jpcf_2010

Learning from Construction Failures due to the 2009L’Aquila, Italy, Earthquake

N. Augenti1 and F. Parisi2

Abstract: An earthquake sequence struck the province of L’Aquila �central Italy� leaving 305 dead, about 1,500 injured, and 29,000homeless. Hundreds of low-intensity events occurred between January and March, 2009. The mainshock took place on April 6, 2009, andits epicenter was located at about 6 km southwest of L’Aquila town; three stronger aftershocks happened on April 7 and 9, 2009. Thispaper focuses on actual performance of older and more recently constructed building structures during the earthquake sequence. After themain seismological characteristics of the sequence are described, the most significant observed damages are analyzed and associated withtheoretical failure modes for both reinforced concrete and unreinforced masonry buildings. Since older masonry structures were moreseriously damaged, the effects of the earthquake are described with more emphasis to ordinary masonry and cultural heritage buildings�churches, palaces, and castles�. In conclusion, a number of lessons may be learned from the L’Aquila earthquake sequence. Severalfeatures are highlighted and some proposals are given to upgrade the current methods of structural analysis, as well as the existing codes.

DOI: 10.1061/�ASCE�CF.1943-5509.0000122

CE Database subject headings: Earthquake engineering; Losses; Site surveys; Buildings; Structural failures; Italy.

Author keywords: Earthquake engineering; Losses; Site surveys; Buildings; Structural failures; Italy.

Introduction

In 2009, an earthquake sequence struck the Abruzzo region �cen-tral Italy� whose capital town is L’Aquila, which was built be-tween 1240 and 1259 by Federico II, Holy Roman Emperor andKing of Sicily, and is positioned approximately 92 km northeastof Rome. Hundreds of low-intensity tremors took place in thatarea up to the seismic event of March 30, 2009 whose local �i.e.,Richter� and moment magnitudes were estimated as ML 4.0 andMW 4.4, respectively. The continuous occurrence of aftershocks,along with the presence of individuals and organizations pretend-ing they had been able to predict time and location of the eventsbased on measurements of radon gas releases from the Earth’scrust, and raising alarms about the next occurrences, resulted in avery high level of concern in the population �Kerr 2009�.

On April 6, 2009, a strong earthquake hit the L’Aquila prov-ince at 03:32:39 a.m. local time �01:32:39 UTC�, at about 6 kmsouthwest of the capital town. It was the most destructive eventafter the ML 6.9 Irpinia earthquake occurred in the Campaniaregion �southern Italy� on November 23, 1980, which killed 2,914people, injured more than 10,000 people, and left 300,000 home-less.

The Italian Department of Civil Protection �DPC� respondedafter only 3 min to the catastrophic event and the first team was

1Professor, Dept. of Structural Engineering, Univ. of Naples FedericoII, via Claudio 21, 80125 Naples, Italy. E-mail: [email protected]

2Ph.D. Student, Dept. of Structural Engineering, Univ. of Naples Fe-derico II, via Claudio 21, 80125 Naples, Italy �corresponding author�.E-mail: [email protected]

Note. This manuscript was submitted on July 31, 2009; approved onJanuary 21, 2010; published online on January 28, 2010. Discussion pe-riod open until May 1, 2011; separate discussions must be submitted forindividual papers. This paper is part of the Journal of Performance ofConstructed Facilities, Vol. 24, No. 6, December 1, 2010. ©ASCE, ISSN
0887-3828/2010/6-536–555/$25.00.
536 / JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES © AS

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ready to departure for L’Aquila in about 43 min, reaching theaffected area at 6:30 a.m. local time �that is, just about 3 h afterthe earthquake�. The volunteers’ mobilization started at about9:30 a.m.

Several groups of rescue workers, technicians, inspectors, andscientists coordinated by DPC went to L’Aquila immediately afterthe event, in order: �1� to carry out emergency operations; �2� tostart preliminary visual inspections on the built environment; and�3� to install mobile accelerometric stations in the affected area.The emergency management activities were complicated by thecollapse of the Prefecture building �Fig. 1� so a temporary centralcontrol center, named DICOMAC, was established inside a largegymnasium of an army school in Coppito �outside L’Aquila� andseven local management centers were placed in the affected area.

About 3,000 volunteers, 2,250 firefighters, 2,000 policemen,1,500 army personnel, and more than 1,000 technical employeesof the Abruzzo Regional office were directly involved in theemergency operations. Twenty-one days after the mainshock, 31tent cities and field hospitals were installed to provide for careand housing of the homeless, reaching the amount of about 5,700tents with a capability of 36,000 people. Other inhabitants weretemporarily housed in hotels on the Adriatic coast and privateresidences.

The L’Aquila earthquake sequence caused 305 fatalities, about1,500 injured, and 29,000 homeless. More than 60,000 buildingswere seriously damaged or destroyed and about 70,000 inhabit-ants were evacuated. A total of 81 municipalities were affected bythe sequence and 49 of them were classified in the range VI-X ofthe Mercalli-Cancani-Sieberg �MCS� macroseismic scale, whichis 1.2 times the modified Mercalli intensity, more widely used inthe United States. Among the villages around L’Aquila, Onna andPaganica �Italy� were reported to be the most damaged ones be-cause they are located on soft alluvial deposits of 300 m, in theAterno River Valley. A total of 203 and 37 fatalities were reportedfor L’Aquila and Onna, Italy respectively. Shaking intensities of
up to 10 MCS were estimated for Onna, Paganica, and Casteln-
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uovo, Italy; while no more than 6 MCS was evaluated northwestof L’Aquila in neighboring villages placed on bedrock materials,such as Tussio and Monticchio. This damage pattern seems to beconsistent also with the extension direction of the fault planerupture of the mainshock, showing a combination of near-sourcedirectivity effects and local �both stratigraphic and topographic�amplifications of the seismic ground motion �Geo-engineeringExtreme Events Reconnaissance �GEER� 2009�.

