Definition of differential seismic input motions for out-of-plane dynamic testing of unreinforced masonry gable walls considering different roof configurations

Unreinforced masonry gables are widely present in low-rise existing buildings and are particularly vulnerable to seismic events, as demonstrated by the several observed out-of-plane collapses of these structural elements during earthquakes. Since the structural behaviour of gable walls has been scarcely investigated in the literature, a large-scale testing programme (ERIES-SUPREME) has been initiated by research institutions in the Netherlands (TU Delft, TNO) and Italy (EUCENTRE, University of Pavia, IUSS Pavia), to dynamically characterise the gable out-of-plane seismic response. Shake-table tests on full-scale masonry gables are being conducted at the 9D LAB facility in EUCENTRE (Pavia, Italy), incorporating the effects of different ground motions, structures and roof stiffnesses. This facility features both a top and a bottom shake table, allowing for separate input motions: therefore, the effect of the roof dynamic behaviour can be accounted for by applying differential signals. This work presents the procedure used to define such input motions. While for tectonic signals direct earthquake recordings at floor level are accessible from existing monitored masonry buildings in Italy, for induced signals in the Netherlands such data are not available. Thus, in the latter case, numerical analyses are conducted considering a reference unreinforced masonry building subjected to induced earthquakes, with three roof configurations representing flexible, semi-flexible, and stiff diaphragms. Based on the obtained outcomes, input signals are derived for both induced and tectonic earthquake scenarios, leading to the final definition of the testing protocol for the ERIES-SUPREME experimental campaign. The findings of this study are also broadly applicable for the derivation of input motions in the planning of benchmark experiments where parts of the structural system cannot be explicitly reproduced due to testing constraints.