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2.11.1 IntroductionThis contribution refers to both building-like andnon-building-like industrial structures. Regardingthe former type, L’Aquila earthquake representsthe first case in Italy of a wide observation oftheir seismic response. Industrial buildings areoften comprised of reinforced concrete precastelements. The earthquake has shown deficienciesrelated to inadequate design or construction cri-teria. In fact, insufficient separation distancesbetween structures (causing pounding), insuffi-cient size of saddles of precast beams and insuf-ficient strength of non-structural infilling panelsemerged. Moreover, localized failure of supports

of horizontal elements due to insufficient size ofsaddles, and too large concrete cover withrespect to design specifications, were observed.Concerning non-building-like structures theinvestigations refer to the sili, for polypropylenestock, of Vibac in Bazzano close to Onna (AQ).These structures represent an interesting case-study of damages to steel constructions. Some ofthem experienced total collapse, others sufferedlocal and global buckling. In particular three fail-ure modes occurred: (1) crashing of the shell atthe base (elephant foot buckling); (2) deforma-tions due to instability; (3) pounding to close pre-cast reinforced concrete structures.

2.11 Post-event analysis of industrial structures behavior during L’Aquilaearthquake

B. Faggiano1, I. Iervolino1, G. Magliulo1, G. Manfredi1, I. Vanzi2 �

1 Dipartimento di Ingegneria Strutturale, Università degli Studi di Napoli Federico II. www.unina.it2 Dip. di Progettazione, Riabilitazione e Controllo delle Strutture Architettoniche, Università di Chieti. www.unich.it

2.11.2 Building-like industrial structuresIndustrial buildings were built for many years asan assemblage of precast reinforced concreteelements. The April 2009 L’Aquila earthquakehas struck, for the first time in Italy, industrialstructures on a large scale. In fact, the Irpinia1980 earthquake hit an area with few industrialsites; and similarly happened in the Umbria andMolise earthquakes, which moreover were feltwithin a limited area. On the other hand, theFriuli 1976 earthquake damaged industrialstructures, but they were designed with noregard with respect to the seismic action; if anydesign rule was used, this however belonged toinadequate seismic codes. L’Aquila and its sur-roundings are instead undergoing a ratherstrong industrial development. Precast rein-forced concrete buildings, with a column-beamstructure, are the usual type in the industrialareas in Pile, Bazzano, Monticchio and Ocre(AQ). Buildings have generally one storey; twostoreys are seldom observed, moreover only ona more limited area than the first storey. Beamsupports on the columns may be of the saddle orbracket type. Deck beams are usually transver-sally aligned (with respect to the longer side ofthe structure plan) and they are I-shaped, withvariable depth; longitudinal alignment andinversed T-shapes are less commonly observed.In the latter case, the shape is used to support

the tiles. The roof is generally built with tiles ≠-shaped; less often U-shapes are observed. Sky-lights are sometimes present. -tiles are alsoused for the intermediate deck, when there isone. External partitions are either made withbricks, or with precast reinforced concrete shells,with no stiffeners. Structural nodes are those typ-ical of the Italian constructions: beaker footingfor the foundation to column nodes, simple sup-port for the beam to column nodes (with neo-prene bearings and steel pins). Tiles are gener-ally directly resting on the beams, with neitherhorizontal restraint nor neoprene bearings. Pinconnections are seldom present. Tiles may beconnected each other with the upper reinforcedconcrete layer, or simply linked via steel restrain-ers (partly poured within the tiles concrete,partly welded with the next tile restrainer). Parti-tion panels are either supported by the eavesbeam or by the column, via links of many types.They are also sometimes supported by the decktiles. A typical shell-eaves beam connection isvia a steel plate partially put within the concreteshell during pouring. A bolt connects the plateand a steel angle, which is restrained to theeaves beam edge. The shell to column connec-tion is often built with a steel plate within the col-umn and a bayonet with bushing linked to theshell, via a long bolt. This technology is usedalso to connect the partitions to the deck tiles; the

steel angles and bolts connection is less frequent.It is worth to note that structural shell buildingsare much less common than beam-column build-ings. A few precast industrial buildings were

under completion on April 6th, 2009, when theearthquake struck; so it was possible to verify theseismic behaviour of these structures under vari-able degrees of completion.