Main Features of the L’Aquila Earthquake Sequence

The L’Aquila earthquake sequence occurred as a result of normalfaulting �which belongs to the dip-slip fault mechanism� withsouthwest dip on a northwest-southeast oriented seismogeneticstructure in the central Apennines, a mountain belt formed as aconsequence of subduction that runs along the whole Italian pen-insula �Bagnaia et al. 1992�.

The Italian National Institute of Geophysics and Volcanology�INGV� estimated the epicenter location of the mainshock ofApril 6, 2009 as 42.334°N and 13.334°E, approximately at thefollowing distances from the closest principal towns: 75 km westof Pescara, Italy; 85 km northeast of Rome; 115 km southeast ofPerugia, Italy; and 145 km south of Ancona, Italy. Seismologistsestimated the Richter magnitude of the event as ML 5.8, with afocal depth of 8.8 km, while strong-motion data inversion resultedin a moment magnitude MW 6.3.

The fault rupture plane of the mainshock was found to berectangular of about 17�14 km2 and placed at depths between0.6 and 11.8 km from the surface, with angle of 142° with respectto the north-south direction �strike�, slope of 50° �dip�, and slipdirection vertically oriented with respect to the projection of therupture plane on the surface �rake�. Since several subparallelfaults lie in the affected area, the mainshock of April 6, 2009 was

Fig. 1. Global collapse of the L’Aquila’s Prefecture

Table 1. Strongest Events of the L’Aquila Earthquake Sequence

DateOrigin time

�UTC�Lat

�degrees�

April 6, 2009 01:32:39 42.33

April 7, 2009 17:47:37 42.27

April 9, 2009 00:52:59 42.48

April 9, 2009 19:38:16 42.50

JOURNAL OF PERFORMANCE OF CONST


followed by tens of low-intensity aftershocks at focal depths rang-ing from 10 to 12 km, and by three stronger aftershocks withmoment magnitude greater than 5 �Table 1�.

Fig. 2 shows the spatial distribution of this earthquake se-quence. A seismic event occurred on April 7, 2009 southeast ofthe mainshock and was characterized by a moment magnitudeequal to MW 5.5, while two other events with MW 5.4 and 5.2happened on April 9, 2009 in the Laga Mountains area, locatednorth of the mainshock �Ameri et al. 2009�. In other terms, theearthquake sequence moved first southeast and then northwest ofthe mainshock, as clearly shown by the measurements of the Ital-ian National Accelerometric Network �RAN� managed by theDPC. This resulted in a progressive release of energy throughoutthe fault rupture plane.

A graphic representation of the rupture plane projection at thesurface, as well as the epicenter locations of both mainshock andaftershocks with moment magnitude greater than 5, are given inFig. 3. The mainshock of April 6, 2009, which seems to occur onthe Paganica fault, was recorded by 57 stations of RAN and 142broadband stations; even 14 of the latter are placed in the Abruzzoregion.

Strong-motion data were recorded at epicentral distances �Repi�between 4 and 297 km; 23 records were obtained at distanceslower than 50 km and four of them were available at distanceslower than 10 km �Table 2 and Fig. 3�. The latter allowed topreliminarily identify and analyze directivity phenomena amongthe so-called near-fault effects of earthquakes. Velocity pulses inthe fault-normal components of the records induced anomalous�linear and nonlinear� demands on structures with fundamental

Long�degrees�

D�km� ML MW

13.33 8.8 5.8 6.3

13.46 15.1 5.3 5.5

13.34 15.4 5.1 5.4

13.35 17.2 4.9 5.2

Fig. 2. Epicenter locations of the four main events

RUCTED FACILITIES © ASCE / NOVEMBER/DECEMBER 2010 / 537


periods close to one-half of the pulse period �Chioccarelli andIervolino 2010�. Corrected data of waveforms are available at thewebsite of the Italian Network of University Laboratories ofEarthquake Engineering �ReLUIS� �namely, http://www.reluis.it�.Peak ground accelerations up to 0.6g were recorded on soft allu-vial soils, close to Onna and Paganica, with a maximum value of0.676g. The site of L’Aquila is quite different from a geologicalpoint of view because a stiff conglomerate layer rests on the al-luvial soft soil of the valley �De Luca et al. 2005�. Also for thesereasons, complex local amplifications resulted in a peak groundacceleration of about 0.35g just below the conglomerate layer. Anaccelerometric station, named AQM �not included in Table 2�,recorded 1g or more in the vertical and one horizontal directions,but went off scale above 1g in the other horizontal direction. Itsrecordings are still under study, so they have not yet been released�Earthquake Engineering Research Institute �EERI� 2009�.

