effects of extreme climatic conditions

Bogdan Isopescu

Analysis of the behaviour of traditional carpentry joints - effects of extreme climatic conditions

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Czech Technical University in Prague

16

Bogdan Isopescu


2016

ii


Erasmus Mundus ProgrammeADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS

DECLARATION

Name: Bogdan Isopescu

E-mail: [email protected]

Title of the Msc Dissertation: Analysis of the behaviour of traditional joints- effectsofextremeclimaticconditions

Supervisor(s): Graça Vasconcelos Elisa Poletti

Year: 2016

I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work.

I hereby declare that the MSc Consortium responsible for the Advanced Masters in Structural Analysis of Monuments and Historical Constructions is allowed to store and make available electronically the present MSc Dissertation.

University of Minho

28th July 2016

GSPublisherEngine 0.80.100.100

ACKNOWLEDGMENTS:

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS iii

ACKNOWLEDGMENTS:

I would like to thank my supervisors, Professor Graça Vasconcelos and Dr. Elisa Poletti, for their

support, suggestions and patience. Also I would like to thank Mr. Jorge Branco for the advice and tips given

forcarryingoutthisexperiment.

I owe a lot of thanks to Mr. Carlos Palha for all the help given with the preparation of the software and

hardware for the monitoring procedures.

I would also like to thank Mr. António Matos for lending me a helping hand in the laboratory.

And,lastbutnotleast,IwouldliketothankRothoblaasforsponsoringtheexperimentbyproviding

the screws and steel plates for the reinforcements.

iv



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ABSTRACT:

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS v

ABSTRACT:

Timber frame architecture is an important part of European cultural heritage and is very common

across the continent, as well as in other parts of the world. However, Europe’s cultural heritage is being

lost not only because of natural decay and human interventions but also as a consequence of climate

change and natural hazards. Considering the climatic changes occurring in Europe and around the world,

itisimportanttounderstandbetterthebehaviouroftimberstructuressubjectedtoextremeclimaticactions

(suchasfloodsandexposuretoperiodicheavyrains)sincegreatalterationsinmoisturecontent,dueto

prolonged wetting, will lead to a reduction in the mechanical properties of the building. To preserve Europe’s

heritageitisimportanttounderstandtheinfluenceofsuchactions,particularlysinceclimaticchangesled

toanincreaseintheoccurrenceandintensityofextremeweatherevents.

Timber joints significantly affect the mechanical performances of timber frame buildings, being

theweakest points in the structure, and theyeffectively control their response, as they constitute their

maindissipativeelements.Agreat variability exists in termsof typesof connectionsandmechanisms.

Traditionally, timber frame buildings in Portugal (Pombalino buildings) mainly adopted half lap joints for the

main connections of the walls (frontal walls).

A comprehensive experimental campaignwas carried out at the Laboratory of Structures at the

University of Minho (Portugal) to investigate the cyclic response of unreinforced and reinforced traditional

halflapjointsafterbeingsubjectedtosimulatedextremeweatherconditionssuchasfloodandwinddriven

rain cycles.

The results of the pull-out test on the weathered connections were compared to the results obtained on

soundsamplesinordertoassesstheextentinwhichextremeweatherconditionsinfluencethemechanical

characteristics of the connection, the damage patterns resulted and the overall behaviour of the timber

connection.

vi




RESUMO:

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS vii

RESUMO:

As estruturas tradicionais em madeira constituem uma parte importante do património cultural e

construído em toda a Europa, sendo também muito frequente em outros países do mundo. Todavia, o

património cultural europeu tem vindo a sofrer algumas perdas, não apenas por causa de intervenções

humanas e envelhecimento natural, mas também como uma consequência das alterações climáticas e

eventosextremos.

Considerando as alterações climáticas que ocorrem atualmente na Europa e em todo o mundo,

torna-se importante compreender o comportamento de estruturas de madeira tradicionais submetidas a

condiçõesclimáticasextremas(talcomo inundaçõeseexposiçãoa longosperíodosdechuvaeseca),

dado que alterações na humidade, devido a ambientes húmidos e ambientes muito secos, potencialmente

conduzem à redução das propriedades mecânicas das estruturas de madeira.

Assim, para preservar o património construído ao nível europeu, é importante compreender a in-

fluênciadascondiçõesclimáticaseasuavariaçãonocomportamentoestruturaldasestruturasdema-

deira,dadoqueasalteraçõesclimáticassetêmtraduzidoemeventosclimáticosextremossempremais

frequentes e com maior intensidade.

Dado que o comportamento mecânico das estruturas de madeira tradicionais é muito dependente

do desempenho das ligações, dado que estas concentram a capacidade de deformação e dissipação de

energia, é importante obter mais conhecimento no que respeita ao comportamento destas quando sujeitas

acondiçõesambientaisvaráveis.Existeumagrandevariabilidadedeligaçõestradicionais.Asestruturas

de madeira utilizadas nos edifícios pombalinos (paredes de frontal) apresentam frequentemente ligações

meia-madeira.

Nestecontexto,estetrabalhotevecomoobjetivocentraloestudoexperimentaldeligaçõestradi-

cionais de madeira para analisar o comportamento cíclico a esforços de tração após estas terem sido

submetidasaciclosdemolhagemesecagem(simulaçãodeperíodosextremosdechuva)eàsituaçãode

inundação.

Os resultados obtidos nos ensaios de tração cíclica das ligações submetidas a condições ambien-

taisextremasforamcomparadascomosresultadosobtidospreviamenteemligaçõessujeitasacondições

ambientais normais com o objetivo de avaliar o efeito das condições ambientais na resistência, rigidez e

modos de rotura.

viii




REZUMAT:

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS ix

REZUMAT:

Arhitecturapestructurădelemnesteoparteimportantăapatrimoniuluiculturaleuropeanșieste

utilizată pe întregul continentul, precumși în alte părți ale lumii.Cu toate acestea, patrimoniul cultural

alEuropeisepierdenunumaidincauzadegradărilornaturaleșia intervențiilorumane,cișidincauza

schimbărilorclimaticeșiapericolelornaturale.

AvândînvedereschimbărileclimaticecareaulocînEuropașiînîntreagalume,esteimportantsă

secunoascămaibinecomportamentulstructurilordin lemnsupuseunoracțiuniclimaticeextreme(cum

ar fi inundațiile și expunerea la ploi abundenteperiodice), deoarecemarimodificări ale conținutului de

umiditate,dincauzaumeziriiprelungite,vorducelaoreducereaproprietățilormecanicealeclădirii.

PentruaprotejapatrimoniulEuropeiesteimportantsăînțelegeminfluențaunorastfeldeacțiuni,în

specialdeoareceschimbărileclimaticeauduslaocreștereaintensitățiișifrecvențeiaparițieicondițiilor

meteorologiceextreme.

Îmbinăriledelemnafecteazăînmodsemnificativperformanțelemecanicealeclădirilorpestructură

delemn,fiindcelemaislabepunctedinstructurășielecontroleazăînmodeficientrăspunsullor,deoarece

acesteaconstituieprincipaleleelementedisipative.Omarevariabilitateexistăînceeacepriveștetipurile

deconexiunișimecanisme.Înmodtradițional,clădirilepestructurădelemndinPortugaliaauadoptatîn

principal,îmbinărilelajumătatepentruconexiunileprincipalealepereților.

Un studiu experimental a fost efectuată la Laboratorul de Structuri la Universitatea din Minho

(Portugalia),pentrua investigarăspunsulciclical îmbinărilor tradiționale la jumătateîntăriteșinormale,

dupăceaufostsupuseunorcondițiimeteorologiceextremesimulate,cumarfiinundațiileșiciclurilede

ploaie.

Rezultateletestelorpeconexiunilealteratedeintemperiiaufostcomparatecurezultateleobținute

pemostrenealterate,înscopuldeaevaluamăsuraîncarecondițiilemeteorologiceextremeinfluențează

caracteristicilemecanicealeconexiunii,degradarilerezultateșicomportamentulgeneralalîmbinărilorde

lemn.

x




Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS xi

Table of Contents ACKNOWLEDGMENTS: iii vABSTRACT: v RESUMO: vii REZUMAT: ix1. INTRODUCTION 1

1.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.2 Objectives and methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.3 Outline of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Overview of historical timber frame structures 32.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.2 History of European timber-frame constructions . . . . . . . . . . . . . . . . . . . . . . . .5

2.2.1 Classical antiquity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

2.2.2 Middle Ages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

2.2.3 Renaissance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

2.2.4 17th and 18th Century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

2.2.5 19th Century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.6 Portuguese half-timber structures . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Traditional Timber Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3.1 Typology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.4 Experimentalresearchandliteraturereview . . . . . . . . . . . . . . . . . . . . . . . . . 18

3. CLIMATE CHANGE AND THE HISTORIC ENVIRONMENT 213.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2 Overviewoftheeffectsofclimatechange . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.3 Climate change and its impact on timber structures . . . . . . . . . . . . . . . . . . . . . 24

3.3.1 Annual precipitation amount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3.2 Precipitation Days > 20 mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3.3 Consecutive precipitation > 5 days . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.3.4 Wind Driven Rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4. EXPERIMENTAL PROGRAMME: WEATHERING CYCLIC TESTS 294.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.2 Test Specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

xii



4.2.1 Characterization of the wood species . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.2.2 Specimen layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.2.3 Unreinforced connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.2.4 Double threaded screws reinforced connections . . . . . . . . . . . . . . . . . . . 32

4.2.5 Steel plate reinforced connections . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.3 Joint alignment and evenness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.4 Cyclic procedure adopted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.4.1 Flood cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.5 Experimentalsetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.5.1 Experimentalinstallation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.5.2 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.5.3 Monitoring procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.6 Cyclic test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.6.1 Relative humidity and temperature monitoring of the W.D.R. cycles . . . . . . . . . 45

4.6.2 Water migration and content in the samples subjected to W.D.R. cycles . . . . . . . 48

4.6.3 Weight history of the samples subjected to W.D.R. cycles . . . . . . . . . . . . . . 51

4.6.4 Weighthistoryofthesamplessubjectedtothefloodcycle . . . . . . . . . . . . . . 54

4.6.5 Visual inspection of the connections after the weathering cycles . . . . . . . . . . . 54

4.6.6 Watermigrationduringfinaldryingperiod . . . . . . . . . . . . . . . . . . . . . . 55

5. MECHANICAL EXPERIMENTAL PROGRAMME: PULL OUT TESTS 575.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.2 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.3 Test setup procedure and instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . 60

5.4 Results and comparison of the pull out test . . . . . . . . . . . . . . . . . . . . . . . . . 63

5.4.1 Unreinforced connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

5.4.2 Double threaded screws reinforced connections . . . . . . . . . . . . . . . . . . . 66

5.4.3 Steel plates reinforced connections . . . . . . . . . . . . . . . . . . . . . . . . . . 68

6. CONCLUSION AND FUTURE DEVELOPMENT 737. References 75

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS xiii

List of FiguresFigure 1 Distribution of the various types of timber structures in Europe. (Phleps, 1942) . . . . . . .4

Figure 2 Opus catricium: reconstruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Figure 3 Cruck structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Figure 4 Typical wall bracing systems found in the British Isles in the Middle Ages . . . . . . . . . .7

Figure 5 Types of Jettyied connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Figure 6 Plan, sections and details of de l’Orme’s system (Emy, 1856) . . . . . . . . . . . . . . . .8

Figure 7 Palladio timber bridge detail interpretation by Tampone and Funis (2003) . . . . . . . . . .8

Figure 8 Plates III and IV: Carpentry showing ‘Assembly and Old Timbers’ (left) and ‘Modern Timbers‘ (right) half timber frame walls from The Encyclopedia of Diderot & d’Alembert 1751-1780 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Figure 9 Plan and sections of Marac’s barrack showing the inovative system(Emy, 1856) . . . . . 10

Figure 10 Typical facade and facade street front proposed (Cartulário Pombalino 2000) . . . . . . . 11

Figure 11 Structure of a gaiola pombalina building (Cóias) . . . . . . . . . . . . . . . . . . . . . . 12

Figure 12 Axonometricviewofaninternalgaiolapombalinastructure(Cóias) . . . . . . . . . . . . 13

Figure 13 Typicalwallcompositionwithrubbleinfill(right:drawingafterCorreiraet.al.2015;left

Cóias) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 14 Typical metal strap connectors and nails (Cóias) . . . . . . . . . . . . . . . . . . . . . . 14

Figure 15 Typicalconnectionsystemstimberframe:towall,tofloorandtotimberframe(Cóias) . . . 14

Figure 16 Butt joint: 1a closed, 1b opened . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 17 Halved and lapped joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 18 Tenon joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 19 Notched joint: 1a closed, 1b opened . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 20 Dovetail joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 21 Oblique joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Figure 22 L-, X- and T- joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 23 Threats of climate change reported for cultural World Heritage properties . . . . . . . . . 23

Figure 24 Differencemapsforannualprecipitationamounts(Sabbioni et al., 2010) . . . . . . . . . . 24

Figure 25 Differencemapsforannualprecipitationdays>20mm(Sabbionietal.,2010) . . . . . . . 25

xiv



Figure 26 Differencemapsforconsecutiveprecipitation>5days(Sabbionietal.,2010) . . . . . . 25

Figure 27 Differencemapsforwinddrivenrain(Sabbionietal.,2010) . . . . . . . . . . . . . . . . 26

