Low-cycle behavior of wood screws under alternating bending

Abstract

Earthquake-resistant timber structures may be designed accounting either for the dissipative or low-dissipative structural behavior, depending on the relevant ductility class. A timber structure belonging to a given ductility class shall meet specific requirements especially in the type and rotational ductility capacity of connections, since the timber members themselves shall be regarded as behaving elastically. In addition, Eurocode 8 prescribes that only materials and mechanical fasteners providing appropriate low-cycle fatigue behavior may be used in joints regarded as dissipative zones. In this context, the properties of dissipative zones may be determined by tests either on single joints, or on whole structures in accordance with EN 12512. At the same time, the appropriate fastener’s low-cycle behavior is currently deemed to be satisfied if the connectors are sufficiently slender with respect to the thickness of the joined members. Nowadays, this assumption may not be sufficiently reliable because of the actual trends in fasteners technology, which consists in providing heavily hardened connectors in order to achieve higher resistances and ease of insertion into timber. The aim of this study is to investigate the low-cycle behavior of modern wood screws by means of three-point alternating bending tests. The paper describes a new testing apparatus, the related test procedure and assessment criteria specifically designed for this purpose. A preliminary investigation of the low-cycle behavior of different wood screws currently on the market is then carried out and the related test results are discussed.