In some cases, the recorded accelerations are larger than thoseexpected by the Italian seismic hazard map, whose discrete valuesof PGA and spectral shape parameters are listed in Annex B of theItalian building code �Italian Ministry of Infrastructures andTransportation �MIT� 2008�. In fact, the estimated PGA atL’Aquila is equal to 0.261g and 0.334g at life safety �return pe-riod for ordinary facilities: TR=475 years� and collapse preven-tion �TR=975 years� limit states, respectively. In addition, themaximum horizontal accelerations were simultaneous; both EC8�European Committee for Standardization �CEN� 2004� and theItalian building code allow to apply the combination of the effectsdue to an horizontal component of the seismic action with the30% of the ones due to an orthogonal horizontal component.Records of the L’Aquila earthquake show that this combinationrule may lead to underestimate the maximum effects on struc-tures, so the square root of sum of squares criterion is expected togive more conservative results also for linear static analysis, aswell as for modal dynamic analysis with response spectrum. The

Fig. 3. Graphic description of the rupture plane projected at thesurface

Table 2. Mainshock Records at Epicentral Distances Lower Than 10 km

Recordcode

Stationcode

Lat�degrees�

GX066 AQV 42.377

FA030 AQG 42.373

CU104 AQA 42.376

AM043 AQK 42.345



combination with the effects due to the vertical component shouldbe also revised for design/assessment of structures in the nearfield.

Data processing showed a rather short duration of the seismicground motion, because 95% of the input energy was released in10 s or less. Permanent displacements of up to 15 cm were alsonoted in the records.

The RAN’s records were analyzed by several researchers inthe frame of ReLUIS network, to get both elastic and inelasticspectra, as well as some peak parameters of engineering interest�Chioccarelli et al. 2009; Masi and Chiauzzi 2009�. Polar spectrawere developed by Petti and Marino �2009�, in order to accountfor the angle of incidence of the seismic action on building struc-tures.

By applying linear baseline correction and Butterworth band-pass filter �f1=0.1 Hz, f2=25 Hz, order 4� to the originalrecords, Cosenza et al. �2009� obtained both elastic accelerationand displacement spectra for several values of equivalent viscousdamping. Such researchers pointed out that elastic spectra werecharacterized by very high pseudo-accelerations in the low-periodrange, so “rigid” structures such as masonry buildings were sub-jected to high horizontal forces and, thus, to large strength de-mands.

For epicentral distances lower than 10 km, the maximum valueof horizontal spectral acceleration was estimated as 1.72g in theeast-west direction for a period of 0.14 s, and as 1.44g in thenorth-south direction for a period of 0.44 s. Average maximumvalues of the spectral displacement equal to 10 cm for the hori-zontal components and 5 cm for the vertical one were computedat the stations AQA, AQG, and AQV listed in Table 2. Muchhigher values of 24.20 and 10 cm were found for the horizontaland vertical components, respectively, by processing data fromthe station AQK.

It is interesting to note that De Luca et al. �2005� predicted asignificant amplification of earthquake ground motion in the low-frequency range 0.5–0.6 Hz �which corresponds to a period rangeof 1.67–2 s� related to the presence of a sedimentary basin. On theother hand, the period of vibration of both masonry buildings andRC infilled-frame structures, which are the typical structural typesin the city of L’Aquila, did not fall in the frequency range con-sidered by De Luca et al. Hence, the writers believe that severedamage to masonry buildings should be chiefly associated withhigh acceleration demands at closer distances to the seismicsource, rather than with local amplification effects due to soilconditions. As shown by Chioccarelli and Iervolino �2010�, thehigh-frequency content in the seismic input was drastically at-tenuated with epicentral distance. This resulted in high accelera-tion demands on masonry buildings located in the near fault �i.e.,at epicentral distances not larger than 10 km� and lower demandson similar structures in the far field. Therefore, most part of dam-age was mainly caused by the occurrence of the mainshock ex-actly underneath the town of L’Aquila �Fig. 3� and, thus, by the

ges� Soil type

Repi

�km�PGA�g�

4 B 4.8 0.676

7 B 4.3 0.515

9 B 5.8 0.487

1 C 5.6 0.373

Lon�degre

13.34

13.33

13.33

13.40



resulting anomalous accelerations on existing buildings falling inthe low-period range. Nevertheless, this evidence was not in con-trast with past seismological studies on local amplification effectsat low frequencies, because the period range under considerationwas considerably different from that associated with the typicalbuildings located in the affected region.

Peak ground velocity and peak ground displacement were alsocomputed and their maximum values were found to be 40.48 cm/sand 11.87 cm, respectively. A preliminary data processing showedthat spectral displacement can be seen as an engineering demandparameter more stable than pseudoacceleration.

The synthetic aperture radar interferometry, a special tech-nique which merges radar data acquired before and after theearthquake, was applied by the Institute for Electromagnetic Sur-vey of the Environment and INGV based on the radar data fromthe satellites named Envisat and COSMO-SkyMed of the Euro-pean Space Agency �ESA� and Italian Space Agency, respectively.These special data allowed to measure surface deformations in-duced by the mainshock and numerous aftershocks that followedit. Three-dimensional �3D� ground displacement maps from fiveglobal positioning system location sites around the affected areaconfirmed the SAR interferometry measurements. The groundmovement was found to be as much as 25 cm between L’Aquila�9 MCS� and Fossa �7 MCS�. ESA data sets were made availableto everyone �see http://earth.esa.int/ew/earthquakes/Italy_April09/�. This amount of information makes the L’Aquila earth-quake sequence to be one of the best recorded normal fault earth-quakes.

Field Inspections of Buildings

The assessment of the usability of buildings started just two daysafter the mainshock and the seriousness of the situation led to anestimate of about 60,000 affected buildings. Therefore, also be-cause of the continuous occurrence of aftershocks, it was decidedto assess first the less damaged areas and second the historicalcenter of L’Aquila. The latter was entirely evacuated after themainshock because a lot of buildings were likely to collapse evenunder very low-intensity aftershocks.