Figure 28 Generic half-timber wall structure with typical connections . . . . . . . . . . . . . . . . . 30

Figure 29 Assembly and geometry diagram of the unreinforced connections . . . . . . . . . . . . . 32

Figure 30 Assembly and geometry diagram of the double threaded screws reinforced connections . 32

Figure 31 Assembly scheme of the steel plate reinforced connections . . . . . . . . . . . . . . . . 33

Figure 32 Final geometry diagram of the steel plate reinforced connections . . . . . . . . . . . . . . 34

Figure 33 Position of measured gaps: front view (left) lateral right view (right) . . . . . . . . . . . . 35

Figure 34 Sampledailyhourlycycle:W.D.R.(left),flood(right) . . . . . . . . . . . . . . . . . . . . 36

Figure 35 Left: Wind Driven Rain cycle diagram Right: Flood cycle diagram . . . . . . . . . . . . . 37

Figure 36 Planviewoftheexperimentalsetup: 1 1000 l IBC tank, 2 pump, 3 water input, 4 pressure

gauge, 5 water valve, 6 fan/ heater, 7 nozzles, A,B,C samples . . . . . . . . . . . . . . . 39

Figure 37 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 38 Monitoring equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 39 Testing and monitoring rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 40 Load cell equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 41 Gann Hydromette HT 85 T moisture meter equipment . . . . . . . . . . . . . . . . . . . 42

Figure 42 Moisture reading positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 43 Testarrangements:1.Twopointsparalleltothefibertesting;2.Twopointsperpendiculartofibertesting;3.Fivepointsperpendiculartofibertesting . . . . . . . . . . . . . . . . . 44

Figure 44 Perpendiculartothetimberfibrewatermigrationdiagramforcopperandsteelrodsunderwetting and drying cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Figure 45 Ambient temperature and relative humidity . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 46 Tank relative humidity and temperature Sensor 2 . . . . . . . . . . . . . . . . . . . . . . 46

Figure 47 Sensors layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Figure 48 Tank relative humidity and temperature: top Sensor 5, bottom left Sensor 3, bottom right Sensor 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 49 Qualitative water sorption diagram: beam (left), post (right) . . . . . . . . . . . . . . . . . 49

Figure 50 Weight history graph for sample U1 recorded with a load cell . . . . . . . . . . . . . . . . 51

Figure 51 Weight history graph of the samples subjected to the W.D.R. cycles . . . . . . . . . . . . 52

Figure 52 Sorption and desorption isotherms (Esteban, Grill et al. 2005) . . . . . . . . . . . . . . . 55

Figure 53 Infrared image of the connections at the begining of the drying period: left: connections subjectedtofloodcycles;centerandright:connectionssubjectedtoW.D.R.cycles . . . . 56

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS xv

Figure 54 Infrared image of double threaded screws reinforced connection subjected to W.D.R. cycles after 24 hours of drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Figure 55 Infrared image of double threaded screws reinforced connection subjected to W.D.R. cycles after 48 hours of drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Figure 56 GFRPreinforcementandsteelgripfixtureforthepull-outtests . . . . . . . . . . . . . . . 58

Figure 57 GFRP application procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Figure 58 Pull-out test setup (Poletti, 2013) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

Figure 59 Pull-out test procedures adopted: (a) unreinforced connections (b) reinforced connections 61

Figure 60 Instrumentation used during the unreinforced connections pull-out tests . . . . . . . . . . 61

Figure 61 Instrumentation used during the double threaded screws reinforced connections pull-out tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 62 Instrumentation used during the steel perforated plates reinforced connections pull-out tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Figure 63 Damage patterns of the unreinforced connections . . . . . . . . . . . . . . . . . . . . . 63

Figure 64 Outofplanedisplacementoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood . 64

Figure 65 Upliftoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood . . . . . . . . . . . . 64

Figure 66 Cyclic pull-out force-displacement diagrams for the unreinforced connections . . . . . . . 65

Figure 67 Damage patterns of the double threaded screws reinforced connections . . . . . . . . . . 66

Figure 68 Cyclic pull-out force-displacement diagrams for the screws reinforced connections . . . . 67

Figure 69 Outofplanedisplacementoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood . 67

Figure 70 Damage patterns of the steel plates reinforced connections . . . . . . . . . . . . . . . . 68

Figure 71 Cyclic pull-out force-displacement diagrams for the steel plates reinforced connections . . 69

Figure 72 Upliftoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood . . . . . . . . . . . . 69

Figure 73 Failure modes of the specimen P2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Figure 74 Failure modes of the specimen P3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

xvi



List of TablesTable 1 Table 1: Impact of climate factors on cultural heritage [1] . . . . . . . . . . . . . . . . . . 23

Table 2 Table 2: Specimens adopted for the weathering test . . . . . . . . . . . . . . . . . . . . 31

Table 3 Table 3: Connection gap position and dimensions . . . . . . . . . . . . . . . . . . . . . . 35

Table 4 Table 4: Straubing weather parameters May-June 2013 . . . . . . . . . . . . . . . . . . 37

Table 5 Table 5: Environmental data from the W.D.R cycles . . . . . . . . . . . . . . . . . . . . . 47

Table 6 Table 6: Moisture content history of the samples subjected to W.D.R. cycles . . . . . . . . 50

Table 7 Table 7: Weight history of the samples subjected to the W.D.R. cycles . . . . . . . . . . . 53

Table 8 Table8:InitialandafterfinaldryingperiodweightofthesamplessubjectedtotheW.D.R.cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Table 9 Table9:Weighthistoryofthesamplessubjectedtothefloodcycles . . . . . . . . . . . . 54

INTRODUCTION

Erasmus Mundus ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS 1

1. INTRODUCTION

1.1 General

`Climate change is one of the most important and urgent problems facing us today.

Manyhistoric buildings, sitesand landscapeshavealreadyexperiencedand survived significant

climatic changes in the past and may demonstrate considerable resilience in the face of future climate

change. However, many more historic assets are potentially at risk from the direct impacts of future climate

change. Without action to adapt to a changing climate and limit further changes it is likely that these

willbeirreparablydamagedandthecultural,socialandeconomicbenefitstheyprovidewillalsobelost.

Equally,thesignificanceandintegrityof importanthistoricassetscanbethreatenedbypoorlydesigned

adaptation and mitigation responses. The non-renewable character of historic features and the potential

for their damage and loss should, therefore, always be taken into account when adaptation and mitigation

responsesarebeingplannedandexecuted`(Cassar,2005).

Theresearchcarriedoutaimstotackletheyetunchartedterritoryoftheeffectsofclimatechangeon

the mechanical characterization of wooden connections.

1.2 Objectives and methodology

The great motivation and challenge consisted in the complexity of the experimental weathering

campaignanditsexploratorycharacter.

Thus, themaingoalof this thesis is toacquireabetterunderstandingonhowseriesofextreme

weatherconditionsgeneratedandamplifiedbyclimatechangeaffectthemechanicalbehaviouroftraditional

halflapconnections.Thisknowledgeisimportantinthepreservationofhalf-timberstructuresexposedto

environmental conditions.

In detail, the main objectives of the thesis are:

-Understandingthedifferenttypologiesoftimber-framebuildingsandtimberconnectionsandtheir

behaviourduringextremeweatherconditions;

- The design and monitoring procedure of a testing setup capable of generating sequences of wetting

anddryingcyclessimulatingrealweatherevents;

2



-Evaluationof thepull-outcyclicbehaviourof traditionalconnections,andretrofittedconnections

whichweresubjectedweatheringcycles;

-Comparisonof the results obtained in termsof strength, stiffness, failuremodeswith theones

obtained on sound specimens.

Thefinalgoalof thiswork is toprovidean insightonhowextremeweatherconditionsaffect the

mechanical characteristics of half lap timber connections.

1.3 Outline of the Thesis

Besidesthepresentintroductorychapter,thisthesisisdividedinfivemorechaptersasfollows:

Chapter 2 presents a detailed literature review on European timber frame buildings and European

timber connections following their evolution and typology with a focus on the Portuguese ‘Pombalino‘

structures.

Chapter3presentsanoverviewof theeffectsofclimatechangeand the impact ithason timber

heritage structures.

Chapter 4 presents the geometry of the specimens and a detailed description of the retrofitting

techniques.Thischapteralsocontainsanindepthdescriptionoftheexperimentalsetupfortheweathering

cycles, the procedure adopted for the weathering cycles and the monitoring procedure and instrumentation.

Chapter 5 presents a description of the pull-out cyclic tests setup. A description of the damage

patterns in the tested connection is presented, as well as a comparison study of the results obtained from

the weathered connections and sound ones.

Finally,theconclusionsthatderivedfromthisexperimentalcampaign,aswellasrecommendations

for future developments are listed in Chapter 6.

Overview of historical timber frame structures


2. Overview of historical timber frame structures

2.1 Introduction

Wood has been widely used in buildings all over the world as a structural, protective and decorative

materialbeingoneoftheprimaryconstructionmaterials(Mainstone1975;Chilton1995).

In ancient times, the type of construction was mainly dependent on the local resources, the climatic

conditions, the culture, customs and traditions where they were built. The German architectural historian

Hermann Phleps published a study of European wood building traditions. The map (Figure 1) shows

the different typologies of timber constructions found on theEuropean continent (Phleps 1942).Three

main types of timber structures were found: (1) the log-structure, (2) the post and beam structure and (3)

the timber-frame structure. It is interesting to observe on the map how the geographical distribution of

the techniques correlates to the availability of timber resources and the climatic conditions of the various

regions.

The timber-frame typology is mainly found in the central part of the continent and the British Isles,

and it is related to the presence of oak forests and a relatively mild climate. Surrounding this group of

timber-framed buildings like a belt is the log-building typology which corresponds to a harsher climate

and coniferous timber resources. However, there are many regional and local variations within the main

categories(LarsenandMarstein,2016).Forexample,within the log-building typology, theshapeof the

logs varies, the types of the joints and the construction techniques used also vary. This structural technique

ismainlyfoundinthecentralEuropeanAlpineregion,Finland,Sweden,Norwayandextendseastwards

encompassing several East European countries and Russia. It was widely used for all types of buildings

(from churches, residential to utility and storage buildings) in the towns as well as in the countryside (Larsen

and Marstein, 2016).

European immigrants brought the log-building technique to North America in the eighteenth century.

The log-building construction technique is relatively rare when looked at from a global perspective. In

addition to the areas of Europe mentioned above and in North America, log buildings are also found in some

Asiancountries,forexampleinCambodia,theYunnanprovinceofChinaandinJapansomedatingback

to the eighth and ninth century (Larsen and Marstein, 2016).

4



Figure 1: Distribution of the various types of timber structures in Europe. (Phleps, 1942)


1a 1b

2 3

4 5

History of European timber-frame constructions


2.2 History of European timber-frame constructions

2.2.1 Classical antiquity

Timber framed structures can be traced back to the Roman Empire. In the Mediterranean region timber

specieslikefir,pine,oak,cedarandcypresswerepresent,suitableforconstructionandshipbuilding.

In Book Five of the Inquiry into Plants treatise by Theophrastus (370-ca. 285 B.C.) considerable

practical information can be found regarding carpentry and woodworking (Courtenay, 1995). Vitruvius in his

treatiseofarchitecturealsoreferstodifferentspeciesoftimbersuitableforconstructionlikethepoplarfor

pile works, cypress, pine, cedar and larch due to the resilience to insect and rot decay and the oak due to

its strength.

Only few archaeological traces of the opus craticium, the roman half-timbered wall remains, the only

RomanexampleswhichpersistedovertimearetheonesfoundatPompiiandHerculaneum(Figure2).

Themixedstructureiscomposedoutofamasonrybase,ontopofwhichatimberframecomposed

ofposts,beamsanddiagonalbracers formingpanels is set.The infillwasmadeoutofopus incertum

masonry. The partition walls have the same composition. Cases of timber-framed balconies supported by

diagonal braces or vertical posts are found (Adam, 1984).

The ancient builders employed the truss principle, tying the feet of the rafters, creating a system

of triangulation, to use timbers of lesser length and especially of smaller cross-section to introduce wide

spans. In this manner the rafter feet do not spread outward, and the horizontal, overturning force at the wall

head was restrained (Salavessa, 2012).

Figure 2: Opus catricium: reconstruction

6



2.2.2 Middle Ages

The cruck frame has been used from the 1st century, in the British Isles, Germany and Netherlands.

It is composed from inclined timber elements which follow the line of the roof and rest directly on the ground

orareinsertedinit,beingjoinedinpairsattheirapex.TheyresembleaglobalAframe.Thosepairsofcruck

blades are spaced at equal intervals along the building and have a ridge purlin which receives the upper

endsoftherafters.Thecrucktrusscanbeexposedinthegable,framingacompositionofwallposts,studs,

tie beams, rails, wall plates, collars, rafters, braces and window-frames. Timber members of the wall can be

exposedorconcealed(Salavessa,2012).

Figure 3: Cruck structure

Earlymedievaltimber-framingexamplescanstillbefoundtodayinFrance,GermanyandNetherlands,

andarerepresentedbytwotypes:(1)onewithallverticalmembers,juxtaposedbutnotjoinedtogether;

(2)andtheotheronewithcornerandbayposts.Thefirstone,thepalisade-wall,developedtothestabbau,

with vertical timber members assembled through grooves and loose tongue used in Scandinavian churches

(stavkirke/ stave churches), and urban and rural buildings.

