On-site investigation on the remains of the Cathedral of Noto › mada › foto › 073.pdf ·...

Construction and Building Materials 17(2003) 543–555

0950-0618/03/$ - see front matter� 2003 Elsevier Ltd. All rights reserved.doi:10.1016/S0950-0618(03)00057-6

On-site investigation on the remains of the Cathedral of Noto

L. Binda*, C. Tiraboschi, G. Baronio

D.I.S., Politecnico of Milan, Milan, Italy

Received 3 December 2001; accepted 15 August 2003

Abstract

The Cathedral of Noto was damaged after the earthquake that hit Sicily in 1990. Soon after the event, cracks appeared on thedomes of the lateral naves, and also on the pillars. In 1992 some provisional work had been carried out in view of confining thepillars of the central nave that were damaged. Some pictures made after the earthquake also show clearly the presence of moisturerise on the pillars and walls. A sudden collapse due to the damages was probably not expected, so that no other measures weretaken to better strengthen and repair the structures. Only after the collapse of the Civic Tower in Pavia(1989) and the followingresearch(Masonry Int J 6(1992) 11, Second International Conference RILEM on Rehabilitation of Structures, Highett, Australia(1998) 542), it was clearly shown that in case of high stresses on low-strength masonry an existing damage can slowly lead topartial or total collapse of the structure over a long time. It seems a confirmation of this long-term behaviour of the structuresthat the Cathedral collapse took place in 1996, 6 years after the earthquake, which had certainly caused high damages to thestructure.� 2003 Elsevier Ltd. All rights reserved.

Keywords: On-site investigations; Masonry; Flat jack; Sonic tests

1. Damage description

After the removal of the huge amount of ruins(3610m ) and the execution of the necessary provisional3

structuresw3x, the actual damage consequences of thecollapse could be checked and described(Figs. 1 and2). Fig. 3 shows only a partial view of the destruction.Figs. 4 and 5 clearly show the missing parts: the rightpillars, the vault and roof of the central nave, a largepart of the central dome, the domes of the right naveand other local destruction. The feeling of a personwatching the ruins for the first time is really a sense offrustration.

2. Aims of the investigation

The investigation carried out as requested by thedesigners De Benedictis and Tringali in 1998 in theLaboratory of Material Testing of DIS, Politecnico ofMilan, under the responsibility of Binda and Baronioconcernedw4,5x: (i) a study based on-site survey andlaboratory tests concerning the damage of the materials

*Corresponding author. Tel.:q39-2-2399-4318; fax:q39-2-2399-4220.

E-mail address: [email protected](L. Binda).

and of the structural elements and the possibility ofpreserving and strengthening them as the Cathedralreconstruction would startw1,2x, (ii) the choice of thematerials for repair, strengthening and reconstructingcollapsed parts of the structure,(iii ) the control of thechemical, physical and mechanical compatibility of thenew material with the existing ones.The aims of the investigation were the following:(i)

to assist the designers in understanding the safety levelof the remaining parts after the collapse,(ii) to investi-gate on the possibility that the structural and non-structural elements apparently undamaged or with lowdamage could still be efficient(e.g. the remaining pillarsof the central nave), (iii ) to suggest on the basis of thelaboratory tests on original materials and structures themore adequate techniques for the intervention,(iv) todefine the characteristics of the new materials for recon-struction and repair.The time given to the Laboratory for the whole

investigation was 60 days.

3. On-site investigation

Since the collapse of the structure seemed to havebeen caused by the collapse of the right pillars of the

544 L. Binda et al. / Construction and Building Materials 17 (2003) 543–555

Fig. 1. Cracks on a pillar before the collapse(photo G. Attardi).

Fig. 3. The interior of the Cathedral after removing the ruins.

Fig. 4. Longitudinal section of the Cathedral with the left order of thepillars of the central nave.

