Shaking table tests on unreinforced load-bearing masonry walls - Comparison with simple rocking models

Abstract

Assessment of the overall seismic performances of multi-storey unreinforced masonry structures requires an appropriate characterization of the behaviour of their structural components, in particular when these are subjected to a dynamic ground motion input. In order to develop a better understanding on this issue and in a further perspective of investigating the consequences of the presence of 1 cm thick rubber elements used for improving the sound-proofing performances of the building, shaking table tests have been carried out in the framework of the European project SERIES. Four single walls were tested. These were built with high resistance thin-bed layered clay masonry with empty vertical joints. Two of them had an aspect ratio close to 1, while the other two were close to 0.4. One wall of each aspect ratio included rubber devices at its bottom and top to enable comparisons and conclusions about the influence of rubber on the wall behaviour. The test results were then partially compared to results obtained with a theoretical rocking model considering the wall as a rigid body. The results summarized in the present contribution evidence a significant rocking behaviour for the highest input acceleration levels. Characterization of this behaviour is however strongly dependent on the aspect ratio of the wall and on the presence or not of rubber devices in terms of natural frequencies, damping, dynamic amplifications and progressive damage with increasing acceleration levels. It is also showed that the theoretical rocking predictions are in good agreement with the experimental results for high acceleration levels, while the behaviour is closer to the one of a cantilever for the lower levels. It is finally evidenced that, in presence of acoustic rubber devices, amplitudes of the rocking motion are increased but with a more limited damaging of the wall because of the capacity of the rubber to absorb the impact energy. Results of this study on single walls are expected to be further extended to global masonry structures, account taken for the influence of actual boundary conditions of the wall.