The stiffening and strengthening of wooden floors by a thin collaborating concrete slab is a common suitable technique used in the restoration of ancient buildings. It generally consists of a concrete thin slab connected to the wooden beams by means of devices, like screws, nails, and studs, inserted in the beam, in ad hoc drilled holes. In order to avoid any strength reduction of the existing wooden beams due to perforation, which is necessary for the installation of traditional connectors, an innovative type of connector has been conceived. It is a steel collar surrounding the timber beam, which is composed by two parts bolted together at appropriate folded wings; the function of connector is held by the superior wings. A rubber layer is interposed at the interface between the steel collar and the wooden beam, for guaranteeing the complete adherence between elements. Due to the bolt tightening, the collar also provides a transversal ringing action on the beam.

The paper presents the state of the art of the research carried out by the authors on the connector systems, within the International project PROHITECH ("Earthquake Protection of Historical Buildings by Reversible Mixed Technology", 2004-2008; prof. F.M. Mazzolani coordinator). Experimental tests and numerical analyses have been developed on both rectangular and circular specimens, made of new and ancient timber respectively. In particular, push-out tests on different types of connector, which correspond to further improvement and optimization of the system; bending tests on timber-concrete beams and full-scale floor equipped with the collar connectors have been performed.