Gabriele Bitelli editor

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Indice / Index

Capaldo

Paola

HIGH RESOLUTION RADARGRAMMETRY WITH COSMO-SKYMED, TERRASAR-X AND RADARSAT-2 IMAGERY p. 7

Dabove Paolo

QUALITY CONTROL OF THE KINEMATIC POSITIONING INTO GNSS

NETWORKS

p. 17

De Gaetani Carlo Iapige

COVARIANCE MODELS FOR GEODETIC APPLICATIONS OF COLLOCATION p. 27

Guastaferro Francesca

CHANGE DETECTION TECHNIQUES AND GIS ANALYSIS APPLIED TO

SATELLITE IMAGES FOR MAPPING OF BURNED AREAS

p. 37

Nascetti Andrea

HIGH RESOLUTION RADARGRAMMETRY: DEVELOPMENT AND

IMPLEMENTATION OF AN INNOVATIVE IMAGE MATCHING STRATEGY

p. 47

Nobile Alessia

3D SCANNING SYSTEMS FOR METRIC DOCUMENTATION AND

DIAGNOSTIC STUDY OF CULTURAL HERITAGE.

p. 57

Saveriano Francesco

TECHNIQUES FOR MONITORING DEFORMATIONS OF THE TERRITORY p. 67

Steffenino Sara

URBAN LAND COVER MAPPING USING MEDIUM SPATIAL RESOLUTION

SATELLITE IMAGERIES: EFFECTIVENESS OF DECISION TREE CLASSIFIER

p. 75

3D SCANNING SYSTEMS FOR METRIC DOCUMENTATION

AND DIAGNOSTIC STUDY OF CULTURAL HERITAGE.

FROM THE SCALE OF THE BUILDING TO THE URBAN ONE: THE CASE STUDIES

OF THE BASILICA DELL’UMILTA’ IN PISTOIA AND THE SAN GIMIGNANO TOWERS

A. Nobile

Architect e PhD in Electronic Technologies for Cultural and Environmental Heritage

Laser scanner surveyor freelance, Florence, Italy - alessianobile@gmil.com

KEY WORDS: Cultural Heritage, Architecture, Laser scanning, Data acquisition, Data processing, Structural and Diagnostic Analysis

ABSTRACT:

Goal of the research has been to test laser scanning acquisition, management and threedimensional representation methods and techniques

to provide a valid documentation and diagnostics support aimed at the preservation of our cultural built heritage. The widespread use

of scanning techniques does not allow to consider concluded yet a research topic that today is mistakenly identifi ed especially with the

phase of data acquisition. Actually the problem is postponed to the later stages of processing and representation and there are many

issues partially solved through an attempt of cultural integration between restoration, geomatics and electronics: it is both a challenge

and an opportunity, which carries along an effort to overcome language barriers, due to different cultural backgrounds, methodological

approaches and educational paths.

The above-mentioned case-studies raised the awareness that, on the basis of the 3D data set, which can be updated and queried at any

time, it’s always possible to adjust the processing phase according to the fi xed goals shared by all the professionals and the skills involved.

It is therefore proposed a innovative use of the laser scanning surveying technique: attention is not specifi cally given to the artistic and

architectural elements and the aim is not only to represent an object in three-dimensions in order to make qualitative assessments on

its historical and cultural value.

The need for an “irrefutabile model”, which can be used to orient any restoration plan, globally frames the research.

1. INTRODUCTION

1.1 Scientifi c and operational background

The knowledge of a site is the fi rst step towards fi nding a suitable

preservation strategy, and the documentation is the fi rst step of

this process of knowledge (Eppich and Chabbi, 2007).

In recent years the use of computer technology in the fi eld of

Cultural Heritage and Fine Arts has gradually increased: we

are witnessing the creation of 3D digital models of objects of

different sizes and characteristics (monuments, archaeological

sites or artefacts, monumental architecture, etc.) for both the

documentation and the conservation and the displaying.

This gradual growth of interest stems from the availability of

new technologies for the digitization and from the appeal of tools

allowing innovative ways of exploration and documentation,

which arouse inquisitiveness in the non-experts.

The potential of recent instruments has generated new

operating procedures, accelerating and economizing graphics’

production and allowing the defi nition of new products and their

dissemination.

