Design of Steel Collar Connectors for Timber Concrete Composite Floors

In many rehabilitation interventions, the substitution of the horizontal old timber structures with new floors is often proposed. However, this approach is commonly not accepted for historical buildings, which the conservation of the existing structures is required for. The timber-concrete composite (TCC) system is a technique successfully used since the 1980s. It generally consists of a concrete thin slab connected to the timber beams by dry connectors, like screws, nails and studs. It does not require the removal of the beams; it allows the lightening of permanent loads by using small thickness lightweight concrete slabs; it improves the uniform distribution of load among primary members; it provides the in plane stiffness against horizontal forces due to seism. However traditional connectors should be inserted into holes requiring to drill the timber members. This paper analyses the behavior of a reversible connector system, which avoids the perforation of the beams for the installation. It is made up of steel collars, surrounding the timber beam, which are composed by two or more parts, bolted together at appropriate folded wings, with purposely welded studs having the function of connectors. The slipping force transmission between the concrete slab and the timber beam occurs through friction between the contact surfaces, which is guaranteed by bolts tightening. Therefore, on the basis of experimental tests, numerical analyses and analytical studies carried out up to today, main observations about the mechanical characterization of the system and ensuing design criteria are discussed.