Structural Analysis of Historic Construction – D’Ayala & Fodde (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-46872-5

Construction process, damage and structural analysis. Two case studies

R. González & F. CaballéVeclus

J. Domenge, M. Vendrell & P. GiráldezUniversitat de Barcelona

P. Roca & J.L. GonzálezUniversitat Politècnica de Catalunya

ABSTRACT: The paper refers to the studies recently carried out on the church of Santa Maria del Mar inBarcelona and Mallorca cathedral, built during the 14th and 15th centuries. Historical research has providedsignificant insight on the construction processes, which were remarkably different in the two buildings. Thisinformation has been considered to investigate the possible link between construction and existing deformationand damage. As shown by these examples, insight on the construction process (and later man-caused alterations)may be important for an accurate structural analysis.

1 INTRODUCTION

The buildings analyzed, namely Mallorca cathedralin the island of Mallorca and the church of SantaMaria del Mar in Barcelona, show common architec-tural features but also significant dissimilarities which,in turn, have lead to different damage and deforma-tion conditions. As will be later described, one of themain differences is found in the construction processesand their consequences for the latter condition of thestructure.

The studies were undertaken in close cooperationbetween historians, structural engineers, mineralo-gists, architects, geophysicists and other specialists.Detailed research on available historic documents haspermitted the identification of essential issues relatedto the construction process and later events (archi-tectural alterations, earthquakes, fires) having lefttheir imprint on the structure. Geophysics, carriedout by means of seismic tomography, pulse radar anddynamic testing, has been very useful in character-izing essential structural and morphological features.Structural analysis, carried out by means of classicalapproaches (limit analysis) and advanced non-linearnumerical models, has permitted the characterizationof the structural performance under gravity, soil set-tlements and earthquake (Clemente, 2007, Martínez,2008).

Based on the information provided by historical andgeophysical research, a sequential analysis has been

developed, in the case of Mallorca cathedral, as anattempt to simulate some aspects of the constructionprocess.

An essential issue of the diagnosis lays in the dis-tinction of damage related to active phenomena, stillcontributing to further deterioration, from that whichhas resulted from past or already extinguished actions.In some cases, stabilized damage or alterations causedby past actions may be preserved and respected as asign of identity linked to the historical character of thebuilding. In other cases, repairing this type of dam-age may be necessary to avoid problems related todurability or functionality, or to improve the capacityof the building under extraordinary actions (as earth-quake). If repaired, historical or traditional techniquesshould be preferred to alternative possibilities in orderto avoid unnecessary loss of authenticity of materialsand structure.

For obvious reasons, the ISCARSAH Recommen-dations (2005), state that the intervention must alwaysaddress the real causes rather than “the symptoms”.When addressing past or extinguished actions, theneed for intervention should be carefully appraisedand repair and strengthening should be limited to trulyindispensable operations.

Possible historical actions which may have con-tributed to damage, but (in principle) are not expectedto happen again, include anthropogenic ones (wars,fires and other types of destruction, lack of mainte-nance and inadequate restorations) and natural ones (as

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stabilized soil settlements). Earthquake does not layin this group for obvious reasons.Yet another “action”belonging to this group, which by no means shouldbe neglected, is the construction process itself and itsrelated hazards and difficulties.

2 DESCRIPTION OF THE BUILDINGS

Santa Maria del Mar is a rare case of a Gothic churchentirely built during a short period of time spanning53 years. Moreover, the building has not experiencedany significant architectural alteration after its con-struction, resulting in the uniformity and architecturalpurity for which the building is today acknowledged.The overall arrangement of the structure is very sim-ilar to that of Barcelona Cathedral, built during 13thand 14th c., and consists of a three nave structure builton a basilical plan.

