Confusing cracks and difficult deformations: Interpreting structural damage in masonry

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SWrucWural Analysis of HisWorical ConsWrucWions – Jerzy Jasieńko (ed) © 2012 DPNH ProcławH PolandH ISSN 0860-2395H ISBN 978-83-7125-216-7

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Cracks and defçrmatiçns in masçnry are cçmmçn phençmena in histçrical buildings. ff they are interpreted cçrrectlyI they can be an extremely valuable sçurce çf infçrmatiçn çn the lçad histçry çf the premises. keverthelessI this interpretatiçn is nçt always as çbviçus as çne may think.

fn the framewçrk çf a mha research prçjectI an extensive literature review has resulted in an çverview çf SM characteristic damage patterns that can frequently be çbserved in traditiçnal masçnry buildings. ft appears that damages thatI at first glanceI lççk very similar and straightfçrward tç diagnçseI can result frçm very different causes. jçreçverI the research prçject has demçnstrated that specialists frçm the variçus disciplines within building pathçlçgy are nçt always aware çf these “lççkJalikes”. fn çrder tç prçvide an çptimal interventiçn strategy fçr a building with damageI a sçund diagnçsis is indispensable. qhis can çnly be achieved if all relevant hypçtheses are cçnsidered. qhis paper aims tç give architectsI cçntractçrs and engineers a helping hand in interpreting structural damage during visual inspectiçns. ft discusses the subsequent steps çf the diagnçstic prçcessI with their essences and pitfalls. qhe examples prçvided further illustrate what cracksI defçrmatiçns and tilts can tell çne abçut the cause çf damage – and what nçt.

heywords: ptructural damageI jasonryI aiagnosisI aecision support

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lld age cçmes with ailments – fçr peçple as well as fçr buildings. kçt surprisinglyI damage tç histçrical masçnry is a cçmmçn phençmençn. bspecially cracksI defçrmatiçns and tilts can attract attentiçn. qhe çbservatiçn çf these symptçms çf structural damage raises questiçnsW eçw seriçus is the situatiçn? And what shçuld be dçne abçut it? qç be able tç prçperly answer these questiçnsI insight is needed intç the underlying damage prçcesses. gust as in the medical fieldI a diagnçsis is prerequisite. rnfçrtunatelyI establishing a sçund diagnçsis is nçt always an easy task. aamages with different causes can sçmetimes shçw surprisingly similar visual characteristics. As a resultI çne may assume a case çf damage tç be due tç sçil settlementI while in reality the actiçn çf temperature variatiçns has been the malefactçr. ft is impçrtant always tç cçnsciçusly weigh all alternative hypçthesesW an incçrrect diagnçsis can quickly lead tç remedies that may be mçre harmful than the infirmities they were suppçsed tç treat. bspecially the first phase çf the diagnçstic prçcess çffers çppçrtunities fçr imprçvement. qhis is the phase in which hypçtheses are generated. ff in this phase pçssible causes are çverlççkedI chances are small that they will pçp up later çn. qherefçreI çne shçuld cçnsider as many relevant alternatives as pçssible early in the diagnçstic prçcessI in a cçnsciçus and careful way.

tithin the framewçrk çf a mha research prçjectI çver RMM cases çf damage described in literature have been analysed. Based çn this analysisI an çverview has been created çf SM characteristic damage patterns that can frequently be çbserved in traditiçnal masçnry buildings. bach çf these damage

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patterns has been linked tç its pçssible causes xNI Oz. qhis paper aims tç çffer a helping hand in cçnsistently interpreting cracksI defçrmatiçns and tilts. bach çf the steps çne passes thrçugh during a visual inspectiçn will be discussed in a separate sectiçnW

– fs this damage?

– that dçes the damage cçnsist çf? – that dçes the damage tell us?

– thich causes cçuld have led tç this type çf damage? – that dçes the cçntext çf the damage tell us?

– rsing time as a diagnçstic tççl – And then... intervening çr nçt?

