Out-of-plane shake-table tests of strengthened multi-leaf stone masonry walls

Existing unreinforced multi-leaf stone masonry (URM) buildings are one of the most earthquake prone types of construction. Failure typically occurs even at low levels of earthquake-induced loads, with the out-of-plane delamination of masonry leaves and consequent collapse of the whole façade. Although this issue has been tackled by several researchers, dynamic tests reproducing the earthquake behaviour of as-built and strengthened multi-leaf stone URM walls are very limited in the literature. In response to this lack, shake-table testing of eight full-scale multi-leaf stone masonry walls followed by dynamic modal identification was performed. The application of steel tie-rods in the wall cross-section, the injection of the inner-core using hydraulic lime-based grout, and a combination of the two techniques are presented herein as suitable interventions to enhance the monolithic behaviour of multi-leaf stone URM walls. Tying the outer masonry leaves together increased the seismic capacity by a factor of 1.8 compared to unreinforced condition, while injecting grout into the inner-core of the wall provided resistance to peak ground acceleration (PGA) that were 2.3–3.6 times the PGA resisted by as-built walls, depending on the quality in the execution of the intervention. The results obtained in the walls strengthened with both techniques were significantly related to the grout injection only.