In Barcelona Cathedral, the wish for a unitaryand diaphanous inner space, reminiscent of that ofRoman basilicas, laid to an innovative design. Thecentral vaults were built with longer span in both thetransverse and longitudinal directions (12 and 8 m),compared to other contemporary buildings, and weresupported in surprisingly slender piers; the lateralvaults spanned as much as one half of the central onesand were built at a height close to that of the centralones; the external walls were built along the exter-nal perimeter of the buttresses and these were usedas partition walls between lateral chapels. In the caseof Barcelona Cathedral, this combination contributedsuccessfully to create the impression of a unique andwide, even magnificent interior space in spite of thelimited dimensions of the building. As mentioned,the lateral vaults are almost as high (but not so high)as the central ones; in fact, they are adequately posi-tioned to receive the lateral thrust of the central vaultsand carry it to the buttresses, so that structural flyingarches are not needed.

Santa Maria del Mar is the only other Gothic con-struction having been built according to this structuralarrangement. Other Gothic cathedrals have low aisles(as in French Gothic) or have them as high as thecentral nave (as in German late Gothic churches).Furthermore, the builders succeed in improving thepossibilities of the concept in terms of structural econ-omy, unity, diaphanousness and aesthetics, the lattersoundly emanating from the geometrical proportions.This was attained by designing the central vaults asalmost perfectly square in plan, by giving them someextra height (up to 32 m) and by supporting them onaustere but extremely slender octagonal piers (Fig. 1,above). The resulting construction includes four largevaults, spanning 13.5 m in both directions, supportedon 8 piers with circumscribed diameter of 1.6 m. Asin Barcelona Cathedral, the span of the lateral vaults

Figure 1. View of the interior of Santa Maria del Mar(above) and Mallorca Cathedral (below).

is half of that of the central ones, while the buttressesare used to separate the lateral chapels. The building iscompleted with the choir and the façade, whose struc-ture conforms to the uniform arrangement given to theperimeter of the naves. In particular, the façade is builtwith two large buttresses which are, in fact, needed tocounteract the longitudinal thrust produced by the firstsquare vault.

As opposite to Santa Maria del Mar, MallorcaCathedral was built over a large period, spanning for300 years (from 1306 to 1600), and was later sub-jected to significant repairs and reconstructions. Tosome extent, the structural design of Mallorca Cathe-dral seems inspired by Santa Maria del Mar and shareswith it major features, such as the search for spa-ciousness, the high lateral naves (although not sohigh as to take the role of flying arches), the lateralchapels between buttresses and the extremely slen-der, solid octagonal piers. However, and because ofthe large dimensions intended to the nave, the buildersalso resourced to structural devices commonly used inlarge Gothic buildings, such as the double battery oftrue flying arches spanning over the aisles. In a way,

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Figure 2. Arrangement of stone blocs in octagonal piers.

Figure 3. Diaphragmatic arches and dead weight over vaultsin Mallorca Cathedral.

the builders managed to synthesize Northern andSouthern Gothic architecture to produce a uniquelyvast and diaphanous inner space.

The central nave spans 19.9 m and reaches 43.9 mat the vaults’ keystone. The octagonal piers have a cir-cumscribed diameter of 1.6 or 1.7 m and a height of22.7 m to the springing of the lateral vaults.

Other shared features are the diaphragmatic trans-verse arches in the central naves and the dead weightlaid over the transverse arches and central vault key-stones. In Mallorca Cathedral, the latter become par-ticularly conspicuous (Fig. 3). Both constructions wereoriginally built with no pitched roof, rain water beingchanneled to the gargoyles by a tile pavement shapedover the vaults.

The filling over the vaults, however, is different inthe two buildings. In Santa Maria del Mar, the centralvault is partly filled with medieval concrete and thenwith a shallow layer of ceramic pottery (Fig. 4), whilethe central vaults are filled with medieval concrete upto the tile pavement. In Mallorca, a lightweight pot-tery fill was probably removed from the central vaultsduring 18th c., while the lateral vaults are still filledwith pottery. It is remarkable that these differences areconsistent with the distinct structural role of the lateralvaults in each case. In Santa Maria del Mar, the extraweight provided by the full concrete filling is needed

Figure 4. Pottery filling over the central vaults of SantaMaria del Mar.

to adequately counteract the horizontal thrust of thecentral nave.