The conventional drawings, typically two-dimensional, are still

effective in the representation of artefacts characteristically free-

form (for example, the archaeological ruins) and when you should

refer to specifi c vertical or horizontal sections.

The limit is noticeable when the reproduction of reality is needed

with its defects, exceptions, permanencies, overlapping and

interferences; a reality moulded by the fl ow of time and from

those shapes ever designed but simply sculpted, which enriched

the built beyond the original scheme.

In this regard, Saint-Aubin in 1999 defi nes the survey as “a tool

that tries to get the representation of the actual shape of the

building with the defi ciencies, irregularities, changes, additions,

deletions, restorations superimposed over time; a teaching tool,

since it wants to allow the understanding of the functioning of

the work in the complexity of its history and analyze patterns to

which it relates and the innovations introduced; and fi nally a tool

to know the state of health, the structure and its failures and to

look for the therapy from an irrefutable document”.

1.2 Aim of the research

The research addresses and deepens the issues related to the use

of laser scanner for Cultural Heritage, particularly focusing on

the close relationship between the 3D metric documentation and

the investigations aimed to the critical interpretation of large

monumental buildings.

The study was approached on a multi-scale level:

- at the scale of the building, with the Basilica of Santa Maria

dell’Umiltà in Pistoia, under the agreement signed between the

research laboratory of Geomatics for Cultural Heritage of the

University of Florence and the Superintendence for the Historical,

Artistic and Ethno-anthropological Heritage for the provinces

of Florence, Pistoia and Prato, in view of the restoration and

consolidation of the relevant Renaissance structure;

- at the urban scale, with the San Gimignano towers, within the

project “Seismic Risk in Monumental Buildings (RISEM)” funded

by Tuscany Region and coordinated by the Department of Civil

and Environmental Engineering of the University of Florence, for

the identifi cation of seismic risk.

57

2. THE BASILICA OF SANTA MARIA

DELL’UMILTA’ IN PISTOIA

2.1 Historic framework

The Basilica of Santa Maria dell’Umiltà is the most important

example of monumental Renaissance architecture in Pistoia.

The design of the geometric system is by Giuliano da Sangallo,

cooperating with his brother Antonio, Francione and Pollaiuolo;

the construction management, however, was in charge of the

architect Ventura Vitoni from Pistoia who would be replaced, in the

mid-sixteenth century, by Giorgio Vasari as designer and project

manager of the majestic double-shelled dome.

The monumental complex is divided into parts that correspond

essentially to the succession of its constructive phases.

The vestibule by Sangallo, built on the original medieval church,

has a rectangular base, a central dome on pendentives and wings

covered by barrel vaults.

The Vitonian octagonal hall grows vertically in the sequence

of three architectural orders of decreasing height, in addition

to the Vasarian construction of tambour, dome and lantern. The

architectural orders match with the interior walkways that divide

the wall structure in two shells.

The fi rst stone of the Basilica was placed in September 1495

and the construction continues for almost one century. In fact,

in 1569, when the dome is completed in its structures, the fi rst

damages occurred. However, due to the continuous occurrence of

the cracks, the Grand Duke Francesco I entrusts the consolidation

project to Bartolomeo Ammannati, which ascribes to Vasari the

responsibility of the damages, in particular due to the lantern’s

exorbitant load.

His remedies, while allowing to move beyond the height of

the crisis, do not eliminate the causes of damages that continue

cyclically to occur. The last restoration dates back to 1966.

The prolonged absence of maintenance and conservation of the

monumental complex has prompted a widespread state of decay

and has led the Ministry of Heritage and Culture to sign, in 2008,

a Memorandum of Understanding with the Diocese of Pistoia

and the Fondazione Cassa di Risparmio di Pistoia e Pescia for

the start of the fi rst actions to restore the building, designed and

managed by the Government Department responsible.

The MoU has provided the idea for the research agreement with

the Laboratory GeCo and the author’s study, from 2008 to 2011,

within academic research grants.

2.2 3D digital survey

The structure’s spatial arrangement, the geometric complexity

of the ambient and of the vaulted spaces, the decorations’

wealth have called for the integration of different measurement

techniques (topographic and satellite systems, 3D scanning

systems and digital photogrammetry). The prearranged objective

was to supply info-graphic representations with high levels of

detail, metrically correct and in conformity with the fi nality of

the survey and the scale of graphic representation identifi ed as

most opportune for the analysis of both the structure and the

decorations.