Themedievalhalf-timberedwallevolvedfromthecruckframetotheboxframewhichiscomposed

bybeams,posts,studs,railsandbraces.Theinfillusuallyconsistsofwattleanddaubormasonrycovered

withplaster.Usuallytheexposedtimberelementsarepaintedindarkercolourstocontrastwiththerender

but also as a measure of protection from environmental conditions.



Figure 4: Typical wall bracing systems found in the British Isles in the Middle Ages

The construction of those half-timbered walls evolved into the jettied timber frame structure (Figure 5)

whichconsistsofupperfloorssupportedbybracketsprojectingbeyondthelowerlevels.Theinfillconsists

of wattle and daub and later clay brick.

Figure 5: Types of Jettied connections

8



2.2.3 Renaissance

Philipert de l’ Orme, in his treatise of carpentry Nouvelles Inventions pour Bien Bastir et a Petits Fraiz

from 1561, introduces the new principle of build-up beams composed of small timber elements instead of

one massive element. The scope for this new element was to cover large spans which regular timber would

not be able to cover and to reduce material consumption thus making the structure lighter. The segmental

archwaspartofavaultwithedgesofplasteredlathwork.Thelathworkwasfixedinastructureofwood

composed with double wooden staves tied with wooden pegs, forming one curvature which is tied itself to

a covering structure of ogee arches. Each beam has 3 rows of arches, the middle one assembled to the

externalrowsbydrawpegsandkeys.

Figure 6: Plan, sections and details of de l’Orme’s system (Emy, 1856)

Andrea Palladio in his I Quattro Libri dell’ Architecttura from 1570 and in his built projects introduces

the use of bolted metal cramps to join the vertical elements to the beams, this way all the elements of the

timber-frame being thoroughly connected and function as a single element (Figure 7).

Figure 7: Palladio timber bridge detail interpretation by Tampone and Funis (2003)



2.2.4 17th and 18th Century

Twotreatiseshighlightissuesregardingtimberframebuildings.ThefirstonewrittenbyPaulleMuet

is entitled Maniére de bien batir pour toutes sorts de personnes (1681) and the one written by J. Blondel

and M. Patte is entitled Cours d’Architecture (1777).

Acontinuationoftherefinementandascientificapproachinthetimberframebuildingsstartedinthe

renaissance period can be observed.

Most of the discoveries are related to the military architecture from engineers as Sebastien Vauban,

Véritable maniére de bien Fortier (1692), and Bernard Belidor, La cience des Ingénieurs dans la conduite

destravauxdeFortificationetd’ArchitectureCivil(1726),thepublicationofencyclopediaslikethatoneof

Diderot and D’Alembert (1751-1780).

The plates of Diderot and D’Alembert’s from the Encyclopaedia, or a Systematic Dictionary of

the Sciences, Arts, and Crafts show engraving of a carpenter’s yard setup, the tools used, connections,

ornamental elements, composed structures as entire walls or complex objects as stairs (Diderot and

D’Alembert, 1751-1766).

Figure 8: Plates III and IV: Carpentry showing ‘Assembly and Old Timbers’ (left) and ‘Modern Timbers‘ (right) half-timber frame walls from The Encyclopedia of Diderot & d’Alembert 1751-1780

10



2.2.5 19th Century

Jean Rondelet, in his Traité Théoriqueet Pratique de l’Art de Bâtir from 1810 develops a comparative

studyofFrench,RussianandGermanconstructiontechniques.Hemakesafirstdifferentiationbetween

load bearing timber-framed walls and partition walls concerning their thickness and proposed an additional

connectiontotheadjacentmasonrywallsandtothefloorsthroughmetalliccrampsorwrought-ironrods

(Rondelet, 1810).

PaulPlanatinPratiquedelaMécaniqueAppliquéealaRésistancedesMatériauxfrom1887remarks

the fact that the necessary cross-sectional area (reduced in the connection areas by notches or gaps) in

relation with the calculated stress must not go beyond the ultimate limit stages of timber member (Planat,

1887).

Unlike many contemporary treatises Colonel Armand Rose Emy’s work entitled Traitè de l’Art de

la Charpenterie from 1856 scope was to show the present state of the art by assembling a collection of

knowledge and architectural inventions on the workmanship and carpentry of wood (Emy, 1856).

In his construction system (Figure 9), which is often considered a continuation of de l’Orme’s work,

ColonelEmyproposedtheuseofbentflatthinwoodelements,fastenedbymetalplates,stirrupsandbolts.

Emy had even evaluated the possibility of introducing the blood-albumen glue between the thin plates to

strengthen his semi-circular arch. He had realised however that organic glues, then in use, represented a

great weakness in the building system. (Mongelli, 2006)

Figure 9: Plan and sections of Marac’s barrack showing the innovative system (Emy, 1856)



2.2.6 Portuguese half-timber structures

The Portuguese building tradition has a general tectonic character being composed of heavy masonry

structures,wherewoodismainlypresentinthefloorsandrooftrusses.

In the historic documents there can be found a series of suggested timber species to be used in

construction. In Tractado de architectura qué leo o mestre, e archito Mattheus do Couto o Velho no anno

de 1631 (Couto, 1631) it is recommended to use Portuguese stone pine (Pinus pinea), it is described that

the best choice would be the chestnut from Galicia for half timber frames and for the wall plates the use of

oakfromthesameregion.BernardBelidorinhisLasciencedesIngénieursdanslaconduitedestravaux

deFortificationetd’ArchitectureCivil(1729)remarksthatoakisthebesttimbertobeusedinconstruction,

taking into consideration its mechanical properties. He also mentions pine to be used in the construction of

beamsandfloors(Belidor,1729).

The Lisbon earthquake of 1 November 1755 was a turning point in the way buildings were constructed.

The measures taken by the Marquis of Pombal, prime-minister of King D. José I for the reconstruction of

the city took form as a series of urban, architectural and structural regulations such as minimal distance

between buildings, the enlargement of the streets, the creation of building blocks, the restriction of the

height of the buildings, orientation of the buildings and the symmetric design of the facades. (Mascarenhas,

2004).

The types of building proposed (Figure 10) by engineer Manuel de Maia in his (Dissertação”1755-1756)

rangefromtwotofivestorybuildings,withthefaçadesofashlarmasonry,cornersquarepillarsandcornice

andspanslinedbyashlarmasonryframes(AppletonandDomingos,2009;Mascarenhas,2004).

Figure 10: Typical facade and facade street front proposed (Cartulário Pombalino 2000)

12



In many situations the foundations were realized out of timber piles bearing the gravitational loads

excludingtherisksofdifferentialsettingintheaquifersoils.Thetimber-pilesofthegaiolapombalinafrom

Lisbon(BaixadeLisboa)aredisposedinparallelrowsinrelationshiptothefacades(2,3or4),spanned

0.30mto0.40m(Figure11).Theintervalswerefilledwithcompactedmasonrystones.Timberrailings

made out of pine were positioned on top of the piles (Cóias, 2007).

Figure 11: Structure of a gaiola pombalina building (Cóias)

Stone masonry columns supporting arches and vaults made stone of clay bricks compose the ground

level.Thisbottomhorizontalstoneregisterrepresentsafirebarriertowardstheupperpartofthebuilding.

The wall presented a constant width across the section and along the height of the building in the early

Pombalino buildings. They developed later into having a reduced width in section regressing from the

bottom to the top of the wall for each level, thus lowering the overall mass of the structure (Mascarenhas,

2004).

The gaiola pombalina is a three-dimensional frame system composed by repetition of a base module.

The modules vary in sizes depending on the site, overall dimensions of the building and the craftsmen

which realized it. The base module of a rectangular (tending to a square shape) is composed out of a

rectangular cross braced frame and a bottom beam. The elements vary in dimension: the vertical posts

and horizontal members are usually 12×10, 12×15cm and 14×10cm or 15×13, 10×13 and 10×10cm the

diagonalmembershaveareducedsectionof10×10cmor10×8cm(Mascarenhas,2004;Cóias,2007).



Figure 12: Axonometricviewofaninternalgaiolapombalinastructure(Cóias)

As can be observed in (Figure 12) the half-timber walls are orientated in two directions. The reduced

number of openings (doors and windows) correspond to the width of the base module.

The internal half-timbered walls are of two types, load bearing and partition timber walls. The partition

wallsdifferfromthepreviousinareducedsectionbutinmanycasestheywerecomposedonlyfromlath

and plaster without the presence of the diagonal bracing.

Figure 13: Typicalwallcompositionwithrubbleinfill(right:drawingafterCorreiraet.al.2015;leftCóias)

14



The timber elements are notched together or connected by nails or metal straps (Figure 14).

Traditionalconnectionsusedforthetimberelementsvariedsignificantlyinthebuildings:themostcommon

ones were mortise and tenon, half-lap and dovetail connections (Poletti, 2013)

Figure 14: Typical metal strap connectors and nails (Cóias)

The connection between timber-framed walls and masonry walls can be reinforced through bolts.

Theconnectionofthefloorstothetransversemainwallsisthroughmetallicpieces.Theconnectionofthe

timber-framed façade to the masonry which cover the former is through small wooden members called

“hands” (Figure 15). The connection of the timber-framing to the squared stones is through metallic cramps

(Salavessa, 2012).

Figure 15: Typicalconnectionsystemstimberframe:towall,tofloorandtotimberframe(Cóias)

In somesituations, thepostsof the frontalwall extended formore thanonefloor (Appletonand

Domingos,2009).Thetimber-framestructuretogetherwiththefloorsandtherooftrussesactasaglobal

bracing system joining all members together and making them function as one system.

Traditional Timber Connections


2.3 Traditional Timber Connections

2.3.1 Typology

Therearedifferenttypesofclassificationoftimberconnections.Oneofthemdividesthejointsinto

detachableandpermanent(Zwerger2012).Thisclassificationbecomesrelevantwhenthinkingofwooden

structuresasmovableTherearemanyexamplesofstructureswhichhavebeentakendownandre-erected

or fabricated inadifferent location, thenumberingsystemsonthetimberelementsarebearingwitness

of these practices. Another use which comes to mind is the easy replacement of decayed parts of the

structure,forexamplethesillbeamwhicharereplacedregularly.Bypermanentjointitcanbeunderstood

thatthejointcannotbedismantledwithoutdamagingit,forexampletenonswhichareclampedwithhidden

foxtailwedges.

This typeofcategorizationdoesn’tpermitacomprehensiveclassificationof timber joints.Amore

completeclassificationsystemistheoneproposedbyGerner(1992),whichdescribesthetypesofjoints

as: butt, tenon, scarf, notched, forked, step joint, birdsmouth, log construction joint, stave construction joint

and repair joint. This list is further subdivided according to: the form of the joint, the position of the joint,

thedirectionofthejointandifthejointpresentsaflushornot.Regardingtheformofthejointthefollowing

subcategories are created: splicing joints, L-,T- and X-joints. The position of joint refers to its orientation

which can be vertical or horizontal. The direction of the joint refers to its geometric layout as straight, right-

angled or skewed/ oblique.

AnotherclassicclassificationistheonemadebyGraubner(1992)wherethefirsttwodistinguishing

criteria listed by Gerner are swapped. The distinction is made between splicing joints, oblique joints, L-, T-

and X-joints, and board joints, according to their forms. Graubner considers the type of joint as a subordinate

category (Zwerger, 2012).

The butt-joint (Figure 16) constitutes of two pieces of timber with no interlocking between them.

Figure 16:


1a 1b

Butt joint: 1a closed, 1b opened

16



Some examples of halved-and-lapped (Figure 17) joints: edge-halved scarf (1a closed and 1b

opened), stop-splayed scarf (2), longitudinal bevelled halved (3), halved and tabled (4), halved and tabled

with brittle abutment (5).

Figure 17:


1a 1b

2 3

4 5

Halved and lapped joints

The tenon joints (Figure 18) can either be placed in an open mortise (1a closed and 1b opened) or

in a tenon hole (2). A tenon may pass through the hole (3a closed and 3b opened) or rest in it (4a closed

and 4b opened).

Figure 18:


1a 1b

2

3a 3b

4a 4b

Tenon joints

Traditional Timber Connections


The notched joint can be considered a special variation of the halved joint with a shallower recession

(Figure 19).

Figure 19:


1a 1b

Notched joint: 1a closed, 1b opened

Dovetail joints (Figure 20) are designed to withstand tension as well as compression (1a opened and

1b closed). The dovetail joint can be combined with a halved scarf (2a opened and 2b closed).

Both the halved and the tenon joints were all formed at the end grain. When a joint is applied with the

alongsidethegrainitiscalledatongueandgroove(forexamplethejoiningofboards).

Most of the joints presented before can be used identically in both horizontal and vertical applications.

Figure 20:


1a 1b

2a 2b

Dovetail joints

The most common oblique joints (Figure 21) are the step joints with housed oblique tenons (1), the

birdsmouth joint (2a closed and 2b opened) and the brace joint (3).

Figure 21:


1

2a 2b

3

Oblique joints

18



The last types of joint are L-, X- and T-joints (Figure 22) as: open mortise and tenon-joint (1), halved

joint (2), notched halved joint (3), connection between a diagonal member and a post (4) and a forked tenon

(5).

Figure 22:


4

1

5

2 3

L-, X- and T- joints

2.4 Experimental research and literature review

Many restoration works are being conducted on traditional half-timbered structures, most of them

adoptingtextbookretrofittingsolutions,withoutinvestingtheresearchtimenecessarytodevelopaspecific

solutionforeachsituationencountered.Mostoftheseinterventionsdonotprovideanefficientstrengthening

solution(rangingfromaesthetics,theextentoftheinterventiontothenewmechanicalpropertiesachieved).