Fig. 2. The right pillars of the central nave before the collapse: thereis clear evidence of moisture presence at the base of the pillars(photoColl. Arch. P. Giannone). Fig. 5. Longitudinal section with the remaining of the left pillars.

central nave(perhaps a central one or one near theentrance), it was very important to investigate the stateof the left side pillars that are still standing but badlydamaged.The on-site investigation consisted in the following

operations:(i) excavation in strategic sites near the

pillars and the walls in order to identify the type andthe depth of the foundations,(ii) demolition, layer bylayer, of the base of one of the collapsed pillars in orderto study the technique of construction and the materialsused,(iii ) removal of the external stone leaf in order todetect the mechanical characteristics of the internal coreof pillars and walls,(iv) sampling of mortars and stonesin the most representative areas of the structure in orderto characterise the materials in laboratory,(v) survey of

545L. Binda et al. / Construction and Building Materials 17 (2003) 543–555

Fig. 6. Inspection sites of the foundations.

Fig. 8. Sample no. 2: view from the top of the foundation soil withthe foundation masonry of the transept.

Fig. 7. (a) Foundation of pillar E(sample no. 6). Survey of the foundation.(b) View from the top of the foundation of pillar E(sample no. 6).

the remaining pillars in order to know their state ofdamage and the possible type of repair,(vi) single anddouble flat-jack tests to define the state of stress in

compressed areas and the stress-strain behaviour of themasonry, (vii) grout injection of the remains of thecollapsed pillars and of a small part of the lateral wallwith different types of grout,(viii ) ND evaluation ofthe state of damage of the remaining pillars and detec-tion of the effectiveness of the grout injection by theuse of radar and sonic tests.

3.1. Survey on the foundations

The local excavation near the foundations and thesoil coring(in Fig. 6 the areas of excavation are signed)has shown that the foundation of the pillars and wallswere sufficiently well constructed in rubble masonry butwith enough load-carrying capacity for the weight ofthe above structures(Fig. 7a and b). The soil was a sortof a thick layer of natural compact silt and clay(Fig.8).


Fig. 9. Survey of the prospect of pillar C:(a) graphical restitution;(b) photo.

Fig. 10. Horizontal section of pillar C:(a) graphical restitution;(b) photo.

Fig. 11. Prospect of the external wall of the left nave.

3.2. Survey of the masonry sections and of the wallconnections

The layer-by-layer removal of the components of thecollapsed pillars allowed to understand the poor tech-nique of construction used(Fig. 9a and b). Layers oflarge rounded river stones were found in the core of theelements, with thick mortar joints, where the mortar

appeared very weak and dusty surrounded by an externalleaf made with regular blocks of calcarenite for the baseof the pillar (up to 1.50 m) and of a sort of ‘travertine’in the upper part. The connections between the externaland the internal leaves were missing(Fig. 10a and b)and the ‘travertine’ leaf was highly porous with largevoids. The poor technique of construction and the wrongchoice of the materials were probably the cause of earlydamages to the pillars of the Cathedral even if theevidence of damage appeared only after the 1990 earth-quake. The walls were built in a similar way; neverthe-less the internal part was made with smaller sharp stonesalternated with a slightly stronger mortar. In some waythis seems to be a better masonry(Fig. 11).Also the buttresses of the highest part of the nave,

built successively to the Cathedral construction, weremade with a better technique, similar to the one of thewalls (Figs. 12 and 13).Furthermore, characteristic of the structure of the

Cathedral, common to other constructions in Noto, isthe presence of numerous scaffolding holes that some-times occupy the entire cross section(Fig. 14).Some stones were sampled from pillars and walls and

mortar samples were taken from the horizontal andvertical internal and external joints(Fig. 9b and Fig.


Fig. 12. Buttresses built at the top of the lateral naves.

Fig. 14. Scaffolding holes are distributed along the walls and pillars.

Fig. 13. Detail of the buttress masonry.Fig. 15. Spring of the arch on pillar B9 and sampling location of themortar.

