Struetural Evaluation of Historie Walls and Eolumns in the Altes Museum in Berlin Using Non-Destructive Testing Methods

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. The propagation of to define mean values of velocity on each portion the heat into the body depends on material properties of the wall section itself (Valle et ai, 1998; da Porto like thermal conductivity, heat capacity and density of et aI, 2003). the inspected object. If there are inhomogeneities in the near surface region of the structural element this 3.3 Geoelectric will result in measurable temperature differences in the local area ofthe surface (Maierhofer et aI, 2002). The geoelectrical tomography is the reconstruction of A relatively new approach of IT is the pulse phase the distribution ofthe electrical resistivities in the body thermography (PPT) (Vavilov et aI , 1998; Maldague of a structure obtained by current injections across et aI, 1996; Maldague, 200 I). The stored data received many different couples of electrodes. during the IT is analysed in the frequency domain via Two different methods can be used: fransparen cy Fast Fourier Transformation of the transient curve of tomographies or inverted pseudo-sections when only each pixel in a series ofthermal contrast images. This one si de of the structure is accessible. leads to changes in amplitude or phase of the corre The transparency tomographies use an experimen sponding images. The main advantage of PPT lies in tal disposition of the electrodes corresponding to the the phase images, which are reported to be less influ cross-hole tomography in the subsoil: in this case 2 enced by surface infrared and optical characteristics. series of electrodes are fixed along 2 profiles on the That also means less sensitivity to non-uniform heat opposite faces of a masomy structure. The electrodes ing compared with the thermal contrast images of lT are connected in different combinations, performing a (Maldague,2001). high number of measurements (typically several hun dreds). The cross-section covered by the ray paths is 3.5 Single and doubleflat-jack ideally divided into a number of cells (pixels). Their resistivity is computed by means of complex iterative The objective ofthe flat-jack test is to obtain the local routines. The numerical output (resistivity of each cell) state of stress in compression of a masonry element must be converted into an image ofthe distribution of that works under vertical stress. The method is based the velocities in the cross-section to render it usable. on stress release. Another technique, the inverted pseudo-section, The general procedure ofthis test consists on restor uses only one profile with many electrodes on one ing the vertical displacement caused by a horizontal face ofthe structure. Measurements are ma de with the slot made in a loaded masonry. The distance between technique of the so-called resistivity pseudo-sections three or four points fixed across the slot is measured by connecting 4 electrodes at a time with one of the by gages before and after cutting. The device used to typical arrays used in geoelectrics. A high number of restore the displacement is a flat-jack; oil is pumped

333 in the jack until the distance between the gage points Time in ns is restored to the initial situation. Uõ. õ In order to obtain the local state of stress, the restor ing pressure has to be corrected taking into account two coefficients that depend on the mechanical character istic of the fl at-j ack, calibrated in laboratory, and on the relation between the geometry of the slot and the shape of the flat-jack. A double fl at-jack test is carried out by two fl at jacks inserted in two parallel slots at a convenient di stance and pumping oil into both so that a compres sion test is performed. In fact, the two jacks delimit a masonry sample of appreciabl e size to whi ch a uni-axial compression stress can be appli ed. Mea surement bases for removable strain-gauge or LVDTs on the sample face provide information on verti cal and lateral displacements. Several unloading and re-Ioading cycles can be performed at increasing stress leveIs in order to determi ne the deformability modulus, an important parameter in the masonry classification (Binda et aI, 2004). It is interesting to compare th ese last results to the stress leveI measure in order to ver ~ B ify the actual state ofthe masonry in relation with its Depth in em potentialities (Binda et aI, 1999). Figure 4. Investigated column (left) and radargram of a ver tical trace (right) recorded along the total height ofthe column wi th the 900 MHz antenna. The hyperbolas are related to the 4 RESULTS joints between the drums.