At the end çf this paperI an example frçm practice will illustrate what damage can tell us abçut its cause – and what nçt!

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then damage is çbserved in a buildingI the very first step çne shçuld take is tç clçsely inspect this damage. ft is advisable tç cçnsciçusly ask çneselfW that is it that f see? fs this damage? fs this really a case tç diagnçse?

aamage in general is a sign çf underperfçrmanceI the manifestatiçn çf a defect. fn factI anything that dçes nçt meet sçmeçne’s expectatiçns çr demands can be cçnsidered as damage. Althçugh expectatiçns and demands can vary per persçnI fçr buildings sçme assumptiçns are cçmmçnly heldW

– bdges shçuld be straightI nçt curved; – Angles shçuld be rightI nçt acute çr çbtuse; – talls shçuld be verticalI nçt çutJçfJplumb; – talls shçuld be planeI nçt curved;

– clççrs and flat rççfs shçuld be levelI nçt slçped çr sagged.

jasçnryI and especially brick masçnry with its regular cçmpçsitiçn çf units and jçintsI çften renders a cçnvenient grid fçr checking whether a building meets these expectatiçns. aeviatiçns frçm abçve assumptiçns can be cçnsidered as damage.

ptillI it is nçt always cçrrect tç label each and every deviatiçn in shape as damage. fn sçme casesI it has actually been a deliberate design chçice. A leaning façadeI fçr instanceI may well have been purpçsely built with an inclinatiçn tç reduce rainwater ingress. Alsç repair wçrkI interventiçn jçints çr cçrrectiçns incçrpçrated during cçnstructiçn wçrks are prçne tç misinterpretatiçnsI see cigure N. At the start çf a diagnçstic prçcessI çne shçuld be careful tç avçid these pitfalls.

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aamage is çften cçmplexW it rarely presents in isçlatiçn. bspecially histçrical buildings usually suffer frçm mçre than çne defect. qhese defects may be cçrrelatedI but different damage prçcesses can alsç çccur parallel tç each çther. qç arrive at a cçrrect diagnçsisI it is impçrtant tç survey all damage in a structured way.

eenceI when the presence çf actual damage has been cçnfirmedI the next step is tç determine what the damage cçnsists çf. By decçmpçsing it intç separate characteristics – the symptçms – çne can cçme tç a clear and cçnsistent descriptiçn. qhis prçvides a sçlid base fçr the diagnçsis.

qhe three basic symptçms that will be discussed in this paper are cracksI defçrmatiçns and tilts. All three are characterized by displacements çr deviatiçns in shape caused by lçading. A crack is a lçcal gap between wall parts that mçve in çppçsite directiçns. aefçrmatiçns shçw displacements that are mçre unifçrmly distributedW a masçnry wall remains whçleI but may nçt be plane çr rightJangled anymçre. qiltI çn the çther handI invçlves a fullJbçdy rçtatiçn çf a building çr wing. qhe displacement then affects the structure as a whçle.

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then all damage symptçms have been described systematically – preferably bçth in images and wçrds – çne can prçceed with the next stepW interpreting the damage. rnfçrtunatelyI damage rarely

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gives direct indicatiçns abçut its cause. fn mçst casesI the çnly thing çne can immediately deduce frçm it is the directiçn çf lçading. qç understand whyI çne needs tç knçw hçw damage çccurs.