10b). The samples were sent to the DIS Laboratory andcharacterised.Small demolitions were carried out also at other

different positions:(i) at the spring of the arches(Fig.15), where better mortars were found together with thepresence of other scaffolding holes,(ii) at the spring ofthe buttresses between the lateral domes(Fig. 12) inorder to study the connections between buttresses andwalls, (iii ) at the connection between the lateral pillarsand the walls,(iv) at the connection between the lateralwalls and the facade,(v) at the walls of the apse.In the lateral built-in pillar MB(Fig. 16a) coring and

boroscopy were carried out together with small demoli-tion of the external connections(Fig. 16b) in order toconfirm the good connection between external walls andbuilt-in pillars (Fig. 16b). Coring was also carried outin the apse walls and in the buttresses. These walls were

similar to the lateral walls that is to say rather withgood texture, materials and connections.

3.3. Survey of the crack patterns of remaining pillars ofthe central nave

The pillars of the left side of the central nave(A9,B9, C9, D9, E9) showed diffused cracks that could have


Fig. 16.(a) Check point for removal to study the connection pillar-wall.(b) Photographic survey of the connection.

Fig. 18. Large crack found in a pillar.

Fig. 17. Crack pattern survey of the face of pillar B9 toward the nave. Fig. 19. Example of a crack filled with gypsum mortar in the sixties.

been caused by the collapse of the right side. In fact ifthe flat roof beams in reinforced concrete had contrib-uted in keeping the central nave structure connectedtogether during the collapse, they certainly caused dam-age to the left pillars. In order to study better thatdamage and to see the depth of the cracks, it wasdecided to remove samples of the plaster that had beenmade in the fifties. The cracks that could be seen onthe outside of the plaster went deep inside the pillarsand the fissuration appeared diffused starting from thetop of the base until approximately the mid and also

beyond the mid of the pillars(Fig. 17). Some crackswere wide and deep beyond the external stone leaf(Fig.18). Other cracks had been filled with the gypsummortar of the plaster(Fig. 19), showing that they alreadyexisted at the moment when the rendering was done,that is in the 1950s. The survey shown in Fig. 17 wascarried out on all the faces of the left pillars and the


Fig. 20. Location of the flat-jack tests.

Fig. 21.(a) Photographic survey of the test CSJ3S.(b) Plot of the CSJ3S results.

situation was the same everywhere, even on pillar E9,one of the four sustaining the dome.

3.4. On-site flat-jack tests

The flat-jack tests were carried out on pillars A9 andE9. The aim of the tests were to define(i) the state ofstress in compression on the external leaf at the bottomof a pillar, (ii) the masonry mechanical characteristicsof the external and of the internal leaves of the pillars

and of the external wallsw6,7x. The test points arereported in Fig. 20.The single flat-jack test CNJ3S was performed on

pillar E9 with a great difficulty, since the external leafwithout rendering was badly cracked and the verticaljoints were practically void due to lack of mortar. It wasimpossible to set the jack in a position without a verticaljoint; this choice in fact would have made the test morereliable w6x. It is well known that the test is based onthe stress release when a cut is carried out in acompressed masonry and on the measurement of thedisplacements recovery when a jack inserted in the cutis exerting a pressure on the cut surfaces. According toRef. w6x, the test is not valid when the displacementscalculated after the cut are not all recovered during thetest (Fig. 21a and b). Since these conditions were notrespected owing to the above-mentioned causes, the testhas to be considered only as indicative. Nevertheless,the stress value found can be considered greater than0.85 Nymm . Taking into account that the only acting2

force on the pillar after the collapse is its dead load,since the loads of the drum and of the dome are missed,the measured stress is rather high.The double flat-jack tests were carried out on the

external leaf of pillar E9 (CNJ1D) at a height ofapproximately 3 m, and on the internal leaf of pillar A9

