Vergleichende Untersuchungen über den Ausziehwiderstand von Nägeln in von Pilzen befallenem und in gesundem Kiefernsplintholz

Zusammenfassung

Die vorliegende Arbeit behandelt Laboratoriumsversuche zur Ermittlung der Veränderungen des Ausziehwiderstandes von Nägeln in Holz mit zunehmendem Pilzangriff. Die Versuche wurden mit den drei FäulepilzenConiophora puteana, Lentinus lepideus undPoria vaporaria ausgeführt. Schon bei verhältnismäßig geringem Befall wird der Ausziehwiderstand beeinflußt. Bei sämtlichen Versuchen ging der Ausziehwiderstand bei Fäulebefall mit einem Gewichtsverlust von etwa 60% des ursprünglichen Trockengewichtes gegen Null. Es Besteht kein größerer Unterschied zwischen den Pilzarten. Es werden ferner vergleichende Versuche mit unbehandeltem Kiefernsplintholz beschrieben, das unter verschiedenen Verhältnissen in trockenem bzw. feuchtem Klima gelagert wurde. Das feucht gelagerte Holz weist einen höheren Ausziehwiderstand für neueingeschlagene Nägel auf. Bei Nägeln, die zu Beginn des Versuches eingeschlagen wurden und danach in feuchtem Klima lagerten, erhielt man einen geringeren Ausziehwiderstand als bei trocken gelagertem Holz. Dies beruht anscheinend darauf, daß die Lagerung in feuchtem Klima einen gewissen Ausgleich der vorhandenen inneren Spannungen im Holz mit sich bringt.

Summary

Rot around spikes is often found in the wood of sleepers, posts and similar objects. In a series of model experiments the withdrawal resistance of wire nails in rotted wood was investigated. Test specimens of, 25mm×25 mm×110 mm were sawn out of a pine plank, galvanised nails were driven into each one as shown in fig. 1. and than divided into the following sets.

• 1. Specimens kept in an air conditioned space with an air temperature of 20°C and 60% relative humidity.

• 2. Specimens kept in a climate with varying temperature and humidity (fig 3, table 5), but with higher average than set 1.

• 3. Specimens rotted for 2, 4 and 6 months by Coniophora puteana, Lentinus lepideus and Poria vaporaria. The rotting was performed in soil, which the specimens were almost completely buried in.

At the end of each test series the specimens were conditioned at 20°C and 60% rel. humidity and the withdrawal resistance of the nails was determined. The withrawal resistance was also determined for nails driven in after the storage period described above and after conditioning as mentioned for set 1. The loss in weight of the samples due to the rot was also determined (table 8).

The withdrawal resistance of the nails driven in before the storage period of sets 1 and 2 is shown in table 3 and 6 and in fig. 2 and 4. The nail retention strength decreased more in the series kept in the damper climate and reached a maximum of 53%. Trials with nails driven after the storage period of set 2 showed an increase in withdrawal resistance with increasing storage time (table 7, fig. 5).

For rotted specimens the withdrawal resistance of the nail has been shown relative to the loss in weight. The diagrams in figs. 7, 8, 10, and 11 show that the withdrawal resistance decreases with increased loss in weight (increased fungal attack). For rot attack corresponding to a loss in weight of about 60% the withdrawal resistance was null. No difference between specimens rotted by various fungi was observed. All sorts of fungi employed belong to the group which destroys primarily the cellulose.