(URM) buildings of Barcelona. Seismic vulnerability

MODERNIST UNREINFORCED MASONRY BUILDINGS OF BARCELONA (PRE-PRINT)

Modernist unreinforced masonry (URM) buildings of Barcelona. Seismic vulnerability and risk assessment

Gonzalez-Drigo R 1, Avila-Haro JA 1, Barbat AH 1, Pujades LG 2, Vargas YF 2, Lagomarsino S 3 and Cattari S 3 1 Department of Strength of Materials and Structural Engineering. UPC‐Barcelona‐TECH. Barcelona, Spain. 2 Department of Geotechnical Engineering and Geo‐Sciences. UPC‐Barcelona‐TECH. Barcelona, Spain. 3 Department of Civil, Chemical and Environmental Engineering. University of Genoa. Genoa, Italy.

Abstract The main objective of this work is to assess the vulnerability and seismic risk of typical existing URM modernist buildings and aggregates situated in the Eixample district of Barcelona, part of the architectural heritage of the city. The context of the analysis is the methodology proposed by the Risk-UE project. The buildings are characterized by their capacity spectrum and the earthquake demand is defined by the 5% damped elastic response spectrum, considering deterministic and probabilistic earthquake scenarios. A discussion is made regarding the basis of the seismic damage states probabilities and the calculated damage index. An important research effort has been focused on the buildings modelling. All the architectural elements and their mechanical properties have been studied and evaluated accurately. It has been evidenced that a detailed and complete knowledge of all the structural elements existing in this type of buildings influence directly their behavior and hence the calculations and the results. The analysis of the isolated buildings and of the aggregate building has been performed for both mentioned seismic scenarios. Finally, a complete discussion of the results is included. Keywords: Unreinforced masonry, modernist architecture, capacity spectrum method, vulnerability, fragility, risk assessment.

1 Introduction In the Mediterranean area, modern cities accumulate a large number of buildings, infrastructures and facilities that result in an important concentration of socioeconomic value and in high population density. (EUROSTAT 2011; US Bureau of the Census 1991). At present the 75% of European people live in cities with more than 100,000 inhabitants. The seismic hazard is not negligible in this area (Jiménez et al. 2001; Grünthal et al. 1999; Egozcue et al. 1991) and the seismic risk is higher than expected due to the high vulnerability of constructions built in the urban centres where a significant number of the current buildings are constructed with unreinforced brick masonry and without any consideration of the seismic actions. Most of these buildings are more than 100 years old, which means that they largely overpass the service life initially supposed for them. In addition, several circumstances, as the material degradation, some aggressive retrofitting and refurbishing works, and the changes in the Page | 1

MODERN NIST UNREIN NFORCED MA ASONRY BUIL LDINGS OF BARCELONA ((PRE-PRINT)

buildingg load connditions, in ncreased thheir overalll vulnerabiility (Figurre 1). Theerefore, thee vulnerabbility of theese URM buildings, b thhe importan nt populatio on density aand the nott negligiblee seismic hazard in thhe region, decisively d inncreased thee seismic rissk in these uurban areass.

Figure 1. Example of URM U building gs with high sseismic vulnerrability. The addition a of topp levels to the original buildingss increases eveen more their seismic vulneerability.