(Fig. 22a) at a height of 3 m(CNJ2D). The test CNJ1Dwas stopped at the onset of cracking in two stones,respectively, above and below the top jack. The meas-ured stress at that level was 1.9 Nymm and just beyond2

the elastic range. From the experience it is possible tosuppose that the value of the local strength of themasonry is 40% higher than the measured stress andhence approximately 2.85 Nymm w8x.2

The test carried out in the interior of pillar A9 afterthe elimination of the external leaf reached an onset ofcracking at 0.76 Nymm with vertical strains of 40mmy2

mm; the strength can be assumed to be 20% higher, that


Fig. 22. (a) The internal core of pillar A9 after removal of the external leaf.(b) Plot of the results of single and double flat-jack tests on thepillars.

Fig. 23. Double flat-jack tests on external walls:(a) plot of the test results;(b) prospect of the masonry.

is, approximately 1.1 Nymm . The lateral displacements2

were higher, reaching 5.0mmymm. Since this area ofthe pillar was probably already cracked since a longtime and certainly damaged by the collapse, it is possibleto think that the initial strength of the internal rubblematerial, when the mortar was completely hardened,could have been approximately 1.5–2.0 Nymm . Fig.2

22b reports the results of the three tests carried out onpillars A9 and E9. It is possible to observe the differentbehaviour of the internal and external parts of the pillarsand that the stress due to the dead load of the pillar isalready greater than the strength of the interior. There-fore, the internal part had probably settled down some-time after construction, leaving the external leaf as theonly load-bearing last of the pillar.Three double flat-jack tests were performed on the

external walls of the Cathedral(Fig. 23b). The interestdeserved by these walls, which are not load-bearingwalls, is due to the fact that they seem to be made witha technique similar to the one used for the internal part

of the built-in pillars. Therefore, their behaviour cangive some information on the one of the internalconglomerate. Furthermore, these walls have to be pre-served, and then they have to be known. In Fig. 23a theresults of the three tests are reported. Two of themCNJ4D and CNJ5D gave similar results and werestopped at 1.2 Nymm ; the test CNJ6D was stopped at2

only 0.8 Nymm showing a result similar to the test2

CNJ2D of the inside of pillar A9. So it was confirmedthat the wall masonry is similar to the rubble masonryinside the pillars, even if its stiffness is higher and thismaterial is much weaker than the regular stone masonryof the outer leaf.The detailed results of the flat-jack tests are reported

in Table 1.

3.5. Grout injectability tests in pillars and walls

Small areas(500=500 mm) of the external surface2

of the remaining of pillars A and C and of the built-in


Fig. 24. Location of the grout injection sites.

Table 1Results of double flat-jack tests

s (Nymm )2max Ds (Nymm )2 E (Nymm )2s D´ yD´h v

CNJ1d—pillar E9 1.88 0.1–0.5 1760 0.060.1–1 1525 0.09

CNJ2d—pillar A9 0.76 0.1–0.5 190(E )345 (0.89)CNJ4d—3 spana 1.2 0.1–0.5 1215 0.09CNJ5d—1 spana 1.18 0.1–0.5 1205 0.22CNJ6d—5 spana 0.88 0.1–0.5 370 0.15

pillar of the external wall of the Cathedral were chosenfor injectability tests(Fig. 24). The aim of the tests wasto study the possibility of applying the technique ofrepair by grout injection to the walls and to the damagedpillars of the left side of the central nave. The reasonfor using grout injection were(i) to repair cracks andto fill voids caused by the collapse,(ii) to strengthenthe internal part of the pillars where the mortars werevery weakw9x. Four different grouts were tested and theinjections were carried out as described in the followingtext. Holes were drilled in the pillars up to a depth ofapproximately 600 mm; this depth was chosen in orderto be sure that the grout could enter beyond the externalstone(the depth of the stones is in fact varying from200 to 400 mm). The driller had a hard point and wasworking at low speed in order to avoid damage to themasonry. The holes were performed slightly downwardat a distance of 250 mm from one another and at aheight variable from 300 to 800 mm. After drilling,water was injected in order to wash away the powderand to wet the stones and mortars. Soon after thisoperation, sonic tests were performed in order to meas-ure the sonic velocity before injection.Four grouts were injected, named N, M, P, C. The

injectability was controlled during the injection by meas-uring the injected grout quantity and 28 days after theinjection by repeating the sonic tests and removal of theexternal leaf in order to check the injection diffusion.

