Shaking table tests on unreinforced load-bearing masonry frames

The last years have seen an increasing interest of engineers for unreinforced masonry structures, leading to strong improvements in the knowledge of their behaviour in usual conditions. Further investigations are however still required about their seismic behaviour. Indeed, the current design rules for such situations are commonly admitted as rather conservative, limiting thus the use of these structures, included in low or moderate seismic areas. This conservative character is in particular associated with the facts that walls perpendicular to the seismic action are usually neglected and that horizontal spanning elements are not properly considered, leading to an underestimation of the favourable frame effect. The present contribution describes shaking table tests on unreinforced load-bearing masonry sub-structures aiming at a better understanding of their dynamic behaviour. The tested specimens are two single-storey frames with respectively T- and L-shaped masonry piers coupled by a RC lintel and a slab. In particular, the T-shaped piers of the first frame are oriented in such a way to create a non-symmetric system. The L-shaped piers of the second frame are made of two perpendicular walls connected by different methods. The experimental study focuses on specific topics, such as the frame behaviour and the contribution of walls perpendicular to the direction of the seismic action. The issue of global and local torsion, the influence of the wall-to-wall connection technique and the gravity loading patterns are also investigated. The paper summarizes the main test results, including characterization of the dynamic properties of the specimens. A significant rocking behaviour is also evidenced for the highest input acceleration levels. Direct post-tests observations show the importance of the torsional effects, of the connection type between walls of a pier and of the loading configuration.