The assessment of ordinary buildings was based on visual in-spections and relied on simple forms produced by DPC. About1,500 inspectors were deployed to evaluate about 1,000 buildingsdaily. Around 65% of the buildings were green tagged �i.e., readyfor occupancy�, while 27% were red tagged �i.e., unsafe for oc-cupancy�.

The operations aimed to assess the structural safety of monu-mental buildings �churches, castles, and palaces� and to preservethem by other tremors were coordinated by the Italian Ministry ofCultural Heritage. Dedicated forms were used for assessing theusability of historical buildings and special units of firefightersoperated together with experts to make postearthquake safety op-erations. About 53% of the monumental buildings were declaredas totally unusable, whereas about 23% were found to be readyfor immediate occupancy. Also, several international teams of ex-perts visited the affected areas.

In the following sections, the findings of the postearthquakereconnaissance field mission carried out by the writers undermandatory of the Ministry of Cultural Heritage are presented,with special reference to both ordinary masonry and cultural heri-tage buildings. Since RC building structures suffered damagesunder the L’Aquila earthquake sequence as well, some discus-
sions are made also on the more interesting features of seismic


performance of these more recently constructed facilities.

Damages to RC Buildings

The collapse of existing RC buildings in L’Aquila was generallydue to story mechanisms caused by the �brittle� shear failure or�ductile� flexural yielding at end cross sections of columns. Ex-tensive cracking and ejection of infill walls were typically ob-served during the L’Aquila earthquake sequence �Figs. 4 and 5�.Such nonstructural elements contributed to resist against the seis-mic action up to damage occurrence by stiffening the framedstructural system, while a story mechanism happened after thecollapse of all the infill walls placed at the same floor level �Fig.6�.

Among the most important RC buildings in L’Aquila, the SanSalvatore Hospital, which was built between 1974 and 1987, andwas opened to public in 2000, performed well enough during theearthquake sequence. Just three exterior marginal columns weredamaged; Fig. 7 shows the brittle failure of a column. This type ofmechanism is likely due to large vertical components of the seis-mic ground motion, along with the lack of effective stirrups at endcross sections of columns. In this case, the longitudinal steel barswere not confined and, hence, reached the Euler instability. Ma-

Fig. 4. Collapse of infill walls in a recently constructed RC building

Fig. 5. Ejection of infill walls in a RC building



jority of damage was to partition walls and to suspended ceilingsystems. It is interesting to note that the excitation of the heavyletters constituting the title of the Hospital, supported by exteriorwalls of the main façade at the top story, caused the collapse ofthe walls. Therefore, this shows that care should be paid to designnonstructural components based on their interaction with the sup-porting structures.

The Duca degli Abruzzi Hotel, a cast-in-place constructionbuilt in the 1970s of the last century, partially collapsed under theearthquake due to the presence of a number of significant struc-tural deficiencies. The structural system was a 3D masonry-infilled frame having pilotis at the ground floor, vertical elements

Fig. 6. Soft story mechanism of an infilled RC frame

Fig. 7. Brittle failure of a RC column in the San Salvatore Hospital



with different heights, and poor construction detailing. Therefore,the high irregularity in elevation resulted in a soft story mecha-nism of the building. Fortunately, no casualties were caused bythis accident. The story mechanism did not propagate thanks to astructural joint which split the whole structure in two independentparts. Fig. 8 shows the main façade of the Hotel prior to theearthquake, while Figs. 9�a and b� explain well its conditions afterthe mainshock. The benefit of the structural joint on seismic per-formance of the building can be clearly understood by observingFig. 9�b� on the left side.

The global collapse of the student house dorm of the Univer-sity of L’Aquila caused seven deaths �Fig. 10�. The Prosecutor of

Fig. 8. Main façade of the Duca degli Abruzzi Hotel before theearthquake �source: Google Street View�

Fig. 9. Duca degli Abruzzi Hotel after the earthquake



L’Aquila opened a criminal procedure immediately after the eventand a team of technical consultants were appointed to investigatethe causes of the disaster. However, this building was character-ized by high irregularity in plan.

Another case of interest in the field of Forensic Engineering isa recently constructed RC building totally collapsed under theearthquake causing 23 fatalities. Fig. 11 shows the area occupiedby the building.

A particularly interesting case of global collapse is shown inFig. 12. The whole second level of a four-story RC building “dis-appeared” under the earthquake. Actually, both the third andfourth floors overlapped perfectly on the first one. Figs. 12�a andb� show this particular mechanism in detail, which was probablydue to brittle collapse of columns, rather than to the presence of asoft story, because no plastic hinges developed at end cross sec-tions. Figs. 12�c and d� show the complete ejection of columnsfrom the second story. This was probably due to: �1� large verticalaccelerations of the seismic ground motion and �2� insufficientpresence of steel bars into beam-column joints. Also this collapsecaused a lot of fatalities.

Damages to Ordinary URM Buildings

The older masonry buildings built in the Abruzzo region are typi-cally composed by two- or three-story walls made up of stone

Fig. 10. Global collapse of the student house dormitory of the Uni-versity of L’Aquila

Fig. 11. Global collapse of a RC building



masonry with mortar joints. Instead, more recently constructedhouses are made up of rubble stone, clay bricks, or even concreteblocks.

