Struetural Evaluation of Historie Walls and Eolumns in the Altes Museum in Berlin Using Non-Destructive Testing Methods
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Structural Analysis of Historical Constructions - Modena, Lourenço & Roca (eds) © 2005 Taylor & Francis Group, London, ISBN 04 1536 379 9 Struetural evaluation of historie walls and eolumns in the Altes Museum in Berlin using non-destructive testing methods b C d e C. Maierhofe~, M. Hamann , C. Hennen , B. Knupfer , M. Marchisio , F. da Porto f , L. Bindag & L. Zanzig a Federal lnstitute for Materiais Research and Testing (BAM), Berlin, Germany b lnstitute for Applied Science in Civil Engineering (laFB), Serlin, Germany c Stiftung Luthergedenkstiitten in Sachsen-Anhalt, Lutherstadt Wittenberg, Germany d GEOClSA, Research and Development, Madrid, Spain e University of Pisa, Dept. of Civil Engineering, Pisa, ltaly f University ofPadova , Dept. of Construction and Transport, Padova, Italy g Po/itecnico di Milano, Dept. ofStructural Engineering, Milano, Italy ABSTRACT: The methodologies developed in ONSITEFORMASONRY were applied to assess the structure and material properties ofselected structural elements in the Altes Museum in Berlin-Mitte. Since at ali time the Altes Museum was of great concern in the archival studies, a lot of information exist about former destruction and restoration which support the interpretation of data recorded with the different testing methods. INTRODUCTION Analysing the damages and other problems affecting historical constructions for their structural evaluation, methodologies based on the application of non destructive (NDT) and minor destructive (MDT) testing methods have been designed during the ONSITEFORMASONRY-project according to the type of damage or problem, the construction typology, the leveI ofassessment and the environrnental conditions. These methodologies are being applied on real cases Figure I. Altes Museum in Berlin-Mitte, view from the Lustgarten. like the Altes Museum in Berlin for their validation. The Altes Museum (old museum) in the city centre At ali time the Altes Museum was of great concern. ofBerlin was designed by Karl Friedrich Schinkel and Thus archival studies of the Technical University of was built between 1823 und 1830 on the Lustgarten. Berlin provided a lot of information about the struc Figure I shows a view from the Lustgarten. The build ture. These studies are of fundamental interest for ing was designed with an atrium containing pillars and ongoing NDT and MDT in the frame of the European a central cupola related to the Roman Pantheon and Research Project ONSITEFORMASONRY. having anti que temples as an archetype. It represents With radar, geoelectric, microseismic, sonics, the eldest exhibition hall in Berlin. During the Second impulse-thermography and flat-jack, different testing World War parts of the Altes Museum burned down, problems have been solved which are described in and it was rebuilt in 1966. more detail below. In 1999, the planning stage started for a broad reconstruction in the frame of a master plan con cerning the whole Museumsinsel (museum island) 2 OBJECTIVES taking into account contemporary requirements for a museum building. Extensive investigations have to be The Altes Museum has been chosen as pilot site performed to assure structural integrity and to provide because several questions are also typical for other a basis for a sustainable and considerable conversion historic structures in general. In the frame of recon ofthe building. struction, testing problems mainly occur related to 331 Figure 2. Cross-section of the Altes Museum showing the different construction elements in the entrance hall, in the rotunda and in the cellar. Figure 3. Structure of the supposed reinforcement stone the inner strueture of different struetural elements ring and position of the investigations. like eolumns, floors, eeilings and walls. In this paper, Therefore, at least the basement eonsisting of natu the following objeetives have been analysed (see also ral stone is exposed to moisture. The inner earrying Figure 2): wall whieh was seleeted for the investigations is - Investigation of the inner strueture of the outside aeeessible from both sides, one side is eovered with eolumns in the entranee hall ofthe museum. Here, mortar. From the floor up to a height of 70 em, the outer eolumn loeated at the west part of the the wall eonsists of a pedestal made of lime stone. entranee hall was seleeted for solving the following Above the pedestal, there is still stonework made of questions: How are the single drums eonneeted to lime stone up to a total height of 2.0 m. The eon eaeh other? Is it possible to loeate the different mate neetion to the eeiling was closed by two to three riais used for restoration at the eylindrieal shell? A layers ofbriekwork. At both sides ofthe wall, there seaffold was raised for performing measurements are wall porehes whieh are eonneeted to the wall. along the whole length. Radar and ultrasonie inves At the side without mortar, lhe wall shows