Receent studies in earthqu uake engineeering are oriented o to the developpment, valiidation andd applicattion of techhniques to assess a the seeismic vuln nerability off existing buuildings. (Y Yépez et al.. 1996; B Barbat et al. 1998; Barb bat et al. 20 06a; Barbatt et al. 2006 6b ; Carreñoo et al. 2007 7; Barbat ett al. 20088; Lantada et e al. 2009; Pujades P et aal. 2012) Barccelona is a city locateed in a low w-to-moderaate seismicitty region inn the north heast of thee Iberian Peninsula and a in the western w coa st of the Mediterranean M n Sea. Duriing the 19th h century, a high poopulation pressure and d a city opppressed by y the medieeval walls were the determinant d t circumsstances thatt generated a major urrban expansion project. During th the first perriod of thiss expansion, from 1860 to 194 40, most off the buildin ngs constru ucted were unreinforceed masonryy (URM) buildings. Today, man ny of those buildings, more than one hundreed years old d, still standd (Lantadda 2007) andd are part off the architeectural herittage of Barccelona. Thee main objecctive of thiss work is to assess the t seismic vulnerabilitty and risk of those bu uildings, sittuated in the Eixamplee district of Barceloona by using the methhod proposeed in the Risk-UE R prooject (Miluttinovic andd Trendaffiloski 20033). The stru uctural anallysis is perfformed by means of tthe TreMurri computerr program m (Lagomarrsino et al.. 2008) thaat has been n specificallly developped for the linear andd nonlineaar analysiss of URM M buildingss. Differentt MATLAB B codes ((Matlab v.2 2009b Thee MathW Works) have been develloped in ordder to obtaiin the fragillity curves and the dam mage indexx

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correspoonding to each e studied d model. Thhe most imp portant resu ults of this aarticle are the t fragilityy curves aand the dam mage probab bility matricces obtained d for this building typollogy.

2 The urban exp pansion p project an nd the buiildings In 1850, Barcellona still rem mained as a walled city y; in 1854 th he decree foor the urban n expansionn project was approvved. The urrban planninng was desiigned in 18 859 by the ccivil engineeer Ildefonss Cerdá. T Thus, the mediaeval m walls w were deemolished and a the plaiin area betw ween the city y walls, thee Mediterrranean coaast and the Collserola C H Hills was opened o to be urbanizedd (Lantada 2007). Thee new disstrict was called Eixample (enllargement). Figure 2 shows a ty typical secttion of thee Eixampple district. Now wadays, the Eixample district hass 247,418 inhabitants,, a populatiion density y of 33,1488 2 inhabitaants/km andd 8,658 buiildings. Mosst of these buildings b were w built beefore 1960, being 1931 the aveerage year of construcction. Todaay, the unreeinforced brick b masonnry buildings supposee nearly 770% of the buildings b off the Eixam mple (Lantad da 2007).

Figure 2. A view of a section s of the Eixample disttrict (CCCB, 2009). 2

Althhough the buildings weere built inddependently y, most of them were cconstructed by sharingg the laterral load wallls with the existing adj djacent build dings. In con nsequence, the masonrry buildingss of the E Eixample district d form m large squuared aggreegates consstituting thee so called d islands orr blocks, following the t urban frramework shhown in Fig gure 2. The frameworkk of the urban plan is a net of ssquared blocks sided 133 1 m long on averagee. The streeets, 25 m w wide on aveerage, crosss orthogoonally between the blo ocks. This framework makes buiildings desiign conditio onal to thee orthogoonal shape of the bloccks and thee buildings can be fittted togetheer if they are a outlinedd followinng repetitivve patterns. In the midd side of th he blocks, central c builddings have orthogonall perimetters with a ratio r betweeen the dimennsions in plan of at least 2 to 1. Att the end off the blocks,, ure 3 showss the cornner buildinggs are more irregular annd have a typical pentagonal perim meter. Figu the flooor plan of an a actual and characteeristic row of aggregaate buildinggs, which in ncludes thee buildinggs analyzedd in this stud dy. In this ffigure, the names n of th he buildingss studied in this articlee are alsoo shown. Inn any case, even connsidering modern m build dings, the sshape in pllane of thee buildinggs does noot depend on the buiilding typo ology (unreeinforced m masonry or reinforcedd concretee), but it onnly depends on the geom metrical fit of the build ding into thee block aggrregate.

