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Sustainableinterventions:Rehabilitationofoldtimberstructureswithtraditionalmaterials
TiagoIlharcoFacultyofEngineeringofPortoUniversity
[email protected]
InstituteofConstructionFacultyofEngineeringofPortoUniversitypauperio@fe.up.pt
JooGuedesFacultyofEngineeringofPortoUniversity
[email protected]
[email protected]
ABSTRACT
Theinterventioninbuiltheritageisawayofpreservingculturalidentity.Therefore,itdemandsspecialcareandsensibility.
Inparticular, therehabilitationofoldbuildingsconcernsnotonly
faades,butallthestructuralelements,namelyfloors,roofs,and
insidewalls,aspartofamoreglobalandconsistentheritage. However, most
of the interventions on old buildings consist in the substitution
of thestructuralelements
insteadoftheirrehabilitation.Thissituationresultsmostlyofa
lackofknowledgeandunderstandingoftheexistingmaterialsand(or)oftherehabilitation/strengtheningtechniques.Ingeneral,thepreservationofthestructuralelementsresultsinbenefits,notonlyintermsofheritagepreservation,butalso
intheminimizationofthe interventionsandtheir
impact.However,evenwhenthis strategy is followed, the
rehabilitation/strengthening techniques using traditionalmaterials
hasbeenoften ignoredand substitutedby
techniqueswhichusemodernmaterials,
frequentlyexpensiveandsometimeswithdoubtfulefficiency.Thissituation
isparticularlycommon
inoldtimberstructures,namelyroofsandfloors,whichexistallovertheWorld,insomecaseswithmanycenturies.Therefore,an
effort should be done to invert this situation i.e., to show the
community that it is possible
topreservetimberstructuresand,atthesametime,tousetraditionalmaterialsandtechniques,leadingtomoresustainedactions.Inordertopromotesustainable
interventions,contributingtoarealmaintenanceofthebuiltheritageand
respecting the International chartsand ICOMOS
(InternationalCouncilonMonumentsandSites)recommendations,NCREP (1)
(Nucleus for theConservation
andRehabilitationofBuildingsandBuiltHeritage,ateamwithinFEUPFacultyofEngineeringoftheUniversityofPorto)havebeenparticipatingin
many rehabilitation projects, analyzing the state of conservation
of buildings and
designingrehabilitationsolutions,inparticularusingtraditionalmaterials,likewoodandsteel.ThepresentpaperwillfocusNCREPexperienceintheinterventionofoldtimberstructures,namelyatRodriguesdeFreitasschool,ValadaresPalace,andValongoandCorpusChristichurches.
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1.
INTRODUCTIONMostofthebuildingsbuilttillthebeginningoftheXXcentury
inPortugal
ismadeofmasonry,mainlystone(exteriorandsomeinteriorwalls),andtimberelements(floors,roofs,ceilings,interiorandsomeexteriorwalls).
Ifproperlyconnected, theseelementspromoteagoodglobalbehaviour:
themasonrywalls support the floor beams and roof trusseswhich, on
the other hand, act as horizontal
braces,inducingamoreuniformdistributionofstiffnessandloadingthroughoutthestructure.Thus,ifproperlydesignedandingoodconditions,thesesystemsconstituteefficientstructures.Thistypeofconstructionisdisseminatedalloverthecountryandrepresentsmostofourbuiltheritage,justifyingthe
increasing intereston itspreservationasmemoryofcultureand
identity.Unfortunately,mostof it
isdegradedandabandoned,demandingurgent intervention.However, the
interventiononoldbuiltheritageisnotaconsensualissueandmayresultonlessconservativeapproaches.Inparticular,substituting
structuralelements insteadof rehabilitating
ithasbeenawidespreadpolicy that resultsmainly from the lack of
knowledge on thematerials and on the techniques and their
efficiency. Ingeneral, direct intervention on the elements,
avoiding substitutions, not only results on
heritagepreservation,but also on theminimization of the necessary
actions and their impact. Though, evenwhen this option is
considered, the intervener often prefers newmaterials, specially
polymers
andcomposites,sometimeswithhighercostsandnotalwayswithprovedefficiency,
insteadoftraditionalmaterials.In this field, and particularly for
old timber structures,NCREPs option has beenmostly oriented
totechniquesusingtraditionalmaterials,likewoodandsteel.Thesetechniques,consisting,forinstance,intheadditionoftimberelementsandsteelplates,havebeenappliedintherehabilitationofoldbuildingswith
very good results. Some exampleswill be analysed in this paper,
namely: Rodrigues de FreitasSchool (Porto, beginning of XX
century), Valadares Palace (Lisbon, reconstructed after the
1755earthquake),ValongoChurch(Valongo,XIXcentury)andCorpusChristiChurch(VilaNovadeGaia,XVIIcentury).At
thesametime,and inorder tosupport the interventions,acampaignof
laboratorial tests isbeingperformed inold
timberbeams,notonlytounderstand themechanicalbehaviourof
theseelements,butalso toassess theperformanceof techniques
involving theuseof traditionalmaterials,analysingtheir efficiency,
field of application, and evaluating advantages and disadvantages
in comparison toother techniques. The tests are being done in LESE
(Laboratory for Earthquake and
StructuralEngineering)ofFEUP,intimberbeamsremovedfromoldbuildingsfloorsthat,foranumberofdifferentreasons,wouldbedemolished.Theresultsobtainedwillbesharedwiththescientificcommunityattheendofthecampaignandwill,hopefully,contributetomoresustainedinterventionsandinaccordancetointernationalchartersandrecommendations.
