PUSH-OUT TESTS ON TIMBER-STEEL HYBRID JOINT WITH SCREWS CONNECTIONS. NUMERICAL AND EXPERIMENTAL INVESTIGATIONS

The increasing spread of timber as structural material strongly seeks for deeper investigations concerning its behaviour, in static and, even more, in cyclic conditions. It is well known that timber is characterised by several favourable properties, as lightness (significantly lower than e.g., concrete and steel), high strength-to-weight ratio, proneness to reusability and recyclability (under certain conditions taken into account since the early design phases), but some other properties are detrimental and should be handled. One of the main unfavourable characteristics that is source of several issues in timber structures is the material low ductility, especially in tension and shear where brittle behaviour is acknowledged. In order to provide adequate ductility, avoiding significant unexpected strength loss, proper design of connections is the key to guarantee ductile structural behaviour; moreover, it is very common to combine timber with steel, giving rise to timber-steel composite (STC) assemblies, where desirable properties of both materials are highlighted. This solution allows for significant environmental advantages with comparable structural performance in terms of static loading with reference to traditional solutions, according to available literature findings; on the other hand, very few experimental campaigns with cyclic loading conditions were encountered and this issue was the reason behind the motivation of this research: timber structures are now spreading in areas, as southern Europe, where seismicity is generally significantly higher than e.g., northern Europe where timber is very common but seismicity is low. This paper presents both static and cyclic push-out tests, firstly numerically designed, in order to select experimental tests to carry out in the laboratory, according to European Standard EN 12512. Screw shear connectors with two diameters (8 mm and 12 mm) are considered. On the basis of results, equivalent viscous damping is calculated, acknowledging effects of screw diameter.