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2.1 Thee buildings Thiss study evaaluated 3 ex xisting isolaated buildin ngs and an aggregate of 2 buildings. All off them haave 7 storiees. The build dings corre spond to a row aggreg gate of a bloock in a maain street inn the cityy of Barceelona. Figu ure 4 show ws the faççades of th hese buildiings, which h are veryy represenntative for the t Eixamplle district; aall of them are URM sttructures wi with load-beaaring walls.. Foundattions are shhallow, runn ning throughh surface paads under th he walls or, in case of more m recentt buildinggs, they are isolated foo ots under cooncrete pillaars. Thiss discussionn will refer to t the rectanngular build dings as M0 01, M02 andd M03 (Fig gure 3). Thee aggregaate correspoonds to thee sequence M01-M01. This meaans that thee aggregatee has beenn designed by meanss of two twiin URM buuildings buillt together. We will reffer to this aggregate ass A01. Fiigure 3 show ws the existting aggreggate. Other data d relativee to storey heights, waalls density,, loads annd walls thiccknesses are shown in Table 1, Taable 2, Table 3 and Tabble 4.

Figure 3. Floor plan off a characteristtic row of agggregate buildin ngs located in a main street of the Eixam mple district off Barcelonaa.

Figure 4. Façades of thhe analyzed bu uildings locateed in Barcelon na.

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The resistant elements are bearing walls and, in the ground floors, there may also exist masonry columns or cast iron columns. In general, these buildings only have the necessary elements to ensure the stability of the structure. More details of the specific architectonic features of the masonry buildings of the Eixample district are given by Paricio (2008). TABLE 1 Geometric properties and load conditions of the isolated building M01

Properties Storey Height (cm) Walls density +X Dir Walls density +Y Dir Dead load (daN) Live load (daN) Main façade Post facade Walls Staircases Thickness Inner bearing walls (cm) Intermediate bearing walls Distribution walls

1 420 0.089 0.029 0.059 350 200 45 30 30 30

2 340 0.059 0.037 0.022 350 200 30 30 15 15 15 5

3 340 0.059 0.037 0.022 350 200 30 30 15 15 15 5

Storey 4 340 0.059 0.037 0.022 350 200 30 30 15 15 15 5

5 340 0.059 0.037 0.022 350 200 30 30 15 15 15 5

6 340 0.059 0.037 0.022 350 200 30 30 15 15 15 5

7 330 0.059 0.037 0.022 350 100 30 30 15 15 15 5

TABLE 2 Geometric properties and load conditions of the aggregate A01


1 420 0.089 0.029 0.041 350 200 45 30 30 30

2 340 0.059 0.037 0.022 350 200 30 30 15 15 30 5

3 340 0.059 0.037 0.022 350 200 30 30 15 15 30 5

Storey 4 340 0.059 0.037 0.022 350 200 30 30 15 15 30 5

5 340 0.059 0.037 0.022 350 200 30 30 15 15 30 5

6 340 0.059 0.037 0.022 350 200 30 30 15 15 30 5

7 330 0.059 0.037 0.022 350 100 30 30 15 15 30 5

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MODERNIST UNREINFORCED MASONRY BUILDINGS OF BARCELONA (PRE-PRINT) TABLE 3 Geometric properties and load conditions of the isolated building M02

Properties Storey Height (cm) Walls density +X Dir Walls density +Y Dir

Walls Thickness (cm)

Dead load (daN) Live load (daN) Main façade Post facade Staircases Inner bearing walls Intermediate bearing walls Distribution walls

