the temple of s. maria del tricalle in chieti - wit press€¦ · and vibration monitoring ... a...

The temple of S. Maria del Tricalle in Chieti:

chemical-physical analysis, structural behaviour

and vibration monitoring

A. Salvatori*, R. Quaresima\ G. Scoccia^

"Dipartimento di Ingegneria delle Strutture, delle Acque e del

Terreno, University of L'Aquila, Monteluco di Roio, 67040

L'Aquila, Italy

D̂ipartimento di Chimica, Ingegneria Chimica e Materiali

University ofL 'Aquila, Monteluco di Roio, 67040 L 'Aquila, Italy

Abstract

In the present work the global features of an historical monument settled in theAbruzzean coastal environment are studied. A chemical-physical-mechanicalanalysis is performed to achieve the exact values of the structural parametersneeded to characterize the masonry, together with a theoretical computationwhich simulates the global structural behaviour of the church. On the basis ofthese results, an in situ traffic vibration monitoring has been performed,allowing the correlation between numeric and experimental data, and thedevelopment of a correct restoration and maintenance of the temple.

1 Introduction

The temple of S.Maria del Tricalle is situated in Chieti, located in Abruzzoregion, in the middle part of Italy. During the '80s the church gave prominenceto some problem concerning the formation of several damages in the dome andalong the vertical corners. A complete investigation concerning the materialproperties, and the global static and dynamic characteristics of the church wascarried on in collaboration with the Artistic, Environmental, Architectonic andHistorical Heritage Superintendence of Abruzzo.

An historical analysis of the monument has first been performed to achievevarious information about the age of the temple, the constitutive materials, theconstructive techniques, the seismic history and any restoration made in thepast. The church was built during the XIV century over the ruins of a pre-existing ancient roman temple dedicated to Diana. It is a church with anoctagonal shaped plan, with a hemispheric dome. A planimetry and a lateralview of the church are evidenced in Fig. 1.

Transactions on the Built Environment vol 15, © 1995 WIT Press, www.witpress.com, ISSN 1743-3509

294 Architectural Studies, Materials & Analysis

1571

Planimetry Cross-sectional view

Figure 1: planimetry and cross-sectional view of the temple.

Before the restoration of 1879, in front of the church there were the ruinsof an ancient arcade with an altar, which are now completely destroyed. Exceptfor the frontal wall, the other ones have a smaller thickness, due to the presenceof niches; so the dome is effectively based on the masonry corner piles formedby the intersection of the walls (where the relevant thickness is greater).

There is also a little circular window in the middle part of a staircasesituated inside the east wall, and two greater windows in the lateral walls.

The dome is formed by two masonry structures laid one upon the other,and is closed in the keystone by a little bell tower.

The study of the temple regards the complete knowledge of the constitutivematerials and their behaviour under several conditions; samples of bricks weretaken from different parts of the temple, and an experimental investigation hasbeen performed to examine the chemical and physical properties of thestructural materials in order to understand the forms of decay.

Further investigation has been carried out to correlate the properties of theused materials with the structural behaviour; some laboratory tests (compressivestrength and strain gauges analysis) have been made on the bricks to determinethe mechanical properties of the material.

Because of the neighbourhood of two thoroughfares, and of some kind ofstructural damage probably due to traffic, an experimental investigation hasbeen executed on the structure of the temple, surveying the vibrations driven bytraffic by means of seismometric instruments. The processing of the datapermitted to obtain the maximum and effective values and the spectral densityof vibration amplitude, and the first three vibration modes, together with thedynamic parameters of the structure.