2.
INTERVENTIONSINOLDTIMBERSTRUCTURESUSINGTRADITIONALMATERIALS
ThestructuralinterventionTheneed for the interventionon timber
structures isusually related to
theexistenceofdamagesoralterationsofusewith load increase.Between
themostcommondamages,onecanrefer thenaturalones
(knots,splits,etc.)and thoseresulting frombioticattacks (insectsand
fungi)and from incorrectconstructivedetailsor structural
interventions.These causesnotalwaysoriginate the collapseof
thestructuralelementsorstructures,butareoftenassociatedtotheirdeficientbehaviour,withhighlevelsofvibrationsanddeformations.Consequently,inordertoensurethesafetyand,atthesametime,the
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properperformanceofthestructures, it isnecessaryto intervene
inthedamagedstructuralelementsthroughrehabilitationactions.Thedecisionaboutthetypeofinterventionshouldbetakenonlyafterarigorousandcarefulsurveyofthe
structure (3).According to the results obtained in the survey and
to the circumstances of eachsituation, the intervention on a
particular element or structure can take two different
ways:Rehabilitation or Substitution. Rehabilitation can be seen as
the natural solution that allows themaintenance of the element or
the structure. This option may involve a strengthening
action,particularlywhentheoriginalstructuresare
improperlydesignedorwhenchangesofuse(withhigherloads)areexpected,demandingahigherstrength.Inalimitsituation,theinterventioncanconsistintheSubstitutionoftheelementorstructure,asolutionthatshouldbecarefullyanalysedtakingintoaccountthepercentageandintensityofthedamage.
ThechoiceofrehabilitationtechniquesThe rehabilitation of timber
structures can be done using different techniques,with pros and
consconcerningeffectiveness, compatibility, intrusiveness,etc.
Someof them imply theuseof traditionalmaterials, such aswood and
steel, andothers involve theuseofmore
innovativematerials,namelycomposites
(e.g.epoxy,FRPs).Theselectionof thebest techniquemust take
intoconsideration theparticularities of the construction, namely
the existence of constructive elements with
particularinterest,e.g.ceilingswithdecorativeelements,or the
increaseof loadoranycollateraleffect to thewalls, for instance.
Besides of that,when choosing the techniques andmaterials to use,
there are,amongothers, twocriteria linked toheritageprotection that
shouldbe
respected:CompatibilityandReversibility.Compatibilityislinkedtothephysicalandchemicalinteractionbetweentheexistingstructureandtheinterventionsolution.Inparticular,theelements,materialsand(or)techniquesimplementedshouldntreactwiththoseoftheexistingstructureorintroducehigherstiffnessinlocalizedstructuralareas.Thiscriterion
avoids the introduction of new damage in the structure through the
intervention. A goodexample of that are the glued or very rigid
connections in timber elements that may
induceconcentrationofstressesintheinterfacearea,i.e.theoccurrenceofnewdamage.Reversibilityislinkedtothewillthattheinterventionsbesubstitutablesothattheycangiveplacetomoreefficientand(or)protectiveinterventionsinthefuture.Generallyspeaking,thelessintrusivesolutionsareoftenthemorereversibleones.TheefforttakenbyNCREPintheuseanddevelopmentoftechniqueswithtraditionalmaterial,aswoodandsteel,isrelatedtotheabovementionedfactors.Ifcorrectlyanalysedandapplied,thesetechniquescanbeanexcellentsolution
to rehabilitation interventions inold timberstructures.As (4)
refers, theintervention shallbedone throughadetailedanalysisof the
techniquesand the
technologieswhichwereoriginallyusedintheconstruction.