1 420 0.107 0.028

2 340 0.062 0.034

3 340 0.062 0.034

Storey 4 5 340 340 0.062 0.062 0.034 0.034

6 7 340 330 0.062 0.062 0.034 0.034

0.079 350 200 45 45 30 15

0.028 350 200 30 30 15 15

0.028 350 200 30 30 15 15

0.028 350 200 30 30 15 15

0.028 350 200 30 30 15 15

0.028 350 200 30 30 15 15

0.028 350 100 30 30 15 15

30

15

15

15

15

15

15

5

5

5

5

5

5

TABLE 4 Geometric properties and load conditions of the isolated building M03


1 420 0.092 0.034 0.058 350 200 45 45 30

2 340 0.068 0.035 0.033 350 200 30 30 15 15

3 340 0.068 0.035 0.033 350 200 30 30 15 15

Storey 4 340 0.068 0.035 0.033 350 200 30 30 15 15

5 340 0.068 0.035 0.033 350 200 30 30 15 15

6 340 0.068 0.035 0.033 350 200 30 30 15 15

7 330 0.068 0.035 0.033 350 100 30 30 15 15

30

15

15

15

15

15

15

5

5

5

5

5

5

2.2 The walls The walls of the street façade, the inner courtyard of the block and the walls between buildings, usually called intermediate walls, are the main bearing walls. In the first storey, metallic columns (foundry columns in some buildings) and girders are present (Figure 5) and, usually, above those girders and for all the upper stories, additional bearing walls (usually two) are added parallel to the façades. This constructive solution, which avoids placing inner walls for the first or for the first two stories, is very common, permitting larger clear spaces, allowing the ground floors being used for trading or catering activities and for office or administrative activities in the mezzanines. In addition, each building has one or more nuclei around the Page | 6


staircasees and smaall internal courtyardss made to provide p nattural light tto the interrnal rooms.. These nnuclei are paartially clossed by masoonry walls and a are also used as beaaring elemeents (Figuree 6b). Finnally these buildings b allso have a ssecondary system of in nterior wallss which, in general, doo not have a significcant contribu ution to theeir strength;; these wallls have a thhickness low wer than 100 cm and their main function is to separate the volumees and to pro ovide acousstic insulatio on.

Figure 5. Metallic girdders and iron columns c at thee base floor off the M01 building.

(b)

(a)

(cc)

uilding (M01 in Figure 3). aa) Half buildin ng. b) Base Figure 6. Cross sectionns of the isomeetric view of aan isolated bu Characteristic floor. floor. c) C Page | 7


In ggeneral, the inner wallss, which cann reach lengths of up to 10 m, arre poorly co onnected orr connectted neither to t the façad des nor to thhe walls bettween adjaccent building ngs and, therrefore, theyy cannot bbehave as bracing b walls. Furtherrmore, when n there are openings ffor doors, windows w orr balconiees, they havve lintels orr parapets oof variable dimensions; the wall ssections oveer lintels orr parapetss are extrem mely weak areas a wheree cracks duee to the effeect of differrential mov vements cann be obserrved. Bothh the street façade and the inner ccourtyard walls w have siignificant oppenings witth windowss and ballconies. As the level increases, these open nings are sm maller, so tthe presencce of largee openinggs is usual in the first levels, makiing these walls weakerr even if theeir thicknesss is greater.. Figure 6 shows a complete c grraphical desscription of one of the studied buiildings (M0 01 in Figuree 3). The intermediaate walls sh hared betweeen adjacentt buildings are solid an and do not present p anyy openingg. The first building b raiised up incoorporates an n intermediaate wall with th a thicknesss of 30 cm m at the fi first floor. From F the second level until the to op of the bu uilding, the thickness of o this walll diminishhes to 15 cm m. Over thee entire heigght of the wall, w some unreinforcedd masonry columns c aree embeddded at a reguular distancce of 3.5 m to 5 m from m each other. When thhe adjacent building iss raised, iit directly shares s the in ntermediatee wall of thee first storey and it com mplements until 30cm m the thicckness of thhe wall at the t upper fl floors. This means that in each bbuilding thee maximum m support of the floorr beams is 15 1 cm on thhese walls (F Figure 7). Details D of thee organizatiion of thesee walls arre shown in Figure 8. An iinteresting geometric g parameter p iss the density y of walls which w is deffined as the ratio of thee area off the cross section of all the waalls of a sp pecific storeey to the to total area of o the floorr (Gonzálles 2010). For F the anallyzed buildiings, Table 1, Table 2,, Table 3 annd Table 4 include thee density of walls, thhe values of o thicknesss correspond ding to the different w walls and th he dead andd gs, we tookk into accou unt only thee live loads correspoonding to diifferent leveels. For all the building g for diffferent storiies. walls haaving a thickness greater than 10 ccm. All the values are given 2.3 Thee floors From m 1860 to 1960, most of the flooors of the unreinforced u d buildings of the Eixaample weree solved w with unidireectional slab bs. But, at ddifferent peeriods, the materials m off the elemen nts used forr the flooors changedd. From 186 60 to 1890 approximaately, the flo oors were oone-way tim mber floorss with sinngle or overrlapped wood planks iincluding an n additionall concrete ttopping. Fro om 1890 too 1940, irron beams and brick vaults v were widely useed. This is the case off the studied buildingss (Figure 9 and Figuure 10). Aftter 1940, duuring the Spanish postt-war periodd, there waas a time off o reinforceed concrete beams andd shortagees when iroon and steell were scarcce. Thereforre, the use of brick vaaults or ceraamic blocks was the sollution for th he floors.

