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Author(s):	Ringhofer, Andreas; Brandner, Reinhard; Schickhofer, Gerhard
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Abstract:	Der Beitrag behandelt die Optimierung der Geometrie von vorwiegend axial beanspruchten selbstbohrenden Holzschrauben für den Einsatz in einer Stahl-Holz-Laschenverbindung unter Zug parallel zur Faser. Mit Fokus auf den Stahlbruch werden der Kopf und Ansatzbereich des Gewindes adaptiert und die Veränderungen im Last-Verformungsverhalten anhand von Prototypen versuchstechnisch an bauteilgroßen Laschenstößen und mittels einer numerischen Modellierung verifiziert. Es zeigen sich eine gegenüber herkömmlichen Schraubentypen um 2 bis 8 % gesteigerte Tragfähigkeit, eine Verlagerung des Versagens der Schraube von der Stahlblech-Unterkante tiefer in das Holz sowie die Ausbildung eines Fließgelenks am Beginn der geschaffenen Freistrecke. Letzteres lässt einerseits eine homogenere Lastverteilung zwischen den Schrauben infolge eines erheblich gesteigerten Duktilitätspotenzials und andererseits eine Verbesserung des Tragverhaltens solcher Anschlüsse bei Langzeit- und Zugschwellbelastungen erwarten. Zudem wird ein Vorschlag für den Nettoquerschnittsnachweis für zugbeanspruchte Laschenstöße mit selbstbohrenden Holzschrauben unterbreitet. Development of an optimized screw geometry for high-stressed steel-to-timber joints This paper deals with the geometrical optimization of mainly axially loaded self-tapping screws applied in steel-to-timber joints under tension parallel to grain. Focusing on steel failure, the head geometry and the zone before the thread were adapted. Consequently, differences to standard products were verified by laboratory tests on full-scale steel-to-timber joints and also by numerical modeling. A 2 to 8 % increase of load bearing resistance, a displacement of the location of screw failure deeper into the timber member as well as the development of a plastic hinge close to the head are the essential results of this study. Especially the yield deformation leads to a more homogenous load sharing between a group of screws, caused by an increased potential of ductility, and to an enhanced bearing behavior under long term as well as pulsating tensile loadings. In addition to that a proposal for the verification of the net cross-section of tensile joints with self-tapping screws is given.
Source:	Bautechnik 90 (2014), No. 1
Page/s:	31-37
Language of Publication:	German

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