seismic vulnerability assessment and structural improvement … · 2014. 5. 20. · (vulnus) and...

Seismic vulnerability assessment and structural improvement proposals for the building typologies of the historic centers of Vittorio Veneto (Italy)

M. R. Valluzzi, A. Bernardini & C. Modena University of Padova, Italy

Abstract

This vulnerability study of the historical centres of Vittorio Veneto (TV, Italy) aimed at suggesting compatible solutions of structural improvement in seismic areas. Macro-modelling using kinematics models has been adopted by using a computational procedure set up at the University of Padova in the 1980s (Vulnus) and recently updated in Visual Basic ambient. Several building typologies have been identified in the study and the main characters affecting their vulnerability are discussed here. Keywords: seismic vulnerability, masonry, building typologies, colonnades, macro-modelling, limit analysis, kinematics mechanisms.

1 Introduction

Historic structures in seismic areas are characterized by several typologies, especially in minor urban centres, where continuous stratification and superposition occurred during time. Isolated and arrays of buildings, complex aggregates, often located on slopes, can be found. Moreover, existing buildings may have construction features that can induce specific vulnerability problems such as: arcades, loggias and colonnades, large halls. The large variability of the masonry material and the low effectiveness of structural connections among components (walls, floors and roofs), make the assessment of the seismic vulnerability of this class of buildings a particularly hard task. In such a context, common procedures usually adopted for structural evaluations based on the box-

© 2005 WIT Press WIT Transactions on The Built Environment, Vol 83, www.witpress.com, ISSN 1743-3509 (on-line)

Structural Studies, Repairs and Maintenance of Heritage Architecture IX 323

behaviour under seismic actions are not reliable and, when applied, can led to inaccurate results. Recently, methods for the evaluation of the seismic vulnerability, based on the application of single or combined kinematics models involving the equilibrium of macro-elements, have been validated by direct comparison with the real damage occurred [1] [2]. Macro-elements are defined by single or combined structural components (walls, floors and roof), considering their mutual connections and constraints (e.g. the presence of steel ties or concrete ring-beams), the constructive deficiencies and the characteristics of the constitutive materials [3]. Procedures based on the abovementioned approach have been applied to the two historical centres which compose Vittorio Veneto, namely Serravalle and Ceneda [4] [5]. They consist of about 420 and 690 buildings, respectively, and comprises several typologies, which have been grouped in different categories, following the combination of three classification criteria: (i) dimensions (palaces, buildings, large complexes, annexes), (ii) presence of contiguous constructions (isolated and row buildings), (iii) presence of colonnades at the ground level, considered for all the abovementioned cases. Vulnerability analyses for the whole center and the proposal of improvement interventions are presented and discussed in the paper.

2 The historical centers of Vittorio Veneto

Vittorio Veneto is a small town located along the foothills of the Alps in the Veneto region (Treviso province). It is composed by two historical centers, Serravalle at North and Ceneda southwards, whereas the middle portion comprises now more recent buildings (fig. 1). Its origins go back to the paleo-Veneto period (around 1000 B.C.), but it achieved more importance later, during the Roman Times. Ceneda originally included Serravalle into its defense curtain walls, which was named separately only since the Middle Age. They develop independently until 1866, when they were officially joined under the name Vittorio, which became Vittorio Veneto after in 1923.

Ordinary buildings have mainly 3-4 storeys, made of rubble stone masonry and poor quality mortar, with scarce connections in the thickness and among walls; timber floors and roofs and some tie-rods connecting the main walls are also present. Few cases are in brickwork and better fabrics (cut stones with good mortar and improved connections) are generally recorded for more important constructions (palaces, churches, etc.). Specific vulnerabilities are due to the presence of colonnades at the ground floors and loggias, especially in buildings organized as rows, attics of reduced height at the top, and large halls in the palaces. Alteration of the constructive systems during time led to substitutions of roofs and floors with combined solutions of concrete joists and lightweight tiles or r.c. slabs.

The surrounding area was subjected to relevant earthquakes during the last centuries (up to VIII MCS intensity), that make the region classified into medium-high seismic hazard zones. Therefore, systematic evaluations of the


324 Structural Studies, Repairs and Maintenance of Heritage Architecture IX

seismic vulnerability of the buildings are in need, in order to execute provisional analysis aimed at reducing the structural risk and improving the safety conditions.

SerravalleSerravalle

CenedaCeneda

SerravalleSerravalle

CenedaCeneda

Figure 1: Orography of the zone of Vittorio Veneto and view of the centre from the Meschio river, which runs through the town.

3 Classification of the existing building typologies

Serravalle and Ceneda consist of about 420 and 690 buildings respectively, characterized by different age and historic and architectural value, and belonging to several constructive typologies. By integrating the data of previous database available from the Town Council with the direct survey performed during the research, it has been possible to summarize specific information as follows.

