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Seminario Intemazionalen ternational Seminar

Teoria e pratica del costruire:saperl strumenti modelliEsperienze didattiche e di ricerca a confronto

h eory and practice o construction:knowledge means modelsDidactic d research experiencesRavenna 27-29 ottobre 2005

Volume 2

DAPT - D P,\R1 I lb m DI R U ~ l T L R .. ' ,,_l PI, \Nlnf \ l ION) T cRRITORIi\LI, ,. , iUni\'crsitil li Bologna ,

F O ~ D M J O E FL \ M N IRA\[ONN.\

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Reinforced brick vaultThe development o a construction system

The aim of this paper is to study the way in whichEduardo Torroja used the reinforced brick vault, andto show that it is a system widely used for decades inSpain when Torroja begun to employ it. The principalcharacteristic of this construction system is the use ofthe brick wall as formwork to buildup a reinforcedconcrete shell, where the masonry resists compression stress as well. The main advantage of thesystem is it reduces cost y eliminating the need forformworks and scaffold .

FOREWORDStone materials have been used traditionally as construction materials.

Tbe tensile resistance of these materials are negligible: to improve the performance of stone materials relating to tensile resistance several solutionshave been proposed. The aim of these solutions is toincrease the tensile resistance. The increase of ironproduction in the 8 th century increase the use ofmetallic parts in masonry.i

Use of iron elements to reinforce masonrystructuresFrom 1825 to 1843 the engineer Marc IsambardBrunei designed the tunnel under the Thames whereamong other innovative ideas, he put into practice the

Joaquin Antufia Bernardo

use of masonry walls reinforced with steel to formthe tunnel walls. (Hansen 1933).

The success obtained with this use of metallicreinforcement inside the masonry leads him to designa new system mixing steel with masonry. During thefollowing years he built masonry arcs reinforced withmetallic elements, and a series of 21ft span T-beamsmade in brick reinforced with 1.25 inch*0 .65 inchsteel strips. This kind of arcs had been tested for twoyears and finally in 1838 they broke under a load of6832 lb.

Hansen (1933) shows several tests carried out in1925 in EEUU where several ways to organize beams(the beams were constructed in brick reinforced withsteel bars or strips, using or not transversal reinforcement) had being studied. The main conclusion wasthat the hypothesis used in concrete structures calculations could also be used to calculate brick reinforced units. The ratio between modulus of elasticityof steel to masonry isn=20

Construction of mortar reinforced with iron meshthin shellsOne of the main application of reinforced concretedescribe in the first patents was the vault construction.One of these is the Cottencin patent. This patentproposes a system to build up thin shells in plasticmaterial reinforced with a metallic mesh big enough

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408 J Antuna Bernardo

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Item Hoe, I \0 a I f )tI 7 0 01 407 .... , 8i(.. :11 t 17.01 364 o 172 42 300 I 820 102I f.a I , i, J 7 0t 104 27'800 'w'I .2t .533 268 6 247 I 060 70n 7 01 806 I I . ...17 0 387 407 o 172 42 300 1620 102 1801 --., -Uem Hoe. &0 6. .

Figure 1Transversal section o f a beam buil t with bricks a nd re inforced with steel bm's in the lower face of the bea m. T he dotted linere presents the transversal re inforce ment that is not used in every beam tested .

to res ist the stress applied . The innovation was theway to produce the metallic framework . In thedescription of the possibilities for the new products,it states that it is fit f6t: masonry .

Timbrel vaultThe co nstruction of timbre l vault was a commonstructural system used in Spain. The system wasbased on the use of thin hollow bricks (about 4 cmdeep) called rasi llas . With these spec ial bricks sev-eral layers (generally two or three) were build. Thefirst one is jointed with quick se tting plaster mortar.With this system, the centring is not necessary, andonly light arch brace are needed , which make easierthe ,redes ign . Next layer is jo inted with ce ment mor-tar.'