The in situ work has been carried out in fi ve measurement

campaigns (Tucci et al., 2012).

A topographic net, including the internal and external vertices

of the Basilica, has been created (‘Zenith Ingegneria s.r.l’, a

spinoff of the Engineering Department, University of Ferrara).

The measurements have been carried out with both a total

station (TPS802, Leica Geosystems) and geodetic GPS receivers

(GPS1200, Leica Geosystems). The maximum planimetric range

of the network, which is extended in parallel to via Madonna, is

equal to about 480 m x 170 m, while the proportional development

ranges from 0 up to about 47 m.

The calculation and the compensation of the coordinates of the

vertices of the main network were performed with rigorous

methods applying the least squares principle. The results are

varying depending on the network’s type and hierarchy (Table 1).

The survey of the interior and of a large part of the exterior

was realized with a phase-based scanner (HDS6000, Leica

Geosystems). For the survey of the dome and of the lantern a

time-of-fl ight scanner has been necessary (Scanstation2, Leica

Geosystems), for the greater instrument/object distance (about

100 - 150 m).

The resolution has been planned for each scans on the basis of

the shapes and of the dimensions of the investigated spaces. To

estimate the acquisition times we considered both the scans’

execution times and the instrument’s movement ones.

We performed 164 scan stations for a total amount of 57 GB of

raw data.

The acquired data were aligned mainly through points with known

coordinates and, consequently, referenced in the topographic local

system. The alignment was solved with a residual lower than 1 cm.

The overall three-dimensional model, consisting of over 3 billion

points, was organized in sub-projects to facilitate the visualization,

management and analyses on portions architecturally coherent.

2.3 Architectural output

The task of interpreting the point model, in order to identify both

the geometries and the anomalies, is not easy for an inexperienced

operator. The critical understanding, that with other survey

techniques is done in situ, here is postponed to the phase of

graphic rendering. The essential basis on which to sketch out a

proper drawing, allowing to associate to the geometry, already

studied, assimilated and decoded, the metric dimensions of the

3D database.

From the point model eighteen architectural boards were prepared:

in particular, for the basilica: fi ve plans, a longitudinal section

(Figure 1) and three elevation drawings (via Vitoni, via Madonna

and the courtyard). For the vestibule: two plans of the extrados (an

architectural plan and a structural one) and the development of

the intrados of the eastern barrel vault, one longitudinal and two

cross sections, the photomap of the main façade. For the octagonal

hall: a cross section and a transverse one.

Net type σmed

(m) σmax

(m)

Main

x = 0.002

y = 0.003

q = 0.001

x = 0.004

y = 0.005

q = 0.004

Minor

x = 0.005

y = 0.003

q = 0.001

x = 0.007

y = 0.007

q = 0.001

GPS

x = 0.006

y = 0.018

q = 0.006

x = 0.012

y = 0.029

q = 0.029

Table 1. Average and maximum standard deviation

for the three types of network

58

2.4 Diagnostic and structural output

The metric documentation provided is a key part in the project

of restoration and consolidation. Specifi cally, it was possible

to deepen the knowledge of the construction showing, for

the vestibule: the out of plumb of the outer cladding and the

misalignment of the vaults’ coffers. For the octagonal hall and for

the dome it was possible to identify: the thicknesses of the two

shells; materials and constructive techniques; internal connections;

the number, size and position of the ribs and of the chains; the

crack; the interventions of consolidation; the links between

construction technique and deformations.

Figure 1. Detail of the longitudinal section.

Original in scale 1:50

Figure 2. On the left, the small dome’s drawing by Giovan Battista Bettini (1725). On the right, which highlights the little dome’s

drawing showing the panels located above the iron chain. In the top right: section of the panel with the metal tie-rod highlighted in red

2.4.1 The Vestibule: The state of degradation and instability of

the vestibule, in particular of the dome and of the barrel vaults,

already exposed in 1725 by Giovan Battista Bettini in his report

with some surveys of the status quo (Romby, 1992), concerning

the out of curve of the stone tiles of the three upper rings of the

dome. It’s interesting to note that the encircling chain perfectly

fulfi lls its structural function while maintaining the position of

the panels at the lower heights. The upper part, however, is free

to move due to the thin shell of 25 cm, formed by 10 cm of stone

and 15 cm of coating clay. To overcome this problem has been

provided for the insertion of metal tie-rods capable of welding the

stone tiles on the bricks of the extrados (Figure 2).