3.1 Dating

The preliminary analyses confirmed that buildings still standing in Ceneda are older than in Serravalle. Serravalle is currently composed by around the 24% of buildings built in 1840-1900, while around 50% is dated before 1800 (14% of this was built in the XV-XVI centuries); Ceneda has more than 50% of buildings built in 1840-1900, and only around the 14% before 1800 (see fig. 2).

3.2 Architectural value

The architectural value was represented, in the preliminary database, by a parameter which resumes information about the architectural quality, age and conservation conditions. Four levels are considered: 0 (no value); 1 (absence of elements having architectural values); 2 (presence of original elements with architectural value even if not extended to the whole construction); 3 (remarkable architectural value extended to the whole construction); 4 (historical and monumental value).

Results showed that Serravalle comprises the 22% of buildings in classes 3 and 4, while in Ceneda only less than the 6% belongs to these categories (fig. 3).



This distribution agrees with dating results, as the correspondence among highest value classes and oldest buildings is confirmed.

Dating of buildings in Vittorio Veneto

0,00

10,00

20,00

30,00

40,00

50,00

60,00Pe

rcen

tage

of b

uild

ings

Serravalle 1,50 6,70 8,40 11,40 22,10 13,60 23,60 6,70 4,00 2,00

Cenada 0,15 0,00 0,40 2,30 10,80 9,10 52,50 15,40 6,90 2,35

before XIV c.

XV XVI XVII XVIII 1800-1840

1840-1900

1901-1946

1947-1970

after 1971

Figure 2: Comparison of the dating detected for the two centers.

Architectural value for buildings in Vittorio Veneto

0,00

5,00

10,00

15,00

20,00

25,00

30,00

35,00

40,00

45,00

50,00

Per

cent

age

of b

uild

ings

Serravalle 3,30 4,80 17,80 20,10 24,40 7,50 6,50 2,00 13,60

Ceneda 8,10 7,10 46,20 14,40 13,10 5,40 3,40 0,30 2,00

val. 0 val. 0-1 val. 1 val. 1-2 val. 2 val. 2-3 val. 3 val. 3-4 val. 4

Figure 3: Comparison of the architectural value detected for the two centers.

3.3 Typology

The two centers include a large variety of buildings, having different morphology and use. The typologies have been classified grouping the different categories following the combination of three criteria:

a) dimensions: palaces, buildings, large complexes and annexes have been distinguished;

b) presence of contiguous constructions: isolated buildings or row buildings; c) presence of colonnades at the ground level, considered for all the

abovementioned cases. Constructions having specific functions as churches or towers-bastions have been also distinguished from buildings.



a)

b)

c)

d)

e)

f)

g)

h)

i)

j)

k)

l)

Figure 4: Examples of building typologies in Vittorio Veneto: a) isolated palace with colonnades (Palazzo Casoni – Serravalle); b) isolated palace without colonnades (Palazzo Palatini – Ceneda); c) row palace with colonnades (Loggia della Comunità – Serravalle); d) row palace without colonnades (Palazzo Muzzi – Serravalle); e) row building with colonnades (Via Casoni 10,12 – Serravalle); f) row building without colonnades (Via Roma 81 – Serravalle); g) isolated building (Via Tiziano 159 – Ceneda); h) large complexes (Bacologia – Serravalle); i) annexe (to Palazzo Palatini – Ceneda); j) church (Cathedral of Ceneda); k) l) towers-bastions (Torre di S.Martino and Porta di S.Giovanni, both in Serravalle).



Therefore, a total of eleven cases have been selected in the study, as follows (fig. 4): a) isolated palaces with colonnades, b) isolated palaces without colonnades; c) row palaces with colonnades, d) row palaces without colonnades; e) row buildings with colonnades, f) row buildings without colonnades; g) isolated buildings; h) large complexes; i) annexes (mainly used as stores or garages); j) churches; k) towers and bastions. Results are summarized in fig. 5. They showed that in Serravalle more than 8% of palaces can be found, more than half of which have colonnades at the ground level, while in Ceneda almost all the palaces (7%) are without colonnades. The most diffused typology is the row buildings without colonnades (58% in Serravalle, about 66% in Ceneda). Nevertheless, Serravalle has more than 10% of row buildings with colonnades, whether in Ceneda only the 1% is included in this category. Finally, Serravalle has the highest percentage of large complexes.

The main difference between the two centers concerns the presence of colonnades: Serravalle has the 15% of the whole number of buildings with colonnades, whereas Ceneda has only about the 2% in this category. According to their historic developments during centuries, from a general view Serravalle is composed by long rows of buildings, where oldest ones are located along the main streets, while Ceneda have more spreads constructions, which develops into a intricate streets pattern.

