Validation of displacement-based procedures for rocking assessment of cantilever masonry elements

Abstract

The seismic assessment of cantilever elements in masonry structures is a relevant topic because of their high vulnerability and since they often involve artistic assets (such as bell-gables, parapets or pinnacles). Due to the complexity of nonlinear dynamics of cantilever systems, displacement-based assessment (DBA) procedures have been developed with the main advantage to be less demanding and, therefore, engineering practice-oriented. Various international codes already adopt these procedures but with different choices in their implementation, e.g. in the idealisation of the single degree of freedom or the method to assess the seismic displacement demand. However, despite their widespread use, a systematic validation and comparison among them is not available yet. The aim of this paper is to assess the reliability of five DBA methods available in literature and codes. To this aim, three cantilever elements with a different slenderness were analysed, both considered as laying on the ground floor or atop a supporting structure. Then, incremental dynamic analyses (IDA) have been performed by using several recorded time histories and the results were considered as the reference solution to be compared with the ones obtained by applying the examined DBA procedures. In particular, the results were processed in terms of the peak ground acceleration (PGA) alternatively leading to the attainment of the ultimate limit condition assumed by the codes or to the block overturning. The IDA clearly highlighted that the displacement demand is very sensitive to the intrinsic features of each record. The comparison in terms of fragility curves allowed evaluating robustness, reliability and safety margins of the static displacement-based previsions. Despite the complexity of the problem, the results showed that, as long as proper definitions of the ultimate displacement capacity and proper assumptions for evaluating the seismic displacement demand are adopted, the DBA approach provides safe and reliable estimates.