Among the other consolidation interventions proposed we can

mention:

- the repositioning in plumb of the walls through the insertion of

metal chains;

- the raising of the main facade to set the new roof;

- the construction of two buttresses in facade to support in the

restoration of the dome and roof (Figure 3).

The most signifi cant deformation is the outside warping of all of

the fronts except the northern one stiffened by the octagonal hall.

The extraction of the fi ve cross-sections showed an accentuated

out of plumb in the two sections almost tangent in the dome’s

springer. This thesis confi rms the weaknesses already identifi ed

in the eighteenth century and which, as noted, continue to exist

despite the addition of the chains.

The orthogonal view of all the cross sections eloquently

summarizes the distribution of the deformation: maximum

at the dome’s springer, null in correspondence to the chains,

demonstrating the fact that these fulfi ll their structural function

(Figure 4).

The out of plumb individuated in the outer walls results in a

deformation of the barrel vault, accentuated in the east front,

probably never restored by the intervention of the eighteenth

century (Figure 5).

The deformations were quantified on all the façades of the

vestibule through the comparison with a vertical reference plane.

The diagnostic outputs confi rmed what has already emerged from

the critical interpretation of historical documents and architectural

boards.

The elevation map, made by extracting portions of points every

5 cm, is shown in false color calibrated to represent the different

elevations of the front from a zero height (almost in plumb, in red).

The elevation maps in false colors have been further elaborated in

contour lines (Figure 6) to improve the readability. The warping of

59

Figure 4. On the left, view of the fi ve cross-sections of the

vestibule, those near the small dome highlight the external

rotation of the main façade. On the right, the orthogonal view

of all the cross sections denounces the maximum deformation

correspondent to the small dome’s springer

Figure 5. 3D surface model of the intrados of the vestibule.

Detail of the eastern barrel vault. In yellow, the ideal line that

was supposed to follow the perimeter of the vault; in white, the

actual line warped. Beside it, a detail photo of the laceration, in

the point of maximum deformation, fi lled by a mortar wedge

Figure 6. Vestibule’s main façade. On the left, elevation map,

represented in false colors, of the front’s overhangs. On the

right, the map of the contours, traced with a pacing of 5 cm

Figure 7. 3D Model of the vestibule with the map of

the contours, traced with a spacing of 5 cm. The bigger

misalignments are found in the main facade with

a maximum deformation of about 25 cm

Figure 3. Views of the point model of the four exterior fronts and of the vestibule’s extrados (the one inside the mesonry are

dashed). The bolt-anchors are all indicated by the letters of the alphabet. On the sides,

some 3D views of the point model with an indication of the chains

60

Figure 8. Executive project of consolidation with the

introduction of a new structural system, spider-shaped circling

the small dome, formed by ten steel rods and two new

metal chains near the eastern and western fronts

(Prof. Carlo Blasi, University of Parma)

Figure 9. 3D Model of the vestibule with an indication of the

eighteenth century chains (in red) and of the new metal chains

(Prof. Carlo Blasi, University of Parma)

the main facade is evident, with a maximum in the central part of

20-25 cm, near the dome’s springer, which lessen, reaching zero

in correspondence of the metal chains I and L.

The northern front, however, present deformations near zero

thanks to the stiffening due to the adjacent octagonal body.

On the side façades, the higher out of plumb is near the springer

of the barrel vaults, bigger on the courtyard and smaller towards

via Vitoni as was to be expected since the large deformation of

the barrel vault in the south-east corner. We are, in fact, in the

order of 10 - 15 cm in the east front and 5 - 10 cm in the west one.

Even in this case, the warping is attenuated, to zero, in

correspondence of the chains ST and BA.

The hypsometric map has been reported on the 3D model to get

a complete view of the out of plumb in order to reach a deeper

knowledge of the process of cause and effect, associating to each

deformation the possible ineffectiveness or non-existence of the

structural elements (Figure 7).