Typologies detected in the Vittorio Veneto area

0

10

20

30

40

50

60

70

Perc

enta

ge o

f bui

ldin

gs

Serravalle 0,50 1,00 3,90 2,90 10,60 58,00 14,70 4,30 1,70 1,20 1,20

Ceneda 0,00 1,30 1,20 4,60 1,00 65,70 15,60 3,05 6,50 0,90 0,15

isolated palaces with colonnades

isolated palaces without

colonnades

row palaces with

colonnades

row palaces without

colonnades

row buildings with

colonnades

row buildings without

colonnades

isolated buildings

large complexes

annexes churchestowers-

bastions

Figure 5: Comparison of the different typologies detected for the two centers.

4 Seismic vulnerability of pilot buildings

4.1 Structural macro-modelling analysis

The analysis of about 60 buildings belonging to the two centres has been performed adopting the macro-modelling approach proposed by the VULNUS procedure [6], developed at the University of Padova, and the application of single kinematics models. VULNUS gives three indexes: I1 and I2, which define the seismic coefficient connected to the in-plane shear resistance and out-of



plane weakest mechanisms, respectively, and I3, which defines five categories of vulnerability classes (very low, low, medium, high, very high).

Results showed that the vulnerability level is strongly depending on the presence of the portico at the ground level and of the high dimensions of some constructions. Palaces and large complexes are more vulnerable than others (they often present storey heights higher than 3 m, very long sets and walls), especially regard shear, when colonnades are present, as they reduce the resisting section at the base. Isolated palaces and buildings have generally lower vulnerability than rows. Isolated buildings and annexes present the lowest seismic vulnerability: they have a reduced storey height (often lower than 2.4 m) and often present ties connecting opposite walls at least in one direction.

By simulating different seismic levels (a/g = 0.16, 0.28 and 0.40, where a is the ground acceleration and g the acceleration of gravity) it is possible to say that for high hazards the vulnerability increases for all the buildings except for isolated ones and annexes, which keep low values (fig. 6). The survival probability is comparable for the two centres for different seismic levels: Ceneda has the highest probability of collapse for in-plane shear mechanisms (I1 index), whereas Serravalle has the highest probability for simultaneous shear and flexural collapses (fig. 7). The punctual assessment with the kinematics models confirmed the high vulnerability of the façade sects to global overturning mechanisms, for both whole walls and corners. The global collapse probability is higher for Serravalle than Ceneda for every seismic level, even if values are very close for both centers (tab. 1).

The grouping of the most significant typologies (palaces and buildings, isolates or rows, with or without colonnades) allowed to synthesize the Vulnus results as showed in fig. 8.

Collapse of typologies of buildings

0

0,2

0,4

0,6

0,8

1

1,2

a/g

Perc

enta

ge o

f bui

ldin

gs

0,16 0,994 0,478 0,945 0,8 0,629 0,593 0,129 0,996 0,111

0,28 1 0,979 1 1 0,976 0,964 0,393 1 0,639

0,40 1 1 1 1 1 1 0,806 1 0,968

isolated palaces with colonnades

isolated palaces without

row palaces with

colonnades

row palaces without

colonnades

row buildings with

colonnades

row buildings without

colonnades

isolated buildings

large complexes

annexes

Figure 6: Percentage of buildings belonging to different typologies which collapse for different seismic levels.

4.2 Intervention proposals

Possible applications of strengthening measures have been simulated applying the same macro-element analyses used for the vulnerability assessment. For the improving of the in-plane behaviour, injections and/or limited rebuilding can be adopted in order to re-establish the mechanical condition of the



masonry. For out-of-plane collapses prevention, tying is the most effective intervention; also the stiffening of floors and roof with compatible materials (dry connection with timber reinforcement, for example) or, where necessary, the thickening of walls, are suggested.

I1>A and I2>A I1A I1>A and I2A and

I2A andI2

Effect of interventions on I1 index

0

0,1

0,2

0,3

0,4

0,5

0,6

P.C

ason

i

P.To

desc

o

P.L

ioni

P.Pa

latin

i

P.M

ozzi

P.Tr

oyer

Alb

ergo

del

le M

use

Logg

ia

P.C

esan

a

P.G

iust

inia

ni

viaC

ason

i,2

viaC

ason

i,10,

12

viaC

ason

i,16

viaC

ason

i,20

viaC

ason

i,24,

26

viaC

ason

i,30

viaC

ason

i,34

viaC

ason

i,40,

42

viaC

ason

i,68

viaR

oma,

102,

104

viaR

oma,

108,

110

viaR

oma,

112

viaR

oma,

122

viaR

oma,

128

lgLa

Pia

zzol

a,4

viaR

oma,

57

viaR

oma,

77,7

9

viaR

oma,

71

viaR

oma,

73

viaR

oma,

81

viaR

oma,

37

viaR

oma,

22

viaR

oma,

40

viaR

oma,

35

via

Da

Cam

ino,

24

Bac

olog

ia

Ex-

Osp

-ant

ica

Ex-O

sp-r

ecen

te

anne

sso-

sini

stro

anne

sso-

dest

ro

I1

before after

Figure 9: Comparison of the safety level before and after intervention for in-plane shear strength index.