4. 1 Structure 01 co/umns in the entrance hall 4.l.l Radar For getting an overview four evenly distributed traces in direction of the longitudinal axis (vertical) of the selected column were recorded with the 900 MHz antenna along the whole height (10.2 m). A measuring wheel mounted to the antenna performed measurement triggering and recording of the path. Figure 4 shows one of these radargrams. Clear signals related to the surface and to the backside refl ection can be detected. The traveI time of the backside echo increases when going fro m top to bottom corresponding to an increase of the diameter of the column. Close to the surface reflection, hyperbolas occur representing the reflec tion of the joints between the different drums. Due to the high intensity of these reflections, it is assumed Position in cm that these joints contain plumb layers that were used as a non-seizing compound for the alignment of the Figure 5. Top: Rectangular void in the upper part of each column drums. drum used for transportation and alignment. Bottom: Radar For detailed investigations on the joints between the gram ofa horizontal trace recorded with lhe 1.5 GHz antenna drums, horizontal traces at different areas close and far in lhe upper par! of one of the drums. fro m the joints were recorded. The measurements were performed radial along the surface ofthe column with the 1.5 GHz antenna. One of these radargrams below of the antenna around the column (trace of antenna: ajoint is shown in the bottom ofFigure 5. Due to the 360°). The reflections at opposite antenna positions cannelures the backside refl ections appears in a wave (180°) are similar. From this reflection profile it can like shape. Noticeable reflections can be detected at a be concluded, that in the middle ofthe drum below the depth between 70 and 75 cm. The position and intensity joint, a rectangular hole exists (with a length of ca. 7 ofthis reflection is changing with the angular position to 10 cm and a width of2 to 3 cm) which was used for

334 23201'IV' Figure 7. Photo (left) and phase image (right) of the same Figure 6. Investigated column (left), tomographic recon area ofthe column after a heating of5 mino The delaminations struction ofthe section (right). appear in the phase image as dark areas. mounting, see figure 5, topo This hole was only located 4.2 Plaster detachments at columns in the rotunda at the top of each drum and was presumably used for 4.2.1 Impulse-thermography mounting and alignrnent of the drums. There were no The experimental set-up consists of a thermal heating hints to metal compounds as pins between the drums, unit, an infrared camera and a computer system, which only this lead dies. enables digital data recording in real time. For the It was also possible to locate the restored areas, but heating of the surface of the columns a conventional the thickness of the replaced structures could not be electric fan heater has been used with a heating power resolved. of2000 W avoiding temperatures at the surface higher than 50°C. The infrared camera is an lnframetrics selooo with a PtSi-focal plane array detector with 4.1.2 Sonics a resolution of256 VS. 256 pixels. lt detects the emit On the same column, also a sonic tomography was ted radiation in a wavelength range from 3 to 5 !-lm. For carried out in order to check the distribution of differ accessing ali parts ofthe column, a lift was used. Large ent materiais. A horizontal section, 1.10 m high from areas with delaminations appear in the lower parts of the levei of the entrance floor and 0.10 m above the the column as demonstrated in the dark parts of the lower ashlar, was chosen for the sonic tomography phase image in Figure 7 right after 5 min of heating. (Figure 6, left and tomo 3 in Figure 4, left). A very From comparisons with results obtained at test speci simple acquisition grid with six points located on the mens with different mortar thickness in the laboratory, outer perimeter of the column was chosen to carry it is assumed that these delaminations belong to the out the tests. Three measurements per point have been stone/mortar interface. But this assumption was not recorded and they were subsequently processed with proved with destructive tests. software purposely developed in Visual Basic 6 and based on the theoretical non rectilinear propagation of elastic waves. The investigated section was divided 4.3 Properties 01 a carrying wall in the cellar into nine large square pixels. The tomographic reconstruction gave uniform val For the investigation of the structural and material ues ofvelocity in the section, with velocities included parameters ofthe inner carrying wall in the cellar (plan between 2330 and 2540 m1s (about 8% scatter, Fig view in Figure 8, part of the wall with a large crack ure 6, right). The lowest values ofvelocities were actu is shown in Figure 9), severa I tomographic and indi ally located around an area restored with a pigmented rect and direct transmission investigations had been mortar after the bombing that damaged the columns. performed with sonics, microseismics, geoelectric and No other differences were found in the column com radar. Flat-jacks had been applied at four positions as position, such as the presence of large inner core, etc. shown in Figure 8. It has to be noted that a higher number of transmit ting/receiving points, in order to have the cross section 4.3.1 Sonics more densely investigated, would have improved the Direct sonic tests were carried out on two positions of accuracy ofthe obtained results. The sonic tomography the load bearing wall in the cellar (PI and P2 in fig allowed detecting areas built with different materiais ure 8) . In correspondence to the flat-jack tests, the tests (macroscopic phenomena consistent with the tested were carried out on a 6 x 8 grid (six rows and eight cross section dimension) but its resolution is toa low, columns, 15 cm x 15 cm) of transmitting/receiving also in terms of wavelength, to detect the position of points, for a total of 48 points. The thickness ofthe wall small iron fasteners or minor irregularities. was 1.71 m. A single measurement per point has been

335 2SOOIfll. 2. 50",/, 2400 .... /. Room 0.22 2350 mk E 23OOml. () 2200 ml • .5 2150ml. .<:: 210(1"11 • Cl - :1'000"11. 'ãj J: lSSOm/.

