Carla Ceraldi

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.

EXPERIMENTAL VALIDATION OF IN-PLANE FRICTIONAL RESISTANCES IN DRY BLOCK MASONRY WALLS

This paper presents the experimental and analytical validation of the lateral strength of dry block masonry walls under in-plane loading. The analytical evaluation of the in-plane frictional resistances activated at the onset of the rocking-sliding mechanisms is revisited in order to account for the different contributions of the self weight of the wall and additional loads. It is assumed that the wall is arranged in a running bond pattern, with rigid blocks and dry contact interfaces governed by cohesionless Coulomb failure criterion. The accuracy and robustness of the analytical results are assessed by experimentally testing both the resultant frictional resistances and their applications points. Both pure sliding and rocking-sliding failure modes are simulated with a testing device designed and realized ad hoc (no standard equipments and procedures were found in the literature). A good agreement between the analytical and experimental results is shown for the selected cases. 2607 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2607-2618

The Influence of Dowel-Bearing Strength in Designing Timber Pegged Timber Joints

ABSTRACT The employment of timber pegs in timber structure joints is a widespread technology in the field of timber frame building in the United States, where the Timber Frame Engineering Council has published a special Standard to supplement the National Design Specification for Wood Construction. The authors have been studying the possibility of supplementing the Eurocode 5 design formulas, thought for timber joints with metal connectors, with specifications needed for a reliable design when employing timber pegs. The field of application envisaged is that of restoring timber structures and results obtained until now are quite encouraging. In this step of the research, more attention has been paid to deformation process: fir and chestnut samples have been tested to determine their dowel-bearing behavior with steel and ash timber peg while double-shear plane joints made of the same wood species, and fastened with steel as well as timber pegs, have been analyzed.

Stop-Splayed Scarf-Joint Reinforcement with Timber Pegs Behaviour

Restoring ancient timber structures often involves cutting or reinforcing stop-splayed scarf-joints in beams or truss-rods. Steel nails, bolts and plates or adhesive resins and rods are commonly used, however these jointing technologies cause some disadvantages, such as moisture between steel and timber surfaces, hard reversibility of the intervention and a questionable aesthetic output in uncovered structures. The employment of timber pegs, inserted perpendicular to the grain, could be an efficient solution and is already preferred in some applications. Since no design rules for traditional timber joints or for timber pegged connections are given by European codes, investigations on scarf joint behaviour before and after reinforcement are needed aiming to reliable design procedures. In this study, the role of the fastener inside this tension resisting carpentry joint and its contribution in yield strength and stiffness have been investigated. Specific attention has been addressed to stiffness, which is positively influenced by the insertion of timber pegs. Three samples of fir scarf-joints have been tested, a total of eight specimens, with different configurations: without fasteners, with timber pegs and with steel pins. The different failure modes under tension load of the samples and their rheological behaviour have been studied and compared to trace force distribution between the resisting elements, that is the ash key and the added fasteners.