Figure 7. Iron beams (ssliced) simply y supported onn the wall.

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The buildings studied in this article as typical for the URM building of the Eixample, were built between 1920 and 1935. Basically, their floors are composed of girder beams whose heads lay on bearing walls or on main beams. There are main beams only at the first level floor, sustained on cast iron columns (Figure 5 and Figure 6b), allowing large open spaces as described before. The support length of the girder beams on the perimeter walls depends on the wall thickness. For intermediate walls, the supporting length is 15 cm. In the case of façade walls, it is 30 cm for lower stories and 10-15cm for upper stories. This very common solution for the floors required girder beams with a separation ranging from 60 to 120 cm. The floor thickness is reduced, varying from 15 up to 20 cm, while the timber floors, older than these, have thicknesses that duplicate and even triplicate these values. Between the girder beams, the floor is solved by placing small vaults or, in more recent cases, case-bays. In all the cases, those elements spring on the girders flanges. In addition, the groins are filled with plaster and chippings and, then, the floor is smoothed, levelled and covered with the pavement (Figure 9 and 10). Due to their stiffness, the single bridging is not needed in these floors.

Figure 8. Architectural floor plans (building M01). a) Façade. b) Base floor. c) Side elevation. d) Intermediate floor [the dimensions are in m].

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The total weighht is due to o the dead loads and the t live loaads. The loaad values used u in thiss article aare in accordance to the characteriistic values from the ciity council rregulations documentss (Paricioo 2008) prevvious to all the buildinng codes thaat appeared and were ccurrently in n force afterr 1960 (M Ministerio de la Vivienda 1963;; 1988; Miinisterio dee Fomento 2006). Forr structurall analysess, 200 kg/m m2 was assig gned to the floor weigh ht; the load d due to thee distribution walls hass been esttimated in 100 1 kg/m2; the weight of an ordin nary tiled floor pavemeent has been n evaluatedd 2 in 50 kgg/m and haas to be added to the ccorrespondiing floor peermanent looad. In conssequence, a permaneent load of 350 kg/m2 and a variaable load off 200 kg/m2 are the coonsidered vaalues in thee calculattions of the intermediate floors, w while 350 kg g/m2 and 10 00 kg/m2 arre those con nsidered forr the terraace roofs.

Figure 9. Floor system m. Iron beams and a brick vaullts.

Figure 100. Details of a floor system observed duriing the demolition of an Eix xample buildin ing.