Timbrel vault reinforced with iron wiresFrom the eighteen eighties Ant onio Macia built inSpain concrete works using the Monier s Patent. In

1889 Mac ia patented a new sys tem consisting in rein-forc ing o ne or more brick layer ma sonry with a mes hembedded in cement mortar. With thi s material hedes igned se wers , pipes , depot and cupules.

That system co nsists in built one or more layerso f hollow thin tiles and reinforced them with a meshof iron wires that is co vered with mortar of Portlandce ment.

In the patent text, it is me ntioned that no structur-al ca lcul ation is included due to the fact that it isacce ptable to consider the resistance of the new ele-me nt as the addition of metallic elements , mortar andbricks ones , and the traditional genera l mechanicstheory applied to co nstructions could be used .

ConclusionsTh e use of different types of masonry reinforced withsteel bars or strips were a system wide ly knew andused around the world in the first dec ades of the 20Thcentury.This kind of structures are analysed like rein -fo rced concrete structures

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Reinforced brick vault 409

Figure 2Section of a sewer constmcted following the Maeia'ssystem. t consists in a rasilla layer cover in the inner parlby a cement mortar rendering and with concrete reinforcedwith steel bars in the ex ternal face.

igura 3Transversal section of a 2 diameter pipe built up following the Mac in's system. t consists in two rasillas layerscover in the inner part by a cement mortar rendcring andwith concrete re inforced by nat ion strips in the circumferential direction and with round bars in the longitudinaldirection Secci6n

Reinforced Timbrel vault First Torroja s woks.Foundations caissons o Sancti Petri s Bridge,Cadiz

Foundation caissons are auxiliary works used toexcavate the foundation of bridge pillars in soils withsome determined characteristics. n Cadiz Bay thissystem was commonly used in the nineteen twenties ,and was well known by Torroja .n those days, foundation caissons were construction

reinforced concrete with a shape similar to an up sidedown mortar box. Doing this, it was possible to create a chamber where the workers could stay andexcavate down to the rock. At the same time the caissons were buried are enlarged to maintain the upperpart over the water level.

In 1926 Torroja presented a design for the foundation of Sancti Petris's bridge . In this design he propose a cylinder shape caisson. The caissons consistedof two concentr ic \valls. The external one had a 7,00m diameter. In the lower 6,00 m the diameter wasenlarged to give 7,50 m in the bottom of the caisson.The inner cylinder was 1,00 m in diameter to allowthe workers to through it.

This structure' has two peculiarities: The shape, isa section of a revolution hyperboloid, and the construction system, is a vault rtade with a thin layerreinforced with a 4 cm thick reinforced concretelayer.

The shape o the caissonThe section of the inner cylinder in the part situatedbetween the base and the vertical duct is a doublecurvature surface with different signs (transversalsection is a hyperbole). These conditions mean that ina reinforced concrete section the reinforcement couldbe set-in following the direction of the straight linesof the resultant hyperboloid (figure 5).

Once the caisson is constructed, it is placed in theposition, aud submerged to where the excavation hasto begin. Then, th e space between the two cylindersis filled with concrete. When the excavation takesplace, the structure is a vertical cylinder. The dimensions of the cylinder are 7,50 m diameter and 50 cmthick at the base, the diameter goes to 7,00 m and thethickness goes to 3 m at the 6.00 m from the bottom.After this elevation, it is a continuous 7 ,00 m diameter and 3 m thickness cylinder.

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410 1 Antufia Bernardo

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Figure 4Design of the foundations caissons project of Santi Petri' s bridge. They show the two walls of the cylinder which in the lowerpart has the shape of one hyperbola. In the project, the stmcture is in reinforced concrete. There are not references to the timbrei vault.

To analyse the structure it is assumed that it is aperfectly elastic mass . In the technical documentsaccompanying the design Torroja mentioned thePoschl procedure (Berlin 1922), but it is stated thatThe solution to the equations system is extremely difficult, ....we do not know any theoretical study forpractical integration in the case of non uniformloads so we think it is useless to develop all the calculation here . The inner wall with a hyperboloidshape is submitted to the uniform pressure of compressed air and the analysis is just to assume the ele-

mental equilibrium in a section. t is assumed as wellthat only the steel resists the compression and tensileforces .