3 HISTORICAL INFORMATION

Construction of Santa Maria del Mar church beganon March 25, 1329. It involved, in the first place,the formation of the full perimeter, including the but-tresses, chapels, lateral walls, choir and façade (Fig. 5),which were fully completed by 1350. There is evi-dence suggesting that this phase was followed by theconstruction of the arches, both the longitudinal (orclerestory) and transverse ones, and both at the lat-eral and central naves (Vendrell et al.). At this stage,a normal use of the building would have been pos-sible thanks to a provisory wooden roof supported onthe transverse arches. The construction was completedby building the vaulted roof on the already existingarches, starting, in each bay, with the lateral vaultmembranes and then the central one. The last stonewas placed on November 3, 1383. Remarkably, thisprocedure does not agree with the construction plan(supposedly) developed in most Gothic Cathedrals,which involved a gradual extension in the longitudinaldirection starting from the choir and finishing with themain façade. In fact, Barcelona and Mallorca Cathe-drals are known to have been built according to thislatter plan.

In 1379, when the last bay was almost com-pleted, a fire destroyed the scaffoldings and causedsome damage to the stone. Another fire, provoked in1936, caused significant damage to the piers, archesand vault keystones. Earthquakes are known to haveoccurred in several occasions, as in 1373, causingthe collapse of the upper body of one of the façadeclock-towers, and 1428, when the collapse of the rosewindow killed a number of people (Fontseré, 1971).

The building has also experienced damage duringbombardments against the city in1714, (during the

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Succession War) and the Spanish Civil War (1936–1939), among other episodes.

The architectural unity and the consistency of theconstruction process suggest that a fully developedproject should have been well established before 1329,when the construction began.At this moment, not eventhe choir of Barcelona Cathedral, frequently regardedas the immediate precedent, was finished.

Construction of Mallorca Cathedral began by year1300 starting with the presbytery (which comprises theso-called Trinity and Royal Chapels). According to themost widely accepted interpretation, by 1330 it wasdecided to build the remaining construction accordingto a three-nave plan and yet, by the mid of 14th c., it

Figure 5. Construction of Santa Maria del Mar. 1: founda-tion; 2: perimeter; 3: arches and vaults.

was decided to increase the height of the vaults. Theconstruction of the main nave developed during the restof 14th and 15th c (with a major interruption from 1460to 1570). The main façade, of noticeable Renaissancestyle, was built from 1594 to 1601, when the cathedralwas consecrated.

Research on the historical books has provided sig-nificant hints on the construction process. As shownin Fig. 6, the construction of the nave progressed,bay after bay, from the presbytery towards the façade(the last part to be built). Construction of the chapelswas ahead because of the funding provided by noblefamilies or corporations willing them as pantheons orgremial chapels (Domenge, 1997).

Figure 6. Construction stages of Mallorca Cathedral.

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It has been possible, at least for one of the bays(the 4th one), to identify the process leading to its com-plete construction (Fig. 7). Once again, it started withthe lateral chapels, followed by the piers, then one lat-eral vault, then the other and finally the central one.In the case of this bay, the construction of the vaultslasted 7 years. It should be noted that during a periodof about 5 years), the lateral vaults were already push-ing against the pier while the lateral vault was not yetthere to counteract their thrust.

The building has experienced significant prob-lems and repairs. The 4th vault (previously discussed)

Figure 7. Mallorca Cathedral’s 4th bay constructionsequence.

partially collapsed 30 years after its construction.A significant number of vaults were repaired or recon-structed during the 17th, 18th and 19th centuries. Dueto the concerning out-of-plumb (about 1.3 m), the orig-inal façade was taken down replaced by a new oneduring the second half of 19th c. Demolition wasdecided in March 1851 and hence was not connectedto the earthquake occurring in May the same year.