3.5.1. Description of the grouts(1) Grout N was a natural hydraulic lime with high

silica content and additives as fluidiser and bondingagents. The ratio waterybinder (WyB) was 0.85. Themixing of the grout was carried out at speed 1500–2000 turnymin; this speed was kept constant for 3 min,then reduced for the whole time of injection. With N,injections were carried out into pillar C and into thebuilt-in pillar MB. The grout was injected starting fromthe bottom toward the top in order to avoid trapping airinside the pillars. This grout was penetrating very wellin pillar C, less in pillar MB, pillar C being badlycracked during the collapse.(2) Grout M is a special hydraulic binder with no

reaction with chlorides and sulfates eventually present

inside the masonry. The ratio WyB was 0.4. Theinjection was carried out as described above.(3) Grout P is defined as hydraulic microfine binder

also non-reactive with salts(sulfates, chlorides, nitrates,etc.). The grout is characterised by high fineness(onlya small percentage of grains has a diameter equal to 25mm) and a mechanical strength that can be programmedwithin a large range of values. The WyB ratio was 1 inweight.(4) Grout C was prepared on site while all the others

were ready to mix. The composition was the following:3:1 pozzolana to hydrated lime. The ratio WyB was0.77 with a rather good fluidity. Nevertheless, thepozzolana grain size was too large and therefore thegrout penetration was very low. Pozzolanicity tests werecarried out on the pozzolana used for the grout with thesame fineness and a lower one(150mm). The analyses


Fig. 25. Penetration of grout N.

Fig. 26. Penetration of grout P.

gave a very low reactivity for the larger grains and amuch quicker reactivity with the 150-mm grains.After 28 days, on all the injected masonries the sonic

tests were repeated and the sonic velocity variation wasmeasuredw10x.After the sonic tests the injected parts of pillar C

were dismounted and the following comments can bemade:

– The grout N has well reached all the cracked partsbut has not completely filled them, as it is possibleto see from Fig. 25. This defect is also common tothe other grouts. Other defects of the grout N were adiffused shrinkage, the presence of air bubbles insidethe injected material and apparently a low strength.

– The grout M had a very good penetration but itsfluidity was too low. Not all the cracks were reachedand filled.

– The grout P showed good stability and fluidity andcould reach all the cracks connected with the injectionhole (Fig. 26).

– The grout C could not injected successfully in pillarC due to its very low injectability.

Some parts of very well injected material were sam-pled and taken to the laboratory. Cubes and prisms werecut out and submitted to compression and splitting tests.Due to the low number of specimens and to the highscattering, the results can only be considered as indica-tive. The splitting tests gave tensile strengths varyingfrom 0.2 to 0.4 Nymm on 40=40=80 mm prisms,2 3

while the compression tests gave values from 0.89 to6.1 Nymm . Some cylinders prepared in laboratory,2

injected with the same grouts and tested after injection,gave similar variability, indicating once again the greatinhomogeneity of the masonry and the impossibility forthe grout to penetrate and distribute uniformly.