The graphics elaborated by the three-dimensional survey, provided

a metric documentation supporting the executive consolidation

project (Prof. Carlo Blasi, University of Parma), which introduced a

spider encircling the small dome, formed by ten steel rods, and two

new metal chains near the eastern and the western fronts (Figure 8).

In the 3D model, we can appreciate the new structural system, in

yellow, and the connection with the preexistent chains, in red. The

structural analysis has confi rmed the calculation of deformations:

new stiffening elements were inserted in correspondence of the

maximum out of plumb as in the front, chains 3 - 4, and in the side

façades, chains 6 - 7 and 1 - 12 (Figure 9).

2.4.2 Octagonal hall and dome: The two shells of the octagonal

hall have a wall section almost equal (about 1 m for the outer shell

and 80 cm for the inner one).

The dome is hemispherical with an outside diameter of 26.70

and inside diameter of 21.70 m. Its double shell grows along the

extension of the lower double-shell. Only from around 33 - 34

m, the thickness tapers gradually to reach a minimum of 35 cm

below the lantern (Figure 10).

The two shells are connected by means of 32 ribs: 8 angular, 16

median and 8 central which support the lantern.

The outer covering of the octagonal hall:

- is composed of pebbles, rough-hewn sandstone and brick for the

fi rst three architectural orders. The brickwork is set with irregular

ledges and presents no scarfi ng: only in correspondence of the

edges sandstone blocks of various sizes are inserted to reinforce

the structure.

- is entirely laid in horizontal courses of brick punctuated by pillars

and cornices of sandstone in the tambour.

The dome is covered with brick tiles on the rib vaults and copper

on the corner ribs.

The layers of bricks, in the ribs and in the internal covering of

masonry, are horizontal with a slight inclination that in the top does

not exceed 20° - 25°. The round silhouette of the dome is obtained

by approximation through the progressive overhang of a row on the

other, towards the top where reaches 4 - 5 cm (Tucci et al., 2012).

It is this constructive feature in horizontal rows to question, even

today, the dome by Vasari. The fi rst to investigate the technique

is Lafri, in its “Relatione” of 1620. He states that “The shells are

bad manipulate, because now move to the third acute, now to

semicircle, then return to the third acute, and so they go swaying;

then to another third that are the angles of the ribs of the dome

that scrape so that false intersections are created”.

In summary, he ascribes the instability at the poor quality of the

bricks (from fl uvial and not mining extraction) and to the mediocre

construction technique devoid of clamping between the vaults,

between the vaults and the ribs and between the two shells probably

61

caused by the inconstant presence of Vasari on the construction site.

The bricks have variable sizes, in thickness and length, grossly laid

loosely and bound together by irregular and thick mortar layers,

thicker than one centimeter (Figure 11).

Later, in 1753, also Giovan Battista Nelli with his “Discorsi di

Architettura” investigates the construction technique taking as

a reference the Brunelleschi’s dome (inner diameter, 45 m; outer

Figure 10. Cross-section of the octagonal hall and of the dome.

Original in scale 1:50

Figure 11. Detail of a corner: on the left, between adjacent

vaults and on the right, between vault and rib.

It is evident the lack of connection

Figure 12. Dome of Santa Maria del Fiore in Florence. On the

left, isometric cross-section of the “corda blanda” (bland rope)

track (Drawing by L. Ippolito and C. Peroni); on the right,

graphical representation and fi berglass model of a

portion of the edge (Corazzi and Conti, 2011)

diameter, 54 m; cathedral height, 116.50 m; dome height, 34 m),

characterized by bricks layers curved upward, to form what is

called a “bland rope”.

The “bland ropes”, according to Salvatore Di Pasquale, have the

great advantage of achieving a structural continuity between two

adjacent vaults also thanks to the use of angular bricks in the

edges (Figure 12).

Vasari, while clearly inspired by the work of Brunelleschi in the

double shell structure and in the lantern, opts for a different and

approximate construction technique that causes the fi rst lesions

only few years after its conclusion.

There are two groups of lesions:

- the fi rst, due to the weak link between the vaults, is mainly along

the edges of all the vaults on both shells where the discontinuity

points mentioned by Di Pasquale are created;

- the second, due to the relative movement between the two

shells, cuts the median ribs and those of the lantern, causing

Figure 13. Domes comparison: in red,

that Vasari one; in black, the Brunelleschi one.