Architectural Studies, Materials & Analysis 295

2 Chemical-physical analysis of the structural materials

To assess the physico-chemical as well as the mechanical characteristics of thetemple bricks, an accurate and detailed sampling has been carried out, incompliance with Norms NORMAL (CNR -ICR*)

On the basis of both macroscopic characteristics (colour, size, type andmixing inclusions) and visual surveys (determination of stratigraphic buildingunits), the main brick typologies have been determined and the followingexperimental methodologies have been performed:- X-ray fluorescence spectrometry (XRF) for the analysis of the main elements(Na, Mg, Al, Si, K, Ca, Ti, Fe);

- loss on ignition (L.O.I) at 950°C;- COj volumetric gas measure by calcimeter (Dietrich-Fruhling method) for theestimation of the calcite content;

- X-ray diffraction (XRD) for the identification of the mineralogicalcomposition;

- polarized optical microscopy on petrographic thin sections (CNR-ICR̂ );- scanning electron microscopy (SEM) and X-ray energy dispersive analysis formorphology evaluation of the crystalline phases (CNR-ICR*);

- mercury and nitrogen porosimetry, helium pycnometer for the estimation,respectively, of the porosity (P), real density (y%) and apparent or bulk density(y) (CNR-ICR*);

- volume imbibition coefficent (CiV) and water saturation index (IS)(CNR-ICR*).

To define the computational model of the structure compression tests havebeen made both on cubic (60x60x60mm) and prismatic sized brick samples,determining, in the first case, the compressive strength ((?<,), and, in the secondcase, the compressive strenght (cj and the tangent modulus at the origin (E).

Brick colour has been determined by means of a reflection colorimeter;measurement has been carried out on brick powder tablets in order to get even-coloured samples. Data, expressed according to a red index (RJ, refer toMansell scale.

Three main typologies of bricks have been determined - see descriptiongiven in Table 1 - for the discussion of the results obtained.

Composition of main elements expressed in oxides is given in Table 2,while physical characteristics and mechanical testing results of the varioustypologies of bricks are shown in Table 3.

Fracture surfaces obtained by SEM for the various brick typologies aregiven in Fig. 2.

Analyzing Table 2 it is clear that bricks type A (SiO%=46.82, CaO=13.05)have a different composition (likely depending on the use of a non- selectedclay) if compared with all the others (types B and C). This difference seems toaccount for the sample colour (yellow) with respect to all the other ones (typesB and C). Moreover, higher LOI value of A type with respect to B type and the



lack of pyroxenes could be seen in relation to a different firing of the first typeof brick, even if more oxidizing firing conditions for B type bricks cannot beexcluded.

Table 1 - Results of the petrophysical characteristics.

Brick TypeColour

DimensionMacroscopicmix

Thin Sectionskeleton:- quantity- distribution

- granulometi

MineralogicaComposition

BottomPaste

Porosity

Ayellow

a=63-67mmDescription:

homogeneous;yellow colour;small lightinclusions

Specification

poornot homogeneoushomogeneous

y (100-300nm);prevalent 300um

QuartzK FeldsparsPlagioclaseCalcite

Amorphous phase

light colour;general aspect:

homogeneous withpresence of

carbonate clots(around 100-200um);where these are

absent the aspect isopaquepore shape:

heterogeneous;pore radii100|im-2mm

Blight red

b=290-298mm

homogeneous;light red colour;

small darkinclusions

relatively plentifulnot homogeneous

heterogeneous(60fim-4 mm);prevalent 500u,m

QuartzK FeldsparsPlagioclaseCalcite

PyroxenesAmorphous phase

dark colour;general aspect:

homogeneous withpresence of

carbonate clots(around lOOum);where these are

absent the aspect isopaque

pore shape:variable;pore radii

400u,m-10mm

Cred

c=l 14-1 19mm

heterogeneous;red quenched colour;small light and dark

inclusions

relatively plentifulnot homogeneous

heterogeneous(60pm-4mm);prevalent 400-

TOOjamQuartz

K FeldsparsPlagioclaseCalcite

PyroxenesGehlenite

Amorphous phaselight colour;

general aspect:homogeneous with

presence ofcarbonate wreck(around 100pm);where these are

absent the aspect isopaque

pore shape:variable;pore radii100[im-2mm

In fact, as CaO is to be almost exclusively referred to the presence of calcite(since secondary calcite, except a few samples, is on the whole negligible), thisinvolves that firing temperature reached by brick A type was lower than



temperature at which total dissociation of carbonates (750-800°C) occurs andtherefore in these samples the lack of pyroxenes (see Table 1) - present on theother hand in B type samples - would be accounted for.