The construction o the caisson

The design specifies that the caisson is made in reinforced concrete (page 7 in the technical documents ofthe project) , but it do not say anything about how tomade this special shape. Nevertheless the graphics

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Reinforced brick vault 4

Figure 5Foundation caisson scheme .One of the straight lines is marked to show the position in which the reinforcement couldbe set-in avoiding the need for curving the reinforcementbars.

are clear and it shows that at least two different procedures to build up the caissons where used:Redesign the reinforcement using the shape of thecaisson and build closed to it a wall made with rasillas to be used as formwork. (Figure 6).

b) To erect the shape of the caisson with a rasillas' wall and put the reinforcement over the wall andlater the concrete (figures 7 and 8).

In both cases the used of timbrel vaults is due toconstructive needs. A well known constructive system and used in a different kind of works is used. Butin this case is used as auxiliary work to obtain a reinforced concrete surface with a determined shape.Doing this the need of a formwork in wood is eliminated and the cost of the work is reduced.

The way to construct is very similar to this onepatented by Macia approximately 30 years before. tis possible to state that this way of construct concretelaminar structures was known ancl used widely inSpain at least 30 years before

Conclusionsn 1925 when Torroja begun to work the first parab-

Figure 6To found the pillars of the bridge some caissons were buill.From the documents we have, it is deduced that two construction methods were used. The figure shows one of themconsisting in place the inner profile shaped reinforcementand a closed to it a wall in th e inner part to be lIsed as a formwork for the following concrete filling. Down left it ispossible to see a worker making the rasillas masonry.

oloid hyperbolic shape concrete reinforced shells,had been erected. t was a technique not extended butknown.

In Spain in those days the use of masonry as auxiliary work to build up laminar structures with simpleshapes , generally in a cylindrical section was aspread system and was the object of several patents .

The innovation introduced by Toroja is to used aknown system and apply it to a regulated surface .

n the structural analysis the material is considered homogenous and elastic

The churches in the Pirineos th possibilities of aconstruction systemThrough the year 1953, after a travel to SouthAmerica, where Torroja visited several countries giving cow'ses and seminars, Torroja designed someworks to Empresa Nacional i d r o e h ~ c t r i c aRibagorzana (ENHER). The most important onewas the vault dam in Canelles. n addition to thisproject, he made some churches designs to be constructed in the area near the Noguera Ribagorzana

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4 2 J. AnlUiia Bernardo

Figure 7t is possible to appreciate the conditions needed for the tim-brei construction. Just some wooden simple guides used forthe redes ign and to survey the way in which the masonry isconstructed. When the masonry is fini shed, the reinforce-ment and the concrete are placed. Down right it is possibleto appreciate the wood board that acts as a guide

Figure 8Once the masonry work is fini shed , it is rendered in theexternal part and in the inncr part the reinforcement is pla-ced between the two brick layers. It is possible to see thevertical guidance to survey the external face shape.

River: Xerrallo's church, Sancti Spirit' s mountain hutand Pont de Suert 's church.

In all of these projects, to make the roofing vaultswith two or three rasilla layer reinforced with a rein-forced concrete layer were used. The list of shapes isextensive, they use: sferical domes , pointed arches.pointed domes and pointed vaults and double curva-ture surfaces generates whith spirals curves, . ..

In Oschendorf 2003, the coincidence with theTorroja's travel to south America and the construc-tion of these roofing structures using a system mixingmasonry and steel reinforcements was discussed. Wedo not know if Torroja meet the Eladio Dieste'sWorks in Uruguay, but it is possible to state that thesystem used by Torroja is fully different to the systemused by Dieste.

n that moment he was working in his bookRazon y ser de los tipos estructurales where

Torroja regrets that architects were not be able toexplore the reinforced vaults shape possibilities.

t is possible to understand the design of thesechurches as a resea rch of the possibilities to build dif-ferent shapes using timbrel vaults reinforced with alayer of reinforced concrete.