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2.11.3 Damage and seismic performance analysisThe response of the structural elements of theindustrial buildings to the April the 6th 2009earthquake was generally in accordance withtheir design level: no column collapsed, eventhough, in many cases a plastic hinge wasobserved, due to the high intensity of the seismicaction (Fig. 1). In some cases such plastic hingewas not observed at the column base, i.e. at thecolumn-foundation joint, but even one meterabove, where the longitudinal reinforcementdecreases. Furthermore no plastic hinge wasobserved in beams or tiles due to the increment ofthe vertical action. However, the damage of theprecast industrial buildings should be wellanalysed; indeed, it was characterised by col-lapse of parts of the buildings, which, if the main-shock had happened during the working timeinstead of at 3 a.m., it would have caused victims.The static scheme of such structures is charac-terised by large deformability; consequently, themost of the observed damages of structural ele-ments (made by reinforced concrete) depend onthe relative displacements between the elements.Indeed, many cases of pounding between ele-ments of the same structure were observed. Fur-thermore, pounding between adjacent buildingswas frequent, in the case of both precast andcast in situ structures, due to the insufficiency ofseparation joints. In figure 2, taken by Giordanoet al. (2009), the pounding between the tiles andthe beam of an industrial precast buildingplaced at Bazzano is shown.Confirming the numerical studies (Magliulo etal., 2008; Capozzi et al., 2009) performed inthe last years, the connections represented theweak parts in terms of seismic performance ofboth old and new precast buildings. Some build-ings have shown damages at the beam-columnconnection: the only observed case of precastbeams collapse was due to the damage of suchconnection and to the following support loss.Indeed, as shown by numerical analyses(Capozzi et al., 2009), the splitting of the jointbar cover happened where the thickness wasminimum. In other frames of the same structure,it is also possible to observe the collapse of thebeam due to support loss at the side without jointbar, caused by too large displacements, and thepounding between the beam and the column top

fork (Fig. 3).The phenomenon of the joint bar cover splittingcan be also noted at the intermediate level ofsome two-storey precast buildings, where, asalready written, the beam-column joint is on cor-bel. The same phenomenon has also charac-terised the collapse of some tiles. In this case,indeed, even where the joint had been fastenedby a steel bar, the little thickness of the bar coverof the beam, also characterised by the lack ofstirrups, collapsed, causing the tile support loss(Fig. 4a). Obviously, such support loss easilyhappened where the tile-beam connection wasnot fixed and/or there was no connectionbetween tiles; particularly unlucky situationswere characterised by buildings in phase ofassembly, where the floor slab, joining the tiles,was not made yet.However, the most important and spread dam-ages of precast industrial buildings caused bythe April the 6th earthquake are those concern-ing the elements on the perimeter; indeed, thelarge damage of such elements, even though thestructural typologies are different, associatesprecast buildings to the in situ cast ones. The topconnection of the vertical panels to the side ofthe gutter beam, made by a profile drowned inthe panel, bolt with nut and angle stirrup, insome cases gave way due to the angle stirrupbreaking and/or to the bolt head going out fromthe profile (Fig. 4b). This last phenomenon alsocaused the collapse of panels connected tocolumns by a profile drowned in the column andbayonet with bushing joined to the panel bybolt; some of these last connections, instead, col-lapsed due to the bayonet breaking at bushingposition. Some other failures where due to thegoing out of the whole profile from the panelwhere it was drowned. A better seismicresponse was shown by panels joined to thestructure by angle stirrups and bolts. In the caseof perimeter elements made by bricks, the seis-mic action determined their out of plane defor-mation, in many cases up to the expulsion ofbricks and the consequent partial or total col-lapse of the perimeter element. Finally, amongthe carrying out mistakes, it is noteworthy, forprecast structures, the local failure of the beamsupport. In figure 5, taken by Camata et al.(2009), a near collapse condition is shown,