4 EXISTING DAMAGE

Four different types of alterations, visible in bothbuildings, are here highlighted and discussed:

1- Cracking in piers. Cracks exist in a few piersof Mallorca Cathedral and most piers of SantaMaria del Mar (Fig. 8). Vertical or oblique crackshave developed across the stone extending, insome cases, to several rows. They tend to concen-trate close to the corners of the octagonal section(the less confined parts) and, in some cases, shapefull wedges partially or totally detached from thecore of the pier. In the case of Santa Maria del Mar,the cracks are related to additional forms of dam-age (black patina and crusting, superficial loss ofstone and mortar at joints) which can be clearlyassociated with the severe fires experienced. Thereason for similar cracks in a few piers of Mallorca,randomly distributed, is less clear.2-Cracking in arches and vaults. In the lateral navesof Santa Maria del Mar, a longitudinal crack hasdeveloped following the keystones of the transversearches (Fig. 8, right). The longitudinal cracks in theaisles are due to a differential settlement betweenthe pier and the buttress. The arches do actuallyshow the deformation and damage which shouldbe expected from this type of settlement (Fig. 9,left). In a few cases, initial deformation appeared

Figure 8. Cracking in piers (Mallorca Cathedral, left, andSanta Maria del Mar, repaired, right).

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Figure 9. Aisle arches of Santa Maria del Mar. Deformationand cracking (left). Arch deformed due to accidental removalof centering causing expulsion of unhardened mortar (right).

due to an early or accidental removal of centering(Fig. 9, right) related, perhaps, to the fire of 1379.3-Cracking in walls and façade. Cracking, mostlydeveloped along the mortar joints, can be also rec-ognized in the exterior or clerestory walls. It can belinked to the out-of-plumbing experienced by thefaçade in the case of Mallorca Cathedral and thefaçade clock-towers in Santa Maria del Mar.4-Deformation. The deformation of the overallstructure is perceptible in Mallorca Cathedral. Thepiers show significant lateral deformation reaching,in some cases, up to 30 cm, i.e., 1/100 of height atthe springing of the lateral vaults. Remarkably, boththe magnitude and the shape of the deformationvary very significantly (almost randomly) amongthe different bays, or even between the two halvesof a single bay (Fig. 10). Conversely, the piers ofSanta Maria del Mar show a more regular patternboth in direction and value, with maximum valuesranging between 2 and 6 cm (8 cm in a single case),about 1/300 of the height at the springing of lateralvaults.

These deformations have been measured with respectto the ideal un-deformed geometry of the structure.For that purpose, the “ideal” profiles are reconstructedbased on the information on original geometric param-eters (radii, positions) which can be derived (orguessed) from the present geometry.All deviations dueto construction defects, positioning errors, deforma-tion of centering and plastic mortar settlement (amongother possible effects) are ignored. Because of it,real deformations cannot actually be determined andthe above measurements can only be understood asa coarse estimation. The possibility of the deforma-tions mentioned for Mallorca Cathedral being mostlya consequence of errors and hazards experienced dur-ing the construction cannot be disregarded. The sameapplies to possible soil settlements estimated as a

Figure 10. Deformation of the bays of Mallorca Cathedral.

difference between architecturally related vertical ref-erences (such as opposite imposts, capitals or archspringings), whose unevenness might be due, at leastin part, to construction inaccuracies.

5 CONSTRUCTION PROCESS AND DAMAGE

From a theoretical point of view, structures based onthe balance of arch thrusts, as Gothic cathedrals, attainfull stability only at their final and complete con-figuration. Moreover, adequate equilibrium requires(again, theoretically) the simultaneous activation ofall the arches and vaults by first building the entiresystem and then removing all the centering almostat once. This is not obviously the case of the build-ings discussed in this paper (as it is not either thecase of most similar constructions). Conversely, realconstruction processes involved intermediate stageswere equilibrium was reached only thanks to auxil-iary devices or, in a more hazardous way, by relying inthe capacity of the incomplete structure. The order inwhich the structural members were built was essentialto make the entire construction viable or to limit theconstruction difficulties.