CracksI defçrmatiçns and tilts all develçp under lçading. A material çn which a lçad is impçsed will cçme under stress andI as a resultI will defçrm. pçme materialsI such as rubberI shçw large displacements even under relatively lçw lçads. cçr çther materialsI the defçrmatiçn due tç an impçsed

cigK N qhree examples in which assumed damage is nçt damage at all. crçm left tç rightW A marked jçint

resulting frçm an interventiçn may be misinterpreted as a crack; sçJcalled varkens tç cçrrect subsidence that apparently çccurred during the cçnstructiçn wçrks; and kink in a church tçwerI alsç used tç cçrrect settlement lçad is nçt even visible fçr an unaided eye – until the stress exceeds the strength çf the material and the material fails. At that pçintI a crack will develçp. jasçnryI natural stçne and cement shçw this latter type çf behaviçur. iimeJbased mçrtarI hçweverI has mçre capacity tç defçrm. Because çf thisI histçrical masçnry may accçmmçdate even cçnsiderable defçrmatiçns if slçwly applied.

qhere are many fçrces that can act in and çn buildingsW their çwn weightI the weight çf furniture and peçpleI but alsç windI snçwI sçlar radiatiçn and pressure frçm sçil and water. qç be able tç carry these lçadsI each building needs tç deliver reactiçn fçrces. qhis always invçlves defçrmatiçns çr cracks whichI as sççn as they gç beyçnd çur standardsI can be cçnsidered as damage.

eenceI what we label as damage in fact is the way in which a building accçmmçdates a certain lçad cçnditiçn. then establishing a diagnçsisI the main pçint is tç deduce frçm the symptçms çf damage the unknçwn cause. cçr each çf the three main symptçmsI we will list which characteristics may be çf help in dçing this. qhe starting pçint is always the çbserved displacement.

4KNK fnterpreting cracks

Cracks in masçnry çccur where tensile stresses exceed tensile strength. qhe directiçn çf a crack is always perpendicular tç that çf the tensile fçrce çrI tç be mçre preciseI the directiçn çf the maximum tensile stress. eçweverI as a result çf eccentricity çr bendingI pressure can alsç bring abçut tensile stresses. pince these tensile stresses çccur perpendicular tç the cçmpressive stressesI cracks due tç pressure appear parallel tç the applied lçad. qhe five basic types çf cracks are shçwn in cigure O.

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cigK P aisplacement çf wall parts çn either side çf a crackW inJplaneI perpendicular tç the directiçn çf the crack;

inJplaneI parallel tç the crack; and çutJçfJplaneI perpendicular tç the crack

cigure O demçnstrates that çne can infer the directiçn çf the principal stresses frçm the directiçn çf a crack. But alsç the displacement that becçmes apparent at a crack can give interesting infçrmatiçnI see cigure P. qhe directiçn in which wall parts çn either side çf a crack have mçved away frçm each çther gives insight intç the directiçn çf the impçsed lçading. mlease nçte that impçsed fçrce and reactiçn fçrce always act in cçuples. qherefçreI tç determine the directiçn çf the impçsed lçadI çne shçuld check which wall part has remained in placeI and which part has displaced.

qhe mçst telling characteristic çf a crack is its variatiçn in size çver length. qhis variatiçn can be determined by measuringI at different pçints alçng a crackI the distance between what used tç be adjacent pçints. A cçnstant crack size çver length indicates a translatiçnI a pure shift. qhis must have resulted frçm pure tensiçn. A crack that is widest at çne sideI çn the çther handI pçints tç a rçtatiçn andI henceI bending. And a crack that is widest halfway and tapers tçwards bçth ends is a sign fçr shearing. fn this wayI the tapering çf a crack can be used tç determine the type çf basic lçad as shçwn in cigure O.

Crack size in itself may seem a striking characteristicI tçç. keverthelessI viewed apart it has little diagnçstic value. At mçstI the size çf a crack shçws the magnitude çf the displacement that has çccurred. qç assess the tçtal displacementI hçweverI çne shçuld be sure tç cçnsider all cracksW a dçzen çf cracks çf N mm wide each pçints tç a larger displacement than a single çne çf R mm!

pummarisingI three characteristics are essential tç cçnsider when diagnçsing cracks. crçm the directiçn çf a crackI çne can deduce the directiçn çf the maximum tensile stress. Cçmbining this with the displacement çver the crack then helps tç determine the directiçn çf the impçsed lçading. And by using the tapering çf a crackI çne can infer the type çf basic lçad.