Position in cm

Figure 10. Sonic velocity distribution as obtained from direct tests at position P I.

Average sonic velocity 3000~------. Figure 8. Part from the plan view ofthe cellar showing the 2800 cross-section of the investigated inner wall and the different 2600 measurement positions. PI , P2: Direct sonic tests. RI to R5: 2400 Microseismic profiles. TI toT5: Geoelectric profiles. BAMI, l2200 BAM2: Radar tomography profiles. AMJ I S to AMBS: Sin .~ 2000 gle flat-jack by Po/imi. AMJ2D: Double flat-jack by Po/imi. u il1800 FJOI to Fl04: Single flat-jack by Geocisa. > 1600 1400 1200

1000+-----r-----r-----r----.-----.----~ 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Height from floor (m)

Figure 11. Sonic velocity measured in direct tests on test area P I and P2 versus height from floor.

also in other tested area in the cellar. The mean values of direct sonic measurements taken at different heights on the cellar wall are shown by Figure li. The values of sonic velocities are typical of masonry in fair good/good condition (Berra et ai, 1992; Forde et ai, 1985). With similar thickness, multi-Ieaf stone masonry walls with internai filling with poor mechan ical properties, internai voids and detachrnent of the Figure 9. Part ofthe investigated inner carrying wall in the cellar showing a large crack. The arrows mark the position of externallayers, in bad conservation condition, usually the radar traces for tomography. give lower values ofvelocity (Riva et ai, 1997).

4.3.2 Microseismics recorded. The velocities ranged between 1600 and Seismic velocity profiles were performed on the base 2600 m/s, with a high scatter (38%), about 1000 m/s. ment wall of the cellar in five positions (RI to R5 in The results ofposition PI are presented in Figure lO. Figure 8). The mean value is 2150 m/s. The upper part of the Some examples of seismic velocity profiles are tested area presented lower velocities and the lower shown in Figure 12. part ofthe tested area was characterised by higher val The figures show the so-called dromochrones, that ues. This might be related to higher moisture content is the arrival times for a single shot plotted versus the in the bottom of the wall, considering that the pres distances from the shot point. The slope ofthe straight ence of moisture results in apparent increases of sonic parts of the dromochrones are the reciprocal of the velocity (Riva et ai, 1998). This trend was observed propagation velocity of the micro-seismic waves.

336 @J 'W Log Resis ti vity ;: 0.5 (Ohm- m) o ~ 5.4 V=2413 mls 5.2 5 ~ V.2280 m/. 4.8 4.6 o 4.4 4.2 4 200 400 600 800 100 120 140 160 180 200 220 3.8 Height geofoni (mm] 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 2 1.8 Ê ;: 0.5 O V=2775 mls

.(l.4 -0.3 -0.2 -0.1 Oepth[m]

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 Height geofoni [mm] Figure 13. Left: Electrode array for geoelectrical measure ments. Right: Reconstructed electrical resistivity distribution Figure 12. Velocity profiles recorded with microseismics. in the wall calculated from geoelectrical measurements (T2).