In general, it can be stated that just the buildings with poor-quality masonry and significant irregularities suffered large dam-ages or fell down. A lot of masonry structures in L’Aquilaperformed very well under the earthquake, thanks to the betterquality of materials �e.g., bigger size of masonry units, squaredstones or clay bricks, and good-quality mortar joints�, regulardistribution of mass and stiffness, and good construction detail-ing. More than 50% of the masonry buildings were severely de-stroyed in some little villages such as Onna, Paganica, andCastelnuovo, where multileaf �called a sacco� masonry walls,with an inner core of smaller rubble masonry and mixture of limeand mud mortar, had been typically used without bond stonesconnecting together the exterior wythes. Due to lower site ampli-fication effects, other towns such as Barisciano, Santo Stefano,and Monticchio, even if they are close to the more damaged ones,experienced smaller failures �Geo-engineering Extreme EventsReconnaissance �GEER� 2009�.

Along with the analysis of damages induced by the L’Aquilaearthquake sequence, let us classify theoretical failure mecha-nisms of masonry buildings. They are typically modeled as as-semblage of walls oriented along any direction. The most usedand effective methods of structural analysis of masonry buildingsunder seismic actions are based on the macroelements geometri-cal discretization of each wall �Augenti 2004�. By means of thisapproach, a masonry wall with openings is divided into threetypes of two-dimensional elements: �1� pier panels, which are thevertical structural elements between openings; �2� spandrel pan-els, which are the horizontal structural elements between open-ings; and �3� cross panels, which link pier and spandrel panelstogether �Fig. 13�. Each macroelement has height H, length B,and thickness s.

Structural failures can involve individual panels, for both regu-lar and irregular walls, through the following mechanisms:1. In-plane �longitudinal� mechanisms, which involve indi-

vidual panels of each wall and consist of several types ofcrack patterns

a. Crushing failure due to the exceeding of the compressivestrength of masonry induced by the vertical componentof seismic motion �Fig. 14�; vertical cracks develop firstthroughout the vertical transversal cross section s�H ofthe masonry panel �splitting� and finally along the longi-tudinal cross section B�H. Fig. 15 shows the total lossof internal integrity of a masonry panel due to a crushingphenomenon which occurred after the splitting failure ofthe wall.

b. Tensile failure due to the exceeding of the tensilestrength of masonry induced by the horizontal compo-nents of seismic motion; horizontal cracks develop alongthe horizontal cross section B�s of the masonry panel;they are not simply visible when the seismic input van-ish, because of their closure due to gravity loads.

c. Flexural failure, in which compression vertical cracksand tensile horizontal cracks are localized at the toes ofthe panel due to yielding of masonry; in such cases themacroelement can be fully or partially resistant. Also thistype of mechanism is complex to be observed because:�1� tensile cracks close with seismic action reversal and�2� as the seismic ground motion increases, the masonrypanel experiences also shear cracks which are more evi-
dent than the flexural ones. Figs. 16�a and b� show the


flexural cracks of a pier panel and spandrel panel, respec-tively. Diagonal cracks developed as well in the pier.

d. Diagonal shear cracking, in which tensile cracks developalong a diagonal of the longitudinal plane B�H, fromthe centroid to the toes. As a result, the masonry panel isdivided in two parts that move away from each other.This kind of failure mechanism is shown in Figs. 17�aand b� for pier and spandrel panels, respectively.

e. Sliding failure, where stepwise or horizontal cracks de-velop along the longitudinal plane of the masonry panel,which is divided in two parts that slide along their frac-ture surface.

Crack patterns related to these failure mechanisms are quite dif-ferent for regular and irregular masonry walls. If the contours of

Fig. 12. Story cru

Fig. 13. Geometrical modeling of a masonry wall



the openings are both horizontally and vertically aligned, the ma-sonry wall is called regular and pier panels are simple to bemodeled. When the openings are not aligned nor have the samedimensions in horizontal or vertical direction, the wall is calledirregular �Augenti 2006�. Fig. 18 shows the crack pattern of anirregular wall of a masonry building in L’Aquila. In this case, careshould be paid to geometrical modeling of pier panels, becausetheir effective height may significantly change with the orienta-tion of the seismic action. This occurs also for peripheral pierpanels because the overlying cross panels are not entirely con-fined and, thus, may suffer diagonal cracks with average slopeangle of 30°–45°. The aforementioned mechanisms are referred toall inner and peripheral panels of masonry walls not well con-nected to transversal ones.2. Out-of-plane �transversal� mechanisms, also called first mode

mechanisms, which may involve individual panels or panelsystems of a given masonry wall; the latter is typically di-vided in different rocking elements in the vertical transversalplane s�H. Along with global collapses of masonry struc-tures, a large number of buildings in the historical center ofL’Aquila suffered out-of-plane mechanisms due to lack ofsteel ties or ring beams, or to poor connections between lon-gitudinal and transversal walls. Figs. 19�a and b� show out-of-plane mechanisms of individual pier panels at the upperstory of a building, along with large horizontal displacementsof the roof slab. Fig. 20 shows first mode mechanisms in-

in a RC building
shing
volving more panels at several floor levels. In both cases, the



floor slabs did not constrain the walls along their transversaldirection.

3. Combined mechanisms, in which in-plane actions are fol-lowed by out-of-plane components of seismic motion thatinduce rocking mechanisms of panels previously damaged intheir own plane �Fig. 21�. In other terms, the masonry panelis first damaged by in-plane seismic excitation and seconddestroyed by out-of-plane components. The probability ofoccurrence of such collapse phenomena is dramatically in-creased by aftershocks and successive events of an earth-quake sequence.

4. Corner mechanisms, which involve end panels placed at thecorners of the masonry building when perimeter walls arewell connected together. In such cases, biaxial bending in-duces the ejection of the corner of the masonry building �Fig.22�. This failure mode does not frequently occur, given thatlongitudinal and transversal masonry walls are generallybuilt up in separate construction stages, rather than togetherat the same time. No methods for safety verifications againstcorner mechanisms are provided by the current seismiccodes, so future research is needed to build up theoreticalmodels able to describe this class of failures as well.