Fewexperimentalworkshavebeencarriedoutuntilnowtoassesstheseismicbehaviouroftimber

frame walls. Reports have been written after recent earthquakes to quantify the qualitative performance

of half-timbered structures (Gülhan andGüney 2000; Langenbach 2009;Dogangun 2006;Gulkan and

Langenbach 2004).

In plane cyclic tests on unreinforced half-timber walls have been carried out by Meireles and Bento

(2010), Santos (1997). Gonçalves et al. (2012) performed cyclic tests on traditional Portuguese timber

framewallswithandwithoutinfill.

WorkofretrofittingtraditionalPombalinobuildingfromLisbonhavebeendonebyusingFRPsheets

in for the connection strengthening (Cóias, 2007), by including damping systems consisting of injected

anchors and bracing systems linked to frontal walls and to the outer masonry (Cóias, 2007).

Experimentalresearchandliteraturereview


Inrecentyears,studiesassessingtheexperimentalbehavioroftraditionalhalf-timberedwallsand

theirretrofittingsolutionshavebeencarriedout(Vasconcelosetal.,2013;Gonçalvesetal.,2012).

Theexperimentalworkregardingtimberconnectionstendtobeconcentratedarounduniversitiesor

reaserch institutions mainly investigating local typologies and cases.

Various studies are found in the literature assessing the mechanical behaviour of traditional joints,

namelyofbirdsmouthconnections(Branco,2008;ParisiandPiazza,2002),roundeddovetailconnections

(Tannert et. al, 2010),mortise and tenon (Shanks andWalker, 2005; Descamps et al., 2006; Koch et

al.,2013), dowel-type connections (Xu et al., 2009), pegged timber connections (Burnett, et. al., 2003),

wood pegged timber frames (Bulleit, et al., 1999), traditional Nuki joints (Chang et al., 2006), Dou–Gon

joints (D’Ayala and Tsai, 2008), Kama Tsugi and Okkake Daisen Tsugi joints (Ukyo et al., 2008), steel-wood

nailconnections(Vieux-Champagneetal.,2012).

Avastnumberofstudiesonretrofittingtechniquesfortraditionaltimberconnectionsarealsoavailable,

namelybirdsmouthjointreinforcements(Branco,2008;ParisiandPiazza,2002),andglassfibrereinforced

polymers (GFRP) reinforcement (Premrov et al., 2004).

An extensive experimental campaign called the Characterization of the seismic behaviour of

traditional timber frame walls has been developed by Elisa Poletti (2013) at the University of Minho under the

supervision of Prof. Vasconcelos. The campaign consisted in real scale mechanical testing of unreinforced

and reinforced half-timber frame walls, timber frame walls and timber connections, adopting dimensions

found in real structures and considering different infill types (brickmasonry and lath and plaster).The

workathandusestheexperimentalcampaigncarriedoutbyPoletti(2013)asageneralframeworkand

reference.

20




CLIMATE CHANGE AND THE HISTORIC ENVIRONMENT


3. CLIMATE CHANGE AND THE HISTORIC ENVIRONMENT

3.1 Introduction

Climate change is defined by the United Nations Framework Convention on Climate Change

(UNFCCC) (UN, 1992), in its Article 1, as ‘a change of climate which is attributed directly or indirectly to

human activity that alters the composition of the global atmosphere and which is in addition to natural

climate variability observed over comparable time periods. The UNFCCC makes a distinction between

‘climate change’ attributed to human activities altering the atmospheric composition, and ‘climate variability’

attributed to natural causes.

The Intergovernmental Panel on Climate Change (IPCC) states in its Third Assessment Report (2001)

that ‘The Earth’s climate system has demonstrably changed on both global and regional scales since the

preindustrial era, with some of these changes attributed to human activities’. During the 20th century, the

average global temperature increased by 0.6 °C. This increase is likely to have been the largest of any

centuryduringthepast1,000years.Tolimittheextentofclimatechange,thereductionoftheemission

and enhancing the sinks of greenhouse gases is needed, but the same report mentions that ‘adaptation is

anecessarystrategyatallscalestocomplementclimatechangemitigationefforts(Raoetal.,2007).

Thedirectimpactofachangingclimatewillhavemajoradverseeffectsonsociety,theeconomyand

the environment, including world cultural heritage.

3.2 Overview of the effects of climate change

Climate change will have physical, social and cultural impacts on cultural heritage. It will change

the way people relate to their environment. This relationship is characterised by the way people live, work,

worship and socialize in buildings, sites and landscapes with heritage values.

The character of cultural heritage, namely built heritage, is closely related to the climate. Climate

change can be subtle occurring over a long period of time. However, some climate change parameters

such as freezing, temperature and relative humidity shock can change by large amounts over a short period

oftime.Toidentifythegreatestglobalclimatechangerisksandimpactsonculturalheritage,thescientific

community uses the climate parameters shown in Table 1.

22



Climate parameter Climate change risk Physical, social and cultural impacts on cultural heritage

Atmospheric moisture change

• Flooding (sea, river)

• Intense rainfall• Changes in water

table levels• Changes in soil

chemistry• Ground water

changes• Changes in

humidity cycles• Increase in time

of wetness• Sea salt chlorides

• pH changes to buried archaeological evidence• Loss of stratigraphic integrity due to cracking and

heaving from changes in sediment moisture• Data loss preserved in waterlogged / anaerobic /• anoxicconditions• Eutrophication accelerating microbial decomposition

of organics• Physical changes to porous building materials and

finishesduetorisingdamp• Damage due to faulty or inadequate water disposal

systems;historicrainwatergoodsnotcapableofhandlingheavyrainandoftendifficulttoaccess,maintain, and adjust

• Crystallisation and dissolution of salts caused by wettinganddryingaffectingstandingstructures,archaeology, wall paintings, frescos and other decorated surfaces

• Erosion of inorganic and organic materials due to floodwaters

• Biological attack of organic materials by insects, moulds, fungi, invasive species such as termites

• Subsoil instability, ground heave and subsidence• Relative humidity cycles/shock causing splitting,

cracking,flakinganddustingofmaterialsandsurfaces

• Corrosion of metals• Othercombinedeffectseg.increaseinmoisture

combined with fertilisers and pesticidesTemperature change

• Diurnal, seasonal, extremeevents(heat waves, snow loading)

• Changes in freeze-thaw and ice storms, and increase in wet frost

• Deterioration of facades due to thermal stress• Freeze-thaw/frost damage• Damage inside brick, stone, ceramics that has got

wet and frozen within material before drying• Biochemical deterioration• Changesin‘fitnessforpurpose’ofsomestructures.• Forexample,overheatingoftheinteriorofbuildings

can lead to inappropriate alterations to the historic fabric due to the introduction of engineering solutions

• Inappropriate adaptation to allow structures to remain in use

Sea level rises • Coastalflooding• Sea water

incursion

• Coastal erosion/loss• Intermittent introduction of large masses of ‘strange’

water to the site, which may disturb the metastable equilibrium between artefacts and soil

• Permanent submersion of low lying areas• Population migration• Disruption of communities• Loss of rituals and breakdown of social interactions


1a 1b

2 3

4 5

Overviewoftheeffectsofclimatechange


Wind • Wind-driven rain• Wind-transported

salt• Wind-driven sand• Winds, gusts

and changes in direction

• Penetrative moisture into porous cultural heritage materials

• Static and dynamic loading of historic or archaeological structures

• Structural damage and collapse• Deterioration of surfaces due to erosion

Desertification • Drought• Heat waves• Fall in water table

• Erosion• Salt weathering• Impact on health of population• Abandonment and collapse• Loss of cultural memory

Climate andpollution actingtogether

• pH precipitation• Changes in

deposition of pollutants

• Stone recession by dissolution of carbonates• Blackening of materials• Corrosion of metals• Influenceofbio-colonialization

Climate andbiologicaleffects

• Proliferation of invasive species

• Spreadofexistingand new species of insects (eg. termites)

• Increase in mould growth

• Changes in lichen colonies on buildings

• Decline of original plant materials

• Collapseofstructuraltimberandtimberfinishes• Reduction in availability of native species for repair

and maintenance of buildings• Changes in the natural heritage values of cultural

heritage sites• Changes in appearance of landscapes• Transformation of communities• Changes in the livelihood of traditional settlements• Changes in family structures as sources of livelihoods

become more dispersed and distant

Table 1: Impact of climate factors on cultural heritage [1]

In the pie chart (Figure 23) a proportional distribution of the threats generated by climate change has

been drawn in regard to the World Heritage properties. This does not take into consideration the lesser

architectureexampleswhicharenotonthespecifiedlist.Thedamageinducedbyrainfall(storms,floods

andwinddrivenrain)makeupforapprox.22%ofallthreats.

Figure 23: Threats of climate change reported for cultural World Heritage properties

(survey by the World Heritage Centre in 2005)NOTE: [1] Principal climate change risks and impacts on cultural heritage’ in Background Document UNESCO WORLD HERITAGE CENTRE in coop-

erationwiththeUnitedKingdomGovernment‘WorldHeritageandClimateChange’forthebroadworkinggroupofexpertsatUNESCOHQ16-17March2006 and in Working Document 30 COM 7.1 prepared for the 30th Session of the World Heritage Committee, Vilnius, July 2006 which can be found at http://whc.unesco.org/archive/2006/30com-en.htm

24



3.3 Climate change and its impact on timber structures

TheatlasofclimatechangeimpactonEuropeanculturalheritage(Sabbionietal.,2010)aimstofill

thegapexistinginstudiesontheeffectsoffutureclimatevariationsonculturalheritage,producingmaps

that link climate science to the potential damage to the material heritage.

3.3.1 Annual precipitation amount

Water is the main cause of most physical, chemical and biological decay processes.

The maps (modelled over 30-year averages of annual precipitation) show that annual precipitation

predominates in western coastal and mountain areas. The prediction results consist in a decrease in annual

precipitation in Southern Europe and an increase in Northern Europe (Sabbioni et al., 2010).

Figure 24: Differencemapsforannualprecipitationamounts(Sabbioni et al., 2010)

3.3.2 Precipitation Days > 20 mm

ThefrequencyofriverandlocalsurfacefloodingeventswillincreaseinmanyareasofEurope,as

tomorefrequentrainydays,thepredictedmaximumdailyrainfallisalsolikelytoincrease(Sabbionietal.,

2010).

Climate change and its impact on timber structures


Figure 25: Differencemapsforannualprecipitationdays>20mm(Sabbionietal.,2010)

3.3.3 Consecutive precipitation > 5 days

AllareasofEuropewillexperiencerainyperiodslongerthanfivedaysinboththenearandthefar

future. Long rainy periods can cause accelerated deterioration of organic as well as inorganic materials due

to changes in volume, an increased risk of biological attack as well as possible frost damage. Moreover,

theamountofprecipitationcantriggernaturaldisasterslikefloodsandlandslides,asthereductionofrainy

periodscancausedraughtandwildfire(Sabbioni et al., 2010).

Figure 26: Differencemapsforconsecutiveprecipitation>5days(Sabbionietal.,2010)

26



3.3.4 Wind Driven Rain

Wind driven rain is when wind drives rain into vertical surfaces that would otherwise be sheltered

from vertically falling rain. The largest amount of wind driven rain can be found over the areas close to the

AtlanticOcean.Inthefuturethechangesintheamountofwinddrivenrainisexpectedtospreadslightlyin

most of Central Europe, with an increased presence in the northern areas of Europe and a decrease in the

areas of Southern Europe (Sabbioni et al., 2010).

Figure 27: Differencemapsforwinddrivenrain(Sabbionietal.,2010)

3.3.5 Conclusions

AsdeterminedbytheclimaticriskmapspresentedinSubchapter3.3.themajorityofextremeclimatic

conditionswillincreaseinintensityandinduration.Theweatheringeffectstowhichhistoricandvernacular

structuresareexposedtowillbemoreintenseandthusmoredamaging.

Temperature is one of the worst climatic parameters. In central Europe, it ranges from –25°C to

about+30°C.Allbuildingmaterialsaresensitivetotemperature,andtheycanexpandwithanincreasein

temperature and contract with a temperature decrease for the majority of building materials.

Water acts on historic materials and structures in all its phases and together with temperature or

other parameters, can cause decay or even destroy a monument if protective measures are not taken.

Water increases the relative humidity of the air and creates conditions that increase the moisture content of

Climate change and its impact on timber structures


materials as well as the life of biological agents of decay. Among the greater threats to building materials in

historic structures are cyclical changes of moisture content which can mobilise soluble salts or cause clay

materials to swell. The interaction of temperature and moisture causes repeated and uneven volumetric

changes resulting in the propagation of defects.

Floodscausedamageandfailureduetostaticanddynamicloads(waterpressure,waterflow,uplift

forces),duetotheimpactoffloatingobjects,duetothewettingofbuildingmaterials(whicharedifficult

to dry) and due to the risk of transfer of chemical pollutants and biological contamination. Even though a

floodmaybeashortevent,rightingtheconsequencesrequiresalongandenormouseffort.Wetmaterials

andstructuresgenerallylosetheirstrengthandstiffnessandtheyexhibitsubstantialvolumetricchanges

(Sabbioni et al., 2010).

However,itisnotjustthetypeofmaterialswhichinfluencesthesensitivityofstructuresandelements

toweather conditions; the importance of themorphology of buildings, that is their shape and physical

contextmustalsobeconsidered.