TechniqueswithtraditionalmaterialsTherearemanydifferentwaysofusing
traditional rehabilitation techniques inold timber
structures,namely:(A)thefixationoftimberpiecesorthinsteelplates,withvariedconfigurations,tothesidesofthe
element (themostly used byNCREP in the interventions, as it can be
seen inpoint 3.); (B)
theintroductionofthinsteelplatesintheinterioroftheelement;(C)theinstallationofsteelbeltsaroundtheelement;
(D)the installationofnewstructuralelements
(timberorsteel)paralleltotheexistents,amongothers(5).To increase
knowledge on the efficiency of these techniques in order to give
useful information
todesignersandconstructorsaboutthesuitabilityofeachtechniquetosolvespecificsituations,NCREPisdevelopingalaboratorialtestingcampaign(seepoint4.).Asamatteroffact,theinformationrelatedto
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research on rehabilitation techniques on old timber structures
using traditional materials is quitelimited. For instance, in the
case of traditional carpentry joints, despite of being widely used,
thenumberofstudiesontheirmechanicalperformanceandonpossiblestrengtheningtechniquesisscarce.With
few exceptions, research on timber joints has been oriented towards
new engineeringconfigurations. Simultaneously, only few studies
were developed in elements subjected mainly
tobending;someauthorsperformedbendingtestsinbeamsreinforcedwithsteelelements,butreachingcontradictoryresults.Themajorityofthestudieswasdoneinelementswithhighaxialorshearforces.Strengthening
techniques on floors to improve the diaphragm behaviour have also
been analysed,proving experimentally its efficiency, but advising
that further refinement is still needed for
thetechnologytobeapplied
intheconstructionpractice(6).Concerningtheconnectionsbetweentimberstructures(roof,wallsandfloors)andmasonrywalls,althoughitisusuallyappointedasakeyelementtotheoverallbehaviourofabuilding(7),inparticularunderseismicevents,nosignificanteffortshavebeenspentontheirstudy.
3. INTERVENTIONSWITHTIMBERANDSTEELELEMENTS
IntroductionTheuseof timberelements in the rehabilitationofold
timber structures isaverycommon
solution.However,intheseinterventionsitsimportanttohavetimberelementsofthesamewoodspeciesandwithsimilarcharacteristics:density,strengthandstiffness,tothoseoftheoriginalstructure.(8)referstheconvenienceofusingoldtimberelements,withthedryingprocesscompleted,andtheimportanceof
having compatible moisture contents between new and old elements to
avoid physicalincompatibilities.When itsnotpossible toobtain
similarwood, timberelements retrieved from thedemolition of old
buildings can be used or, as alternative, the new elements, already
dry, can bepreviously placed in the constructionswhere theywill be
installed to acquire amoisture content
inequilibriumwiththeconstructionenvironment.On theotherhand,
solutionswith steelelementsarecommonlyused in interventionsonold
timberstructures,particularlyontimberfloors, leadingtoan
increaseofstrengthandstiffness.Eventhough,when using these
elements, two questions should be analysed: the compatibility with
the timberelements (the behaviour ofwood and steel is considerably
different) and the fire resistance of
themetallicelements.Infact,timberstructuressupporttemperaturesforwhichsteelstructureswouldhavealreadyfailed.Therefore,toavoidthesteelelementstobecometheweakestpointofthestrengthenedstructure
its important to improvement their fire resistance, which can be
done through physicalbarriers or fire retardant products.
Simultaneously, steel elements should be protected
againstcorrosion.ThefollowingsectionsdescribefourrehabilitationinterventionsofNCREPonoldtimberstructures:thefirsttwousingmainlytimberelementsandtheothertwousingmainlysteelelements.
