Shaking table tests of unreinforced and retrofitted rectangular three-leaf masonry walls under triaxial seismic excitation

The paper reports on the findings of the EU/H2020-funded project REBOND/SERA and investigates, by means of shaking table tests, two key questions on the seismic behaviour of multi-leaf masonry walls. The first one concerns the potential detrimental effects of the vertical component of ground motion on the strength degradation of the wall. The second relates to the effectiveness of a retrofitting scheme based on galvanized steel glass fibres inserted through the wall thickness. Investigating these two issues helps identify cases where the vertical ground motion component should be used in the seismic assessment of both as built and retrofitted masonry structures. It can also indicate cases. The ground motion is incrementally applied with scale factors ranging from 10 % to 120 %, unless collapse is reached at a lower intensity level. These results are compared with those previously published on an identically designed wall tested neglecting the vertical component of the ground motion. The dynamic tests of the retrofitted wall are also comparatively discussed. It is shown that the vertical ground motion component significantly affects the response of the three leaf wall, with more severe cracks and damage levels being observed at lower seismic intensities. With the 100 % scaled record, the consideration of the vertical component caused residual drifts of 0.25 %, corresponding to damage that was not observed under horizontal excitation only. Notably, the first residual vertical displacements were recorded at 75 % of the input earthquake and increased to 2.5 mm at 100 % of the input earthquake. On the other hand, the proposed retrofitting scheme, as anticipated, increased the wall strength and delayed crack formation. The first residual displacements in the retrofitted wall were recorded at 120 % of the earthquake input, which is strong evidence of the effectiveness of the proposed retrofitting scheme.