Eurocode 8: comparison of different methods of analysis for the assessment of existing r.c. frame buildings

Abstract eng:
The assessment of the seismic response of existing structures built according to out-of-date or even non-seismic codes is in general difficult, since the lack of considerations of the nonlinear response in the design stage leads to relevant uncertainties about location, extension and ductility capacity of nonlinear mechanisms. The main consequence is the strong gain in complexity of the assessment procedures proposed in the present codes, which promote the use of nonlinear methods of analysis to compute the seismic demand. In particular, according to Eurocode 8, the possibility of performing linear analyses is subordinated to strict conditions of applicability (rarely satisfied), while the use of the nonlinear static analysis based on 2-D conventional pushover is recommended. In this study, four existing r.c. frame buildings, built according to out-of-date codes and characterized by different structural configurations, are analyzed with linear dynamic, nonlinear static and nonlinear dynamic analyses, performed on the base of the recommendations of Eurocode 8. The obtained results are then compared to each other with the following aims: i) checking if the applicability conditions of linear methods are appropriate, or too severe, in particular when the purpose of the analysis is to get only general indications about the need of retrofitting; ii) giving a judgment about the reliability of the results obtained performing the nonlinear static analysis based on conventional 2-D pushover, particularly for configurations characterized by torsional effects; iii) identifying, for the considered structures, the most appropriate method of analysis among those proposed in Eurocode 8, in terms of both accuracy of the results and required computational efforts.

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