D. Delikaraoglou, A. Georgopoulos, C. Ioannidis, E. Lambrou, G. Pantazis Department of Surveying Engineering National Technical University of Athens, About the project Using Geodetic and Laser Scanning Measurements for Measuring and – The monument of interest Monitoring the Structural Damage of a Post – The local setting and influencing factors Byzantine Church contributing to the monument’s pathology 31 May – 2 June, 2010 Patras, Greece – Current vulnerability state of the monument by quantifying its structural deformations and micro-movements

The monument of interest to this project The Church of Megali Panayia The local setting – Samarina,

• The Great St. Mary’s Church in • The highest in elevation (~1450 m) populated village in Greece … and Samarina, Grevena reportedly in the whole the • Post-byzantine church, built ca. 1816 • Situated on the wooded slopes of Mount Smolikas in the Pindos Mountains, in northwestern Greece, approximately 70 km west of Grevena (1995, 6.6 M quake) • Timber-roof type, three-aisled, 40m long basilica with narthex and porch- • A small town with its Vlach population that has enjoyed (up to the early 19th c.) three successive centuries of exceptional economic growth and type galleries in the south and west cultural development. sides Delikaraoglou et al., NTUA Delikaraoglou et al., NTUA

The local setting – Samarina, Grevena The local setting – Samarina, Grevena • Unfavorable geological • Very harsh wintertime conditions and geomorphological – Continuous rainfalls and heavy snow cover characteristics of the • Increasing underground water runoff greater area around the during spring & summer village ÆSoil erosion and ground loading effects, i.e. additional causes of structural problems

Æ play a vital role in the various geotechnical problems causing structural damage in buildings, fences, constructions, roads, etc. Delikaraoglou et al., NTUA Delikaraoglou et al., NTUA

1 The local setting – Samarina, Grevena Megali Panayia – Current state

• The church is constructed of local stone and has very shallow foundations sitting on unfavorable ground, composed mainly of clay, • Lack of adequate geodetic silt and peat, with the solid rock found in depths of more than 15 m control benchmarks in the area from the surface Æ Impact on the geodetic • There is a ‘leaning’ church tower (only 2 parts remain today; a observation strategies for the 3rd top part collapsed in the 1930’s … poor connection between project structural elements? Seismic event? gravity taking its toll?) Delikaraoglou et al., NTUA Delikaraoglou et al., NTUA

Megali Panayia – Current state Megali Panayia – Current state • The church is the area’s main religious landmark, as well as a wonder of nature – The roof of the altar … “accommodates” a big pine tree with no sight of the tree’s roots to be found within the church or outside the wall

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Loads and reactions Large visible must be in equilibrium cracks outside … if not the monument of the building responds to internal forces

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2 Large visible cracks inside the chapel of Saints Peter and Paul

Large visible cracks inside the church

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L1/L2 GPS geodetic grade receivers JAVAD Techniques used for the monument’s structural health monitoring GPS • GPS geodetic control network locallocal Epoch control • Precise Conventional Surveying Spectra network Precision Measurements • Laser Scanning & Photography for 3D modelling GPS outer reference network-EUREF

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Recently calibrated electronic instruments used Å Leica TDA 5005 and Leica TCRM 1201 Æ The monitoring S 3 • Distances S 4 geodetic network • Horizontal and zenith angles S 5 nitoring semi-portable pillars e basic mo The ork tic netwo S 12 geodeti S 13 angular S 2 measurements S 9 S 15 S 14 with a precision S 8 S 10 S 11 of ±1.5cc and ±3cc S 7 respectively and distance small brass measurements benchmarks with a precision S 1 0 5m m 10m m of ±1 mm ¾ inter-station distances determined with a Special retroreflective S 6 With reflectors or precision of the order of ±0.5 mm tape targets Delikaraoglouretroreflective et al., NTUA tape

3 Laser scanner positions for acquiring several scenes with a large field of Scan of the west porch (taken from inside) view • Georeferencing of the available cloud points using Cyclone (Leica sw). (collection of • For each scene, georeferencing was done separately using the visible special point clouds) reflective targets from each Laserscan position – Scanned scenes were subsequently connected using their common targets • Done separately for the scans of the exterior and the interior of the church • 9 scans for the exterior & 14 for the interior of the church • 4 scans for the north side façade and the west-side porch – Initial adjustment of all data • Automatically registered point-clouds: 10.800.000 (exterior) – Mesh reconstruction of point clouds between scanned scenes, in order to achieve and 17.600.000 (interior) points covering practically all a further improvement in the results details of the church – Second adjustment resulting in uncertainties between 1mm (min) and 1.7cm (max)

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Part of the interior (west part of the church) with voids

South sideview Point clouds from the laser scans After the registration with the Cyclone sw

3D modeling using the Geomagic Studio 10 sw • Takes as input a 3D scatter point clouds and returns a tight, triangulation for surface reconstruction (of the inside and outside of the church) • In a prior step, any data voids were filled for the areas of the model where inadequate North-east sideview point clouds existed due to shadowing effects or obstructions during scanning

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Δημιουργήθηκαν περίπου 3.000.000 τρίγωνα για το τρισδιάστατο μοντέλο του εξωτερικού της εκκλησίας και περίπου 11.000.000 τρίγωνα για το εσωτερικό της