4KOK fnterpreting deformations

fn histçrical masçnryI apart frçm cracks çne typically finds defçrmatiçnsI tçç. qhis is due tç the use çf limeJbased mçrtarI which has sçme capacity tç defçrm. kewer masçnry with a cement mçrtar hardly has this capacityI if at all. pince defçrmatiçns will çnly çccur if they can grçw graduallyI this type çf damage pçints tç a lçngJterm lçading.

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aefçrmatiçns tend tç fçllçw the directiçn çf the impçsed lçadsI see cigure 4. As a resultI defçrmatiçns are relatively easy tç interpret. eçweverI there is çne exceptiçnW under large cçmpressiçnI relatively slender elements such as walls can becçme laterally unstable and bend çutJçfJplane. qhis is called buckling. fn these casesI the displacement çccurs perpendicular tç the directiçn çf lçading.

qhe abçve makes clear thatI fçr diagnçsingI the mçst impçrtant characteristic çf a defçrmatiçn is the directiçn çf the displacement. lne can discern between defçrmatiçns inJplane and çutJçfJplane. qhe fçrmer refers tç defçrmatiçns in which the wall is still planeI but nçt at right angles anymçre. An example is shçwn in cigure R EleftF. lutJçfJplane defçrmatiçns çften çnly catch the eye under çblique lightingI see cigure R ErightF. qhey can be typified by either inward çr çutward mçvements.

4KPK fnterpreting tilts

qilt is the rçtatiçn çf a building çr wing as a whçleI withçut cracks çr defçrmatiçnsI see cigure S. qhe cause almçst always lies in the interactiçn between building and subsçilW the building seems tç have lçst its balance. plenderI tall buildings such as tçwers are mçst vulnerable tç tiltI since they cçmbine a relatively high lçad with a small base area. keverthelessI alsç lighterI freeJstanding structuresI such as garden wallsI can start tç leanI fçr example under the lateral fçrce çf windI the push çf retained earth çr the push çf tree rççts.

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pymptçms çf damage can çffer insight intç the directiçns çf the fçrces that have acted çn a building. qhis is still rather abstract. qhe next stepI therefçreI is tç translate these abstract fçrces intç cçncrete causes. qç dç thisI çne needs tç be aware çfI and understandI the different types çf lçads that can lead tç cracksI defçrmatiçns and tilts in masçnry.

cigK R aisplacement inJplane EleftFI presenting itself with bed jçints that are nç lçnger hçrizçntal; and displacement

çutJçfJplane ErightFI which is revealed by çblique lighting

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te distinguish between three types çf prçcessesW sçil mçvementsI çverlçading and hindered dimensiçnal changes. bach çf these prçcesses takes place at a different scale level. pçil mçvements are abçut the interactiçn between buildingI fçundatiçns and subsçil. lverlçading cçncerns the way lçads are transferred and balanced within a building. And hindered dimensiçnal changes take place at the level çf the building elementI fçr example at the cçnnectiçn between twç materials.

All lçads that act çn a buildingI ranging frçm thermal expansiçn tç the weight çf a filing cabinetI shçuld be carried by the structure andI eventuallyI transferred tç the subsçil. then in equilibriumI all lçads and reactiçn fçrces are in balance. aamage can çccur when this equilibrium is disturbedW as a result çf changes in space çr in timeI a building is fçrced tç adapt tç mçdified cçnditiçns. fn the fçllçwing sectiçnsI we will discuss fçr each çf the three basic prçcesses the situatiçns that may invçlve such changes.

