Self-tapping screws are an interesting solution for timber-to-timber shear connections due to their performance, their economic advantages and their ease of use. The screws are preferably used inclined with respect to the shear flow direction, to improve the stiffness and the strength of the connection. The shear transfer mechanism is influenced also by the withdrawal capacity of the screw and by friction between timber elements. These connections are useful for the bending reinforcement of existing timber floors, but the design of these composite sections requires the knowledge of the connection behaviour. However, very few data are available on the long-term behaviour.
An experimental campaign to follow the connection behaviour during time has been performed. The results of a first group of twenty-four identic specimens were already presented. The last results of another group of sixty-three specimens are here reported. One half of the specimens was stored in a controlled environment, one half was stored in a not-controlled environment. Air temperature and humidity were regularly recorded. Push-out tests (as soon as built and after 6, 12 and 24 months) were performed and the main mechanical parameters of the connections as strength, stiffness and ductility at different ages are here compared.
