Parameter influence on moisture induced eigen-stresses in timber

Moisture induced stress in timber is dependant on many factors. The driving force behind is the moisture variation in the surrounding air which causes induced stress due to restraint of hygro-expansion within timber elements (this can to some extent be seen analogous to thermally induced stress in steel). Today's computational power together with advanced constitutive models offers a  valuable tool towards understanding and determining moisture actions on timber. However, it seems that the issue concerning uncertainties of the input parameters is seldom addressed. This paper presents results on how various factors affect the resulting moisture induced stress by a  parametric study of the input values. A small numerical change of one parameter may possibly result in a  major change of calculated stress levels. It is for example, shown that coating (paint) and cross-sectional dimensions play an important role for spatial stress distribution.ZusammenfassungFeuchte induzierte Spannungen im Holz hängen von vielen Faktoren ab. Einen wesentlichen Einfluss haben Feuchteänderungen der umgebenden Luft, die wegen behinderter Feuchtedehnung innerhalb der Holzelemente innere Spannungen verursachen (vergleichbar mit Temperatur induzierten Spannungen im Stahl). Die modernen Hochleistungsrechner und verfeinerten Werkstoffmodelle erlauben, Feuchtevorgänge im Holz besser zu verstehen und zu bestimmen. Es scheint jedoch, dass die Unsicherheit der Eingangsdaten dabei bisher selten berücksichtigt wurde. Mittels einer parametrischen Studie der Eingangswerte werden in der vorliegenden Arbeit Ergebnisse vorgestellt, wie verschiedene Faktoren sich auf Feuchte induzierte Spannungen auswirken. Eine nur geringe numerische Änderung eines Parameters kann zu einer großen Änderung des berechneten Spannungsniveaus führen. So wird unter anderem gezeigt, dass eine Beschichtung (Anstrich) und die Querschnittsabmessungen eine wichtige Rolle bei der räumlichen Spannungsverteilung spielen.

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