Shake table tests on unreinforced load-bearing masonry sub-structures

The field of application of unreinforced load-bearing masonry has been widely extended in the past two decades thanks to a better understanding of the structural behaviour and a better control of production methods, leading to improvements of their design and a more rational use of the material. Multi-storey apartment buildings and lightweight concrete houses are now widespread. Nevertheless, this structural solution is still questionable in seismic areas, even for low-to-moderate activity, and requires additional investigations to properly understand the structural behaviour under these specific horizontal dynamic actions. Moreover, these new applications are associated to new requirements, like the individual comfort or the low energy-consumption, achieved by resorting to technical solutions that are likely to influence on the dynamic response of the structure.
In this context, experimental shake table tests have been performed on unreinforced loadbearing clay masonry sub-structures. In this paper, the main observations derived from the direct experimental measurements are summarized and followed by resulting preliminary conclusions. A major observation is a significant rocking behaviour for the tests with the highest seismic input, strongly influenced by the presence of rubber devices and the frame effect. Dynamic characterization of the tested specimens (natural frequencies and modal shapes) is also detailed.