Table 2 - Chemical composition: XRF experimental results.

Brick TypeABC

L.O.I Na?O MgO A1,(X SiO, R,O CaO TiO, Total Fe9.64 2.49 5.19 12.88 46.82 2.92 13.05 0.67 6.548.88 1.17 6.17 12.19 33.74 1.95 29.68 0.57 5.633.9 0.97 4.38 12.24 39.05 2.52 29.62 0.42 6.86

Table 3 - Physical and mechanical characteristics: experimental results.

BrickTypeABC

Y*kgcm2.772.692.74

Ykgcm"1.711.801.64

P(%41.36.33.

)266

o<N/m213043

m*534

EN/iW

123071398616660

/o/

383228

Vo).1.9.7

IS

92.4789.8985.44

Mansell

8.010.914.6

It is well-known that reaching high temperatures allows total dissociationof mixing carbonates first, and then their reaction with phyllosilicates gives riseto the formation of new compounds such as pyroxenes and, where calcitecontents are high, gehlenite.

Neither in colour nor in chemical composition B and C type bricks seem toshow basic differences. The substantial difference concerns LOI values, sharplylower in the C type respect to the B type of bricks (Table 1).

Such a change seems to depend on a different firing of the two bricks; infact, in the C type, fired at higher temperature, besides pyroxenes, gehlenite andcarbonate wreck have been observed. (Table 1).

High mechanical characteristics - see Table 3 - and porosity seem onceagain to be directly related to brick firing. Among the various bricks, in fact, Ctype, i. e. those fired in best conditions, shows higher compressive strength.

Adequate firing conditions and high temperatures yield, besides formationof compounds such as pyroxenes and gehlenite, a good particle sintering, ahigher fraction of amorphous phase, and consequently a lower porosity ofmanufactured goods.

Such phenomena are evident when observing micrographs of fracturesurfaces of the various bricks obtained by SEM; in Fig. 2c, corresponding tobrick C type, intragranular fracture surface can be observed, whereas for lowerfiring temperatures; in Fig. 2b (brick B type) the fracture occurs with grain-boundary detachment (transgranular fracture). Moreover, comparing the twomicrographies a higher sintering can be observed in brick grains of type C. InFig. 2a - corresponding to brick A type, one may observe that particle sinteringhas not occurred and that amorphous phase is lacking.



Figure 2: SEM micrographs showing: a) the fracture surface of the bricks typeA; b) the intergranular fracture of the bricks type B; c) thetransgranular fracture of the bricks type C.

The brick deterioration is mainly due to the rainwater (washout) processesexpecially if they have unappropriate chemical and physical properties (clay richareas, high porosity and imbibition capacity). Using hydrophobic products thedecay can be reduced.

3 Structural behaviour of the temple

The brick masonry structure of the temple has been analysed through a linearF.E.M. technique, to characterize the structural response both to static loadsand to seismic loads. A F.E.M. static analysis has been performed to detectcorrespondence between the observed structural damage and the tensile stressesobtained from the computational model. The use of a linear technique (withplate-shell finite elements with three or four nodes) allows to obtain goodresults in the static analysis, because the tension level in the masonry is not veryhigh (about 0.54-1.0 N/mnf), as confirmed by the mechanical tests.

The low tensional level found confirms that the structure has generally alinear elastic behaviour, except for those parts where tensile stresses have beenfound (for example, the middle part of the inner octagonal dome, the top of theopenings and of the niches); these zones coincide with the cracks found in thestructure.

The maximum horizontal displacement at the basement of the dome is 0.35mm, due essentially to the drift imposed by the dome to the upper ring beam.



The maximum compressive stress is -0.491 N/mnf, near the foundation of thecorners of the walls (according to the presence of eight greater masonry plinthsunder the masonry piles). As the walls have practically only compressivestresses, the dome has a more complicated tensional picture, correspondingperfectly to the presence of cracks (where the tensile stress is 0.14 N/mnf, notconsistent with the correct modelization of the masonry). It appears evident thatthe main damages to the temple structure arise from its static behaviour;furthermore, the church had undergone some light earthquakes (Chieti area hasa low level of seismicity), after the restoration of 1879, but it was not damagedby seismic events occurred in neighbouring regions.