3.6. Sonic tests

The tests were carried out at different heights of theleft pillars (A9, B9, C9, D9, E9) where the steel confine-ments allowed the accessw10x. The sonic velocity values

at the base of the pillars where the calcarenite was usedhad an average value of 1500 mys; above the basewhere a sort of ‘travertine’ was used went down to anaverage of 500 mys. In fact, the ‘travertine’ having alower density due to the big voids in its structure has alower density but also a lower strength. Among all thepillars tested, D9 and E9 seem to have the highest velocityat 3.00 m of height. Pillar E9 on the contrary shows avery low velocity at 5.00 m of height. It is only possibleto suppose that pillar E9 presents the highest damage at5.00 m and above due to the damage caused by thecollapse of the dome.The sonic tests carried out after injection gave evi-

dence of some improvement in the masonry character-istics, but not so much excitingw10x.Presence of voids andyor cracks are also confirmed

by the radar tests carried out on pillar E9; these testscould be performed with great difficulty due to thepresence of high humidity inside the pillar up to a levelof 3.00 m w11x.

4. Discussion of the results

The survey and the investigation carried out on siteand in the laboratory allowed the designers to takeconcrete decisions on the reconstruction of the Cathe-dral. In detail the investigation gave an answer to thefollowing questions:(i) which damage suffered the non-collapsed bearing elements,(ii) in case of high damagecould these elements be preserved or had to be demol-ished and reconstructed,(iii ) is it possible to givereliable experimental values of the mechanical parame-ters required as input values by the structural analysis.These answers can be found in the following discussionof the results.

4.1. Foundations

The foundation depth was observed by excavation ofthe Cathedral floor around the pillars and walls. Thedepth was variable as a contradiction of a hypothesismade soon after the collapse that the depth was follow-


ing the soil slope. Concerning the pillars of the centralnave, the maximum depth of the foundations reaches3.00 m for the pillar B. In the cases when the depthwas greater, a pyramidal foundation was made, and inthe cases when the depth was smaller, the foundationwas enlarged(Fig. 6). The constructive technology ofthe foundations seemed to be good even if they werebuilt with regular courses of round river stones. It wasnot possible to excavate near A9, B9, C9, D9, E9 for safetyreasons.Also, the mortar analyses shows that they are better

than the ones used for the pillars. The foundation soilfrom the chemical analysis results to be calcium carbon-ate for the 95%. The aggregate size detection gave an8% of clay, a 72% of silt and a 20% of sand.

4.2. Morphology of pillars and walls

The removal by layers of the remains ofpillar Callowed to understand how the internal and externalcourses of the masonry were built and their connection.The technique of construction used had created a weakinternal part made with a sort of low strength and highdeformability conglomerate. Along the time under thedead load and the effects of earthquakes, the externaland the internal leaves of the masonry were certainlysubjected to differential movements also due to the lackof connection between the two parts and in the fourcorners of the pillars. These movements caused a differ-ential stress distribution with concentration of stressesin the external leafw8x. The dilatancy of the conglom-erate as also detected by the double flat-jack test in thecore of pillar A9 also could have caused a distributionof stresses normal to the external leaf. The situation wasevolving for a long time(it should be remembered thatit was already present in the 1950s) also due to apossible creep behaviour of the calcarenite; the syner-getic effect of the earthquake damages caused a quickevolution toward the collapse, which certainly took placein the pillars.The use of ‘travertine’ above the pillar base has

certainly contributed in the reduction of the load-carry-ing capacity of the element.Another negative aspect of the structure was the

presence of niches in each pillar at a certain height andthe presence of a pulpit excavated in pillar D, whichprobably was bearing the highest damage.It was possible to state that the built-in pillars and

the external walls of the Church were built at the sametime and connected with continuity. Furthermore, longtransversal stones were found connecting the two exter-nal leaves of the pillars, while the internal conglomeratewas made with sharp pieces of calcarenite and ‘traver-tine’ with thick mortar joints apparently stronger thanthose of the central pillars. Therefore, these external

pillars seem to be more reliable than the ones of thecentral nave.Nevertheless, a common problem of pillars and walls

is represented by the frequent presence of scaffoldingholes crossing the whole section of the masonry. Thispeculiarity should be taken into consideration in thedesign for reconstruction.