2.11.4 Non-building-like structures: the casestudy of the Sili Vibac in Bazzano.The sili of the Vibac multinational (a chemicalcompany which produces plastic films), locatedin Bazzano, close to Onna (Fig. 6) representan exceptional case of damage to steel con-structions. They also represent an emblematiccase of damage induced by the earthquake ofApril 6th. The sili are used for the storage ofpolypropylene pearls, and they were full whenearthquake struck (EERI, 2009). Some sili col-lapsed, some other remained standing eventhough strongly deformed, both locally at somerings and diffusely (Fig. 7).A more close visual inspection indicated thatthe collapses occurred for overturning due tothe crushing of the base rings and the hopper.Moreover, along the sili height, deformationsinduced by buckling phenomena of the wallpanels are apparent. In some cases an effectof pounding on the adjacent precast rein-forced concrete constructions took place, thelatter have achieved the partial failure of theinfills, which have induced strong deforma-tions of the shells of the sili. Such type of dam-ages are a clear effect of the earthquake ver-tical component, whose importance they high-lighted (Fig. 7).The Vibac sili have a metallic structure. Gener-ally for their conception sili have a very lowstructural weight, normally significantly lowerthan the weight of the contained material. Sucha characteristic implies a very slender struc-ture. It is evident that such structures are sensi-

tive to both local and global buckling phenom-ena. In fact the most common failure mode isthe instability of the wall panels due to theeffects of the axial force in compression. Suchactions are due to the friction between thesilage material and the walls. The horizontalradial pressure, acting on the cylinder surfacefrom the silage material, has a stabilizing effectagainst the buckling of the silos’ walls, givingrise to a tension stress field of membrane type.The distribution and intensity of the internalforces in every constituting part of the silos, thecylinder and the hopper, are strongly influ-enced by the material extraction behaviour,

caused by the large column cover due to the fireprotection provisions; indeed, due to such provi-

sions, a volume of concrete without reinforce-ment works as beam support.

Effects on structures and infrastructures

Fig. 1Plastic hinge in columns ofindustrial buildings: (a) FIATgarage at Pile; (b) buildingused for bovine-breeding atFossa.

Fig. 2Effects of pounding betweenthe cover tiles and the beam(Giordano et al. 2009).

a. b.

Fig. 3Collapse of beams due to

loss support of a building atFossa used for bovine-

breeding.

Fig. 4(a) Tiles collapse due to

cover splitting and supportloss of a FIAT garage at

Pile. (b) Collapse ofperimeter panels due to thebreaking of the angle stirrupor to the bolt head goingout from the profile in abuilding used as materialand machine deposit at

Bazzano.

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which in turn depends on the shape of the silo.The Vibac sili have an elongated shape typi-cally used for the storage of plastic material.Therefore the predominant extraction mode isof the so called “mass” type, having the char-acteristic that the first material coming out isthe one inserted as first in the silos, all thematerial mass is in movement at the leakage. Incase of sili with a stocky shape, the extractionbehaviour of “funnel” type prevails, it has thecharacteristic that a central tube forms in thematerial mass, which is sucked by the hopper.Such a “tube” is fed by the silage material allalong the height, the part of material externalto the tube rests during the leakage. In particu-lar, in elongated sili, when completely full,along the height of the cylinder, from the higher

ring bands the radial pressure grows towardsthe base up to assume a constant value, then atthe section variation, it reduces from the ringwhere the hopper is installed, and high stresslevels arise. Obviously in case of empty or par-tially full silos the behaviour is different, the sta-bilizing effect of the radial pressure is lost inthe empty part with a consequent abrupt vari-ation of the critical stress. Pressure variationsinside the silos depend also by the leakage ofthe material through the hopper, which causesa backwash effect and thus depressions. Inorder to control and regulate such an effect, siliare provided with pressure valves. Given that itis plausible that on one side the effect of theseismic vertical component provoked a sharpand important increment of the actions in com-

a. b.

