P_1.2.3 hardwood_connection

The experiments carried out so far with ash by holz.bau forschungs gmbh in the context of the P02 project “Use of hard deciduous woods in the form of rod-like and plane-like products in the building area“ concerning the screwing-in behaviour have revealed a good suitability of use of self-drilling screws. The ideal screwing-in lengths and extraction resistance at various angles between strength and grain and strength and screw access, respectively, are still to be determined in the context of the PO2 project.

On the basis of these results, the bearing strength and deformation behaviour of screw connections relevant to practical application between deciduous woods shall be examined in order to be able to achieve compact and highly bearing connections that exhibit the desired failure behaviour.

The distances between the connection techniques influence the wood’s readiness to split in connections with rod-like connection techniques. Minimum distances reduce the risk of a sudden failure through splitting. In cases of long screwing lengths, breakages of the screw can occur. In an optimum connection, the bearing strength is reached after desired deformation at an acceptable brittle breakage risk, while overstraining nearly leads to increased deformation. In order to come as close as possible to this ideal, the connection distances shall be examined with screws and dowels.

However, for a model formation of the bearing and deformation behaviour of screws crucial material specific parameters concerning the splitting, transverse tension and longitudinal pressure behaviour – which all also require further examination in the context of this research project – are still missing as far as the dowel connections are concerned. Here, the idea is to derive a simplified calculation model from the numerical or breakage-mechanical model for screws. The models shall then be verified using screw connections that are relevant in practical application. For an exemplary testing as to a suitability of application with other types of deciduous wood, comparable examinations shall also be carried out with beech.