North side South side 3D models - Geomagic Studio 10 East side Top view of the roofs

Left: cracks shown in the south interior wall of the church Right: cracks in the north interior wall Delikaraoglou et al., NTUA DelikaraoglouNorth et al., side NTUA view & section South side view & section

4 Photo orientation in the Image Master sw

View of the temple Adding texture to the 3D model using the Image Master sw Combination of the 3D model with color high resolution digital photos • Orientation of all images in a unified adjustment

Æ Accuracy achieved: Sx=1.4 cm, Sy=0.7 cm, Sz=0.9 cm. • Adding texture from each photo to the corresponding part of the 3D model Æ a higher level of detail together with a good metric accuracy • The end result is the creation of a faithful virtual reality environment (in VRML format) Delikaraoglou et al., NTUA Delikaraoglou et al., NTUA

Planar (Δr) and vertical (ΔΗ) displacements of the network points Sep - Oct 2009 July - Sep 2009 June - July 2009 Summary of the preliminary findings Point Δr (mm) ΔΗ (mm) Δr (mm) ΔΗ (mm) Δr (mm) ΔΗ (mm) Points outside the Church To date, we have an assessment of the first results obtained S1 4.8 +10.4 16.1 -2.9 18.3 +1.8 from four epochs of repeated (multi-temporal) observations S2 0 0 0 0 0 and their combined adjustment S3 3.1 6.7 1.0 -7.0 1.2 -1.6 S4 2.7 -4.9 4.6 -1.5 14.3 1.5 – GPS monitoring of the local control network S5 5.9 -3.7 8.6 0.1 18.3 -1.8 – Terrestrial network adjustments S6 8.5 -4.9 12.2 -3.2 15.6 -2.2 – Overlay of the displacements, e.g. of the northeast corner of the Points inside the Church church onto the laser scanner 3D model S7 7.1 -9.3 9.4 5.0 14.6 -0.3 9 The results show a tendency of the surrounding ground to S8 7.2 -2.6 14.1 1.6 6.3 -1.9 slide towards the northeast direction in a very slow tempo S9 13.5 -2.7 17.9 2.2 23.9 -3.1 9 The observed displacements between characteristic control S10 3.8 -3.2 6.7 2.4 18.2 -3.4 points on the building itself tend to demonstrate a slow S11 10.0 -4.0 23.1 1.0 25.4 -2.3 varying periodic effect S12 4.3 -1.6 12.6 0.1 18.4 -5.2 S13 6.2 -3.4 9.2 1.6 19.7 -2.5 S14 7.9 -4.5 15.7 -0.1 12.2 0.9 S15 8.6 -4.0 10.4 0.9 11.5 -1.9

First epoch interval (June - July 2009) results Second epoch interval (July–September 2009)

• Planar displacements are of • Planar displacements are of •• Planar Planar displacements displacements are are the order of 10mm the order of 10mm alsoalso of of the the order order of of 10mm 10mm •• with with a a direction direction mostly mostly •• for for all all external external façades, façades, toto the the northeast northeast for for the the inin the the direction direction to to the the northernnorthern and and the the northwest,northwest, whilewhile all all the the internal points show easterneastern façade façade of of the the internal points show movementmovement to to a a churchchurch northeasternnortheastern directiondirection •• as as the the southern southern •• Maximum Maximum displacement displacement in in façadefaçade appears appears to to elevationelevation difference difference movemove to to the the south south observedobserved is is 5mm 5mm,, butbut in in an an upward direction this time andand the the western western upward direction this time one to a one to a Vertically, the tendency is a lowering of the points on During the third epoch interval (September – October 2009) the northwesternnorthwestern the walls by a considerably smaller amount, at the planar displacements are confined to 5mm while the points retreat vertically down directiondirection order of 5mm to 6mm. The direction of all point movements shows a west-northwest tendency.

5 Part of the north façade from the 3D model (‘dressed’ with the digital photos), indicating also in vectorial form the micro-movements of specific the control Detail of the north façade from the 3D model (‘dressed’ with the digital targets (note that the scale of the micro-movements is 50 times larger than the photos), with the micro-movement of the the targets 101 and 102 between scale of the 3D model) the four epochs of measurements

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What knowledge is still missing Follow on work • This project is still in progress. Following the past winter period, • Possible likely reactions of the monument in response a new observing campaign is likely to take place this month or to the loads obviously acting on its structure by the end of the summer – Horizontal and Vertical movements (some effects visible – i.e., to investigate further any unusal structural behaviour due to ground already, magnitudes partially known) rebounding, or other winter environmental conditions-induced causes • To be fully determined will possibly require continuous • In the meantime, other groups of structural mechanics engineers monitoring have received the results of our preliminary findings and are – Bending moments (still largely unknown) already seeking ways of taking proper actions , e.g. • Causes of concern – Strengthen the structural characteristics of the monument – Restoring the roofs – Natural forces, e.g. earthquake episodic events – Rehabilitate the continuity of the mansory through local mansory-crack – Internal forces (i.e. loads ≠ reactions) rebuilding

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See full paper in: http://users.ntua.gr/drag/files/Download/Delikaraoglou%20et%20al.pdf Delikaraoglou et al., NTUA

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