The construction process has been, in no few cases,a hazardous phase contributing by itself to initial dam-age and deformation. Repairing this damage may havebeen possible during or after the construction. Cor-recting the deformation is difficult or impossible and,in most cases, it has stayed as a testimony of thisinitial phase.

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Nevertheless, Santa Maria del Mar was built fol-lowing a procedure which would ascertain, at anymoment, an easy balance of forces. First, the con-struction of the entire perimeter structure (includingbuttresses, walls, chapels along the choir, sides andfaçade) would provide a stiff system able to laterallybuttress the rest. Then, the construction of all longitu-dinal and transverse arches (of both central and lateralvaults) would provide the necessary lateral stabilityto the slender piers. The transverse and longitudinal(or clerestory) arches would also grant full stabilityduring the formation of the entire vaulted roof. In thelongitudinal direction, the stability was ultimately pro-vided by the choir and façade buttresses, already built.This is probably the reason why, yet at present, thepiers are showing such a limited drift in spite of theirslenderness.

The process, however, may have generated an incon-venient side effect. The construction of the vaultstook place about 30 years after the perimeter struc-ture had been built. As should be expected, the lateralstructure had by then already experienced most partof its possible soil settlement. Due to the settlementof the piers, the new members built across the aisle(arches and vault membranes) experienced a verticaldeformation (or differential settlement). The laterallongitudinal crack along the keystones of the trans-verse arches may have been caused by this effect. Infact, settlements may have been important during theconstruction because the foundation soil, composedof rubble and loose sand, is certainly deformable.However, a later significant increment of differen-tial settlements between lateral structure and piersseems unlikely because the rubble existing over thevaults (a sort of medieval lime concrete supposedlyplaced in a later stage but still during the construc-tion) does not show any crack in correspondence tothe one seen at the intrados of the vaults. More-over, the arches appear more damaged than the vaultmembrane, which does not either accompany theirsignificant deformation (figure 9, left); the only expla-nation is the later construction of the vaults (afterthe arches had been built) and the possible devel-opment of most the settlement while the material ofthe vault membranes was gradually placed on thearches, but yet with the possibility of correction oralmost free deformation while the mortar had not yethardened

As mentioned, the construction of Mallorca Cathe-dral followed a different path involving the subsequentconstruction of the bays. The lateral vaults were built(as in Santa Maria del Mar) before the construction ofthe central ones. In this case, historical research hasnot provided, so far, any hint on the way the structureswere stabilized while the central vault was not yet built(third stage of Fig. 7). Several possibilities, however,may be considered.

First, the lateral vaults could have been stabilizedby means of previously built transverse arches, as inSanta Maria del Mar. If so, the almost 20 m span archeswould have needed some stabilizing extra weight toresist the thrust of the lateral vaults without experi-encing inward deformation or collapse. Extra weightactually exists (Fig. 3), although its original purposemight be different. Second, they could have been sta-bilized by means of auxiliary devices such as steel ortimber ties across the lateral arches or struts acrossthe central one. Third, they could have been builtwithout any stabilizing element, the partial structurebeing (precariously) stable by itself thanks mainly toavailable tensile strength.

Whatever the method, there was some hazard andchance for damage and deformation. This is consis-tent with the fact that the lateral deformations at thepiers, as already mentioned, are very variable (almost“random”) although large in average, and suggeststhat the outcome was very sensitive to the skills andmethods used by the different builders. Moreover, dif-ferent approaches (as the three ones mentioned) mayhave been used during the certainly long and irregularconstruction process.

The longitudinal stability at intermediate stages iseven more challenging as the piers had to face theunbalanced longitudinal thrust of both the lateral andcentral vaults. According to the historical informationavailable, a previous construction of all the clerestoryarches (as a way to stabilize the bays at intermediatestages) should be clearly disregarded. The use of pos-sible temporary devices (temporary ties or buttressingwalls) appears as a likely possibility.

