Reinforcement of ancient floors by timber-concrete composite systems with collar connector

Timber-concrete composite (TCC) systems have been successfully used in built heritage. They provide an efficient solution for improving the seismic response of masonry buildings in which timber floors are generally used. TCCs commonly consist of a thin concrete slab connected to the timber beams by connectors. The paper focuses on a steel collar connector, appropriately conceived for surrounding the timber beam, avoiding any drilling into the wood. It is composed of parts bolted at appropriate wings, with the superior one or purposely welded studs working as connectors. A rubber layer interposed between the collar and beam can both reduce damage to the beam surface and ensure the adaptability of the system to irregular surfaces if applied to existing beams. Friction at the wood-(rubber)-steel surface is guaranteed by bolt tightening. This paper describes the experimental and numerical research activity carried out. Monotonic push-out tests were performed on different types of collars, which allowed the evaluation of the system behaviour and failure modes, with the aim of system optimisation. Bending tests on either timber-concrete beams or a full-scale floor equipped with collar connectors were also performed. An application of the TCC system with collar connectors to a historical timber floor is briefly described.