4.2.1. MaterialsThe material characterisation has been described in

detail by Bindaw4,5,8,12x. Nevertheless, a general infor-mation and comment is given here. Thecalcarenite usedfor the external leaf of the pillars is characterised by afairly good strength when tested dry up to constant mass(18.0 Nymm in compression, 2.2 Nymm in tension of2 2

cylinders of 50-mm diameter and 100-mm height) anda lower strength when tested saturated up to constantmass(11.6 Nymm in compression and 1.3 Nymm in2 2

tension). This means a reduction of the 35.5% of thecompressive strength and of the 39% of the tensilestrength. The ‘travertine’ used in the core of the pillarsand in the external leaf above the base has a muchlower strength than the calcarenite(5.2 Nymm in2

compression as an average value measured on dry prismsof 100=100=200 mm dimension). The different3

mechanical characteristics of the two stones were alsodetected by sonic tests in laboratory and on sitew13x.Another type of stone calledgiuggiolena (a sort ofcompact ‘travertine’) was used for the construction ofthe dome. This stone also shows a different behaviourwhen tested dry or saturated: 5.3 Nymm in compression2

and 1.0 Nymm in tension when dry, and 5.05 Nymm2 2

in compression and 0.8 Nymm in tension when2

saturated.The mortars based on putty lime were obtained by

using probably a local calcareous aggregate with anexcessive fineness; this property was the cause of thelow physical and mechanical characteristics of the mate-rial. The mortars used for the walls, the arches and thedome were of better composition.

4.3. Crack pattern survey of the remaining pillars of thecentral nave

From the survey the following remarks can be made:– all the cracks surveyed on the rendering penetrateinto the external leaf of the pillars and in some casesthey reach the core showing that the damage eithercaused by the collapse or already present before itwas deep and serious;

– the removal of the rendering has shown that manylarge and long vertical cracks had been filled withgypsum mortar in the fifties.

Among the surveyed pillars only E9 seems to haveless damage, even if it is also showing vertical cracks.


The high state of damage found in pillar A9 alreadypresent before the earthquake suggests that by symmetryalso pillar A was badly damaged before the collapse,even if no provisional confinement has been carried outfor this pillar as it was done for B, C, D. Therefore, thecollapse could have started from A instead of from D.

4.4. On-site mechanical tests

The double flat-jack tests have shown the low strengthand high deformability of the internal core of the pillarsand the limited strength of the ‘travertine’ leaf. Takinginto account the different behaviours investigatedbetween the internal and external parts of the pillars,the hypothesis can be formulated that soon after theconstruction of the structure the stress distribution wasrather uniform. As differential movements took placebetween the internal and the external leaves caused bythe higher deformability of the first one and by the lackof good connection between the two, the highest stresswas supported by the second one, which was also builtwith two different materials. In fact, from 1.50 m up tothe top the travertine was used. So the damage probablystarted above the base with thin vertical cracks thatslowly propagated during the centuries after the con-struction. On the other side, the bad connections in thecorners did not help the external leaf to act as aconfinement.

4.5. Grout injection tests

The investigation by sonic tests carried out afterinjection and furthermore by demolition showed thatapart from grout C, all the others were effective. Nev-ertheless, the grouts are successful in filling voids andeven thin cracks, but they do not improve the behaviourof a weak mortar because the mortar cannot be injected.Therefore, the grout injection can be successful for theexternal walls and pillars, but not to strengthen thecentral nave pillars.

5. Conclusions

The following answers could be given by the authorsto the designers De Benedictis and Tringali after theinvestigation carried out in laboratory and on site:

– The partial collapse of the Cathedral was not onlycaused by the damages due to the 1990 earthquakebut was also due to the already unsafe condition ofthe central pillars.

– The lateral walls, the arches and the remaining lateraldomes that were built with a better technique can berepaired and preserved by grout injection and localreinforcements.

