Historical buildings and structures should be maintained as cultural monuments in their rich architecture and preferably with authentic materials for the coming generations. Also historical monuments often have a considerable importance for a regional economy. Their preservation is a challenge involving many scientific areas, especially for the protection against environmental deterioration processes.
Up until now monitoring was mostly limited to periodic visual inspection, which is not very effective, or to the registration of climate and air pollution data as a base for damage prediction. Scientists of the university of Stuttgart, together with other research groups from several European and Mediterranean countries, have now developed intelligent wireless systems for the long-term monitoring of historical buildings. Thus owners or restorers could be warned about risks or recommendations for actions could be given.
The experts tested the new systems at five historical sites in different climate zones, among them the museum island in Berlin, the portals of the minster in Schwäbisch Gmünd or the Old Town of Hebron in the Palestinian administered areas. Within the scope of "research behind the scenery“ Prof. Christian Grosse from the material testing institute of the university of Stuttgart (MPA Universität Stuttgart) explained the research project on the 9th of June and showed with a prototype of the wireless measuring instrument how non visible damages could be detected.
Intelligent measuring technology detects damages
Christian Grosse has shown a prototype of a wireless sensor node, whose sensors are fastened to a historical stone column, recording data in real time. On a computer several metres away (which could be under real conditions also in the office of a restorer) appeared measuring values for temperature and strain changes. A specific measurement feature shows the activity of acoustic emission according to crack evolution.
”Values of temperature and strain must be considered always together“, explains Grosse, ”only if an acoustic emission, which could be explained as a micro earthquake in the stone, exceeds normal values and the values of temperature and strain are also unusual, damage processes will take place, which require further examination.“ The intelligent measuring instruments should simplify the long-term monitoring of historical structures in which they observe and evaluate many parameters at the same time. ”Miniaturised robust sensors will be installed in buildings and give thus information about temperature, humidity, wind speed, material strain, cracks, acoustic emission, vibration, irradiance or even a possible chemical attack“, he explains the aim of the research project.
An important milestone is although – based on integrated material models – the intelligent data processing in the sensor node. This means that the sensor systems will be enabled to evaluate and filter the measured data independently. Thus only relevant data are sent to the central computer or respectively to the owners or restorers which are warned or provided with recommendations for actions.
A total of 14 research institutions from Germany, Italy, Austria, Poland, Croatia and the Palestinian administered areas are involved in the project. Under coordination of the university of Stuttgart the intelligent systems will be tested under real conditions; therefore case studies will be carried out in five historical sites. ”With the museum island in Berlin and the portals of the minster in Schwäbisch-Gmünd, the Palazzo Malvezzi of the province Bologna, the Old Town of Hebron and the chapel at Schönbrunn castle in Vienna objects from three different climate zones as well as indoor and outdoor objects are available“, explains Grosse. He expects that the intelligent systems which will be developed within the scope of the project ”Smart monitoring of Historic Structures (SMooHS)”, funded with 1.4 million Euros by the European Union, are ready for application at the latest in two years.
For a broader application of these techniques he focuses on the development of a user friendly modular software on Open Source basis, which can be continuously improved and extended, as well as on inexpensive miniature sensor systems (an individual measuring node will cost between 100 and 200 Euros). And the range of application of the new technology are various: This can cover the whole spectrum of monitoring from historical buildings over routine safety checks for instance at motorway bridges up to stability examinations of buildings for example with strong snow load or after earthquakes.
From wind energy plants to outer space
However, these are not the only fields on which Stuttgart material experts could score with non destructive measuring methods. Thus they have just concluded a research project founded by the Federal Ministry for Economy and Technology to the non destructive testing of rotor wings of wind energy plants. A robot system was developed which adapts and automates the up to now usual "hammering examination" of the rotor wings and checks whether material damages affects the function or require even an exchange of the wing. In another recently started project founded by the German research council the researchers examine so-called impact craters of meteorites. Participants are Christian Grosse together with other research institutes from Germany. The researchers expect explanation about the origin of the earth and solar system.
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