6 STRUCTURAL ANALYSIS

Structural analysis has been carried out using limitanalysis and non-linear FEM calculations. Previousresults concerning dead loading and seismic per-formance of Mallorca Cathedral have been alreadypresented (Clemente et al., 2006, Martínez et al, 2006,Martínez, 2008). The present discussion focuses onthe performance of the structures subjected to deadloading and the possible influence of the construc-tion process. The non-linear FEM analyses have beencarried out using a continuous damage constitutivemodel (Clemente et al. 2006). The material proper-ties have been estimated based on laboratory testson cores taken from the buildings or the originalquarries. The overall stiffness (value and distribution)was assessed by comparing experimental and numer-ical natural frequencies, the obtained from ambientvibration measurements (Martínez et al. 2006).

In the case of Santa Maria del Mar, the hole drillingtest was used to measure the average compressionstress at the base of two piers. The obtained value,

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Figure 11. Comparison of damage parameter for an instan-taneous analysis (above, deformation × 300) and a sequentialanalysis involving two stages (below, deformation × 50).

of 3,0 MPa, agreed very well with the correspondingnumerical prediction (2,9 MPa).

In order to take into consideration the constructionprocess, a sequential analysis can be carried out inwhich the changes experienced by the construction aresubsequently simulated and adequately superposed. Inthe case of Mallorca Cathedral, a tentative simulationof the construction process has been undertaken usingmodel of the typical nave bay (Clemente, 2007, andFig. 11). The third possibility mentioned in section 5(the partial structure being stable by itself) has beenanalyzed in detail by means of a sequential analysisinvolving the following steps: (1) Construction of thelateral nave (buttresses and lateral vaults) and (2) con-struction of the central vault. According to the FEManalysis (in which a small tensile strength is assumed),the stability of the partial structure generated in step(1) is possible, but at the cost of significant deforma-tion and certain damage. Compared to instantaneousanalysis, the final lateral deformation attained by thepiers increases by a factor of 2.5. In turn, additionaldamage appears in the upper part of the piers, lateralvaults and upper flying arches. This damage might beconnected to some cracks and deformation still visibletoday (as in the upper flying-arches), although most ofit may have been probably repaired during the con-struction itself. The constitutive model describes thisdamage as an scalar whose values range between “0”for intact and “1” for totally damaged material.

7 CONCLUSIONS

As shown by the two cases investigated, the con-struction process may have significant influence onthe initial condition of the structure. Some of thealterations (large deformation, damage) which can beobserved in historical buildings might be attributed,at least in some cases, to the hazards and difficultieslinked to intermediate construction phases.

As in the two examples presented, historicaldocuments may provide, in some cases, meaningfulinformation on the construction process. A detailedinspection may also provide important clues on theway the structure was constructed and the possiblehazards encountered by the builders. In turn, structuralanalysis may contribute with a better understanding ofthe structural significance and risks involved by theintermediate stages associated to incomplete or provi-sory configurations of the structure. For this purpose,a sequential analysis (in which the different stagesare subsequently simulated) is preferable to a moreconventional instantaneous analysis.

Later anthropogenic actions (accidental or inten-tional fires, architectural alterations, repairs) shouldalso deserve attention and should be always includedas part of the historical investigation. In fact, a signifi-cant part of the alterations which have been recognizedin the buildings discussed in this paper are linked to theconstruction process or to this second type of actions(as the fires experienced by the structure of SantaMaria del mar).

It turns out that some insight on the construc-tion process may be needed for an accurate structuralanalysis, while structural analysis itself constitutes apowerful tool to better understand the constructionprocess.

ACKNOWLEDGEMENTS

The studies of Santa Maria del Mar and MallorcaCathedral have been respectively funded by theGeneralitat de Catalunya and the Spanish Ministryof Culture. The assistance provided by the Parish ofSanta Maria del Mar and the Chapter of MallorcaCathedral are also gratefully acknowledged.

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Clemente, R., Roca, P., Cervera, M. 2006. Damagemodel with crack localization. Application to histor-ical buildings. 5th Int. Conf. of Structural Analysis

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