RKNK poil movement

bvery building eventually transfers all lçads impçsed çn it tç the subsçil. qhis leads tç sçme cçmpressiçn çf the sçil under the buildingW the sçil settles. qhe building that stands çn this sçil has nç chçice but tç fçllçw this sçil mçvement.

fdeallyI a building is carried by the sçil in a unifçrm wayW buildingI fçundatiçns and sçil are in balance. Changes in çne çf these three actçrsI hçweverI can lead tç sçil mçvement. bspecially when this dçes nçt çccur in a unifçrm wayI damage may be the result. qypical cases areW

– A nçnJunifçrm lçadI impçsed by the building çn the sçilI fçr example a difference in weight between tçwer and nave çf a church;

– A nçnJunifçrm fçundatiçnI fçr example a hçuse built çn piles with an extensiçn built çn shallçw fçundatiçns;

– A nçnJunifçrm sçil cçmpçsitiçnI fçr example a lçcal filled ditch çr a peat lens.

lf cçurseI such a nçnJunifçrmity dçes nçt necessarily lead tç damageI as lçng as it has been taken intç accçunt during the cçnstructiçn. lne mayI fçr instanceI prçvide a church tçwer with strçngerI deeper fçundatiçns than the rest çf the churchI çr keep tçwer and church separated. eçweverI if such measures are nçt prçvidedI a crack can çccur between the twç building parts.

pummarisingI nçnJunifçrm sçil mçvements can be evçked by differences çr changes in the weight çf a buildingI in its fçundatiçns çr in the subsçil. qypical fçr this damage prçcess is that the fçrce is applied at the underside çf a building. eçweverI this dçes nçt mean that the displacement is alsç largest at the bçttçm side.

RKOK lverloading

lverlçading is abçut balance between building parts. qhe structure çf a building needs tç carry all kinds çf lçads and transfer these tç the fçundatiçns and further dçwn tç the subsçil. cçrces will always travel alçng the path that is mçst resistantW weaker elements will simply fail çr bend awayI leaving the lçad nç çther çptiçn than tç fçllçw the stiffest rçute. aamage due tç çverlçading çccurs where çne çf elements alçng the lçad path is nçt capable çf resisting its share çf the burden.

jany çf the lçads that act çn a building were taken intç accçunt at the time çf cçnstructiçnI fçr example wind. lthers may nçt have been anticipated EexplçsiçnFI çr turned çut tç be larger than expected Eincreased use lçadF. ft is alsç pçssible that a structure has been changed çr weakened çver time tç such an extent that it is nç lçnger capable çf carrying the lçads it used tç carry. A wellJknçwn example is the sçJcalled plumber’s çr electrician’s rçtI in which the lçadbearing functiçn çf beams is impaired by nçtching tç make way fçr the installatiçn çf services. Alsç illJcçnsidered remçval çf walls çr tie beams can lead tç çverlçading and damage. As a resultI çne can state that damage due tç çverlçading can result frçmW

– A change in lçading; – A change in lçad path; çr

– A change in the resistance Elçadbearing capacityF çf the building cçmpçnent.

ft is useful tç discern the variçus lçads çn the basis çf the directiçn in which they act. teightI fçr exampleI usually results in a verticalI dçwnward fçrce. oççf trusses and vaultsI hçweverI alsç bring abçut hçrizçntal thrust fçrces. Ançther pçint is that relatively slender building elementsI such as halfJ brick cavity wallsI may fail laterally under a vertical lçadI and bend çutJçfJplane. eenceI while fçrmulating hypçthesesI çne shçuld pay particular attentiçn tç geçmetrical aspects such as the cçherence between building elements.

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RKPK eindered dimensional changes

Alsç within building elementsI fçrces act. aimensiçnal changes generally çccur as a result çfW – Changes in temperature çr mçisture cçntent;

– Cçrrçsiçn çf irçn incçrpçrated in the masçnry;

– crçstI i.e. the fçrmatiçn çf ice crystals within the masçnry; çr – paltsI the fçrmatiçn çf salt crystals within the masçnry.

there such dimensiçnal changes cannçt be accçmmçdated sufficientlyI damage may çccur.

aamage due tç hindered dimensiçnal changes develçps at the scale level çf the building cçmpçnent. qhe classic lçcatiçn is at çr near the cçnnectiçn between twç materials. Alsç the influence çf climate is impçrtantI fçr instance the effect çf temperature changes çr the expçsure tç precipitatiçn.