RodriguesdeFreitasSchool,PortoThesurveyofthestructuresofRodriguesdeFreitasSchoolevidencedaprecariousstateofconservationof
the timber roofs, involving an area of about 4000m2. The choice of
the type of
interventionwascarefullyanalysed;theglobalsubstitutionwasanoption,althoughthepreferredsolutionwas,sincethebeginning,therehabilitationwith
localizedsubstitutionofstructuralelements.AdetailedstudyontheexistingstructuralelementswasperformedbyNCREP
todefine thephilosophyof the
intervention,namelytheapprovalandrejectioncriteria,allowingestimatingtheareaswhererehabilitationandsubstitutionswereexpected
(9).Thisstudyconfirmed that therehabilitationwas
thebestoptionandthefollowingtechniqueswererecommended:
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a)Additionofnewelementstothesidesofthedamagedelements
Thisoperationconsisted
inthefixationofnewtimberpiecesonbothsidesofthedamagedstructuralelements,withM16stainlesssteelthreadedrodswithhexagonalnutandbroadbrimmedwashers(toincrease
the tensiondistribution),endowing itofanhigher
inertia,Fig.1andFig.2.Thenew timberpieces had physical
andmechanical characteristics similar to the in situ elements
andwere
treatedagainstbioticattacks;thesteelrodsweresubmittedtoatreatmenttoincreasetheirfireresistance.
Existent timberelement
New timberelements(5cm thick)
Threadedrod M16
Damagedarea
Hexagonalnut M16
Broad-brimmedwashers
Fig.1Strengtheningofthedamagedstructuralelementswithtimberpieces.
Fig. 2 Strengthening of a damaged tie beam with
timberpieces.
b)Introductionofbracingelements
Theintroductionofnewtimberbracingelementswassuggestedtoreducethelengthofthecompressedelements(raftersandstruts),decreasingthepossibilityofbuckling.Thesenewbracingelementswereinstalledinbothsidesofthereinforcedelementandadequatelyscrewedtothebattensortotheridges,Fig.3andFig.4.
Fig.3 Introductionofbracingstoreducethebuckling
lengthofthecompressedelements(rafters).
Fig.4 Introductionofbracingstoreducethebuckling
lengthofthecompressedelements(struts).
c)Partialsubstitutionofthestructuralelements
Incertainsituationsitwasnecessarytosubstitute(globallyorpartially)thedamagedelementsbynewones.Whileinthecaseofthestrutsandridgesitwasconsideredconvenienttosubstitutethecompletelengthoftheelement,inthecaseofraftersandtiebeamsitwaspossibletosubstituteonlyapartofit,withtheconnectionbetweenthenewandtheexistentbeingdonewithnewtimberpiecesineachsideoftheelements,fixedwithM16threadedrodsandscrews,Fig.5andFig.6.
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Existentstrut
New timber element(section similar tothe existent one)
Screw M14
New timberelement 3cm thick
Existing timberelement
Threaded rod M16with hexagonal nutand broad-brimmedwashers
Fig.5Substitutionofapartofastructuralelement.
Fig.6Substitutionofapartofsecondarytiebeam.
ValadaresPalace,LisbonTheinterventioninValadaresPalaceconcernedtherehabilitationofthevaultedceilings,supportedbytimber
beamswith a length of approximately 8,0m. After the survey of these
beamswith the
nondestructiveequipmentcalledResistograph,itwaspossibletoconcludeabouttheintensedegradationofthebeamssupportsduetobioticattacks:insectsandfungi.Itwasalsonoticedaconsiderabledeflectionatthemidspanofthebeams(about20,0cm),causedbytheloadofaheavysupportsystemofalamplocated
at the top of themain stairs (10). Therefore it was recommended a
local intervention
torehabilitatethebeamssupportsandaglobalinterventiontocorrectthebeamsdeformations.a)Supportsrehabilitation
Therehabilitationofthetimberbeamssupportswasperformedthroughthefixation(withscrews),totheirsides,ofnewtimberelements.Thesenewelements,madeofthesamewoodspeciesoftheinsituelements,createdthenewsupportofthedamagedbeams
inthewalls.Afterwardsthenewelementswereconnectedtoamudsill
installedatthetopofthewall,toguaranteetheglobalbehaviourofthebuilding
and their correct connection to the stone masonry wall, Fig. 7 and
Fig. 8. The
damagedextremitiesofthebeamswerecutandtheremainingwoodwastreatedagainstbioticattacks,Fig.9.