With this respect, timber architecture is particularly vulnerable to climate change. Wooden architecture

ismainlyspreadintheNorthern,CentralandEasternpartofEurope,whereclimaticchangesareexpected

toshifttomoreextensivewetperiods.Inparticular,woodreactsandissensitivetochangesinrainfallandin

general the presence of water, resulting in moisture content changes that can lead to mechanical stresses.

Thenecessityofexperimentalapproachestowardstheassessmentofthemechanicalcharacteristics

of building elements and systems undergoing continuous weathering cycles become more indispensable.

Thistypeofapproachisessential,inordertounderstandtowhichextentdoesthebuiltheritagehas

to adapt to the physical changes accelerated or generated by climate change.

28




EXPERIMENTAL PROGRAMME: WEATHERING CYCLIC TESTS


4. EXPERIMENTAL PROGRAMME: WEATHERING CYCLIC TESTS

4.1 Introduction

Following the increasing relevance of climate induced damage to the envelope of historic buildings

andthedurabilitychangesof theconstitutingmaterials, itwasdecidedtocarryoutanexploratorywork

aiming to analyse the effect of different extreme environmental conditions regarding the mechanical

behaviour of traditional timber connections.

Therefore,thischapterpresentsanexploratoryworkregardingthedevelopmentofacyclicextreme

weather condition simulator, including the installation, as well as the methods and procedures necessary to

monitortraditionaltimberconnectionssubjectedtopre-definedweatherconditions.

The timber species, the geometry of the connections and the types of reinforcement are the same

as the ones used by Poletti (2013) in order to have a comparison model for the mechanical testing of the

timber connections.

4.2 Test Specimens

4.2.1 Characterization of the wood species

The natural geographic distribution of Pinus pinaster is: France, Spain, Portugal, Italy, Morocco,

Algeria and Tunes. In Portugal the industrial purposes vary from Pallets and Packaging (34%), Civil

Constructions(27%),Furniture(16%)andothers(23%).AcommondefectofPinuspinasteristhetrunk

curvature,theprocessedtimberelementsusuallynotexceeding2.5minlength,thusconditioningit’suse

in the construction industry (Sanz et al. 2006).

The physical characteristics of the wood are:

• Density (green wood) = 1000 kg/m3;

• Density(12%)=average510kg/m3 (between 470-650 kg/m3);

• Volumetricshrinkage=13.2-16.7%;

• Tangentialshrinkage=7.2-10.1%;

• Radialshrinkage=4.1-6.0%.

30



The mechanical characteristics are:

• Compression parallel to grain: strength = 39.0 - 68.5 N/mm2;

• Static bending strength = 80-151.9 N/mm2;

• Modulus of elasticity in static bending = 8800-11500 N/mm2;

• Tension parallel to grain: tensile strength = 46-162 N/mm2.

4.2.2 Specimen layout

The type of connection studied herein can be often found in the internal three-dimensional timber

structure (gaiola) of Portuguese `Pombalino` Buildings. As highlighted in Figure 28, the half-lap joints

connect the base plate of the wall with the posts. This type of joint is also used to connect the overlapping

diagonals(St.Andrew’sCrosses).Eveniftheselectedconnectionismorecomplexinreality,thediagonal

bracing system was not taken into account when building the specimens.

The typical timber framewalls from thePombalinoBuildingsaremostlyfilledwithbrickmasonry

orrubblestonemasonry,theinfluenceoftheinfillwasnotconsideredinthemechanicalbehaviourofthe

traditional timber connection.

Figure 28: GSPublisherEngine 0.7.100.100

Half-lap joint, diagonal

cross halving joint

Half-lap joint, tee halving

joint

Half-lap joint, cross halving

joint

Generic half-timber wall structure with typical connections

Test Specimens


Besides the unreinforced timber tee halving connection two additional strengthened connections

wereconsideredintheexperimentalprogram.Twodifferentstrengtheningsolutionswereadopted,namely

with double threaded screws and with steel plates connected with bolts and screws. The selection of

differentmethodsofstrengtheningaimedatabetterunderstandingofthebehaviouroftheunreinforcedand

reinforcedconnectionunderextremeweatherconditionsandalsotoassesswhichstrengtheningsolutionis

more vulnerable to these conditions.

Intermsofextremeweatherconditionstwosituationsweresimulated,namely(1)afloodand(2)

wind driven rain. Therefore, nine specimens were considered for the weathering cycles, three of each type:

(a)unreinforced, (b)double threadedscrewsand(c)steelplates reinforcement.Asseen inTable2six

specimensweresubmittedtowinddrivenraincycleswhiletheotherthreetothefloodcycles.

Extreme weather condition Specimen ID Type of strengthening

Wind Driven Rain

U1 unreinforcedS1 double threaded screwsP1 steel platesU2 unreinforcedS2 double threaded screwsP2 steel plates

FloodU3 unreinforcedP3 double threaded screwsS3 steel plates

Table 2: Specimens adopted for the weathering test

4.2.3 Unreinforced connections

Thegeometryoftheteehalf-lapjointconsideredfortheexperimentaltestingisdisplayedinFigure

29. The dimensions of the elements were adopted based on a previous linear elastic analysis of the

connection, fromwhich itwaspossible toobtain thestressandstrainfield in for the loadingconditions

consideredintheexperimentalprogram.Theideawastohaveatimberconnectioninwhichthestressfield

was completely inside its geometry. As mentioned before, all half-lap traditional connections were built out

of Pinus pinaster similar to the tests carried out by Poletti (2013). The timber moisture content has been

stabilizedatapproximately12%inanenvironmentalchambersetat20°Candat60%R.H.Thetraditional

connectionhasacommonwirenail4,5x100mmfasteningthepostandbeamatmidheightofthebeam.

32



Figure 29: Assembly and geometry diagram of the unreinforced connections

4.2.4 Double threaded screws reinforced connections

One very common way to strengthen timber connections is the insertion of threaded screws due

to the simplicity of in-situ application. The reinforced connections were assembled with the same wood

speciesandkeptunderthesameenvironmentconditions.Theexistenceofthesteelnailintheunreinforced

connections was not taken into account for the reinforced connections.

For the strengthening, four WT 8.2x190 mm screws from Rothoblaas were inserted into the

connection: two inserted at a 60° angle in the timber post passing in the beam and two inserted in the timber

beam at a 30° angle passing through the post and stopping in the beam, see Figure 30. The position of the

screws has to be changed if the diagonal crosses cannot be taken out during the strengthening procedure.

Figure 30: Assembly and geometry diagram of the double threaded screws reinforced connections

Test Specimens


4.2.5 Steel plate reinforced connections

The second type of reinforcement consists in applying perforated steel plates (type LBV 2 mm from

Rothoblaas) on both sides of the connection. As one plate was not enough to cover the whole connection,

two plates were considered, one applied horizontally and one vertically overlapping the connection area

aimingatprovidingadditionalstrength.Theplateswerefastenedwithfourhexheadcappartiallythreaded

bolts10x160mm,nutsandwashers.

As it was considered that the 5mmholes in the plateswere not sufficient to have an effective

connection of the steel plates to the wood members, bigger holes were drilled to accommodate steel bolts

on both sides. One bolt is positioned to go through the actual joint connection passing through two steel

plates on each side in the post and in the beam. The other bolts are positioned to fasten the steel plates

to the beam left and right of the joint and the post to the steel plates half way the height of the steel plate.

LBS5x50mmround-headedscrewswithcylindricalunderheadsfromRothoblaaswereinsertedon

bothsidesoftheconnectiontobetterdistributethestressesintheplates.Sixscrewswereusedtofasten

the plate to the post and four screws to fasten each plate to the beam on the left side of the joint, the two

plates to the post in the joint area and the plate to the beam on the right side of the joint.

Figure 31: Assembly scheme of the steel plate reinforced connections

34



Figure 32: Final geometry diagram of the steel plate reinforced connections

4.3 Joint alignment and evenness

As far as the traditional half-lap joints are concerned, it is possible to have gaps with different

thickness in the interfaces between the beam and post. Distinct clearances can be associated to the quality

ofworkmanship.Inprincipal,iftheworkmanshipisofagoodquality,itisexpectedthattheclearancesatthe

interfaces are low. On the other hand, it is considered that the overall quality of the connection can generate

differentweatheringpatternsanddeterminedifferentresultsinthemechanicaltests,asthewatermigration

intheconnectionsshoulddependonthegapsizes,astheyactasdirectinfiltrationchannels.

To take into account these variables the general quality of the connections was assessed by

measuring the gaps between the post and the beam with a calibre.

It should be mentioned that the gaps appeared after the drying process because the timber was cut

intoshapehavingapproximately30%humidity(aroundthefibersaturationlevel).Therefore,accordingto

the diagram shown in Figure 32, the gap dimension between the left and the right side of the post and beam

connection was measured (L and R respectively). The thickness of the gap at the interface between the top

surface of the beam and the post (designated with the letter T) was also measured. The values of the gaps

measured are presented in Table 3. Additionally, the values of the vertical surface deviation of the beam in

relation to the post were also recorded.

Cyclic procedure adopted


Figure 33:


LR

T

+ -

Position of measured gaps: front view (left) lateral right view (right)

Specimen ID Gap position and dimensions [mm]L R T +/-

U1 2.4 0.4 0 3.6S1 0.8 1.5 0 -1.6P1 0 3.6 0 2U2 1.8 0.7 0 -1.2S2 0 2.9 0 1.6P2 0 1.2 0 0U3 1.7 1 0 -0.8S3 1.2 0 0 -3.2P3 0 0.6 0 -0.4

Table 3: Connection gap position and dimensions

The total joint gap varies from 0.6 to 3.6 mm with several values ranging from 2.3 to 2.9 mm between

the post cheek and the beam’s lateral shoulders. No spaces were observed on the top side of the joint, the

post’s shoulder (T), mainly because the connection was constructed so that the post always rests on the

beam even if the post’s cheek passes or comes short to the bottom limit of the beam. The alignment of the

postandthebeam,exceptoneofthem,haveimperfectionsvaryingfrom0.4to3.6mmtowardsoutsideor

inside.

4.4 Cyclic procedure adopted

Theclimatesimulationshavebeendesignedtoreplicaterealtimefloodandwinddrivenrainevents.

The general parameters of the climatic event, such as hourly rainfall and total daily rainfall, temperature,

36



relativehumidity,intensityanddirectionofwind,flooddepthanddurationwereanalysedaimingattranslating

thelargescaleclimatedataintothebuildingscaleexposureconditions.

The geographic region selected for the weather data input is lower Bavaria due to often recent

extremeclimateeventslikethe2006,2013,June2016flood,largenumberofhalf-timberframebuildings

present in the region (Germany, Czech Republic, Austria, Switzerland) and due to availability of free historic

weather data from the Deutcher Wetterdienst Climate Data Centre (CDC).

4.4.1 Flood cycle

Forthedefinitionoftheperiodsofrainandfloodconsideredintheexperimentalcampaign,weather

datafromGermanywasinitiallyanalysed,morespecificallythedatafromDeutcherWetterdienstClimate

DataCentre(CDC),correspondingtotheMay-June2013CentralEuropeanflood,wherehighvaluesof

rain were recorded over the Elbe, Rhine and Danube catchments. The data was acquired for the Straubing

weather station, which is situated North-East of Munchen on the Danube in an area known as the Gäuboden,

whichisoneofthelargestloessregionsinGermanyspreadingapproximately15kmalongtheDanube.

Theareahasbeensubjectedtomanyfloodingeventsalongthehistory.

An example of the daily information about the quantity of precipitation, temperature and relative

humidityfortherainandfloodperiodscanbeseeninFigure34.Thedefinitionofthenumberofcyclesand

theparametersspecificforeachcyclewascarriedouttakingintoaccountthementioneddata.Themodel

definedintheexperimentalcampaignwassimplifiedtoanextentwhichwasconsideredfeasibleforthe

laboratory conditions.

Figure 34:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24PRECIPITATION mm/h 0,9 0,4 0,2 2,2 1,4 3,7 0,9 0,3 0,2 0 0,5 0,1 0 0,6 2,7 5,5 1,8 0,5 0 0,1 0,3 3 2,2 0,2R.H. % 97 97 96 97 97 97 97 95 95 92 94 93 92 94 97 98 97 96 95 96 96 97 97 97TEMPERATURE °C 11,5 11 10,9 10,9 10,7 10,6 10,3 10,2 9,9 9,8 9,2 9,2 9,3 9,2 8,7 8,4 8,2 8,2 8,3 8,3 8,2 8,1 8,1 8

0

20

40

60

80

100

120

0

1

2

3

4

5

6DAY 520130602

PHASE A WIND DRIVEN RAIN

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24TEMPERATURE °C 8 7,9 7,7 7,8 7,9 8,3 8,6 9,3 9,9 11 11,8 13,7 13,5 15,4 15,2 15,2 15,3 15,2 13,9 13,3 12,9 12,8 12 11,7R.H. % 98 97 100 100 97 97 100 95 94 87 86 82 76 68 70 71 68 70 83 93 93 95 98 99

0

20

40

60

80

100

120

0

2

4

6

8

10

12

14

16

18DAY 720130604

PHASE BFLOOD

Sampledailyhourlycycle:W.D.R.(left),flood(right)

Cyclic procedure adopted


Therefore, the rain cycles were derived from the observed total amount and duration of the

precipitation, thus determining an hourly mean amount of precipitation. The determined mean value of

1.1416 mm/h (l/h) corresponds to a light rain intensity according to the Glossary of Meteorology (June

2000) by the American Meteorological Society.