The velocities of the elastic (or seismic) waves in 4.3.3 Geoelectric a homogeneous body depend on lhe elastic properties Electrical tomographies were perforrned on the base of the body and on its density. ment wall of the celIar at five positions. There are 4 The propagation velocity of the pressure (longitu vertical electrical tomographies (from TI to T4) and I dinal) waves, Vp , is given by: horizontal electrical tomography (T5) (Figure 8). In Figure 13 , the geoelectric measurements ai T2 v _/1 + 2,u _ E. 1 - v are shown together with the reconstructed tomogram. p - O - O (1 + v)(1 - 2v) In the lower part, the material is relatively more con ductive. Probably this is due both to change ofmaterial while the propagation velocity of the shear (transver and presence of moisture. sal) waves, Vs , is given by: 4.3.4 Radar Radar measurements in transmission mo de were per formed along the two traces marked in Figure 9 using two 900 MHz antennas (BAM 1 and BAM2 in Fig ure 8). The transmitting antenna was placed at the wall where À and U are the constants of Lame; E is the in a fixed position, while the receiving antenna was Young modulus; v is the modulus of Poisson; 8 is the moved along the measuring trace on the opposite side density. ofthe wall from left to right with constant velocity. The The elastic moduli can be derived from the veloc next measurement was carried out with the sending ities and density. These elastic moduli are referred as antenna shifted of about 10 cm. The measurement was dynamic elastic modu/i as they refer to very small then completed in a similar way (shifting oftransmitter stress and deformations, while the static values are after each trace) with a total of 15 sending positions. measured with much higher values. The data were reconstructed by TOMOPOLI (Valle Ifboth V and V are known, the Poisson ratio can p s et ai, 1998). The respective velocity distributions are be computed: shown in Figure 14. The velocities in the lower tomo gram are lower than in the top tomogram which might Vp =P(l- V) be related to a higher moisture content in the bottom V, 1-2v ofthe wall. In both tomograms, two areas with higher velocity can be recognised being perpendicular to the AlI the velocity profiles are well consistent. Veloc x-axis and parallel to the z-axis. The position ofthese ity values are high (from 2400 to 2800 m1s). These areas can be correlated to the position of the crack values correspond to dynamic elastic moduli val as shown in Figure 9. In the area of the crack, there ues of 80000-1 10000 DaN/cm2 (Gucci et ai, 1997; might be several voids which have a higher penetration Marchisio et ai, 2002). velocity for electromagnetic waves.

337 R1 15 Receiver R15

~-~ 140

~ 17175 , 16 5 16 15.!: 15 14.5 1. 13.5 13 125 12 11.5 11 10.5 10

Figure 15. Flat-jack insi de the slot. -, --T -~-r------T ------, , --,- O 20 40 60 ., ' 00 120 1<0 T1 T15 15 Transmitter perforrned in the stone assuring good contact condi R1 15 Receiver R15 tions between the flat-jack and the masonry (stone). To guarantee a correct measure the surface ofthe wall is arranged and points are fixed with a rigid adhesive. I The initial distance between gage points is the refer 14.5 ence measure to achieve the test. The control of the 1. gage displacement was done with a mechanical exten 13.5 someter with an accuracy ofO.OOI mm. The slot was 13 made with a diamond circular saw (radius 115 mm), 12.5 the cutting was guided to ensure a horizontal plane 12 using a platform fixed to the wall (see Figure 15). 11.5 The flat-jacks used in both procedures have

11 circular shapes. In the first case, the size was

10.5 350 mm x 250 mm x 4 mm, with a calibration factor

10 ofO.88 and a geometrical factor ofO.93. In the second procedure, the length of this flat-jack is 211 mm, the depth is 70 mm and it is 3 mm thick. The calibration O 20 40 00 80 100 120 140 constant was determined at laboratory and the value T15 T1 15 Transmitter obtained is 0.5. The geometrical factor is 1.0 because the prepared slot has the same shape as the flat-jack. Figure 14. Reconstructed horizontal velocity distribution Afier cutting the slot the distance between gage along the cross section of the basement wall. Top: Profile points was measured, obtaining a c10sing movement. along the top trace (BAMI). Bottom: Profile along the bottom trace (BAM2). The values are in 10- 1 m/ns. The flat-jack was introduced into the slot as shown in Figure 15 , increasing gradually the internai pressure while the distance between gage points is controlled 4.3.5 Flat-jack until the distance is restored to the reference measure. Polimi and Geocisa carried out severa I single flat-jack The use of a flat-jack of smaller dimensions allows tests localised at 4 positions at the inner carrying wall the testing of elements of smaller dimensions as and at the outside wall as shown in Figure 8. colurnns. The test procedure used by Polimi was per Figure 16 shows the results of the single flat-jack forrned accordingASTM test (ASTM, 1999) (AMJl S, test carried out by Polimi. The recovery of the slot AMJ2S, AMJ2D, AMBS ) taking into account 4 displacements was reached in ali the measuring points, measurement points and cutting in the mortar joint. almost at the same stress. Geocisas single flat-jack tests (FJOI to FJ04) fol A double flat-jack test (AMJ2D) was carried out by lows an own developed procedure also based on Polimi at the inner carrying wall as shown on figure 8 ASTM, but modifying some testing conditions for a according to ASTM (ASTM). faster and friendly use equipment: at each position, The results are summarised in Table I. three gage points are placed centred in the future slot The stress- strain diagram of the double flat-jack as the flat-jack has smaller dimensions and the cut is test AMJ2D (not shown here) demonstrates the good

338 Place: Altes Museum - Berlin Date: 15/01 /2004 40,------,,------,------, E 3 : 30 +------___jf------_+------f Clc ~ :ll 2 20+-~~----___jf_------_+------f Õ c o

16. ~ 1O +-""'--' ::O"'-----:::-1~:__------+------l >

O+------+----'==~~~------~ 0.00 0.50 1.00 1.50

Stress CJ. [N /mm' J

Figure 16. Results of the flat-jack tests carried out accord Figure 17. Cross-sections ofthe 3D radar data showing two ing ASTM (AMJ2S). main reflections at about 45 and 80 em.