5. Global mechanisms, which progressively involve differentparts of the building or even the whole structure. A cornerbuilding unit which suffered global collapse under the earth-quake is shown in Fig. 23. Fig. 24 shows the total destructionof adjacent building units along a main street in L’Aquila,while the collapse of the upper floor level of a three-storybuilding located in Santa Maria a Coppito Place can be seen

Fig. 14. Crushing of masonry

in Fig. 25.



After the 1703 earthquake �MW�6.7�, masonry walls werestrengthened by inserting timber ties aimed to connect them and,thus, to obtain a better global behavior under seismic loading. Fig.26 shows the rupture of these ties induced by the out-of-planemechanism of a wall and the resulting collapse of the roof. Insome cases, RC ring beams realized into existing masonry build-ings were found to be harmful and did not prevent local collapsesin masonry walls.

The theoretical classification of failure modes in unreinforcedmasonry �URM� building structures given above is consistentwith those provided by other researchers, such as Magenes andCalvi �1997� and Calderini et al. �2009�. Nevertheless, combinedand corner mechanisms had never been observed before the 2009L’Aquila earthquake sequence, so the writers believe this ex-tended classification will be helpful for both future research andpractice in earthquake engineering.

Damages to Cultural Heritage Buildings

Cultural heritage suffered large damages due to construction char-acteristics of the building or to wrong seismic strengthening/upgrading interventions. The most significant case studies of thehistorical center of L’Aquila are discussed in the following.Above all, serious damages to three monumental buildings andseveral churches are shown in detail.

Spanish Fort

This fortress is one of the most impressive Renaissance castles in

Fig. 15. Crushing failure after splitting of masonry

Central and Southern Italy. It is located on the highest part of



L’Aquila and was built up between 1534 and 1541 under theappointment of Don Pedro de Toledo, the Spanish viceroy of theKingdom of Naples. Fig. 27 shows the ground floor plan of thecastle and the surrounding fosse. This monumental building iscurrently home of the National Museum of Abruzzo, so largedamages to artworks �e.g., paintings, sculptures, and ancient fur-niture� were caused by structural failures and collapses during theearthquake sequence.

The seismic events resulted in many losses including the col-lapse of the covering at the upper story, which was realized in the19th century and recently restored. Figs. 28�a and b� show theentrance of the castle before and after the mainshock, respec-tively. Fig. 29 allows to see the whole main façade with the ac-

Fig. 16. Flexural mechanisms of �a� pier panel; �b� spandrel panel

cess bridge. A newly constructed RC roofing structure collapsed



due to its considerable mass and, thus, to large inertia forces at thetop level. Fig. 30 shows the upper floor level from inside thecourtyard: we notice the partial collapse of the perimeter wall dueto an out-of-plane mechanism. The whole façade experiencedrocking rotation toward the courtyard. Fig. 31�a� shows the arcadeat the ground floor: a stepwise crack on the left column can beseen in Fig. 31�b�.

Fig. 32 points out the colonnade at the first floor of the castle,whose covering barrel vault suffered longitudinal cracks along itslength owing to outward rotation of the façade. Fig. 33 showspaving cracking close to columns, whose maximum amplitudewas about 25 mm.

Fig. 17. Diagonal shear cracking of �a� pier panel; �b� spandrel panel

Fig. 18. Crack pattern of an irregular masonry wall



Fig. 34�a� illustrates the crushing of a bearing masonry wall atthe first floor, while a partially destroyed wall placed at the sec-ond floor can be seen in Fig. 34�b�. Damaged sculptures andpaintings are visible in both images.

Part of the second floor collapsed under the mainshock; all theremaining bearing walls and vaults located at the same story andat the first floor were seriously damaged. While little damages tothe ground floor were observed, no failures were detected at theunderground floor. Severe damages suffered by the building firstrequired urgent shoring systems under the seriously damagedroofing structures, as well as to openings of masonry walls. Thelatter were closed by means of clay brick masonry. In order tostop outward rotation of the façade and to reduce the probabilityof occurrence of out-of-plane mechanisms under further after-shocks, the main exterior façade and the one facing the courtyardwere connected together by means of metallic tendons. Let usnotice that older stone URM structures experienced just large fail-ures, while global or local collapses occurred only in buildingparts with newly constructed RC slabs, ring beams, and pitchedroofs.

Library of the L’Aquila Province

This monumental building was realized at the end of the 19thcentury and was designed by Alessandro Mancini in order to takethe library of L’Aquila. Among several failures experienced by

Fig. 19. Out-of-plane mechanism of an individual story

such a structure, detachment at the corner of perimeter façades is



very interesting from an engineering point of view. Fig. 35�a�shows the whole damaged corner of the building, while Fig. 35�b�shows a detail of the detachment between masonry walls. Urgentsafety interventions were made by placing a number of tendonsalong the perimeter ledge of the building and connecting themthrough metallic plates.

Head Office of the University of L’Aquila

Carli Palace is currently the Chancellor office of the University ofL’Aquila. The earthquake sequence induced huge damages tosuch a building. However, a diagonal crack on the corner masonry

Fig. 20. Out-of-plane collapse mechanism of a masonry wall

Fig. 21. Combined failure mechanism of a masonry wall



pier at the upper story developed and was followed by anotherone on the opposite building �Fig. 36�. This damage pattern was aclear evidence of the seismic action orientation.