On the top right, comparison of construction techniques:

the Brunelleschi “corda blanda” (bland rope)

against the Vasari horizontal bricks layers

62

worrying detachments between the shells and the ribs.

The causes can be:

- the thickness of the outer shell, too similar to that of the inner

shell while, generally, it is signifi cantly lower to avoid burdening

the underlying structure. Just think of the one of Brunelleschi’s

dome which is about 0.70 m compared to 2.30 m of the inner shell;

- the excessive weight of the lantern, 1/18 of the total weight

compared to 1/25 of the Florentine lantern;

- the construction technique of the shells, in horizontal rows, and

without clamping the corners;

- The profi le of the dome, which Vasari designed semicircular

instead of the pointed arch designed by Vitoni (Figure 13).

To contrast the fi rst group of damages 8 hoops were inserted, 7 on

the extrados of the outer shell of the dome and 1 on the extrados

of the inner shell at the level of the tambour.

The consolidation interventions carried out to contrast the second

group of crack provided for the insertion of 21 chains crossing

the two shells both in the tambour and in the dome.

For each chain has been suggested a dating and attribution

carefully following the interpretation of the historical documents.

The chains have all been tabulated in a chart indicating the type,

planimetric and altimetric position, the structural function, dating

and a hypothetical attribution.

The total number of chains is 78, of which 39 in the dome (Tucci

et al., 2012).

3. THE SAN GIMIGNANO TOWERS

The historic centre of San Gimignano has been chosen as a pilot

site because it represents an urban environment unique in the world

for its monuments strongly at risk in the event of an earthquake.

The territory is located in an area of relatively low seismic hazard,

with the highest recorded event in 1869 with an intensity of VII

on the Mercalli scale. The effects, although not disastrous, are still

representative of a particularly intense and widespread damage

to the monuments, thus resulting in the importance of estimate

of shaking expected during future seismic events, potentially

dangerous for this type of building with a predominant vertical

development.

3.1 Historic framework

The oldest formation of San Gimignano dates back at least to

the third century BC as evidenced by the several archaeological

discoveries in the surrounding area.

In 1199, in its full economic splendour, the centre gained its

communal independence but not without infi ghting between

Guelphs and Ghibellines. An urban aristocratic class arose

and expressed his political and social supremacy through the

construction of 72 towers. Today there are only 16, while the

others can only be glimpsed within the urban fabric.

3.2 3D digital survey

The survey with laser scanning technique was carried out by the

author, 2011-2012, as part of an academic research fellowship at

the GeCo Laboratory of the University of Florence.

To allow for documentation of both the towers and the urban

context in which they are included we adopted a multi-scale

approach with a common referencing of data.

The work on-site, organized in fi ve measurement campaigns

(Figure 14), has been carried out with a range phase-based laser

scanner (HDS6000, Leica Geosystems): 41 scan position for a

total amount of 44 GB of raw data.

The acquired data were aligned mainly through homologous points

and referenced in a local system coincident with one of the scan

locations. The registration has been solved with a residual error

of about 1 centimetre. The overall three-dimensional model is

constituted by more than 1.5 billion points.

3.3 3D wireframe output

On one hand, the 3D model allowed the possibility of creating

a cartography within which the individual buildings could be

contextualized. Second, the reading of the relations linking

the towers: typological scheme, constructive, constituent and

distributive characters.

To document the scale of the building we surveyed the external

geometry of each tower with the aim to defi ne the conservation status

and allow the construction of a metric support for the interpretation of

the structural behaviour through a successive numerical modelling.

In particular, at the urban scale, it was performed the three-

dimensional metric acquisition with laser scanner of the exterior

surfaces of thirteen towers: Salvucci, Pettini, Chigi, Collegiata,

Propositura, Grossa, Rognosa, Ardinghelli, Becci, Cugnanesi, Coppi

– Campatelli (Figures 15 and 16).

Figure 14. Reference plan of the historical center of San

Gimignano with indication of the towers captured

for each measurement campaign

Figure 15. Top view of the overall point model. In orange, the

towers captured. Note the position of the origin of the

reference system in Piazza delle Erbe

63

3.4 Diagnostic and structural output

At the scale of the building, considering the twin towers of the two

most important families (the Guelphs Salvucci and the Ghibellines

Ardinghelli) as a case study:

- the analysis of structural transformations;

- geometric analysis to locate the geometric centre of gravity;

- the computation of the deformation.

