Die Holz‐Wasser‐Interaktion am Beispiel ausgewählter fremdländischer Holzarten. Das hypothetische Hydratwasser

Discussion of the interaction between wood and water based on selected foreign wood species as examples, and the concept of hypothetical hydration water. The interaction between wood and water is of crucial significance for the practical application of wood. The moisture content influences virtually all wood properties. The strength of the bond between water and wood varies across the hygroscopic range of the sorption isotherm. The different water bonding types are characterised by different chemical, physical and capillary forces. Water can bond to very dry wood to such a degree that contraction occurs in the sorbed layer. Water absorption in this layer is not accompanied by swelling. The physical state of the water is referred to as hydration or crystallisation water. Based on our previous work on the sorption characteristics of different wood species, this paper discusses the phenomenon of hydration water based on complex sorption and swelling measurements on foreign wood species.     

Wasserdampfsorptionsverhalten ausgewählter heimischer und überseeischer Holzarten

Water vapour sorption behaviour of selected domestic and overseas wood species. At 21 domestic and 11 overseas wood species the equilibrium moisture content at 20 °C and 35, 50, 65, 80 and 95% relative humidity was experimentally determined in the adsorption phase. The experimentally determined average values were computed with help of the Hailwood Horrobin model to get selected parameters such as fiber saturation point, mono‐ and polymolecular sorption, specific surface, hypothetical molecular weight as well as inaccessibility of the sorbent to the sorbate. Tables for the equilibrium moisture contents at 20 °C computed in 2% steps of relative humidity are presented. The fiber saturation point computed with the Hailwood‐Horrobin model lies for all examined wood in the range from 22% to 36%, on the average with approx. 30%. There are substantial deviations in the fiber saturation point between the individual wood species. The tendencies for the characteristics of the sorption analysis were pointed out.     

Fundamentplatten aus Stahlbeton und Stahlfaserbeton. Experimentelle Untersuchungen zur Gebrauchstauglichkeit und Tragfähigkeit

Reinforced Concrete and Steel Fibre Reinforced Concrete Rafts Experimental tests on serviceability and ultimate loading performance Houses and residential buildings are increasingly built on rafts instead of strip foundations. The main advantages of rafts are more efficient excavation works and easy concreting of the rafts itself. The use of steel fibre reinforced concrete slabs offers economic advantages if there are no special requirements on service ability such as water tightness or crack limitations. At Aachen University of Applied Sciences a comparative experimental study on the load carrying behaviour of rafts made of concrete, reinforced concrete and steel fibre reinforced concrete was carried out. The tests have proven steel fibre concrete as suitable material for rafts in case of sufficient stiffness of the subbase. In case of special requirements on service ability, reinforced concrete or combined fibre and bar reinforced concrete should be used. In that case stresses should be calculated based on the elastic theory.     

Untersuchungen zur Festigkeit und Tragfähigkeit von Holz unter dem Einfluss chemisch‐aggressiver Medien

Holz zeigt eine hohe Beständigkeit gegenüber den meisten Chemikalien in allen drei Aggregatzuständen. Aus diesem Grund wird es häufig für Baukonstruktionen von chemischen Fabriken oder Lagerhallen für chemische Stoffe eingesetzt. Der Beitrag befasst sich mit dem aktuellen Stand der Erfassung der Korrosion und ihres Einflusses auf die Festigkeit von Holz und Brettschichtholz. Es wird die Berücksichtigung derartiger Einflüsse durch einen Modifikationsbeiwert” “Aggressive Medien” bei der Bemessung von Holzbauteilen erläutert. Studies on the strength and ultimate limit design of timber under the influence of chemically aggressive media. Timber has a high resistivity to chemically aggressive agents. This is one of the reasons why timber structures are frequently being used in the construction of storage halls for chemical materials or of industrial buildings with aggressive environment. In this paper the state of the art of corrosion in timber and the consideration the chemical action by using a modification factor in the limit state design is presented.