d. delikaraoglou, a. georgopoulos, c. ioannidis, e...

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Using Geodetic and Laser Scanning Using Geodetic and Laser Scanning Measurements for Measuring and Measurements for Measuring and

Monitoring the Structural Damage of a Post Monitoring the Structural Damage of a Post Byzantine ChurchByzantine Church

D. Delikaraoglou, A. Georgopoulos, C. Ioannidis, E. Lambrou, G. Pantazis

Department of Surveying EngineeringNational Technical University of Athens, Greece

31 May – 2 June, 2010Patras, Greece

About the projectAbout the project

– The monument of interest– The local setting and influencing factors

contributing to the monument’s pathology– Current vulnerability state of the monument

by quantifying its structural deformations and micro-movements

Delikaraoglou et al., NTUA

• The Great St. Mary’s Church in Samarina, Grevena

• Post-byzantine church, built ca. 1816• Timber-roof type, three-aisled, 40m

long basilica with narthex and porch-type galleries in the south and west sides

The monument of interest to this project

The Church of Megali Panayia


The local setting – Samarina, Grevena

• The highest in elevation (~1450 m) populated village in Greece … and reportedly in the whole the Balkans

• 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)

• A small town with its Vlach population that has enjoyed (up to the early 19th c.) three successive centuries of exceptional economic growth and cultural development.


The local setting – Samarina, Grevena• Unfavorable geological

and geomorphological characteristics of the greater area around the village

play a vital role in the various geotechnical problems causing structural damage in buildings, fences, constructions, roads, etc.


The local setting – Samarina, Grevena• Very harsh wintertime conditions

– Continuous rainfalls and heavy snow cover• Increasing underground water runoff

during spring & summerSoil erosion and ground loading effects, i.e. additional causes of structural problems

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The local setting – Samarina, Grevena

• Lack of adequate geodetic control benchmarks in the area

Impact on the geodetic observation strategies for the project


Megali Panayia – Current state

• The church is constructed of local stone and has very shallow foundations sitting on unfavorable ground, composed mainly of clay, silt and peat, with the solid rock found in depths of more than 15 m from the surface

• There is a ‘leaning’ church tower (only 2 parts remain today; a 3rd top part collapsed in the 1930’s … poor connection between structural elements? Seismic event? gravity taking its toll?)


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


Megali Panayia – Current state


Large visible cracks outsideof the building


Loads and reactions must be in equilibrium … if not the monument

responds to internal forces

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Large visible cracks inside the chapel of Saints Peter and Paul


LargeLarge visible cracks visible cracks insideinside the churchthe church

Techniques used for the Techniques used for the monument’s structural health monument’s structural health

monitoringmonitoring

• GPS geodetic control network• Precise Conventional Surveying

Measurements• Laser Scanning & Photography for 3D

modelling


GPS outer reference GPS outer reference networknetwork--EUREFEUREF

GPS GPS local local

control control networknetwork

L1/L2 GPS geodetic grade receiversL1/L2 GPS geodetic grade receiversJAVADJAVAD

EpochEpochSpectraSpectra

PrecisionPrecision


0 5mm 10mm

S1

S2

S3

S4

S5

S6

S8S14

S9

S7

S13

S10 S11

S15

S12

The basic monitoring The basic monitoring

geodetic networkgeodetic network

Recently calibrated electronic instruments usedLeica TDA 5005 and Leica TCRM 1201

angular measurements with a precision of ±1.5cc and±3ccrespectively and distance measurements with a precision of ±1 mm

With reflectors or retroreflective tape

• Distances• Horizontal and zenith angles

inter-station distances determined with a precision of the order of ±0.5 mm

Special retroreflective tape targets

The monitoring geodetic network

small brass benchmarks

semi-portable pillars

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Laser scanner positions for

acquiring several

scenes with a large field of

view (collection of point clouds)

• 9 scans for the exterior & 14 for the interior of the church• 4 scans for the north side façade and the west-side porch• Automatically registered point-clouds: 10.800.000 (exterior)

and 17.600.000 (interior) points covering practically all details of the church


Scan of the west porch (taken from inside) Scan of the west porch (taken from inside) • Georeferencing of the available cloud points using Cyclone (Leica sw).• For each scene, georeferencing was done separately using the visible special

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– Initial adjustment of all data – Mesh reconstruction of point clouds between scanned scenes, in order to achieve

a further improvement in the results– Second adjustment resulting in uncertainties between 1mm (min) and 1.7cm (max)