Fig. 7 Strengthening of the
damagedstructuralelementswithtimberelements.
Fig.8Strengtheningofthedamagedstructuralelementswithtimberpiecesandasteelbracket.
Fig. 9 Cut of the damagedpartsofthebeams.
Ametallicbracket (L150x15)wasalso fixed to themasonrywall
through threaded rods (crossing
thewholethicknessofthewall)toimprovethebeamssupportsandtocontributetothewallstrengthening,particularlyinoutofplanactions,inaninterventionorientedtotheseismicprotectionofthebuilding,Fig.10.Allthenewtimberelementswerepreviouslytreatedinautoclavewithanantibioticproduct.Ontheotherhand,allthesteelelementsweresubmittedtoatreatmenttoincreasefireresistanceandto
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protect against corrosion. The structural design of the
fasteners respected the recommendations ofEurocode5(11).
Mortar
ScrewHBS6180(6mm)
Fig.10Strengtheningofthedamagedstructuralelementswithtimberpiecesandasteelbracket.
b)Deformationcorrection
Aftertherehabilitationofthesupportsandtheremovaloftheheavy
loadofthe lamp
fromthemidspanofthebeams,theexistingdeflectionwasremovedthroughoutasystemofsteelcables.Beforetherestorationoftheplasters,theceilingsupportwasalso
improvedwiththeuseofsmallthreadedrodsfixedtothetimberbeams,Fig.11andFig.12.
Fig.11
Improvementoftheceilingssupportwiththeuseofthreadedrods.
Fig. 12 Ceiling after the correction of the deformation
andrestorationoftheplaster.
ValongoChurch,ValongoThe testsperformedwith theResistograph in
the timber structural elementsof the roofofValongoChurch confirmed
thedeepdegradationof someof the tiebeamsof the trusses,with
lossesof
thetransversalsectionexceeding,insomecases,50%.Someotherstructuralproblemswerealsoobservedinthetrusses,namelythefactthatsomehangerswereloadingthetiebeams,theexistenceofdeficientconnectionsbetweenstructuralelements,theintensedegradationoftheraftersandridgessupportsinthemasonrywallsandthedeformationofthesteelelementsthatperformtheconnectionbetweenthetiebeamsandthewalls(12).Sincethesubstitutionoftheroofstructurewasntanoption,notonlybyitspatrimonialvalue,butalsobecauseofthetechnicaldifficultyandcostsassociatedtoaninterventionofthattype,thesolutionconsistedinlocalizedstructuralinterventions,asitisdescribedinthefollowingpoints.
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a)Tiebeamssupportrehabilitation
The supportsof the tiebeamswere rehabilitatedwith steel plates,
6mm thick, inboth sides of theelement, through threaded rods
(10mm),up toadistanceof1,0m from thewall toguarantee
theconnectiontothesoundpartofthewood,Fig.13.Thesteelplateswereintroducedinexistentopeningsatthemasonrywalls,thedamagedpartsofthewoodwereremovedandthesoundpartsweretreatedagainstbioticattacksandseparatedfromthesealingmaterialwithaleadsheet.
Threaded rodM8 // 0.15
Stonemasonrywall
0.95 1.05
Trussrafter
Stainless steelplate 10mm
Trusstie-beam
Fig.13Strengtheningofasupportofatiebeamwithsteelplatesandthreadedrods.
b)Repositioningoftheconnectionsbetweenstructuralelements
Theconnectionsbetweenthetrusseselementswerereinforcedwithsteelplates,traditionallyused
intheconstructionoftimbertrusses,Fig.14.
Fig.14Useoftraditionalsteelelementstoimprovetheconnectionbetweentimberelements.
c)Improvementoftheconnectionsbetweenraftersandtiebeams
Stretchedsteelcablesconnectingtheraftersofthetrusseswereplacedtoavoidtherafterstoslideonthetopofthetiebeams.Thesecablesactastiebeamsandcontributetotheproperfunctioningofthetrusses,Fig.15.
Fig.15Introductionofstretchedsteelcablestoconnectraftersoftrusses.