The shape of the nave's roofingThe design of the church is a nave with a rectangularplant with an apse in one end and a baptistery and acommunal hall. n each part a different type of roof-ing is used. but all of them made using timbrel rein-forced vaults . All the shapes are obtained from geo-metrical expressions. Arcs of circles , parabola. loga-rithmic spirals, ellipsis ...

The only shape we will study is the centralnave 's roofing. t consist in five patts of 5.00 m wideeach and [2,00 m span. The roofing of each part is anpointed arc who begin over two niches with ellipsoidshape. The particularity is the way to build up eachpart. t consist in a surface with double curvature,which transversal section is an circle arc withvarable diameter. The diameter becomes bigger arriv-ing to the keystone.

The transversal section of the modulus is a cir-cumference arch with a variable thickness defined bytwo arcs with different diameter. The inner one is aprojection of an warped curve which projection overa longitudinal plan is a parabola beginning perpen-dicularly to the lower niche and has a vertical tangentin the upper part (figure [3). These two conditionsgive the analytical expression for the parabola.

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Reinforced brick vault 413

To detennine the geometrical shape of the lobule,26 points over the edge of the curve are defined usingthe coordinates in the longitudinal projection. Eachof these points is used as beginning of an circumference arc situated in the plan defined by the pointitself and the symmetrical one placed in the warpedcurve . All the planes containing this arches, rotateabout the axis signed in the figure 14 like "eje de girodel piano de las generatrices ."It is difficult to express in an analytical way thissurface, bU l with the data given in the documentsaccompany the design, it is possible 10 build simplesarch braces with a well-defined section. These archbraces will be used as a guide to give an idea ofwhere to put the first layer of "rasillas."This project shows that il is possible to build really complex geometries using the timbrel vault com-bined wilh reinforced concrete. Thi s method allowsbuilding shells wilh complex shapes eliminating theformwork costs.

Figure 10Design of the Pant de Suert s church.

Figure 9

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Drafts foJ' the Xerallo s chrch project. The cover is madewhit the same system U ;ed in the bapti stery of the Pant deSuer 's church.

/

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414

Figure I JTransversal section of the Pont de Suert s church.

Figure 12Geometrical schema of the transversal section

J. Antuna Bemardo

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Longitudinal section of the nave. In the table on the right ofthe image are showed th e coordinates of point on the lobule's border and the radius of the arch of the lobule 's transversal section in this point

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Reinforced brick vault 415

urvo

Figure 4Schema that exp lain the lines that define the shape of the structure. The laying out con be done whit a si mple scaffold, andover them put simple arch braces with the shape of the corresponding circular arch. This arch braces allow to place the rasil las of the first layer.

The structural analysisThe structure is a symmetrical arc. For the analysisthe expressions used are that ones who appeared inTorroja (1951,9).

Taking these considerations, the maximal stressin the start is -7,7 kg/c m' (compression) and +6,2kglcm' (tensile) (figure 15)

onclusionsThe main characteristic of the Pyrenees' churchescupola is the construction system.The traditional reinforced trimel vault as support toerect a reinforced concrete shell avoiding the formwork.

The concrete and masonry working stress are

weak, about a 10% of the admissible resistance of thematerial.

DiscussionIn the beginning of 20th century, the constructionsusing reinforced concrete increase a lot. The successof the new material was so big that today is besidesthe steel structures the main system of construction.However since mid 19 th century several test toimprove the quality and performances of brickmasonry structures using different iron reinforcements have been done . For builders and designers inthe first yeas of 20 th century the use of steel reinforced masonry works were commonly used. Torrojabelongs to the age group of designers that know anumber of techniques to construct in addition to rein-

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416 1 Antuiia Bemardo

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Figure 15.Transversal section of the nave. The pressures curve obtained from the elastic analysis is indicated.

forced concrete; techniques that some times can be aadvantageous competitor for concrete.

In Torroja's work a permanent innovation aim aswell as a new proposals for construction appears. Theprojects with timbrel reinforced vaults were the resultof this research.

The purpose is to offer alternatives to constructconcrete reinforced shells when problems with costof auxiliary means in developed countries make themdifficult to be used.