pression in the sili walls, causing buckling, thecontemporary seismic action in all the compo-nents accentuated the effect of possible asym-metrical distributions of pressure, due either tostructural eccentricities, or to the silos fillingmethod, or to the anisotropy of the silage mate-rial, causing a reduction of the stabilizingeffect of the radial pressures themselves. Fur-thermore, buckling could also occur due toconstructional imperfections at the jointsbetween the coating ring bands of the silos,where joints in any case represent a disconti-nuity in the flow of longitudinal stress in com-pression, with high concentrated stress. Theabove mentioned considerations fully justify thecollapse behaviour observed during the April6th L’Aquila earthquake. 211

Effects on structures and infrastructures

Fig. 6(a) Localization of the plantVIBAC in the Bazzanomunicipality (AQ).(b) Sili before theearthquake.

Fig. 5Local failure of the beamsupport.

a.

b.

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Fig. 7Pictures of the sili after the

seism. Photo by G.Verderame, ISPRA, F.M.

Mazzolani.

2.11.5 ConclusionsMost of the buildings which experienced theApril 6th 2009 L’Aquila earthquake are one-storey precast reinforced concrete structures.The observed damages are mostly related totheir flexibility and to the inadequate perform-ance of connections, especially for the case ofinfilling panels. In fact, pounding occurred; insome cases the beams lost their support, inother cases the bolts and steel connections ofpanels failed. The large number of these obser-vations suggests that more attention must bedevoted towards the connection detailing forthese structures.Concerning non-building-like structures, the

case of the sili of Vibac in Bazzano highlightsthat design of these structures is poor withrespect to earthquake resistance. In fact, it isnecessary to control the risk of damaging thesestructures and the likelihood that an earthquakeevent may trigger industrial accident. In fact, inthe case of sili containing hazardous material,this may greatly increase the earthquake risk.Finally, the observed damages in industrialstructures, building-like and non-building-like,may have been affected by the near-source fea-tures of the earthquake, including the intensivevertical component. Therefore, a revision andupgrade of seismic code provisions to accountfor the near-source effect seems to be required.

ReferencesCamata C., Biondi S., De Matteis G., Lai C., Spacone

E., Vanzi I., Vasta M., Post damage assessment ofthe l’Aquila, Abruzzi, April 6th, 2009 earthquake,

Compdyn 2009, Rhodes, Greece, 22-24 June2009.

Capozzi V., Magliulo G., Manfredi G. - Resistenza ataglio delle connessioni trave-pilastro spinottate

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nelle strutture prefabbricate. Industrie ManufattiCementizi, Giugno/Agosto 2009. Anno 5° n°9.

EERI Special Earthquake Report - June 2009. Learningfrom Earthquakes. The Mw 6.3 Abruzzo, Italy,Earthquake of April 6, 2009. Investigation teamleader Paolo Bazzurro, AIR Worldwide Corp., SanFrancisco http://www.reluis.it/doc/report.html.

UNI ENV 1993-4-1:2002.Giordano F., Rasulo A., Vanzi I., Zambiano A. - Rapporto

dei danni osservati su alcuni edifici industriali a seguitodel terremoto abruzzese del 6/4/2009, RapportoReLUIS, Rete dei Laboratori Universitari di IngegneriaSismica, http://www.reluis.it/doc/report.html

Magliulo G., Fabbrocino G., Manfredi, G. - Seismicassessment of existing precast industrial buildingsusing static and dynamic non linear analyses.Engineering Structures 2008, 30 (9), pp. 2580-2588, doi: 10.1016/j.engstruct.2008.02.003.