In Table 4, the values for the total amount of precipitation and the hours of precipitation for the rainiest

days of May-June 2013 are presented. Based on these values, the average precipitation per hour was

calculated. Additional information is also given in relation to the mean temperature and mean air relative

humidity

Station ID Date Total precipitation

Hours of precipitation

Hourly mean precipitation

Mean temperature

Mean R.H

4911

20130529 10.4 11 0.95 9.33 95.1320130530 11.8 9 1.31 9.7 88.13.20130531 17.7 13 1.36 9.13 96.3320130601 17.1 14 1.22 9.64 9820130602 27.7 21 1.32 9.38 95.7920130603 11 16 0.69 7.94 96.83

Table 4: Straubing weather parameters May-June 2013

Due to hardware limitations it was decided to apply a factor of 10 to the average value of precipitation

previouslycalculated.Therefore,thefinalamountofprecipitationusedis12l/h,whichcorrespondstoa

heavy rain intensity.

The daily Wind Driven Rain program consists of a four-hour wind driven rain period followed by a four

hour drying period. This procedure was repeated 108 times (27 days) followed by a 7 days drying period,

see Figure 35 left.

Forthefloodcycle(Figure35right),itwasdecidedtoconsiderthesameraininganddryingbase

cycle as the one adopted for the wind driven rain, repeated for 4 days. After this, the connections were

submerged for 7 days, after which a drying period of 7 days was implemented.

Figure 35:


4hoursWDR

4hours

DRYING

24hours

FLOOD

24hours

DRYING

7x4x 7x

4hoursWDR

4hours

DRYING4hoursWDR

4hours

DRYING

4hoursWDR

4hours

DRYING

4hoursWDR

4hours

DRYING

24hours

DRYING

27x 7x

4hoursWDR

4hours

DRYING4hoursWDR

4hours

DRYING

4hoursWDR

4hours

DRYING


4hoursWDR

4hours

DRYING

24hours

FLOOD

24hours

DRYING

7x4x 7x

4hoursWDR

4hours

DRYING4hoursWDR

4hours

DRYING

4hoursWDR

4hours

DRYING

4hoursWDR

4hours

DRYING

24hours

DRYING

27x 7x

4hoursWDR

4hours

DRYING4hoursWDR

4hours

DRYING

4hoursWDR

4hours

DRYING

Left: Wind Driven Rain cycle diagram Right: Flood cycle diagram

38



4.5 Experimental setup

4.5.1 Experimental installation

Tobeabletosimulateextremeweatherconditionscapableofoutputtingsuccessivecyclesofheavy

rain and drying, aswell as flood conditions to further assess the influence of these in themechanical

performance of traditional timber connections, it was needed to design a new test setup given the absence

of an available appropriate climatic chamber.

The timber connections were positioned in reused IBC tanks with a 1000l volume. The water is

transferred from the tanks to the spray nozzles through an upstream hydraulic system composed of a

waterpump,3/4PVCpipes,flexiblehoseforthepumpconnectionandbrassaccessories.Thepumpis

connected toanuptakepipeandtoaTeeconnectorspreading thewateroutput in two: thefirstpart is

composed of a L shape horizontal pipe which is linked to a system of three S shape brass connections and

thenozzles;thesecondoneconsistsofavalveandpressuregauge.IneachSshapebrassconnection,

theanglecanbeadjustedintwodirections.Foreachsystemastrainerfilterandawaterpumpfilterwas

added to prevent the nozzles from clogging with impurities. By closing or opening the valves, the pressure

in the system increases or decreases, leading to a water output from 10l/hour to 15l/hour for each nozzle.

The water valve was adjusted in this case to have a 0.8 bar pressure in the hydraulic system so that the

output water in each nozzle was 12 l/hour.

Theadjustablespray’sdiameterfromthecommercialspraynozzleswassetatapproximately300

mm, positioned at a 45° angle regarding the timber connection

It should be mentioned that each tank functions in a closed loop circuit. Each tank works as a water

reservoir, the water pumped through the nozzles and respectively the output valve is being drained back

in the tank.

Threetankswerepreparedtosimulatewinddrivenrainconditionsandoneasafloodsimulator.

In each tank, three connections were placed on a timber bedplate support meant to simulate the contact

conditions found in situ.

Atop each tank an oscillating fan was mounted so that the circulated air will reach all three samples.

After running the test for a period of time it was observed that the fan doesn’t enhance enough the drying

conditions so a 1000 W portable heater was added to each tank to obtain to the drying parameters needed.

Experimentalsetup


Figure 36:


2

3

4

5

6

7

A

C

B

1

Planviewoftheexperimentalsetup: 1 1000 l IBC tank, 2 pump, 3 water input, 4 pressure

gauge, 5 water valve, 6 fan/ heater, 7 nozzles, A,B,C samples

4.5.2 Sample preparation

Before positioning the samples to undergo the weathering cycles, some measures were taken to

achieveamorerealisticrepresentationofin-situconditions.Tosimulatethemasonryinfillanditsinfluence

regarding the water transfer into the connections during the wind driven rain cycles, sheets of recovered

plastic from the tank cut-outs were glued on each sample as seen in Figure 37. The position of the sheets

considered was 20 mm from the connection’s front edge thus preventing direct wetting of the timber element

but allowing an edge were the water can set reproducing more realistically the in situ condition.

A loop screw was inserted in the top of each sample to secure them from overturning during the

experimentphases.TheG.F.R.P.reinforcementappliedat thetopof thepost forensuringanadequate

connection to the vertical anchor in the mechanical testing was protected from direct water contact by

covering it with duct tape.

40



Figure 37: Sample preparation

Three of the prepared samples (unreinforced, double threaded screws reinforced, steel plates

reinforced) will be subjected to 540 cycles (90 days) and will be tested in August 2016 for their mechanical

characterization.

4.5.3 Monitoring procedures

The cycles of wetting (wind driven rain) and drying, were controlled in an automatic way through a

LabVIEWsoftwareaswellashardwareequipmentcomposedofarelaymodule,whichturnsoffandon

therainanddryingcyclesconfiguredinthesoftware,seeFigure.Formeasuringtherelativehumidityand

temperature a data logger system was set up to acquire data every 5 minutes and write it on a SD card.

Figure 38: Monitoring equipment

Experimentalsetup


Figure 39: Testing and monitoring rig

For the monitoring process, a load cell was connected to one unreinforced timber connection

(specimen U1) aiming to record in a continuous way the variation in weight across the wetting and drying

periods. The real time weight of the specimen was recorded at a 5 minute interval trough a data acquisition

board.

Figure 40: Load cell equipment

FLOOD{ W.D.R.

TANK 1{

TANK 2{

TANK 3{

TANK 4{{

42



A daily control schedule was implemented to measure the weight of all the samples after 4 wetting

and drying cycles (1 day). The data was collected each day at the end of a drying cycle (14:00 o ‘clock) and

at the end of a wetting cycle (18:00 o’clock). To be notice that this procedure could be avoided if enough

load cells were available in the laboratory. However, due the lack of this equipment, it was needed to follow

the variations in the weight of the specimens by obtaining these values manually.

Four environmental moisture and temperature sensors were mounted in the W.D.R. tanks.

Additionally, one temperature and moisture sensor was placed outside of the tanks to record the air relative

humidity and temperature in the laboratory. These measurements were taken in order to observe if any

influenceoftheexternalenvironmentconditionsoccurinthedryingprocess.

Another daily control program was set to observe and try to determine the water absorption rate

in the post and to observe the patterns of water migration through the joint. Daily data was acquired by

measuring the moisture content of the timber at a depth of 20 mm in the positions showed in the diagram

below for each connection subjected to the W.D.R. cycles, see Figure 42. To measure the moisture content

of the wood a Gann Hydromette HT85 T equipment was used. The same position of the pins was used for

all the measurements (Figure 41).

Figure 41: Gann Hydromette HT 85 T moisture meter equipment

For the beam this procedure could not be adopted because the top of the beam was always wet

during the wetting cycles.

Experimentalsetup


Figure 42:


25 25

25

50

25

50

2

1

4

3

Moisture reading positions

Inafirstphaseand in theabsenceof reliablemoisturemeasurementequipment, itwasdecided

to carry out preliminary investigations to evaluate the feasibility of using a system to measure the water

migration through the timber specimens in real time, in both wetting and drying cycles based on the

electrical resistanceprinciple, following incertainextent thewayastandardmoisturemeterworks.For

this,twometallicpinswereintroducedatdifferentdepthinprismaticspecimens(Figure43),expectingto

measure the capillary behaviour of the specimen through the variation of the electrical resistance between

the metallic pins. The increase on the moisture content of the area between the pins should result in the

decrease of the electrical resistance.

Differentlayoutsregardingdistanceanddepthhavebeentestedforbothcasesofwatermigration

bycapillarityonaparallelandperpendiculardirectiontothewoodenfibres.Forthisstudyasimilarsample

subjectedtotheenvironmentalconditionshasbeenused,mainlytocheckifthefluctuationsoftemperature

andairrelativehumidityinfluencetheresults.

The measurements carried out appear to indicate some sensitivity of the system to detect moisture

movements, as it can be seen in Figure 44, where the variation of electrical resistance in the transition

period from the wetting to drying cycles by considering cooper and steel pins is shown. In spite of this, it

was decided not to apply this type of measurement in the tested connections, as it is very time consuming

in what concerns the sample preparation, it requires a large amount of hardware and the output data is only

qualitative.

44



Otherfactorslikethewaterproofingofwiringandsoldering,sensitivitytolightshocks,highamountof

noise in the readings and low validity and reliability of the data also add to those presented above.

Figure 43: 1 3

2

Testarrangements:1.Twopointsparalleltothefibertesting;2.Twopointsperpendiculartofibertesting;3.Fivepointsperpendiculartofibertesting

Figure 44:

4.760.000

4.765.000

4.770.000

4.775.000

4.780.000

4.785.000

4.790.000

4.795.000

4.800.000

4.805.000

4.810.000

4.815.000

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

hand

ling

hand

ling

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ng

DC V

olta

ge

Copper

4.350.000

4.400.000

4.450.000

4.500.000

4.550.000

4.600.000

4.650.000

4.700.000

4.750.000

4.800.000

4.850.000

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

wet

ting

hand

ling

hand

ling

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ngdr

ying

dryi

ng

DC V

olta

ge

Steel

Perpendiculartothetimberfibrewatermigrationdiagramforcopperandsteelrodsunderwetting and drying cycles

Cyclic test results


4.6 Cyclic test results

4.6.1 Relative humidity and temperature monitoring of the W.D.R. cycles

The laboratory does not have any H.V.A.C. system which controls the environmental parameters

(air relative humidity and temperature). Therefore, it was decided, as previously mentioned, to monitor the

laboratory environmental conditions by installing relative humidity and temperature sensors. As it can be

observedinFigure45,therelativehumidityandtemperatureinthelaboratoryareinfluencedbytheexterior

conditions.Aselectedperiodoftime,namelyfromJune23toJuly062016,wasselectedforexemplification

due to the data consistency.

Figure 45:

0

10

20

30

40

50

60

24.0

5.20

16

25.0

6.20

16

26.0

6.20

16

27.0

6.20

16

28.0

6.20

16

29.0

6.20

16

30.0

6.20

16

01.0

7.20

16

02.0

7.20

16

03.0

7.20

16

04.0

7.20

16

05.0

7.20

16

06.0

7.20

16

Ambient T.

Ambient R.H.

Ambient temperature and relative humidity

There have been many malfunctions while trying to acquire the relative humidity and temperature

data, mainly due to the sensitivity of the sensors while working in very damp environments which caused

malfunctions in the recording of the data process and its validity. Another problem encountered was related

to the power shortages causing the system to reset in the absence of a UPS battery backup system.

Instances of the system crashing were recorded also because of the overheating of the computer used for

monitoring.

In any case, it was possible to analyse the general trend for temperature and air relative humidity

inside the tanks. For the studied time sequence the ambient temperature minimum value was 20°C and

themaximum29°Cwithanaverageof23.98°Coverthe14days.Theminimumambientrelativehumidity

valuesrecordedare34%andthemaximum48%withanaverageof38.9%whichisarelativelowvalue

46



but valid because of the hot summer days and the absence of activities which can lead to an increase of

these values.

The wetting and drying periods corresponding to the W.D.R. cycles have created a ‘microclimate‘ in

eachtank.InFigure46,twodistinctsequencesofdatawithminimumandmaximumvaluesfortheR.H.

and temperature in the tanks can be observed, namely one corresponding to the drying cycles without the

heater and the second one corresponding to the period in which a heater was added to the tanks trying

toimprovethedryingconditionsTheminimumtemperaturewasslightlyincreasedandthemaximumR.H.

values remain the same but the minimum value for the R.H. decreases in the second period and the

maximumvaluesfortemperatureincreases.

The values of temperature in the drying cycles with only the fan attached were 20°C at minimum and

28°Catmaximumwithanaveragevalueof22.27°C.Concerningthe,R.H.,theminimumvaluesrecorded

wereof53%andmaximumof95%withanaverageof88.61%.Whentheheaterwasadded,theminimum

temperaturewas22°C,themaximumtemperaturewas31°C,withameanvalueof26.65°C.Regardingthe,

R.H.,theminimumvaluewas39%,themaximumvaluewas95%,withanaverageof74.66%.

