Restoring of timber structures: connections with timber pegs

A quite widespread methodology of restoration of ancient timber structures envisages the introduction of new timber elements, connected to the standing structure by a timber-to-timber joint. An efficient alternative to the most used jointing technologies, which employ metallic bolted plates, steel pins, or epoxy resin adhesives, could be the use of timber pegs, if reliable design formulas could be found in codes devoted to timber structures. The design rules currently available for pinned joints contemplate only steel connectors, involve mechanical characteristics of the dowel as well as of the timber elements constituting the joint and are based on Johansen’s theory. The present research has the target of verifying the applicability of this theoretical model, and of the derived design formulas, to the case of timber pegs. At this aim, an experimental research has been performed, devoting special attention to the description of timber peg behavior inside the double shear plane joint and of dowel-bearing strength of the base timber, when a timber peg substitutes the envisaged steel bolt. Obtained results were compared with theoretical ones, showing that the different nature of the material employed for the pins needs more specific evaluation of the mechanical properties to be inserted in design formulas. Moreover, as in the field of new building timber joints fastened by timber pegs are widely employed in prefabricated timber frame industry, contents of the design standard for those structures are also taken into account, especially with reference to the “effective shear” failure mode of the timber peg.