Fatigue Behaviour of notches and self-drilling fully threaded screws for the application as connection in Timber-Concrete Composite Beams

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The main objective of the project is to analyse the fatigue behaviour of timber-concrete composite beams (TCC-Beams) with notched connections under cyclic loading and provide guidelines for the fatigue verification. Firstly, the transferability of accepted methods and procedures in design of steel and steel-concrete-composite constructions should be reviewed. An appropriate fatigue verification should be derived in order to allow for the practical application of this connection in road bridges and other types of constructions with relevant fatigue loading. Compared to other TCC-connection types the notched connection is characterized by very high strength and stiffness values and its ease of construction. First examples of practical application exist, however these are pilot projects. Before a general implementation in the timber standard, some open questions have to be clarified. One issue e.g. is whether the verification process, originally developed for steel- and steel-concrete-composite beams (on basis of S-N-Curves and the linear damage accumulation hypothesis by Palmgren and Miner), is also applicable for timber-concrete-composite beams with notched connections or whether additional limitations are necessary. Therefore, preliminary studies will be conducted to identify possible effects of sequential arrangements in variable amplitude spectrum and the remaining bearing capacity after a cyclic testing for a number of cycles without fracture.Initial experimental investigations of the fatigue behaviour of notched connections have shown a brittle shear failure mechanism in the timber beam in front of the notch. To prevent this brittle failure mechanism, fully threaded screws reinforcing the notch will be analysed as an innovative solution. So, besides the unreinforced notch, reinforced notched connections with screws in front of the loaded edge of the notch will be tested for fatigue. In addition, to the enhancement of the strength of the notch, the second aim is the investigation of the fatigue behaviour of the fully threaded screws. A basic investigation of the fatigue behaviour of fully threaded screws should enable a safe and efficient use of this connection not only for reinforcing TCC notched connections but for other applications. To achieve this, for all three types of loading: shear, pull-out and interaction the fatigue behaviour of fully threaded screws should be analysed in component tests and an appropriate fatigue verification derived.