Figure 46:

0

10

20

30

40

50

60

70

80

90

100

13.0

6.20

16

14.0

6.20

16

15.0

6.20

16

16.0

6.20

16

17.0

6.20

16

18.0

6.20

1619

.06.

2016

20.0

6.20

1621

.06.

2016

22.0

6.20

1623

.06.

2016

24.0

5.20

16

25.0

6.20

16

26.0

6.20

16

27.0

6.20

16

28.0

6.20

16

29.0

6.20

16

30.0

6.20

16

01.0

7.20

16

02.0

7.20

16

03.0

7.20

16

04.0

7.20

16

05.0

7.20

16

06.0

7.20

16

Sensor2 T.

Sensor2 R.H.

Tank relative humidity and temperature Sensor 2

Nodifferenceswereobservedbetweenthereadingsfromthetwodifferenttanks,meaningthatthe

wettingcyclesmaintainedaconstantandsimilaroutputinallthetanks.Differentvaluesinthereadings

were recorded depending on the positions of the sensors with regard to the heat and water sources. The

sensors were positioned at the top side of the tank, distributed as shown in Figure 47. A plastic cover was

manufactured for all sensors to protect them from getting wet.

Cyclic test results


As seen in Table 5, the values of the temperature and relative humidity measured in the same

tankfromdifferentsensorsareshown,thedissimilaritiesareevidentparticularlytotherelativehumidity

recorded during the drying cycles.

Sensor IDTemperature [°C] Relative humidity [%]

PositionMin. Max. Average Min. Max. Average

4 22 31 25.39 29 95 51.65 behind3 20 29 23.77 36 95 62.94 lateral5 21 29 24.32 37 95 73.30 in front

Table 5: Environmental data from the W.D.R cycles

Figure 47:


TANK 2 TANK 1

4 3 5

1

2

Sensors layout

The variation of the RH and temperature values in time are shown in Figure 48. The inconsistencies

observed in the graphs correspond to the following malfunctions of the monitoring equipment: 1). the gap

increase between cycles corresponds to the system crashing and the fact that the cycle remains stuck in

the drying sequence, 2). the gap decrease corresponds to a system reset which involved the restart of the

wetting sequence and 3). the decrease in amplitude corresponds to a low pressure in the pump system or

a clog of the nozzles.

In any case, it is important to stress that the system worked reasonably well, but this type of

deficienciesshouldbesolvedinfutureexperimentalcampaigns.

48



Figure 48:

0

10

20

30

40

50

60

70

80

90

100

24.0

5.20

16

25.0

6.20

16

26.0

6.20

16

27.0

6.20

16

28.0

6.20

16

29.0

6.20

16

30.0

6.20

16

01.0

7.20

16

02.0

7.20

16

03.0

7.20

16

04.0

7.20

16

05.0

7.20

16

06.0

7.20

16

Sensor3 T.

Sensor3 R.H.

0

10

20

30

40

50

60

70

80

90

100

24.0

5.20

16

25.0

6.20

16

26.0

6.20

16

27.0

6.20

16

28.0

6.20

16

29.0

6.20

16

30.0

6.20

16

01.0

7.20

16

02.0

7.20

16

03.0

7.20

16

04.0

7.20

16

05.0

7.20

16

06.0

7.20

16

Sensor4 T.

Sensor4 R.H.

0

10

20

30

40

50

60

70

80

90

100

24.0

5.20

16

25.0

6.20

16

26.0

6.20

16

27.0

6.20

16

28.0

6.20

16

29.0

6.20

16

30.0

6.20

16

01.0

7.20

16

02.0

7.20

16

03.0

7.20

16

04.0

7.20

16

05.0

7.20

16

06.0

7.20

16

Sensor5 T.

Sensor5 R.H.

Tank relative humidity and temperature: top Sensor 5, bottom left Sensor 3, bottom right Sensor 4

4.6.2 Water migration and content in the samples subjected to W.D.R. cycles

As described previously a moisture content measuring procedure was adopted to determine a pattern

of water migration through the wooden connection by measuring the humidity through a moisture meter.

Most points located at 75 mm from the top of the beam presented a constant evolution of the moisture

content preserving with a small margin the initial values of moisture content.

Based on visual observation, and taking into consideration the values obtained by measuring the

moisture content in the post, Table 6, a diagram was drawn on the connection’s wetting evolution, Figure

49. The four stages correspond to each of the four hours forming the wetting cycle. It was observed that

inthefirsthourofthetestonlytheexposedpartofthepostgetssoaked,giventhattheplasticsheetsact

asabarrier.Thepositionoftheheartwoodinrelationshipwiththesectionofthebeamalsoinfluencesthe

pattern of water propagation, having a slower rate in the heartwood than in the sapwood. The presence of

the timber bedplate support facilitates also a faster rate of water sorption for the bottom of the beam due to

the permanent presence of water.

Cyclic test results


Water present behind the plastic sheets can be observed in small amounts only at the end of the

cycle, as sorption perpendicular to the wood grain has a very slow rate of propagation.

The water migration through the post presents two distinctive patterns. The predominant pattern

consists on water migration through the post alongside the wood grain and the other pattern consists in

water migration from the beam to the post by direct contact. The latter pattern is strictly dependent on the

joint quality between the top surface of the bean and the post. Therefore, a direct correlation between the

gaps present in the joint and presence of water in the measured points was observed. Most of the points

where a high moisture level is present correspond to a tight connection between the post and beam thus

facilitating a higher rate of moisture transfer. Highlighted in Table 6 with a darker hue are the values taken

in the points where it could be observed visually that the timber was soaked.

Figure 49: Qualitative water sorption diagram: beam (left), post (right)

50



Table 6:

IDD

ate

Tim

e

Moi

stur

e [%

]Ta

nk 1

Tank

2U

1S1

P1U

2S2

P21

23

41

23

41

23

41

23

41

23

41

23

41

10.0

6.16

18:0

0Lo

ad c

ell

--

--

--

--

--

--

--

--

--

--

211

.06.

16-

--

--

--

--

--

--

--

--

--

-3

12.0

6.16

--

--

--

--

--

--

--

--

--

--

413

.06.

16-

--

--

--

--

--

--

--

--

--

-5

14.0

6.16

20.8

21.5

19.1

20.6

19.6

21.9

49.3

21.8

19.7

20.6

23.9

21.3

20.2

20.1

26.3

19.8

21.7

21.2

2423

.66

15.0

6.16

20.6

21.4

18.7

19.1

18.3

20.3

53.1

20.8

19.1

20.5

23.1

20.8

20.2

19.4

27.9

19.1

21.2

2021

.822

.27

16.0

6.16

20.5

21.3

18.6

19.9

19.2

20.2

58.6

20.6

19.7

21.1

23.7

21.6

20.3

19.7

30.2

19.9

21.5

20.7

22.2

22.6

817

.06.

1619

.921

.418

.920

.619

.519

.863

.220

.620

21.5

24.1

22.3

20.6

19.8

31.5

19.6

2120

.923

.121

.99

18.0

6.16

19.5

20.5

1818

.919

.820

.964

.620

.119

.219

.521

.320

20.5

1929

.518

.920

.220

.121

.420

.710

19.0

6.16

18.6

20.4

18.4

19.2

19.6

19.5

64.6

20.1

19.1

20.2

22.8

2019

.619

.229

1920

.719

.821

.120

.111

20.0

6.16

19.3

20.9

1919

.720

.919

.866

.720

.721

.220

.123

.420

.421

20.7

63.1

19.4

20.5

20.8

2220

.312

21.0

6.16

19.4

2119

.419

.320

.519

.466

.620

.520

.820

24.1

21.3

20.1

2030

.619

.721

.620

.222

.221

.913

22.0

6.16

19.2

20.4

18.9

1920

.419

.566

.820

.120

.420

.123

.620

.619

.819

.830

.419

.422

.520

.722

20.6

1423

.06.

1618

.819

.918

.219

20.3

19.8

68.6

19.9

26.1

20.1

23.3

19.9

19.2

18.3

28.1

18.6

26.1

20.4

22.1

19.8

1524

.06.

1618

.619

1818

.420

.519

.268

.819

.624

.619

.823

.419

.818

.918

.829

.518

.825

.420

.222

.220

.116

25.0

6.16

18.3

18.1

18.4

18.2

19.8

18.8

69.6

19.5

22.5

19.6

24.6

19.6

19.3

18.6

30.6

18.4

25.8

20.1

21.8

19.6

1726

.06.

1618

.118

.118

17.8

19.8

1869

.919

.320

.518

.528

.419

.418

.718

.232

.618

.226

19.6

21.2

19.3

1827

.06.

1618

.317

.918

.218

.319

.218

.468

.919

.521

.219

.228

.919

.619

.418

.331

.818

.625

.619

.821

.619

.619

28.0

6.16

18.4

18.4

18.1

18.1

19.5

18.7

69.6

19.2

2218

.929

19.9

19.8

18.8

32.4

18.2

2519

.421

.819

.520

29.0

6.16

17.8

18.3

17.9

18.2

19.6

18.2

69.8

19.4

21.8

19.4

29.4

19.8

19.2

19.7

32.1

18.4

24.8

19.6

21.8

19.3

2130

.06.

1617

.418

.117

.417

.819

.117

.971

19.1

21.5

18.7

29.7

19.4

19.4

18.3

32.5

18.2

23.4

19.4

2119

.322

01.0

7.16

18.3

18.3

17.7

17.9

20.9

18.4

71.9

19.5

22.3

19.5

36.1

19.8

29.3

25.6

32.6

18.8

25.5

19.7

21.7

19.5

2302

.07.

1617

.818

.118

17.8

19.6

18.2

68.8

19.4

22.5

19.4

34.2

19.9

24.6

19.7

34.6

18.4

24.7

19.8

21.6

19.6

2403

.07.

1617

.617

.917

.818

22.4

17.8

68.6

19.7

23.4

19.8

32.7

19.6

22.8

19.4

32.8

18.6

25.2

19.4

20.8

19.3

2504

.07.

1617

.317

.918

18.2

23.3

18.1

67.6

19.7

23.9

20.2

33.4

19.5

22.7

18.8

3519

23.6

19.6

20.9

19.9

2605

.07.

1617

.818

17.7

18.2

23.1

18.2

68.9

19.5

22.6

20.1

32.9

19.6

22.8

19.7

34.8

18.7

23.8

19.6

20.4

19.4

Moisture content history of the samples subjected to W.D.R. cycles

Cyclic test results


4.6.3 Weight history of the samples subjected to W.D.R. cycles

Two distinct sequences can be observed in the weight history diagrams of the samples, both in the

onerecordedwiththeloadcellandinthedailyweightmeasurements.Inthefirstsequence,theweight

increases (upward trend) in a cumulative way during the wetting periods, only part of the weight increment

islostinthedryingperiod,seeFigure50andFigure51.Thisisassociatedtotheinsufficientdryingpower

of the fans (left part of the diagram). The second one (central part of the diagram) it appears that the

weight gains during the wetting period are compensated by the loss of weight during the drying period.

Thisbehaviourisassociatedtotheinfluenceoftheheateraddedinthetanks,meanttoenhancethedrying

conditions.Exceptforthefirstwettingcyclewhichconsistsina450gramwaterintakeforthetimbersample

most of the wetting cycle describe a regular water intake varying from 30 grams to 170 grams per wetting

cycle with an average of 121 grams per cycle.

If there were no errors in the data acquisition of the weight from the load cell, it could be concluded

thattheheaterlevelledthewettinganddryingcyclesresultinginanapproximatecomplete(round)series

of occurrences. Before adding the heater, the fan didn’t manage to realize this, resulting in a over-wetting

of the sample with a value between 10-20 grams per cycle.

Figure 50: Weight history graph for sample U1 recorded with a load cell

52



It should be mentioned that two types of errors were observed during the data acquisition of the

weight through the load cell: 1). E1 is characterized by the wetting-drying cycles control system crashing,

resulting in the cycle being stuck in the drying period thus leading to a decrease in weight and 2). E2 is

characterized by data loss, the errors are highlighted in Figure 50. It was considered that the problems

which occurred during the data acquisition are not relevant for the analysis of the results.

The weight valuesmeasured daily after the wetting and drying cycles for the different types of

connections (unreinforced, double threaded screws reinforced and steel plates reinforced) are shown in

Figure 51. The manual data (Table 7) is not as accurate as the one obtained with the load cell. It is seen

thatasaconfirmationoftheloadcelltrend,thereisinthefirstphaseacumulativeincreaseoftheweight

associatedtotheinsufficientdryingoftheconnections.Besides,anysignificantdifferenceswereobserved

between thewettinganddryingcyclesamongthedifferent typesofconnections in thefirstperiod.The

uniquedifference is thehigherweightof theconnectionstrengthenedwith thesteelplates.However, it

appears that after the positioning of the heater, the weight of the unreinforced connection and the double

threaded screws reinforced connection, has a slight decreasing cumulative trend. This can indicate that the

heaterenablesamoreefficientdryingconditionfortheconnectionswithoutsteelplates.Thisshouldbe

attributed to the steel plates acting as a barrier for the water evaporation.

Thewettingcyclesdescribedawaterintakevaryingfromaminimumof20gramstoamaximumof

220 grams per cycle with an average of 97 grams per cycle.