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2.4 The bricks and the mortars The brickwork of the analyzed buildings uses solid prismatic bricks, made of fired clayey soils. These bricks are easy to handle and their thickness is lower than 12 cm. Ordinary bricks (29×14×5.5 cm) were mainly used in bearing walls; bricks of 4.5 (29×14×4.5 cm) were used in division walls; medium brick (29×14×3 cm) and thin bricks (29×14×2 cm) were used in the construction of vaults. According to the firing grade, there were four categories of bricks. As the firing grade increases, the strength and the apparent density of bricks and brickwork increase (Schindler and Bassegoda 1955). It was a common practice to select the most resistant bricks for very loaded walls. As the commercialization of ceramic hollow bricks started later, in 1940, they were not used in the analyzed buildings. The studied buildings were built in the late 19th and early 20th centuries and most of their bricks were manufactured in continuous kilns; therefore they have similar properties. In general, they show a rough texture that favours a good adherence to the support. Their surface is rather compact without observable gaps like hollows and holes. Breakage of bricks shows a fine and regular grain and very few impurities of appreciable size in the matrix. There are not vitrified zones. The colour varies between red for the bricks with lower strength (7 MPa) and a more or less pale ochre for the higher strength ones (15 MPa).The strength demand conditioned the mortar selection for the brickwork. In order of decreasing strength, the mortars used were: Portland mortars, natural mortars (roman cement), lime mortars and bastard mortars. 2.5 The brickwork and the walls organization In the buildings studied in this article, the different brickwork differs according to the wall function and its corresponding thickness (PIET 70 1971). The thickness of most of the partition walls was lower than 6.5 cm, without including the plastering. These walls are made of medium and thin solid bricks. In some cases, double partition walls are used, with a thickness between 6.5 and 9 cm without including the plastering. For all the bearing walls, the brickwork is made using solid bricks. Thus, the corresponding thickness is a multiple of the brick width (15 cm). Without taking account of plastering, the usual thicknesses are: 15 cm, 30 cm, 45 cm, 60 cm and 75 cm. The brickwork with ordinary brick in buried walls and in stairway cases is made with hydraulic lime mortar or with Portland mortar. The exterior brickwork is made with lime mortar. For medium range loads, the brickwork uses bastard mortar and, for main loads or in slender pillars, resistant bricks and Portland cement mortar are used. Table 5 shows the values of the design strength of the brickwork made with solid bricks and different mortars. It should be considered that all the values are design values and that they have been obtained by reducing the corresponding characteristic values of strength with a coefficient of 2.5.

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o the arches aabove opening gs. Figure 111. Example off distribution of

Figure 122. Support lenggth for the beaams located ab above opening gs.

2.6 Opeenings and lintels In thhe URM buuildings off the Eixam mple, the do oorways and d window sspans use discharging d g arches oor iron linteels (Figure 11). For oppenings in thin walls, as is the caase of the distribution d n walls, thhe option was w to use wood w elemeents for the lintels of th he doorwayys and windows. In bigg openinggs, the linteels are madee with two,, three or more m beams, accordingg to the walll thicknesss (one beam for eachh 15 cm off wall thicknness), and are a placed parallel p to eeach other. The beamss are fasteened with bolts b housed d into iron tubes that maintain m th he beams at the requireed distance.. The lenngth of the beams b support onto thee walls can be taken ass the edge leength of thee beam but,, in any ccase, it is infferior to 20 cm (Figuree 12). Page | 122


TABLE 5 Design strength of brickwork masonry for solid clay bricks (PIET 70 1971) Design element Brick strength (MPa)

7

15

30

Properties

Design strength of brickwork using mortar (MPa)

Low

Joint thickness (cm) >1.5

Low Medium

1 to 1.5 >1.5

0.9

1.0

1.1

1.2

1.4

-

Low Medium High

1.5

1.0

1.1

1.2

1.4

1.6

-

Medium High

1.5

1.4

1.6

1.8

2.0

2.2

2.5

Low Medium High

1.5

1.6

1.8

2.0

2.2

2.5

2.8

Medium High

1.5 1.5