– The left central pillars cannot be preserved or repaireddue to the high state of damage, the poor technique

of construction and the poor materials that cannot bestrengthened in any way. Therefore, they should bedemolished and rebuilt as the collapsed ones. In fact,in the case that a decision would be taken to preservethem, the structure will be affected by a high lack ofsymmetry and this characteristic would be unsafeagainst future earthquakes. The demolition and recon-struction of the pillars even if apparently non-respect-ful of the conservation theories will lead to a bettersafe structure taking into account the seismicity ofthe place.

– The materials to be used for the reconstruction of thepillars must be more reliable than the original ones:hydraulic mortars, use of the calcarenite in the exter-nal leaf and in the core filling, transversal stones toconnect the external and the internal parts.

– The soil and the foundations are reliable, except forthe foundations of the reconstructed pillars that willsupport higher stresses than the original ones; there-fore they have to be rebuilt or strengthened.

Acknowledgments

The authors wish to thank L. Cattaneo, C. Colla,M.Garau, G. Paccapelo for the collaboration at the on-site survey, and M. Antico, M. Cucchi, M. Iscandry, P.Perolari for their collaboration to the on-site and labor-atory tests. The investigation was supported by thePrefettura of Siracusa.

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w4x Binda L, Baronio G. Cathedral of Noto–Preliminary investi-gation to the reconstruction, Relazione Finale, Contratto Pre-fettura di Siracusa, 1998.

w5x Binda L, Baronio G. Contratto di Consulenza: Studio sullostato di conservazione dei materiali e delle structure e sullapossibilita di un loro recupero in base ai risultati delle prove e`dei rilievi di laboratorio e in situ, Relazione Finale, ContrattoPrefettura di Siracusa, 1998.

w6x ASTMC 1196 (1991). Standard test method for in-situ com-pressive stress within solid unit masonry estimated using theflat-jack method, Philadelphia, ASTM. ASTM C 1197(1991).Standard test method for in-situ measurement of masonrydeformability properties using the flat jack method.

w7x Binda L, Tiraboschi C. Flat-Jack Test as a Slightly DestructiveTechnique for the Diagnosis of Brick and Stone MasonryStructures, International Journal for Restoration of Buildings


and Monuments, Int. Zeitschrift fur Bauinstandsetzen undBaudenkmalpflege, Zurich, 1999; p. 449–472.

w8x Binda L, Baronio G, Gavarini C, De Benedictis R, Tringali S.Investigation on Materials and Structures for the Reconstruc-tion of the Partially Collapsed Cathedral of Noto(Sicily),International Conference Structural Studies, Repairs and Main-tenance of Historical Buildings, STREMAH 99, Dresden,Germany, 1999; p. 323–332.

w9x Binda L, Modena C, Baronio G, Abbaneo S. Repair andinvestigation techniques for stone masonry walls. Constr BuildMater 1997;11(3):133–42.

w10x Binda L, Saisi A, Tiraboschi C. Application of sonic tests tothe diagnosis of damage and repaired structures. Int J Non-destructive Testing Evaluation(NDT&E Int) 2001;34(2):123–38.

w11x Binda L, Colla C, Saisi A, Valle S. Application of Georadarto the Diagnosis of Damaged Structures, Sixth InternationalConference Structural Studies, Repairs and Maintenance ofHistorical Buildings, STREMAH 99, Dresden, Germany, 1999;p. 13–22.

w12x Baronio G., Binda L., Tedeschi C., Tiraboschi C. Caratteriz-zazione dei Materiali della Cattedrale di Noto, SeminarioInternazionale su: Cattedrale di Noto e Frauenkirche di Dresda:Indagini e Studi per il Progetto di Ricostruzione, Noto.

w13x Binda L, Saisi A, Tiraboschi C, Valle S, Colla C, Forde M.Application of Sonic and Radar Tests on the Pillars and Wallsof the Cathedral of Noto, Seminario Internazionale su: Catted-rale di Noto e Frauenkirche di Dresda: Indagini e Studi per ilProgetto di Ricostruzione, Noto, 2000.

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