Langjährige Messung von Kraft‐ und Verformungsgrößen in Neotopf‐Gleitlagern einer Spannbetonstraßenbrücke. Brückenlager‐Monitoring

Longterm Measuring of Forces and Displacements in Elastomer Pot Sliding Bearings of a Prestressed Concrete Road Bridge. Monitoring of Bridge Bearings Two bearings of a three span prestressed concrete road bridge over the lake Aa in the City of Münster were equipped with elastomer pot sliding bearings with measuring devices during the erection in 1987/88, that are able to measure the distance between sliding slab and covering slab and the rotation of the covering slab. Moreover there are dynamometers, which measure the compression stress of the silicone oil in the pot under the elastomer. With these measuring devices the load history of the bearings during the time of erection of the bridge was monitored. In the 18 years that the bridge is in operation, the bearings have been monitored with these measuring devices. Following the completion of the bridge and further in intervals of some years the loads and displacements of the bearings were monitored especially during lorries were crossing the bridge. The bearings show only minimal attrition after 18 years in use.     

Spider colonization of former brown coal mining areas — time or structure dependent?

Colonization of former mining areas by a highly mobile arthropod group, spiders (Arachnida), is studied based on a comparative analysis of four mining areas of different age and habitat structure including adjacent undisturbed areas. Species number was lowest in sparsely vegetated sites, and highest in dense vegetation regardless of age. Species number may exceed that of undisturbed adjacent sites after 70 years. Similarity among the sites ranges from 26 to 75% (Sörensen index). A DCA ordination of sites revealed a grouping into three relatively distinct clusters, one including the vegetation free sites, the second the sparsely vegetated short grass sites, and the third both the plant species rich, mature, short grass sites and the tall grass stands. Environmental variables were related to the species composition by means of CCA. However, most of these relations proved to be spurious being either not significant or if so, showing a low contribution to variance explanation. The influence of scale parameters such as area size and distance (when analysing all data, data from mining areas only, or data from one mining area separately) becomes visible in all analyses. A detailed analysis including age as an independent variable shows that age has some influence on the structure of the whole data set including undisturbed sites, but not within the subset of the mining areas. Using data from one mining area only it is shown that the influence of age and spatial autocorrelation effects cannot be properly distinguished on the larger scales. A more detailed account on the known autecology of the species encountered showed that biological spectra of the communities remain similar in the course of development. Initial colonization occurs very rapidly during the first years after dumping. The most decisive aspect of population establishment is the structure of the vegetation, as expressed by height or volume amenable for colonization. Despite some developmental trends such as increase in species number clearly separated successional stages cannot be distinguished.     

Liquid water flow in Pinus radiata during drying

End-sealed 60×60×250?mm³ Pinus radiata pieces were dried at 65/37 °C (dry bulb/wet bulb temperature) and 4 ms^-1 air speed to study various drying phenomena above fibre saturation point. While drying, an X-ray computed tomography (CT) scanner captured a cross-cut density image every ten minutes. The density data was used to determine moisture content, rate of moisture loss from the core, wetline (boundary line of the free water region) depth and cross-cut area of the wood pieces. Repeating patterns were observed, which indicated that the cavity-size distribution of the wood pieces dictated fluctuations in the rate of moisture loss from the core and cross-cut area shrinkage during drying in the free water phase. It is hypothesised that, while drying an interconnected capillary network in the free water phase, the largest meniscus penetrates a wood piece through the largest cavities, thus also allowing air into the capillary network. The largest meniscus would always get smaller as it penetrates the wood piece until it is not the largest meniscus in the network anymore. Then the new largest meniscus would start penetrating the capillary network, etc. The largest meniscus would also determine the liquid tension in the capillary network. When the largest meniscus gets small enough, and the liquid tension strong enough, deformation and collapse of the remaining liquid-filled cavities can occur. A large liquid-filled interconnected capillary network would eventually fragment into a number of smaller liquid-filled interconnected networks, at which point a receding wetline could be observed.