Table J. Results of single and double flat-jack tests pre 5 CONCLUSIONS AND OUTLOOK senting the local state of stress and the Young modulus at the di fferent positions. 5.1 Struclure ofcolumns in the entrance hall Single flat- Single flat- Double flat- With radar, the joints between the drums could be jackAMJxS jack FJx jackAMJ2D located very easily. The high intensity ofthese reflec Local state of Local state of Young tion could be related to possible plumb layers between stress stress modulus the joints as non-seizing compound. Related to the 2 2 2 Position (N/mm ) (N/mm ) (N/mm ) connections between the single drums, metal com pounds like pins could be most probably excluded. At I 1.13 1.50 the top of each column, a rectangular hole is expected 2 0.96 1.00 33900 which was used for mounting and alignrnent of the 3 0.79 0.9 4 0.7 drums. With radar reflection as well as with sonic tomog raphy, the repaired areas could be located. But it was not possible to determine the depth ofthese structures. characteristics ofthe masonry in terms of compressive The uniform values of sonic velocities vary between strength and elastic properties. 2330 and 2540 m/s. The lowest areas ofvelocity were located around a repaired area.

4.4 Slone ring reinforcement in the dome 5.2 Plaster detachmenls ai columns in the rotunda The radar experiment was planned in a position of a With impulse-thermography, it was possible to detect corridor where the supposed stone ring should be quite delaminations which are most probably related to close to the internaI wall (Figure 3). the stone/mortar interface. But this assumption was not proved with destructive tests. Also, it is planned 4.4.1 3D radar to compare the experimental results with numerical For a more reliable interpretation of the radar images, simulations. the experiment was executed in 3D mode by collect ing a number of dense parallel profiles on an area of 5.3 Properties of a carrying wall in lhe cellar about 80 cm x 80 cm. The data were processed with The main objectives ofthe multifaceted investigations a 3D software obtaining a 3D data volume that con of the carrying wall in the cellar were the analysis firms the existence of the stone ring (Figure 17). The of the inner structure and the moisture content. As two reflections observed at about 45 and 80 cm were NDT and MDT methods radar, sonics, microseismics, respectively interpreted as the reflection from the stone geoelectric and single and double flat-jack have been ring and from the interface separating the first and the combined. second stone layer of the structure. A hole was also Related to the internaI structure, the sonic investiga drilled in the position were the stone ring should be tions resulted in acoustic velocities between 1600 and closer to the corridor wall and a sandstone block was 2600 m/s with a mean value of 2150 m/s. With micro actually found behind a 50 cm brick wall. seismics, velocities between 2400 and 2800 m/s were

339 obtained. These values are typical for fair good/good be related to the reflection from the stone ring and from condition of masonry. But it should be regarded that an interface separating the first and second stone layer. these are mean values over the whole cross section, Videoscopic investigations of a borehole in this area thus only an averaged parameter is given. At the bot should the beginning of the sandstone at a depth of tom ofthe wall, the sonic as well as the microseismic about 50 em (behind a 50 em thick brick wall). investigations give higher velocities in comparison to the results at the topo This might be explained by a higher load and/or by a higher moisture content. ACKNOWLEDGEMENTS The radar tomograms appear homogeneous, some readings could be related to the crack at this area. The This work was funded by the European Commission radargrams recorded in reflection configuration and under the 5th Framework Programo not presented here showed a more or less inhomoge For the assistance in preparation of the measure neous structure related to stones having different size ment campaigns we thank Mrs. Rover (Technical and inhomogeneous joints. University, Berlin) and Mrs. Rüger (German Federal The single flat-jack tests show mainly the same Office for Architecture, Berlin). stress at ali positions. The stress strain diagram of the double flat-jack investigation demonstrate good char acteristics of masonry related to compressive strength and elastic properties. A load set of the museum by REFERENCES a simple engineering method gave significant dif ferences to the stress results of the single flat-jack Abbaneo, S., Berra, M. , Binda, L. (1996): Pulse velocity test to qualify existing masonry walls: usefulness ofwaveform tests. 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