3.4.1 Analysis on the geometry of the 3D model: The diagnostic

use of the laser scanner, especially for structural scopes, is clear when

it is possible to carry out analysis of the geometry from the point

cloud to extract parameters and useful information for the purposes

of assessment of the stability of the structure. A signifi cant fi nding

is the identifi cation of overhangs, particularly important in the case

of slender structures.

The analysis of verticality of the pairs of towers was initially

performed by exporting some slices of reduced thickness (1 cm)

from the model. The double symmetry of the structure has allowed

defi ning the geometric centre of gravity of each section in the 3D

space. The trend of the axis, obtained by connecting the centres of

gravity, showed:

- the Salvucci Towers, swerving negligibly in North-South direction

(maximum distance lesser than 2 cm for the northern tower; 4 cm for

the southern one), while in the East direction has been found for the

southern tower, a slight deviation by the vertical (maximum distance

8 cm) and for the northern tower a deviation greater than 18 cm

(Figures 17 and 18). The overhang so measured is the planimetric

distance between the centre of gravity of the fi rst horizontal section

(at a height of 9 m) and the top of the towers (at a height of 42.38

m for the northern tower and of 44.24 m for the southern one).

- the Ardinghelli Towers, a negligible swerving in East-West direction

(maximum distance lesser than 6 cm), while in the north-south

direction, was found a considerable deviation from the vertical for

both the towers, but in the opposite direction: the southern tower

presents a deviation just over 18 cm in the southerly direction; the

northern tower has a deviation just over 26 cm in the North direction

(Figure 19). The out of plumb so measured is the planimetric distance

between the centre of gravity of the fi rst horizontal section (at a height

of 3.73 m) and the top of the towers (30.76 m the northern tower and

23.77 m the southern one excluding the slopes of the roof).

Figure 18. Salvucci Towers, on the left. Figure 19. Ardinghelli Towers, on the right.

Graph of displacements in x and y given in cm of the geometric center of gravity of the horizontal sections

Figure 17. Salvucci Towers. 3D point model, displayed in gray

scale, indicating the horizontal section profi les useful for the

defi nition of the geometric center of gravity

NORTHERN TOWER

SOUTHERN TOWER

SOUTHERN TOWER

NORTHERN TOWER

Figure 16. View of the 3D wireframe models of the

exterior of the towers

64

Figure 20. Ardinghelli towers. On the left, the towers in their

original structure (De Fleury, 1874). In the middle, a picture

of 1915-1920 with a view of the northern tower before the rise

(Alinari Archive). On the right, picture of the current state

Figure 21. Ardinghelli Towers. Analysis of horizontal

(light blue) and vertical deviation (in red)

Figure 22. Ardinghelli Towers. Summary plan of the direction

of overhang of the external structure. The directions of incline

are indicated by means of arrows with length qualitatively

proportional to the overhang (in red the resulting vector)

(1.97° south) than that of the underlying medieval structure (1.15°

to the north) on the northern front, while the same inclination (0.86°

and 0.83° to the north) on the southern front (Figure 23).

The analysis of the deformation, compared to the interpolating

reference plane, has shown continuous changes of direction, with

alternating concavity and bulges.

In particular, for the northern tower (Figure 24), the observed

deviations from the reference plane are:

- from top to bottom, in the northern and southern fronts affected by

the greater inclination, with a bulge of the order of 5 - 6 cm in the

adjacent portion to the seam between the old medieval masonry and

the one rebuilt in the second decade of the ‘900 (elevation of about

23 m, coinciding with the height of the southern tower);

- in the direction south - north, in the eastern and western fronts, so as

to follow the direction of the slope (north, in fact) with a distribution

that suggests a confi guration linked to torsion phenomena.

Similarly, but in the opposite direction, in the southern tower (Figure

PIAZZA DUOMO

PIAZZA DELLA CISTERNA

In relation to the short time spent for the survey (20% of the total)

and processing (80% of the total), this method of investigation and

restitution of the geometric characteristics allows an accurate analysis

of the height and incline (with an accuracy of about 1 centimetre) of

structures characterized by an elevated height and therefore not simply

detectable with other techniques.