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ft is clear that the cçntext plays a crucial rçle in all three types çf causes. cçr sçil mçvementI the material cçmpçsitiçn çf the sçil is impçrtantI but alsç the geçmetry çf the fçundatiçns and the geçmetry çf the building itself. cçr çverlçadingI it is essential tç understand the geçmetry çf the lçad pathW hçw dç the different structural elements cççperate and transfer lçads frçm çne tç ançther? eindered dimensiçnal changes are strçngly dçminated by material prçpertiesI next tç the influence çf temperature and mçisture.

then the fçrces deduced frçm a damage pattern have been translated intç pçssible causesI it is time tç falsify these hypçtheses. fn dçing sçI çne may take advantage çf the rçle that cçntext plays in abçve damage prçcesses. By analysing the lçcatiçn çf damage in terms çf materialI geçmetry and envirçnmentI it will becçme clear which prçcesses may çr may nçt have taken place.

SKNK Material

As regards the influence çf materialI çne shçuld first çf all cçnsider the type çf masçnry. Certain types çf unit areI fçr exampleI mçre susceptible tç frçst actiçn than çthers. qhe cçmbinatiçn çf materials may pçint tç differences in dimensiçnal changes. Cçncrete and wççdI fçr instanceI typically have higher thermal expansiçn cçefficients than masçnry. qhe presence çf an irçn anchçrI çn the çther handI can be an indicatiçn that cçrrçsiçn may be invçlved.

SKOK deometry

qhe geçmetry çf a structural element prçvides insight intç its preferred lçadbearing behaviçur. fn this wayI the lçcatiçn çf damage within a structure can give a decisive answer çn whether certain hypçtheses are valid çr nçt. eçrizçntal thrustI fçr exampleI is tç be expected near the springings çf archesI vaults çr rççf trusses. kear wall çpenings and belçw beamsI çn the çther handI çne shçuld anticipate stress cçncentratiçns. And within archesI the pçsitiçn çf cracks allçws çne tç deduce the directiçn çf lçadingI see cigure T.

SKPK Environment

cçr sçil mçvementI the mçst essential cçntext factçr is the subsçil. qhe presence çf weak sçils belçw part çf a building may be an explanatiçn fçr EsettlementJF cracks. Ançther significant envirçnmental factçr is climate. jçistureI fçr exampleI is a necessary cçnditiçn fçr the çccurrence çf frçstJ and salt damage. cinallyI interventiçns and events in the envirçnment çf a buildingI such as earthquakesI explçsiçns çr large cçnstructiçn wçrksI may have triggered the develçpment çf damage.

fmpçrtant pçint tç recçgnize is that it is the absence rather than the presence çf a cçnditiçn that allçws çne tç falsify a hypçthesisI nçt its presence. As a resultI establishing a diagnçsis is abçve all a matter çf crçssing çff pçssibilities. ln the basis çf a visual inspectiçn alçneI çne can hardly expect tç end up with a cçmpleted diagnçsis. eçweverI a sçund list çf hypçtheses dçes allçw çne tç better target further research.

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qime can be used in different ways during the diagnçstic prçcess. cirst çf allI it can be used tç link the first çccurrence çf damage tç a specific incident. qhe questiçn isI hçweverI if the damage indeed was

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nçt present befçre the incident çccurred. pince damage çften çnly attracts attentiçn when çne is lççking fçr itI this cçincidence is usually hard tç determine.

jçreçverI abçve reasçning can çnly be used effectively if the cause has a clear begin and endI as is the case with earthquakes çr building rençvatiçn wçrks. But alsç fçr damage prçcesses that develçp in a mçre gradual wayI time can play an impçrtant rçle in diagnçsing. By mçnitçring the increase in damage in timeI çne may be able tç link it tç the develçpment çf a damage prçcess. qç discern seasçnal fluctuatiçnsI measurements shçuld preferably extend çver mçre than çne year.

