The influence of self-tapping-screws used as transversal reinforcement on short and long-term bond behavior of structural elements and joints in glued laminated timber

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In the course of the various investigations on glue laminated timber load-bearing elements and specimens joined and reinforced with screws in the Chair of Structures and Structural Design, has been repeatedly shown that implementation of self-tapping screws, perpendicular to the main load direction as reinforcement, increases bond behaviour of axially loaded screw and load bearing capacity of structural elements. This reinforcement configuration reduces transverse tensile stresses caused by load and especially shrinkage cracks in the bond interface caused by moisture variation, whereby the service life of wooden components can be undoubtedly extended in this way.The research project, proposed here, deals with the material-related interrelationships and the load-bearing effect of self-tapping screws, which are introduced into the wood matrix in particularly perpendicular the grain in order to derive rules and possibly a system for the arrangement of this type of screw reinforcement. The investigations of the influence on the axially loaded screw short-term capacity and long-term response under different climates (service class 1 - 3) will help in development of practical design approaches and expand the range of application in timber structures. Also, it will be investigated to what extent transversely arranged screws can reduce the moisture induced cracks, long-term damage accumulation in the bond and counteract the influence of wood growth irregularities. The experimental investigations (short-term pull-out tests and long-term tests in three different climate conditions) are comparative between transverse-reinforced and non-transverse-reinforced specimens. Parallel to the material investigations, calculations with non-linear finite element methods including anisotropy will be carried out in order to be able to depict the mechanical effect of the transverse reinforcement in the context of load-bearing behavior simulations.