Though static analysis reveals a good approximation in order to understandthe behaviour of the structure, a dynamic one is required to identify some globalstructural parameters, in conjunction with the seismometric monitoring results.The dynamic analysis was performed to better understand the global behaviourof the church under dynamic loads; the church undergoes some daily vibrationsdue to traffic, so it was necessary to study if the traffic dynamic loads cangenerate any damage in the temple structure.

The linear model is used also in the dynamic analysis of the church, and theresults obtained have been compared with experimental ones derived from theseismometric investigation.

Two different dynamic analyses were performed; the first ten linearvibration modes were calculated, obtaining the first mode at a period of about0.18 s; then a seismic analysis with the Italian earthquake dynamic spectrum wasperformed; the significance of this linear analysis resides only in the possibilityof finding the critical blocks in the masonry, and the sites where it is better toset the seismometers in order to analyze traffic dynamic spectrum. It isworthwhile to observe that the examination of the monitored response spectrumcan give some indication about the decay of the mechanical properties of thematerials, because the first vibration modes decrease in value as the materialproperties decay. These indications are very useful, together with the study ofthe results of the chemical-physical analysis and of mechanical testing on themasonry. Thus, after the modal computation, the spectral analysis results wereanalyzed: the values of the linear response of the structure (with the greatestdisplacement at the top of the dome equal to 5.80 mm) and the control of theseismic induced tensile stresses confirm the possibility of damaging of the domeand generally in the upper part of the eight walls. Their lower part has relevantshear forces, especially near the openings and the niches, which are really theless resistant parts of the whole structure. In the dome the shear has lessrelevance, but bending effects become more evident. The global dynamicbehaviour of the church under earthquake is quite good, and puts into evidenceonly localized damages, like those effectively found during the damage relief.The worst theoretical damages can be found in the dome, so it appearsnecessary to put the seismometric instruments near the dome, relating theirrecording with the ones of seismometers located near the foundation of thechurch, possibly in two distinct zones.



&,06| 4.0(mm/s)

xlO<200.(UJULLu

0.0 800 t (s) 1600 00%/*] ., 34(mm/s) ,0.03 ,

,/ Wl(̂') '&* %0 " 10.0 Frequency (Hz) 20.0

» j 7.0(mm7s)0.03] i, , | | j| | | ""* 3 5

*» ''*» '«" %̂ " iffd-p^ySy (Hz) 20.0Figure 3: a) vibration diagrams, b) power spectral eigendensities

4 Traffic vibration monitoring

The neighbourhood of two thoroughfares, built during the '80s, one at about 20meters far from the East side of the church, the other (tunnel) at about 30meters far from the north-east side and at about 2 meters below the churchfoundation level, has become a relevant source of troubles for the templemasonry structure. During the excavation of the highway road tunnel situated atnorth-east, a long crack was born along the frontal part of the dome;extensimetric monitoring confirmed that the damage was generated by theexcavation of the road tunnel, and that after a brief period, the crack remainedunchanged. The Abruzzean Superintendence has then financed a trafficmonitoring campaign, in order to evaluate the continued damage induce by roadtraffic. Three triplets of seismometers were positioned in the church, on the baseof the first dynamic analysis. The first triplet was near the altar, in proximity ofthe highway road tunnel; the second triplet was in the foundation block situatednear the entrance, in the South side of the temple (to detect vibrations comingdirectly from the second highway), and the last one was positioned near thebasement of the dome, in the eastern upper window, at about 5.5 meters abovethe soil level. The vibration recording was carried out for several hours a day, todetect the various kind of traffic; furthermore, a 25 tons truck was chosen tocreate several traffic critical conditions; in Fig. 3a an oscillation sample diagramis shown. The power spectral eigendensities were calculated as a mean of 90successive samples long about 2000 s, in order to evaluate the frequencyspectrum. It is possible to see that the frequency spectrum lowers to zero valuesafter 20 Hz (Fig. 3b). Then the third octave filter analysis showed a maximumvibration velocity equal to 0.104 mm/s. With respect to the Italian UNI 9916, toDIN 4150 and to KDT 046, the values obtained were compared with theminimum dangerous level of traffic vibration. The vibration velocity levelobtained is about 1/30 of the dangerous threshold indicated by UNI, and about1/20 of that indicated by the other european standards. The examination of thepeak distribution in the density functions reveals that the highest peaks are not