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then the cause çf damage is knçwn with sçme certaintyI it is time tç think abçut measures. cirst and fçremçstI it is impçrtant tç determine whether the damage prçcess is still cçntinuingI and the damage

cigK T crçm the lçcatiçn çf cracks in arches çne can deduce pçsitiçn and directiçn çf the impçsed lçad

is still increasing. jçnitçring can prçvide a cçnclusive answer in this. fnterventiçn shçuld then be aimed at halting the prçcessI preferably as clçse tç its sçurce as pçssible.

pçmetimes it is nçt feasible tç cçmpletely remçve the sçurce. qhis isI fçr exampleI the case with thermal actiçn. An alternative isI thenI tç take measures tç keep the damage at an acceptable level. By creating mçvement jçintsI fçr exampleI çne can make sure that mçvement cçncentrates at a certain chçsen lçcatiçn. A better sçlutiçn may even be tç accept that an existing crack will always keep shçwing sçme mçvement. aetermining the çriginal cause çf a crack then at least takes away any cçncern çr uneasiness.

aamage that is stable and dçes nçt increase can be repaired. keverthelessI çne shçuld realize that it will always remain a weak spçt. Chances are that new damage will tend tç cçncentrate at the same lçcatiçn – çr at the cçnnectiçn between repair wçrk and çriginal masçnry. fn this wayI ançther pitfall is created fçr new investigatiçnsW is it damageI çr repair wçrk?

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qç further illustrate the diagnçstic prçcessI we will pass thrçugh the subsequent steps by discussing an example frçm practice. qhe building is a histçrical premises in ieidenI the ketherlandsI see cigure U. ft shçws a number çf different damage symptçms.

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cigK V aisplacement çutJçfJplane halfway the height çf a wall

At the far leftI the façade shçws a defçrmatiçnI çf which a clçseJup has been reprçduced in cigure V. qhe damage can be described as a defçrmatiçn çutJçfJplaneI directed çutward. qhis type çf displacement may be caused by a hçrizçntal fçrce in çutward directiçnI with its pçint çf applicatiçn at the level çf the maximum displacement. eçweverI the defçrmatiçn cçuld alsç be the result çf bulging çf the façadeI due tç a vertical cçmpressive lçad.

qhe causes that cçuld be linked tç this çutJçfJplane defçrmatiçn can partly be deduced frçm the cçntext çf the damage. qhe anchçrs in the wall indicateI tçgether with the pçsitiçn çf the windçwsI that there prçbably is a flççr at the level çf maximum displacement. A hçrizçntal fçrce might result frçm cçrrçding anchçrsI çr perhaps frçm bending çf the flççr that fçrces the façade tç bendI tçç. qhese statementsI hçweverI dç nçt fully exclude the pçssibility that the façade as a whçle has defçrmed due tç bulgingW maybe a beam incçrpçrated intç the wall had been replacedI tempçrarily weakening the sectiçn. lr the anchçrs were insufficient tç prevent the façade frçm bending çutwards under its lçad? curther investigatiçns çn the inside çf the building shçuld address these hypçtheses.

cigK NM aiagçnal cracksI each pair fçrming an archI spanning windçw çpenings

cigK NN aefçrmatiçn inJplaneI halfway the height çf a wall. qhe masçnry belçw dçes nçt shçw any defçrmatiçnI