a eraek tigations in refleetion as well as in tomographie with widths from 0.5 to 3 em at the area close to mode had been planned. the outer wall. The eraek follows the steps of the - Loealisation ofp laster delaminations at the eolumns joints from the lower edge ofthe eeiling down to the in the rotunda. These eolumns belong to the origi floor. For the investigation of the inner strueture, nai asset from 1830. The eolumns eonsist ofmassive for the determination of the moisture di stribution sand stone whieh is eovered with lime plaster having and for analysing the load measurements, investi a thiekness of2 to 3 em. This plaster is the earrying gations had been performed at this wall with radar, layer for the visible stueeo marble layer of3 to 6 mm. geoeleetrie, mieroseismie, sonie tests and flat-jaek. The sand stone eore is massive and it is expeeted that - Struetural investigation of the sand stone ring. it eonsists of single drums. The whole surfaee of the Figure 3 shows the assumption of the arehiteets eolumns is eovered with a net of small eraeks. The regarding the existenee of a stone ring embedded eraeks are very thin, but few ofthese have a width of inside the briek masonry strueture supporting the up to 2 mm. By knoeking on the surfaee, different dome. The objeetive of the investigations was to types of delaminations ean be aeeessed: Delamina validate this assumption and to derive as many tions of the stueeo marble layer, delaminations of information as possible regarding the morphology the plaster and a eombination ofboth. One eolumn of the ring. Thus, radar measurements had been (no 14) had been seleeted for investigations with carried out in reflection mode. impulse-thermography to loeate and quantify these delaminations. 3 METHODOLOGIES - Investigation of the strueture and moisture eontent of an inner earrying wall in the eellar. The founda tion of the Altes Museum is based on wooden piles, 3.1 Radar whieh have been positioned in a dense grid. The top Radar is based on the transmission of short elee of these piles is eovered with wooden frame eon tromagnetic impulses by an antenna at frequeneies struetions. These are the basis for the foundation between 300 MHz and 2.5 GHz (Daniels, 1996). These eonsisting of natural lime stone. The walls eon impulses are refleeted at interfaces with ehanging strueted on this basement are made ofbrieks. Only dielectric properties of the materiais. Also the prop parts of the building have a eellar. The levei of the agation ve loeity depends on the dieleetrie properties. ground water is at 31 mNN (normal levei), while Sinee moisture is influencing this parameter, radar ean the floor of the eellar is at approx. 31.71 mNN. also be applied to detect an enhaneed moisture eontent 332 and to determine the moisture distribution. With radar, measurements (severa I hundreds) is performed. The reflection measurements from one surface as well as measured data, namely the apparent resistivities, can tomographic measurements from both sides are usu be directly plotted versus some kind of pseudo-depths ally performed to obtain information about the internaI to build the so called pseudo-sections. These are purely structure of the structural element under investigation qualitative images. (Maierhofer et aI, 2000; Colla et aI, 2000; Maierhofer By means of a complex inversion process, the dis et aI, 1998). tribution of true resistivities versus true depth can be obtained, that is, another kind of geoelectrical tomo 3.2 Sonics graphy. This is sometimes referred as the impedance tomography. Sonic tests consist in transmitting stress waves within In both cases multi-electrode (24, 48 or more) the frequency range of acoustic waves (20 Hz to automatic switching geo-resistivity-meters are neces 20 kHz), generated by an instrumented hammer, and sary. Very high quality instruments are required. A in measuring their traveI time by means of accelerom particular care must be taken to ensure a good elec eters. For given masomy typologies it is possible to tric contact of the electrodes with the surface of the find a relationship between the sonic velocity and wall (Marchisio et aI, 2000; Cosentino et aI, 1998; the elastic properties of masomy (Riva et aI , 1997). Marchisio et aI, 2002). In general, sonic tests can be applied to get qualita tive information on the morphology, consistency and 3.4 Impulse-thermography state of conservation of masomy (Berra et aI, 1992; Abbaneo et aI, 1996). Besides direct and indirect tests, Impulse-thermography (IT) is an active approach for a carried out through the thickness or on the same side quantitative thermal scanning ofthe surface ofvarious ofthe wall, also sonic tomographies can be performed. structures and elements. A thermal pulse is applied to a In that case, the measures of sonic pulse velocity are surface causing a non stationary heat flow. During the combined along different ray-paths on a cross section cooling-down process the emitted thermal radiation is of masomy, and are subsequently processed in order observed with an infrared camera.