NorthNorth--east sidevieweast sideview

South sideviewSouth sideview

Point clouds from the laser scansAfter the registration with the Cyclone sw


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

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

point clouds existed due to shadowing effects or obstructions during scanning


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

Left: cracks shown in the south interior wall of the churchRight: cracks in the north interior wall


South side North side

East side Top view of the roofs

North side view & section South side view & section

3D 3D modelsmodels

--GeomagicGeomagicStudio 10Studio 10

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View of the temple


Photo orientation in the Image Master sw

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

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 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)

Summary of the preliminary findingsTo date, we have an assessment of the first results obtained

from four epochs of repeated (multi-temporal) observations and their combined adjustment– GPS monitoring of the local control network– Terrestrial network adjustments– Overlay of the displacements, e.g. of the northeast corner of the

church onto the laser scanner 3D modelThe results show a tendency of the surrounding ground to slide towards the northeast direction in a very slow tempoThe observed displacements between characteristic control points on the building itself tend to demonstrate a slow varying periodic effect

-1.9 11.50.9 10.4-4.0 8.6S15 0.9 12.2-0.1 15.7 -4.5 7.9S14 -2.5 19.71.6 9.2 -3.4 6.2S13 -5.2 18.40.1 12.6 -1.6 4.3S12 -2.3 25.41.0 23.1 -4.0 10.0S11 -3.4 18.22.4 6.7 -3.2 3.8S10 -3.1 23.92.2 17.9-2.7 13.5S9 -1.9 6.31.6 14.1 -2.6 7.2S8 -0.3 14.65.09.4-9.3 7.1S7

Points inside the Church -2.2 15.6-3.2 12.2 -4.98.5S6 -1.8 18.30.1 8.6 -3.75.9S5 1.5 14.3-1.5 4.6 -4.92.7S4 -1.6 1.2-7.0 1.0 6.7 3.1S3

0 0 0 0 0 S2 +1.8 18.3-2.9 16.1 +10.4 4.8S1

Points outside the Church ΔΗ (mm) Δr (mm) ΔΗ (mm) Δr (mm) ΔΗ (mm) Δr (mm) Point

June - July 2009July - Sep 2009Sep - Oct 2009

Planar (Δr) and vertical (ΔΗ) displacements of the network points

First epoch interval (June - July 2009) results

• Planar displacements are of the order of 10mm

• with a direction mostly to the northeast for the northern and the eastern façade of the church

• as the southern façade appears to move to the south and the western one to a northwestern direction

• Planar displacements are of the order of 10mm

• with a direction mostly to the northeast for the northern and the eastern façade of the church

• as the southern façade appears to move to the south and the western one to a northwestern direction

Vertically, the tendency is a lowering of the points on the walls by a considerably smaller amount, at the

order of 5mm

Second epoch interval (July–September 2009)

• Planar displacements are also of the order of 10mm

• for all external façades, in the direction to the northwest, while all the internal points show movement to a northeastern direction

• Maximum displacement in elevation difference observed is 5mm, but in an upward direction this time

• Planar displacements are also of the order of 10mm

• for all external façades, in the direction to the northwest, while all the internal points show movement to a northeastern direction

• Maximum displacement in elevation difference observed is 5mm, but in an upward direction this time

During the third epoch interval (September – October 2009) the planar displacements are confined to 5mm while the points retreat vertically downto 6mm. The direction of all point movements shows a west-northwest tendency.

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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 targets (note that the scale of the micro-movements is 50 times larger than the scale of the 3D model)


Detail of the north façade from the 3D model (‘dressed’ with the digital photos), with the micro-movement of the the targets 101 and 102 between the four epochs of measurements


What knowledge is still missing• Possible likely reactions of the monument in response

to the loads obviously acting on its structure– Horizontal and Vertical movements (some effects visible

already, magnitudes partially known)• To be fully determined will possibly require continuous

monitoring – Bending moments (still largely unknown)

• Causes of concern– Natural forces, e.g. earthquake episodic events– Internal forces (i.e. loads ≠ reactions)


Follow on workFollow on work• This project is still in progress. Following the past winter period,

a new observing campaign is likely to take place this month or by the end of the summer– i.e., to investigate further any unusal structural behaviour due to ground

rebounding, or other winter environmental conditions-induced causes• In the meantime, other groups of structural mechanics engineers

have received the results of our preliminary findings and are already seeking ways of taking proper actions , e.g.– Strengthen the structural characteristics of the monument– Restoring the roofs– Rehabilitate the continuity of the mansory through local mansory-crack

rebuilding


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

d. delikaraoglou, a. georgopoulos, c. ioannidis, e...

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