Cathedral of Santi Massimo e Giorgio

This is the cathedral dome of L’Aquila built in 1257 but crumbleddown during the 1703 earthquake. The most recent façade dates

Fig. 22. Corner mechanism due to biaxial bending

Fig. 23. Global collapse of a corner building unit



back to the 19th century. Transept and other large parts of thecathedral fell down under the L’Aquila mainshock of April 6,2009.

Fig. 37 shows the main façade of the church, which experi-

Fig. 24. Total destruction of inner building units

Fig. 25. Global collapse of a masonry building

Fig. 26. Out-of-plane mechanism of a masonry wall with timber ties



enced serious damages to roofing structures �triumph arch, tran-sept, and dome�. Restoration works were ongoing inside thecathedral at the moment of the seismic event.

Church of Santa Maria del Suffragio

This Baroque church, also known as “Le Anime Sante,” was builtafter the 1703 earthquake in the ancient market place of L’Aquila,where the Cathedral of Santi Massimo e Giorgio is located too.The Church of Santa Maria del Suffragio became one of theL’Aquila earthquake symbols, because images of the collapsedtambour and dome spread all over the world.

Figs. 38�a and b� show the church before and after the earth-quake, respectively. Also in this case, as a result of many high-intensity aftershocks, damage to structures increased a lot leadingeven to further unexpected collapse phenomena. In Fig. 39, wecan observe the partial collapse of the tambour, which wasstrengthened with circumferential timber ties in the past. To avoidthe total loss of the tambour, which was been seriously damagedby the mainshock, some safety interventions were carried outthrough aerial platforms given the highly dangerous situation.

Church of Santa Maria di Paganica

Such a Romanesque-Gothic church was built in the 14th centuryand perhaps is the most damaged religious building in L’Aquila.Figs. 40�a and b� show the whole church from the adjacent placeand from an aerial platform, respectively. As one can see, theearthquake induced the collapse of the triumphal arch, dome,pitched roof of the central nave, left aisle, and bell tower. All theother structures experienced severe damages as well. Fig. 41shows the interior of the collapsed church looking toward thealtar and apse. Both the collapsed dome and triumphal arch canbe seen in Fig. 42; the destroyed roof, along with the damagedchapels of the right aisle, are shown in Fig. 43. The older timbercovering structure was substituted with a novel one composed byprestressed concrete �PC� joists and lath bricks resting on a pe-

Fig. 27. Ground floor plan of the Spanish Fort in L’Aquila

rimeter RC ring beam. Just the older chestnut ties were left on site



Fig. 28. Spanish Fort: �a� before; �b� after the earthquake



and thin metallic bars were been added to eliminate thrust in theroofing structure. The novel RC structure, much heavier andstiffer than the older one, triggered the collapse of the masonrywalls of the nave. Observations of the dome’s debris prove thatPC roofing structures were realized over it. Also in this case,high-intensity aftershocks resulted in cumulated damage rapidlyincreasing over time, so the roof shown in Fig. 43 collapsed somedays after the mainshock. Urgent safety and protective interven-tions required also the controlled demolition of some structuralcomponents lying in precarious equilibrium conditions. Since themain façade of the church had experienced outward rotation withdetachment from longitudinal walls of aisles, temporary connect-ing elements were installed to avoid the complete out-of-planecollapse.

Basilica of San Bernardino da Siena

This church was built up in 1472, has a fine Renaissance façade�Fig. 44�, and contained the monumental tomb of the saint deco-rated with wonderful sculptures. Such a facility suffered severedamages during the L’Aquila earthquake, especially to the belltower and tambour of the octagonal dome �Fig. 45�.

Church of San Marco

This church, dating back to the 15th century, was seriously dam-aged with particular reference to the covering. Since inspections

Fig. 29. Main façade of the Spanish Fort

Fig. 30. Out-of-plane mechanism at the top floor



inside the church were not possible because of the serious hazardconditions, the writers entered the breach formed in the upper part

Fig. 31. Outward rocking of the colonnade

of the wall of the nave by means of a firefighters’ ladder �Fig. 46�.



Damages to interior of the church were observed through thisopening. In particular, Fig. 47�a� shows damages to masonryarches, while Fig. 47�b� highlights the novel covering formed byPC joists and lath bricks, along with a RC tympanum resting onthe dome. Such a heavy and rigid element increased the vulner-ability of the structure. Finally, a lateral wall of the church expe-rienced rocking mechanism with about 70-cm large outwarddisplacement.

Church of San Silvestro

This church was built up by inhabitants of the Castle of Colle-brincioni in the first one-half of the 14th century. The bell towerwas reconstructed after the earthquakes occurred in the 15th cen-tury and the completely restored interior structure is divided intothree naves ending with polygonal apses, but without a transept.Fig. 48 shows the main façade of the church along with the belltower. Since the latter had different modes of vibration with re-spect to the remaining part of the structure, a large concentrationof stress occurred along the tower-nave interface of the churchduring the mainshock, resulting in large cracks on both externaland internal masonry walls �Fig. 49�. Serious cracks were de-tected on other walls too: Fig. 50 shows vertical cracks along thecorner between the main façade and the wall placed above thearches of the nave.

Significant Damages to Further Churches

Among other religious facilities inspected after the mainshock,

Fig. 32. Horizontal cracks in vaults due to rocking of the colonnade

the Church of San Francesco di Paola was found to be severely



damaged, owing to multiple out-of-plane mechanisms of both themain façade and lateral walls, as shown in Fig. 51. The Church ofSan Pietro a Coppito, built in the 13th century, suffered largedamages to the main façade, vaults of the nave and aisles, apse’scovering, and octagonal-plan bell tower �Fig. 52�.

