition to the intrinsic differences deriving from the two approaches, the article shows that the choice of the most suitable and effective retrofit and strengthening interventions is influenced also by the seismic design action.