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d)Rehabilitationoftheconnectionsbetweenrafters/ridgesandwalls
Theconnectionsof the raftersand ridges to themasonrywallswere
reinforcedwithsteelplatesandthreadedrods,solutionsimilartotheoneusedwiththetiebeams,Fig.16.
Fig.16Strengtheningofthesupportsofrafters/ridgesandthemasonrywalls.
CorpusChristichurch,VilaNovadeGaiaThesurveyperformed
inCorpusChristichurchevidencedthe
intensedegradationofthetimberroofs(UpperChoirandApse),astheresultofbioticattacks(13).In
theUpperChoirsroof itwasobserved thewarpingofsome trusses
tiebeamsandraftersand
theruptureofsomeotherstructuralelements.Therehabilitationoftheroofinvolvedsomeparticularities,notlinkedtothedirectinterventiononthestructuralelements,butduetotheconstraintsassociatedtotheexistenceofawoodenceilingwithpaintedcoffersconnected
to the
trusses,Fig.17.Thisceiling,withhighpatrimonialvalue,wasrestoredinsituinordertoavoiditsdeterioration,factthatobligedthestructural
intervention to be developed by the upper side of the ceiling. The
care needed to
avoiddamagingthecoffersimpliedsomeadditionalprecautions,suchastheprotectionwithgeotextilesandthemaintenanceoftemporarystrutstosupporttheceiling.The
intervention in the roof consisted in the strengthening of the
structural elements showinginsufficient transversal section, mainly
in the supports, through the introduction of steel
platesconnectedtothesidesand,insomecases,tothebottomoftheelementsthroughthreadedrods,andfixed
to themasonrywalls,Fig.18andFig.19.Theconnectionsbetween
thesupportbeamsand theceilingswere reinforcedwith new timber
elements, inorder to avoid the ceiling to deform. In veryspecific
situations,new timber structuralelementswere introduced to
substitute thedamagedones,Fig.20.
Fig.17Existentwoodenceilingwithpaintedcoffers.
Fig.18Strengtheningof the supportsof ceilingbeamswith
steelplatesandthreadedrods.
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Fig.19Strengtheningofthesupportsoftiebeamswithsteelplatesandthreadedrods.
Fig.20Substitutionofarafterbyanewelement.
InthecaseoftheApsetimberroof,exclusivelyconstitutedbyraftersandwith
intensedegradation,
itwasobservedthecrackingofthesubjacentvaultedceiling.Asthesecrackscouldbestabilizedthroughanefficientbracingofthesupportmasonrywalls,itwasdecidedtocreateanewandstiffertimberroof,Fig.21andFig.22.Thisnewroofwasidenticaltotheoldone,butwithreinforcedconnectionsbetweenstructural
elements by means of traditional carpentry joints and steel
elements, Fig. 23, whichcontributedtoan
increaseofthetrussesstiffnessand,consequently,tothe
improvementofthewallsstructural behaviour.Additionally,
theconnectionbetween the rafters,and
themudsillandbetweenthisoneandthewalls,werereinforcedtomobilizetheglobalstructuralbehaviourofthebuilding.
Fig.21OriginalroofoftheApse. Fig.22NewtimberroofoftheApse. Fig.
23 Steel elements introduced to
increasethestiffnessoftheroof
4.