The Church of Santa Maria della Misericordia, built between1528 and 1531, was seriously damaged as well, especially to theright lateral body, because of significant irregularities in elevation�Fig. 53�. A lot of less important churches suffered many damagesto structural and nonstructural components due to local collapsemechanisms. Fig. 54 shows an interesting example of out-of-plane failure experienced by the tympanum of a church located inthe historical center of L’Aquila.

Conclusions and Lessons from Failures

The 2009 L’Aquila earthquake sequence was a destructive chainof seismic events that induced high damage over time to a lot ofboth ordinary and monumental buildings, as well as several RCresidential buildings, resulting in many casualties and large eco-nomic losses.

The information gathered during the field mission and thegreat amount of seismological and engineering data about theearthquake sequence allow to state that the high level of damageand human losses resulted from a combination of several factors:1. The so-called near-fault effects of seismic events, along with

local amplifications due to complex stratigraphic and topo-graphic conditions, which induced anomalous levels of

Fig. 33. Cracking of the floor �amplitude around 25 mm�

ground motion at the surface and, thus, very high demands



on structures. Source directivity was detected in the recordsof the L’Aquila mainshock and velocity pulses resulted inlarger demands on some building structures. Damages toboth URM structures and RC infilled-frame buildings weremainly due to high accelerations at small distances from theseismic source. Indeed, the role of the high-frequency con-tent in the seismic input was extremely important in suchconditions. In addition, equal PGA values were recordedalong both north-south and east-west directions, so unusualfailure modes were observed in masonry structures.

2. The high vulnerability of both older and some more recentlyRC constructed facilities due to the presence of poor-qualitymaterials, inadequate construction detailing, and wrong re-pair or strengthening interventions, particularly in the case of

Fig. 34. Crushing failure of inner masonry walls

cultural heritage buildings.



3. The collapse of nonstructural components, such as infillwalls, internal partitions, and suspended ceilings.

On the other hand, both URM and RC buildings with good-quality construction characteristics and structural regularity per-formed well enough during the earthquake sequence and werefound to be ready for occupancy a few days after the mainshock.This means that, in general, both the current seismic design cri-teria and past construction rules seem to be effective in order tohave a good global response under earthquake loading. The fol-lowing lessons may be learned from the observed damages andcollapse phenomena:1. The very high PGA values recorded close to the seismic

source show the importance of near-fault effects also in theseismogenetic structures of Italian Apennines, similarly to

Fig. 35. Damaged corner in the library of the L’Aquila province

what was observed, for instance, in California and Japan.



Given that some building structures are particularly prone tosuffer directivity effects, this topic should be analyzed infuture studies in the fields of engineering seismology andearthquake engineering.

2. The accelerations recorded close to L’Aquila show that thecombination rules of seismic effects suggested by the Italianbuilding code and allowed by EC8 should be revised, inorder to get a better estimation of demands on structures. Inaddition, the role of the vertical component should be care-fully taken into account for structures located in the nearfield.

3. Although failure modes and collapse mechanisms can begenerally explained by the current methods of structuralanalysis, future research is needed to solve some specificfeatures for predicting the complex behavior of structuresunder directivity earthquakes. Furthermore, some types offailure modes, such as combined and corner mechanisms inmasonry buildings, should be analyzed in detail by means ofinnovative analytical models.

4. Cumulative damage to masonry constructions is another as-pect to be studied in future, in order to better predict re-sponse under earthquake sequence. Both strength reductionfactors and displacement amplification factors of elasticspectra should be specifically defined for masonry buildings

Fig. 36. Head office of the University of L’Aquila

Fig. 37. Main façade of the Cathedral dome of L’Aquila



Fig. 38. Church of Santa Maria del Suffragio: �a� before; �b� after theearthquake



Fig. 39. Collapsed dome of the Church of Santa Maria del Suffragio

Fig. 40. Church of Santa Maria di Paganica: Global views



Fig. 41. Church of Santa Maria di Paganica: Internal view

Fig. 42. Collapsed dome of the Church of Santa Maria di Paganica

Fig. 43. Collapsed roof and chapels in the Church of Santa Maria diPaganica



Fig. 44. Main façade of the Basilica of San Bernardino da Siena

Fig. 45. Damages to the octagonal tambour and bell tower

Fig. 46. External view of the Church of San Marco



Fig. 47. Damages to arches and vaults in the Church of San Marco

Fig. 48. Main façade of the Church of San Silvestro



Fig. 50. Vertical cracks along the wall intersection



Fig. 51. Damages to the Church of San Francesco di Paola

Fig. 52. Damages to the Church of San Pietro a Coppito

Fig. 53. Damages to the Church of Santa Maria della Misericordia

Fig. 49. Cracks along the height of the bell tower of the Church ofSan Silvestro



through damage models able to describe this kind of evolu-tionary behavior under cyclic loading.

5. Care should be paid to insertions of RC rigid elements inexisting URM facilities, because they may radically changethe global seismic response. Moreover, added mass may in-duce not only higher strength demands on the building, butalso significant irregularities in plan or elevation, leading tounexpected distributions of the seismic action and, thus, todangerous localizations of internal forces within thestructure.

Notation

The following symbols are used in this paper:B � length of the masonry panel;D � focal depth of the earthquake;H � height of the masonry panel;

Lat � latitude of the site;Long � longitude of the site;

ML � local �or Richter� magnitude of the earthquake;MW � moment magnitude of the earthquake;Repi � epicentral distance of the site;

s � thickness of the masonry panel; andTR � return period of the earthquake.

References

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