Ambient vibration testing and seismic fragility analysis of masonry building aggregates

Over the years, masonry structures have shown evidence of good behavior under vertical static loads; however, its characteristics make the use of this heterogeneous material unsuitable for buildings in seismic zones. Masonry building aggregates represent a common structural typology in many cities around the world. The present work addresses the seismic vulnerability assessment of an aggregate of mixed masonry-RC buildings in the region of Lisbon, which is characterized by moderate to high seismicity. Moreover, this typology was built before the enforcement of the first design code for building safety against earthquakes in Portugal (RSSCS). The numerical models were developed using the Applied Element Method (AEM) and calibrated based on experimental tests. The modeling technique applied was capable to identify the global and local failure mechanisms. A probabilistic approach allowed to compute the uncertainty in the seismic response, based on nonlinear static analyses. The site-specific ground motion was simulated using a non-stationary stochastic method. Subsequent fragility curves were derived, showing a significant probability that the structure will suffer moderate to extensive damage for a code compliant seismic assessment, corresponding to a 308-years return period and onshore seismic action.