Linear static procedures for the seismic assessment of masonry buildings: Open issues in the new generation of European codes

Linear procedures (lateral static force method or modal response spectrum analysis) are the standard approach for the seismic design of new structures. On the contrary, nonlinear procedures, in particular incremental pushover analysis, should be used for the seismic assessment of existing buildings, because it is difficult to estimate the behavior factor of a building in the absence of a standardized capacity design. Moreover, in the case of existing buildings, the use of linear procedures provides results that are excessively conservative, therefore unreliable. Despite this, seismic codes consider linear procedures because of their theoretical simplicity and robustness with respect to model uncertainties and non-linear issues, a priori avoiding convergence problems. The paper deals with the critical issues related to the application of linear static procedures for the seismic assessment of masonry buildings. Methods proposed by the present draft of the Eurocode 8 (Part 3) and the new Italian Seismic code (NTC 2018) have been applied to a case study building, under two configurations (regular, irregular); in particular, the modelling options usually adopted by professionals have been considered. Results are compared with the assessment carried out through the nonlinear pushover analysis, which may be assumed as able to better estimate the actual seismic behavior. Anyhow, the aim of the paper is not a validation of the code procedures but a comparison between alternative allowed methods. Conclusions show that even by considering the recent improvements in the codes, in the regions characterized from medium to high seismic hazard, linear methods result almost inapplicable leading to almost all buildings not verified in contrast with the evidences of most recent earthquakes.