LABORATORIALTESTSINREALSIZESPECIMENSInordertosupporttheoptionstakeninoldbuildingsinterventions,acampaignoflaboratorialtestsinold
timber beams is being performed. This campaign aims not only
understanding
themechanicalbehaviouroftheelements,butalsoassessingtheperformanceofrehabilitationtechniquesinvolvingtheuseoftraditionalmaterials,suchaswoodandsteel,attesting
itsefficiency, itsfieldofapplicationandevaluating advantages and
disadvantages in comparison to other techniques. The campaign
focusmainlyontheexperimentalassessmentoftechniquesappliedto
fullscaletimberstructuresretrievedfromoldbuildingsinPortugal.Thetestsarecarriedoutaccordingto(2),withtheapplicationofaseriesofcyclesof
increasingdisplacementtothebeamsuptoa
levelofdisplacementbeyondthemaximumpeak load, Fig. 24. Displacement
transducers and a load cell measure the beam global and
localdeformationandtheappliedload.Thebeams,withaveragediametersandspansofabout0,20and4,0mrespectively,weretestedfirstintheiractualstatetoassesstheoriginalmechanicalcharacteristics,stiffness,strengthandfailuremodes.Afterwards,accordingtothefailuremode,differentrehabilitationtechniquesusingtraditionalmaterialswillbe
applied,namely the linkofnew timber elements to the existingones
throughwooddowels,
Substituted rafter
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screwsandtraditionaljointsandtheuseofinternalorexternalsteelconnectors/plates/belts.Then,thebeamswill
be tested again, following the same setup and loading conditions of
the first test. Thecomparison of the resultswill give a goodmeasure
of the techniques efficiency. The choice of
theinterventionprocedurewill depend on the conservation state and
on the behaviour of the
elementduringthetestpriortotheintervention.Thebehaviouroftheoriginalbeams(firsttest)waslinearelasticuntilafragilerupture,whichhadplaceathalfspan,nearknotsorotherdefectssituated
inthetensionedside,showingtheirstrongeffect inthe structural
behaviour of the timber elements, in particular in the bending
strength. This rupturehappened forvaluesclose to40,0kNand
forhalfspandisplacementsof60,0mm,Fig.24.Afterwards,the beams
responded with a small plastic plateau until higher displacements
(about 90,0mm),followedbyasecond sudden
ruptureandagradualdecreaseof strength.The loadingandunloadingcycles
were applied to the beams after the first rupture until maximum
displacements of
about130,0mm.Thefinalresidualdisplacementswereof70,0mm.Theaveragemechanicalpropertiesofthebeamswere
calculated according to EC5 (11) and are in the range of expected
values:modulus
ofelasticity,Em,g=7,5GPaandbendingstrength,fm=36,2MPa.Theresultofthemodulusofelasticitywasclosetothevaluesobtainedinaninsituloadtestperformedonbeamsofthesametimberfloor(5).
-505
1015202530354045
-10 10 30 50 70 90 110 130 150Displacement (mm)
Load
(kN
)
Beam VABeam VBBeam VC
Fig.24Testsontimberspecimensaccordingto(2)SetupandLoadvsdisplacementdiagrams.
Thetestingcampaignwillallowtheassessmentofthemechanicalcharacteristicsandbehaviourofrealstructures,inparticular:thebendingstiffness,strengthandfailuremodesofthebeams.Itwillbeshownthat
timber structures canbe rehabilitatedusing traditionalmaterials at
low cost, sustaining thenoneed for replacement under partial damage
conditions. Hopefully, the testswill confirm that
thesetechniquescanbeappliedwithsuccess,allowingmorecompatible
interventions,
inbetteragreementwithinternationalchartsandrecommendations.
5. CONCLUSIONSIn general, thepreservationof the structural
elements results inbenefits,notonly in termsofbuiltheritage
preservation, but also inminimization of the interventions and
their impact. Even though,when this strategy is followed, the
implementationof traditional rehabilitation techniques
hasbeencommonly passed over by techniques which usemodernmaterials,
frequently expensive and withdoubtful efficiency. This situation is
particularly common in old timber structures,namely roofs
andfloors,whichexistallovertheWorld,insomecaseswithmanycenturies.Therefore,aneffortshouldbedone
to change this situation i.e., to show the community that it is
possible to preserve
timberstructuresand,atthesametime,tousetraditionalmaterialsandtechniques,leadingtomoresustainedinterventions.Inthisfield,NCREPsoptionhasbeenmostlyorientedtotechniquesusingtraditionalmaterials,suchaswoodandsteel.Thesetechniquesconsist,forinstance,intheadditionofnewtimberelementsandsteel
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plates, and have been applied in the rehabilitation of old
buildings with very good results. Someexamplesaredescribed
inthispaper,namelywithRodriguesdeFreitasSchool,ValadaresPalace,andValongo
and Corpus Christi Churches. At the same time, a campaign of
laboratorial tests is
beingperformedinoldtimberbeamstoassesstheperformanceoftechniquesinvolvingtheuseoftraditionalmaterials,evaluatingadvantagesanddisadvantages
incomparison toother techniques.The testsarebeingdone inLESE
intimberbeamsremovedfromoldbuildingsfloorsthat,foranumberofdifferentreasons,wouldbedemolished.Theresultsobtainedwillbesharedwiththescientificcommunityintheendofthecampaign,andwillhopefullycontributetomoresustainableinterventionsandinaccordancetointernationalchartersandrecommendations.
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