3.4.2 Analysis of construction transformations: The drawings

have allowed the identifi cation of construction transformations that

have invested the four towers. While the Salvucci Towers have been

interested by minor transformations due mainly to the change of use

(commercial businesses on the ground fl oor in Via San Matteo and

residence on the upper levels), the Ardinghelli Towers have undergone

determinants structural alterations. The fi rst signifi cant intervention

dates back to 1870 when, after the earthquake of 26th of September

1869, the towers were reduced at the same height. It is probably

because of this earthquake, the maximum recorded in the town, that

the towers acquired the current wide apart arrangement.

This evident inclined conformation did not prevent, however, the

construction of a raising on the northern tower in 1920 approximately

(Figure 20).

3.4.3 The computation of the deformations: Starting from the 3D

database of the Ardinghelli towers we made an assessment of the

deformations by comparing the façades with two reference planes:

a fi rst one vertical, to observe large deviations of the tower, mainly

due to the incline; the second one, interpolating, to highlight the

irregularities and deformations compared to a not altered situation.

Not having, as often happens, previous surveys characterized

by the same precision and information density, with respect to

which calculating the deformation as differential displacement,

the differences between the points on the towers’ surfaces and the

reference plane, i.e. the deviations, were considered as deformations,

or better, as overall deformations with respect to a hypothetical

condition of regularity of the structures (Doglioni et al., 2007).

The actual deviations of the four fronts of both the towers (Figures

21-24) with respect to the vertical reference plane, confi rm the results

obtained from the geometric analysis of the 3D model: the southern

tower presents a signifi cant deviation from the vertical on the northern

side (slope of 0.87°, out of plumb of 31 cm) and, conversely, the

northern tower has an equal deviation from the vertical in the opposite

direction, on the southern side (slope 0.85°, out of plumb of 41 cm,

assuming it as a single deformed section; slope of 0.86 ° in the oldest

part and of 0,83° of the portion of the twentieth century in the case

of two sections).

It’s interesting to note that the raising of the northern tower, from

the height of about 23 m, has an inclination in the opposite direction

65

Figure 23. Ardinghelli Towers. Analysis of vertical deviations

measured on the northern tower. The slope is calculated by

dividing the tower into two sections: the medieval

and twentieth-century addition

Figure 24. Ardinghelli Towers. Elevation map, represented in

false colors, the overhangs of the fronts. The false colors have

been calibrated to represent the different levels of elevation of

the front from a zero quota (almost plumbed, shown in red,

in the case of a vertical reference plane; portion adherent

to the best fi tting plane, indicated in red, in the case of

the interpolating reference plane) with 5 cm delta

24), the observed deviations from the reference plane are:

- from top to bottom, in the northern and southern fronts affected

by the greater inclination;

- in the direction north-south, in the eastern and western fronts, so as

to follow the direction of the slope (south, in fact) with a distribution

that suggests a confi guration linked to torsion phenomena.

This reveals that the fronts are curved and segmented and still largely

altered compared to ideal conditions.

The observations provided, if included in a framework of general

study including analysis confi rming a state of “fatigue” of the

masonry due to the effect of the tower’s own weight, can be of great

interest and should be taken into account for evaluation about the

stability of the structure (Pesci et al., 2011).

4. ACKNOWLEDGEMENTS

The author would like to thank Professor Carlo Atzeni for willingness

and courtesy and Professor Grazia Tucci for technical and logistical

support.

5. REFERENCES

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Di Pasquale S., 2002, La costruzione della cupola di Santa Maria del

Fiore, Biblioteca Marsilio, Venice, Italy.

Doglioni, F., Mazzotti, P., 2007, Codice di pratica per gli interventi

di miglioramento sismico nel restauro del patrimonio architettonico,

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Pesci, A., Bonali, E., Casula, G., Boschi, E., 2011, Le informazioni

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Saint Aubin, J. P., 1999, Il rilievo e la rappresentazione dell’architettura,

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Tucci, G., Nobile, A., Riemma, M., 2012, Laser scanner surveys and

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con il supporto di

ISBN 978-88-905917-3-0

Dicembre 2013