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Abçve the windçw çpenings there are diagçnal cracks. bach pair çf cracks fçrms an arch that spans the çpeningsI see cigure NM. qhe displacement alçng the cracks pçints çut that the part belçw the archJ like cracks has mçved dçwnward with respect tç the wall parts çn either side. oegarding the cçntextI especially the pçsitiçn çf the windçw çpenings catches the eye. qhe masçnry abçve the upper windçws is suppçrted by a rather narrçw wall pier. qhis pierI in turnI rests right çn the centre çf çne çf the windçws çf the stçrey belçw. tçuld the lintel abçve that lçwer windçw be stiff ençugh tç resist this pçint lçad? then the lintel bendsI and the masçnry abçve it settles a bitI the pier shall have tç fçllçw this displacement and a archJlike crack can çccur abçve the windçws at the secçnd flççrI tçç. At the first flççr cçrnerI the masçnry shçws an inJplane defçrmatiçnI see cigure NN. qhe hçrizçntal bed jçints slçpe dçwn tçwards the cçrner. qhis can be an indicatiçn çf gradual dçwnward mçvement çf this cçrner çrI less prçbableI an upward mçvement çf the left part çf the building.

qhe mçst likely cause çf this defçrmatiçn is settlement çf the cçrner çf the premises. oemarkable isI hçweverI that the masçnry belçw the white cçrnice dçes nçt shçw any defçrmatiçn at all. qhis masçnry alsç seems tç be newer than the defçrmed wall abçve it. eas the grçund flççr façade been renewed? qhis wçuld lead us tç an alternative hypçthesisW maybe there çnce was a shçp windçw at the grçund flççrI with a cçlumn at the cçrner as the çnly lçadbearing element. qhe cçncentrated lçad frçm the upper flççrs çn this cçlumn cçuld have led tç lçcal settlement – çr tç çverlçading and buckling çf the cçlumn. Bçth mechanisms cçuld explain the vertical displacement çf the masçnry çf the upper flççr. Archive investigatiçns and sçil surveys may help verifying these hypçtheses. keverthelessI frçm the fact that the renewed masçnry çn the grçund flççr dçes nçt shçw any sign çf damageI we may cçnclude that the damage prçcess has cçme tç an end already. jeasures in this directiçn are nçt necessary anymçre.

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aiagnçsing damage in masçnry can be a tçugh jçb. qhis is partly because damage in general tells çne less that çne may hçpe fçr. martly it is due tç the fact that peçple have a tendency tç jump tç cçnclusiçns. fn this paperI several pitfalls that are inherent tç diagnçsing have been discussed. curthermçreI we have indicated what damage can tell us abçut its cause – and what nçt.

qhis paper intends tç çffer a helping hand fçr interpreting cracksI defçrmatiçns and tilts in masçnry. As suchI it can be seen as an intrçductiçn tç the diagnçstic tççl that has been develçped by the first authçr xOz. qhis tççlI which is available fçr dçwnlçad via the repçsitçry çf aelft rniversity çf qechnçlçgyI encçmpasses SM characteristic damage patterns alçng with their pçssible causes. ft aims tç assist users in reading structural damages in a cçnsistent wayI and in keeping an çverview çf alternative causes. fn this wayI an unambiguçus diagnçsis çf damage in masçnry will be suppçrted. mlans are tç further develçp the diagnçstic tççl and perhaps set up a digital versiçn. qhe authçrs welcçme feedback and çppçrtunities fçr cççperatiçn.

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xNz sentI f.A.b. de EOMNNF ptructural damage in masonryI developing diagnostic decision support. aelft. Available fçr dçwnlçad at httpWLLrepçsitçry.tudelft.nlLviewLirLuuidWcedMUaaOJcOeUJ4aaUJ VRRVJUTMbfNOdRbaRL

xOz sentI f.A.b. de EOMNNF mrototype of a diagnostic decision support tool for structural damage in masonry. aelft. Available fçr dçwnlçad at httpWLLrepçsitçry.tudelft.nlLviewLirLuuidWeVaPaOfVJ NSbRJ4bOOJaNf4JSRNNfPR4PfSeL

All illustratiçns © f.A.b. de sent.

A autch versiçn çf this paper has been published in the prçceedings çf the ‘eistçrical masçnry’ cçnference çf the autch oijksdienst voor het Cultureel brfgoed Eketherlands Cultural eeritage AgencyFI lctçber OMNO.