Effect of interventions on I2 index

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

P.C

ason

i

P.T

odes

co

P.L

ioni

P.P

alat

ini

P.M

ozzi

P.Tr

oyer

Albe

rgo

delle

Mus

e

Logg

ia

P.C

esan

a

P.G

iust

inia

ni

viaC

ason

i,2

viaC

ason

i,10,

12

viaC

ason

i,16

viaC

ason

i,20

viaC

ason

i,24,

26

viaC

ason

i,30

viaC

ason

i,34

viaC

ason

i,40,

42

viaC

ason

i,68

viaR

oma,

102,

104

viaR

oma,

108,

110

viaR

oma,

112

viaR

oma,

122

viaR

oma,

128

lgLa

Pia

zzol

a,4

viaR

oma,

57

viaR

oma,

77,7

9

viaR

oma,

71

viaR

oma,

73

viaR

oma,

81

viaR

oma,

37

viaR

oma,

22

viaR

oma,

40

viaR

oma,

35

via

Da

Cam

ino,

24

Baco

logi

a

Ex-

Osp

-ant

ica

Ex-O

sp-r

ecen

te

anne

sso-

sini

stro

anne

sso-

dest

roI2

before after

Figure 10: Comparison of the safety level before and after intervention for out-of-plane mechanisms.

5 Conclusions

The extensive analysis of the two historical centers which compose Vittorio Veneto in Italy has been presented. Reliable simplified methods, based on kinematic models describing the loss of equilibrium of structural macro-elements



have been used. The presence of colonnades at ground level and the high dimensions of halls in the palace are the parameters that mainly influence the seismic vulnerability of the several building typologies distinguished in the study. Moreover, the lack of ties for the improvement of the scarce connection among walls, floors and roofs, together with the poor conditions of structures and materials and the non-homogeneity of the foundation soil affect the assessment results. Those results allowed some intervention proposals to be suggested, based basically on the application of ties and reinforcement with compatible materials and techniques (both for floors and for walls).

The study will be developed to provide damage scenarios through fragility curves and damage probability matrices on purpose developed. Those evaluations will be used to calibrate macroseismic scale analyses taking into account distributions defined by cumulative percentage of buildings suffering various damage levels for different earthquake intensities.

Acknowledgements

The authors wish to thank the Vittorio Veneto Town Council for the availability of the preliminary data about the centers, and the students G. Benincà, E. Antoniazzi and E. Barbetta for their collaboration for the integrative surveys and the analyses. The research was supported by GNDT and Civil Protection Dept. in the framework of Italian Ministry Council research projects.

References

[1] Valluzzi, M.R., Michielon, E., Binda, L. & Modena C. Modellazione del comportamento di edifici in muratura sotto azioni sismiche: l’esperienza Umbria –Marche. 10th Conf. ANIDIS, Potenza, Italy, CD-ROM, 2001.

[2] Valluzzi, M.R., Cardani, G., Binda, L. & Modena, C., Analysis of the seismic vulnerability of masonry buildings in historical centres and intervention proposals. 6th Int. Sym. on the Conservation of Monuments in the Mediterranean Basin, Lisbon, Portugal, pp. 561-565,CD-ROM, 2004.

[3] Giuffrè, A., Sicurezza e conservazione dei centri storici. Il caso Ortigia. Bari: Laterza, 1993.

[4] Benincà, G. Analisi della vulnerabilità sismica del centro storico di Serravalle (Vittorio Veneto). Graduation Thesis, University of Padova, Italy, 2002.

[5] Antoniazzi, E. Analisi della vulnerabilità sismica delle tipologie edilizie dei Centri Storici di Serravalle e Ceneda (Vittorio Veneto). Graduation Thesis, University of Padova, Italy, 2003.

[6] Bernardini, A., Gori, R. & Modena, C., Application of coupled analytical models and experiential knowledge to seismic vulnerability analyses of masonry buildings. On: Earthquake Damage Evaluation and Vulnerability Analysis of Buildings Structures, Ed. A. Kortize, INEEC, Omega Scientific, 1990.



seismic vulnerability assessment and structural improvement … · 2014. 5. 20. · (vulnus) and...

Documents