In our view, the construction in clay masonry hastwo different considerations. These considerationsare shown respectively in the works of Eladio Diesteand Eduardo Tonoja.

The difference is the used that is given to themasonry work.

For Dieste's way, form work to place the rein-forcement and the bricks are needed. (This commentis only in relation with roofing structures, where variable transversal section isostatics beams are used, the

comment is not applicable for the construction oftowers or walls where the use of form works are notneeded)

In contrast, for Torroja the formwork is not needed because he use the masonry work as form work.

There are other difference and has a mechanicalnature.

Since in Dieste' way of working the masonryworks at high stress, in TOIToja's one the stress onlyis up the 15% of the load bearing of the structure

CONCLlJSIONS

The reinforced trimelt vaults construction were thepoint for lots of studies in the last years, and the useof reinforced vaults have been recuperated in somecases. The improvements of this kind of structuresobtained mixing the vaults with steel mashes andconcrete layers is a technique appeared in the earlieststage of the concrete use and has not been studied yet.Apart from the churches in the Pyrenees, reinforcedtrimel vaults offers possibilities that are not beenexplored.

The author have proposed in a refurbishmentproject some of this kind of structures. t is expectedthey will be constructed in the following months.

NOTES

I. In the wellknow image of Rondelet (1802) in whichshow the Sainte Genevieve's church projected by 1. G.Soufflot, the disposition of the lintel re inforcement barsare similar to the reinforced bars of current reinforcingbars of concrete beam. This show that in the XVIII century steel bars were used to improve masonry construction.

2. See the patent number 12301 in the Oficina Espaiiolade Patentes y Mm'cas, 9th july 1891: objects of pIastic material with reinforced frames of wires inside.Following the author, the innovation and the advantageis based in the continuity of the iron wire. The idea issuitable to be used among other in depot, vaults orpipes. In all the cases, the metallic mesh is used as anformwork for a plastic material as cement mortar.

3. In Huerta 1999 it is possible to find quite a lot bibliography about reinforced timbrel vault.

4. The Santi Petri' s project, is the document number 19 inthe Eduardo Torroja Archive. The remaining documentsare those ones where the foundation system is described, The drawings of the bridge, the foundation ca is

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Reinforced brick vault 4 7

sons, and the lateral abutment. Several pictures of theconstmction process are conserved as well.

REFEREN E L ST

Antuiia Bernardo. Joaqufn. 2003. Las eS/l'llc/uras de ediji-eac;,) de Edll(/rdo Torroja. Madrid: Tesis doctora\.

Hansen H .. James. 1933. Developments in rcinforced brickmasonry. American Society of Civil Engilleers,Proceedings, 3: 405-427.

Huerta Fermindez. Santiago. Ed. 1999. Las Mvedas deGlIos/avil1o ell Allu;rica. Madrid: Instituto Juan deHenera.

Ochsendorf. John, Anllliia, Joaqufn. 2003. Eduardo Torrojaalld Cerdmica armada. In Proceedillgs J{ the Firs/Illlerna/iurlGl COllgress on Construction History.

Madrid: Instituto Juan de HerreraRondelet. Jean . 1802). Trai/ e /ileorique e/ pra/iqlle de I' or/

de ba/iI'. ParisTorroja , Eduardo. 1951 . Cdlclllo de esJill'rzos en es/ruc/llras

il piezas cllrvas. Madrid: Instituto Tecnico de laConslruccion y el CementoZafra Juan Manue\. 1912.Los metodos de dlculo de CSlructuras derivados deltrabajo elastico, Revista de Obms Pliblicas, Vo\. LX,1938: 539-546; 1939: 561-567; 1940: 586-592; 1942:597-602; 1943: 614-619; 1944,622-626.

Zafra, Juan Manue\. 1913. Los metodos de calculo deestructuras derivados del trabajo ehistico, Revis/a deObms Pliblicas Vo\. LXI 1945: 1-6; 1946: 1316;1947: 29-35.

Zafra , Juan Manue\. 1915. Cdlclllo de es/ ruc/llras. Madrid:Tejada y Martin.