very frequent, and that the frequent peaks have lower values.The vibration level is nearly constant during the day, so some possible

damage could derive from the microcracks induced by local fatigue phenomena.The experimental modes obtained with seismometric analysis (with a flat

frequency response of 1.54-80 Hz, ±3 mm of maximum displacement, and noiselevel less than 0.3 |im/s) gave frequencies of about 4.7Hz, 11.3Hz, 13.8 Hzrespectively, with a damping level of 3% for the first mode, which permittedalso to repeat a new dynamic computation of the model, to calibrate the choiceof the mechanical characteristics of the masonry (in particular, with a Youngmodulus of about 1300 N/mnf, the first modal frequency was exactly 4.77 Hz,and the second modal frequency referred to the walls was about 12 Hz,confirming the accuracy of the computational analysis and of the relative resultsand indications). The good accordance between experimental and computationallinear analyses reveals that the latter can be used to understand the globalbehaviour of the structure, and to individuate the localized damage (also notapparent to direct observation), so to design an appropriate restoration of thetemple.

5 Conclusions

The historical temple of S.Maria del Tricalle in Chieti has been studied tounderstand the origin of some structural damage.

A chemical-physical and a mechanical analysis of the bricks has beenperformed, in order to characterize the basic material properties and the decay.

Then several numeric F.E. computations (both static and dynamic)contributed to individuate the global behaviour of the structure and the morefrequently damaged structural components. The traffic vibration monitoringpermitted to exclude a direct damage on the structure due to the traffic of thetwo thoroughfares, and in conjunction with the dynamic analysis is a non-destructive tool to understand the varying behaviour of the global structureparameters as time goes by.

The computational studies suggest the idea that a static restoration of thedome must be made, also with the positioning of an annular reinforced beam inthe basement of the dome; besides, due to limited space outside the church, anintervention limiting traffic vibration cannot be made, so a restoration of thecontinuity of the foundation structure have to be planned, in order to reduce anydifferential movement of the structure base due to the vibration of the ground.

Acknowledgments

The authors would like to thank Eng. M. Sista and Eng. G L. Ricciardulli forthe fruitful discussions and their contribution for the vibration monitoring.



References

1. CNR-ICR, Raccomandazioni NORMAL, Document 3/80, Roma, 1980.






7. Fratini, F., Chiacchierini, S., Degl'Innocenti, N., Manganelli Del Fa, C &Malesani. P. Bricks composition and physical characteristics as a functionof the raw materials, pp. 229-238, Proceedings of the Int.RILEM/UNESCO Congress "Conservation of Stone and Other Materials'',Parigi, 1993.

8. Aoki, T, Hidaka, K, Kato, S., Structural stability and profile in the domeof Santa Maria del Fiore, in Structural Repair and Maintenance ofHistorical Buildings, Brebbia, C A, ed.

9. Ignatakis, C, Stylianidis, K., Stavrakakis, E, Design of interventions indomes. The importance of consideration of cracking, in Structural Repairand Maintenance of Historical Buildings, Brebbia, C A, ed.

10. Menditto, G, Capozucca, R, Monumental Buildings: mathematicalsimulation, in Structural Repair and Maintenance of Historical Buildings,Brebbia, C A, ed.

11. Kock, H.W., Vibration and structure-born sound in the vicinity of roadtunnels, Journal of Sound and Vibration, 1979, 66(3), 381-386

12. Toshikazu, H., Keizo, U., Michio, M., Rikuo, S., Three-dimensionalanalysis of traffic-induced ground vibrations, 1991, Journal ofGeotechnical Engineering, 117(8), 1133-1151.


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