Figure 51: Weight history graph of the samples subjected to the W.D.R. cycles

Cyclic test results


Table 7:

ID Date TimeWeight [kg]

Tank 1 Tank 2U1 S1 P1 U2 S2 P2

1 10.06.16 14:00 10.62 10.7 14.08 10.48 11.02 13.52 11.06.16 14:00 10.73 10.77 14.37 10.57 11.17 13.593 12.06.16 14:00 10.84 10.83 14.49 10.67 11.21 13.694 13.06.16 14:00 10.93 10.88 14.58 10.76 11.26 13.78

5 14.06.1614:00 10.91 10.96 14.62 10.84 11.36 13.8818:00 11.07 11.04 14.72 10.92 11.42 13.9

6 15.06.1614:00 10.9 11.02 14.62 10.84 11.38 13.8818:00 11.02 11.04 14.72 10.92 11.44 14

7 16.06.1614:00 11.08 11.08 14.76 11.02 11.54 14.0418:00 11.13 11.14 14.88 11.06 11.58 14.07

8 17.06.1614:00 11.16 11.18 14.86 11.04 11.56 14.0618:00 11.23 11.18 14.88 11.06 11.6 14.1

9 18.06.1614:00 11.2 11.14 14.84 11 11.52 14.118:00 11.33 11.3 14.9 11.08 11.66 14.06

10 19.06.1614:00 11.24 11.22 14.9 11.02 11.58 14.1618:00 11.4 11.28 14.94 11.12 11.7 14.16

11 20.06.1614:00 11.36 11.26 14.92 11.18 11.68 14.1418:00 11.44 11.28 14.96 11.2 11.72 14.2

12 21.06.1614:00 11.21 11.16 14.8 11.06 11.6 14.0818:00 11.34 11.28 14.92 11.16 11.64 14.2

13 22.06.1614:00 11.32 11.22 14.94 11.18 11.6 14.2218:00 11.43 11.28 15.06 11.28 11.7 14.26

14 23.06.1614:00 11.29 11.2 14.96 11.22 11.6 14.2418:00 11.45 11.28 15.04 11.32 11.7 14.28

15 24.06.1614:00 11.34 11.26 15 11.28 11.76 14.318:00 11.45 11.33 15.03 11.39 11.84 14.38

16 25.06.1614:00 11.33 11.26 15.06 11.29 11.7 14.3518:00 11.46 11.32 15.1 11.4 11.78 14.45

17 26.06.1614:00 11.29 11.22 15.04 11.26 11.6 14.4218:00 11.44 11.32 15.14 11.46 11.76 14.48

18 27.06.1614:00 11.22 11.22 15.08 11.4 11.66 14.4218:00 11.36 11.33 15.16 11.5 11.74 14.52

19 28.06.1614:00 11.21 11.2 15.1 11.42 11.62 14.4618:00 11.34 11.28 15.2 11.52 11.74 14.55

20 29.06.1614:00 11.36 11.26 15.12 11.42 11.68 14.4518:00 11.39 11.36 15.2 11.54 11.78 14.54

21 30.06.1614:00 11.27 11.25 15.12 11.54 11.64 14.4418:00 11.37 11.36 15.22 11.6 11.74 14.54

22 01.07.1614:00 11.3 11.31 15.02 11.46 11.77 14.518:00 11.43 11.42 15.14 11.58 11.86 14.62

23 02.07.1614:00 11.2 11.22 14.98 11.34 11.56 14.3818:00 11.35 11.34 15.12 11.44 11.68 14.5

24 03.07.1614:00 11.24 11.2 14.88 11.38 11.52 14.3218:00 11.35 11.28 15 11.51 11.62 14.46

25 04.07.1614:00 11.29 10.98 14.78 11.46 11.64 14.2618:00 11.45 11.16 14.84 11.58 11.42 14.42

26 05.07.1614:00 11.36 11.18 14.92 11.48 11.62 14.3618:00 11.53 11.32 15.08 11.58 11.74 14.54

27 06.07.16 14:00 11.39 11.18 14.96 11.56 11.7 14.48

Weight history of the samples subjected to the W.D.R. cycles

54



AsseeninTable8,theweightrecordedattheendofthefinaldryingperiodof7daysforthesamples

subjectedtotheW.D.R.cyclesapproximatelyreachthevaluesrecordedinitially(12%)atthebeginningof

theweatheringcycles.Itcanbeconcludedthatthesamplesapproximatelyreturnedtotheinitialmoisture

content after the drying period before undergoing the mechanical testing.

Sample IDWeight [kg]

Initial12% End of W.D.R. cycles Endoffinaldryingperiod(7days)

U2 9.38 11,56 9.48S2 9.57 11,7 9.62P2 12.44 14,4 12.62Table 8: InitialandafterfinaldryingperiodweightofthesamplessubjectedtotheW.D.R.cycles

4.6.4 Weight history of the samples subjected to the flood cycle

As presented in the sub-chapter 3.3.1. the weathering program adopted consisted in 16 cycles of

fourhoursofwinddrivenrainandfourhoursofdrying,followedbyasevendayfloodperiodandaseven

day drying period.

Sample IDWeight [kg]

Initial12% End of W.D.R. cycles Endoffloodperiod End of drying periodU3 9.86 10.54 12.36 10.26S3 9.9 10.5 12.10 10.18P3 12.38 13.06 14.98 13.02

Table 9: Weighthistoryofthesamplessubjectedtothefloodcycles

4.6.5 Visual inspection of the connections after the weathering cycles

It was observed that on all of the connections subjected to W.D.R. cycles the metallic elements

started to rust: the nail in the case of the unreinforced connection, the drive from the screws head in the

double threaded screws reinforced connection and regions of the pre-drilled holes in the steel plates for the

corresponding connection.

The samples subjected to the W.D.R. cycles presented a colouring of the timber in the parts of direct

contact with the sprayed water due to the fact that the water was not changed and a lot of debris from

Cyclic test results


the connection supports and dust accumulated in the tanks. On some specimens a dark grey and white

coloration was observed, probably due to biological colonization.

Despiteofnovisibledamagepresentafterweatheringcycles,itisknownthatunderspecificcyclic

environmental conditions, the microstructure of timber changes. In fact, the number of hygroscopic states

of equilibrium through which the timber is subjected by always changing the environmental conditions can

generate microscopic damage (irreversible changes in the microstructure of the timber). By increasing the

RH over the initial equilibrium a phenomenon of sorption in the timber (admitting water molecules from the

surrounding environment) occurs. On the other hand, by decreasing the RH the phenomenon developed

is desorption (releasing water molecules into the surrounding environment). Repeated cycles decrease

the wood’s hygroscopicity as demonstrated by (Esteban, Grill et al. 2005). Therefore, further investigation

shouldbecarriedouttodeterminehowthistypeofcyclesinfluencesthemicrostructureandtheoverall

mechanical behaviour of the timber elements.

Figure 52: Sorption and desorption isotherms (Esteban, Grill et al. 2005)

4.6.6 Water migration during final drying period

Using a thermal imaging camera (FLIR-T62101), the water migration in the specimens was recorded

inaqualitativewayduringthefinaldryingperiodof7days.Infraredtechnologyallowstoinstantlyvisualize

thethermalconditionofanobject,allowinginthiscasetocorrelatethedifferenttemperaturesregistered

with the water content in the joint. A lower temperature indicates a higher RH in that zone.

Observingthethermalimagesofthespecimensatthebeginningofthefinaldryingperiod(Figure53),

itisimmediatelynoticeablethedifferencebetweenthespecimenssubjectedtofloodandthosesubjectedto

WDR.Whilethefloodspecimensabsorbedwaterinauniformway,beingsubmergedconstantlyinwater,

WDR specimens have an accumulation of water in the joint region, as the water enters through the gaps

56



that are inevitably present in carpentry joints, and at the bottom of the beam where the support was.

Figure 53: Infrared image of the connections at the beginning of the drying period: left: connections subjectedtofloodcycles;centreandright:connectionssubjectedtoW.D.R.cycles

Alreadyafter24hoursofdrying(Figure54)and48hoursofdrying(Figure55)differencescouldbe

noted in the temperature distribution of the specimens, therefore in the moisture content.

Figure 54: Infrared image of double threaded screws reinforced connection subjected to W.D.R. cycles after 24 hours of drying

Figure 55: Infrared image of double threaded screws reinforced connection subjected to W.D.R. cycles after 48 hours of drying

MECHANICAL EXPERIMENTAL PROGRAMME: PULL OUT TESTS


5. MECHANICAL EXPERIMENTAL PROGRAMME: PULL OUT TESTS

5.1 Introduction

Traditional timber joints work mainly in compression and friction among their elements. Due to the

manual work of the carpenter for the assemblage of timber elements, there can be some irregularities and

clearanceswhichinfluencetheirmechanicalperformance.Therefore,thecontactbetweenthemembersis

commonly improved by strengthening the connections with metal elements. Traditional timber connections

rely mainly on notches, wedges, bearing faces, mortises, tenons and pegs, while metal fasteners are less

present, though nails can be inserted to improve the connection (Poletti, 2013). On the other hand, metal

fasteners constitute an important tool in rehabilitation works.

Mechanicalconnectionsaredefinedasthosewherefastenerspenetratethewoodandareusually

divided into two categories: dowel and bearing (Soltis, 1996). Dowel type fasteners, such as nails,

screws and bolts, transmit either lateral load, by bearing stresses developed between the fasteners and

theelementsof theconnections,orwithdrawal load,whichareaxial loadsparallel to the fasteneraxis

transmitted through friction or bearing to the connected materials. Metal connector plates combine lateral

load action of dowel fasteners and the strength properties of the metal plates (Soltis, 1996). Bearing type

connectionstransmitonlylateralloads,forexampleshearplatesthattransmitonlyshearforcesthrough

bearing on the connected materials (Soltis, 1996).

In this Chapter, the behaviour of traditional connections adopted in Portuguese half-timbered walls

is analysed for joints subjected to wetting/ drying cycles. In particular, pull out cyclic tests were carried

outontheTshapehalflapjointsaftertheyweresubjectedcyclesofsimulatedtofloodsandwinddriven

rain, following the procedures described in Chapter 4. The most important results are herein presented

and discussed, namely force-displacement diagrams, failure modes and some key parameters such as of

strength,displacementcapacityandstiffness.Moreover, retrofittingsolutionsareanalysed, considering

those used and tested by Poletti (2013). A comparison was made of the results obtained to the results

obtainedbyPolettiunderthesameloadingconditions(2013)inordertobetterunderstandtheinfluenceof

the wetting and drying cycles on the degradation induced to the joints.

The evaluation of the deformation patterns and damage progress assists in the further understanding

of the mechanical behaviour, particularly when compared to sound specimens, and in the selection of the

58



mostappropriateretrofittingsolutionsfortraditionaltimberhalflapconnections,respectivelytimberframe

walls,especiallyifextremeweatherconditionsareexpectedtoaffectthejoints.

5.2 Sample preparation

It should be stressed that the test setup for the pull-out tests was designed to test the sound

connections and described by Poletti (2013). According to Figure 56, the specimens were secured at the

topofthepostwithaUsteelprofileandwerecyclicallypulled.Aimingatenablingtheapplicationofatensile

loadingintheconnections,aspecialUshapesteelprofilewasused.Specialattentionshouldbepaidto

thetypeofinteractionbetweentheUsteelprofileforthepull-outtestsandthetimberspecimen,sincelocal

damage should be avoided. The grip is ensured through four threaded rods that pass through the predrilled

holesintheUsteelprofileandthetimberspecimenfixedwithnutsandwashers(Figure56).Toavoidthe

possibility of a premature local failure occurring in the gripping point instead of the failure in the connection

under study it was decided to reinforce the top part of the post where the grip is set.

Figure 56:


GFRPreinforcementandsteelgripfixtureforthepull-outtests

Sample preparation


ThereinforcementwasrealizedbyapplyingtwouniaxialGFRPsheetsoneachsideofthepostwith

theirfibresperpendiculartothetimbergrain,impregnatedinepoxyresin.

Shallowgroovesofapproximately5mmweremade to the frontandbacksideof thepostwitha

heightof200mmequaltotheonethatisrequiredfromthesteelprofile,seeFigure57A.Theareawhere

the FRP would be applied was uniformized with sandpaper, the surface was degreased and all dust and

wood particles were removed by using a cloth impregnated in acetone.

TheGFRPusedisMapeWrapGUNI-AXproducedbyMapei(2012)andtheepoxyresinwasthe

MapeWrap31alsoproducedbyMapei (2013),withmediumviscosity.Theepoxy resinconsistsof two

componentswhicharemixedwitha4:1ratiobyweight,afterwardsthemixtureswasstirreduntilitbecame

homogeneous.

Withtheuseofabrush,theepoxywasappliedonthesurfaceofthetimberandtoimpregnatethe

GFRP strips, see Figure 57 B and C. After the impregnation, the GFRP sheets were positioned on the

timber surface (Figure 57 D) and then a paint roller was used to press the sheet to take the air bubbles out

andtomaximizetheadherencetothesurfaceofthewood,Figure57E.Anotherlayerofepoxywasapplied

andthen,thesecondGFRPsheetwaspositionedoverthefirstone,followingthesameprocedure(Figure

57 F). The same was done for the front and for the back side of the top of the post.

Figure 57: GFRP application procedure

After the procedure was repeated for all specimens they were left for 7 days to dry in order to obtain

themaximumtensilestrengthoftheepoxyresin(Mapei,2013).

60



Afterwards, the holes for the positioning of the threaded rods were drilled by using the steel grip

profileasaguidesothattheholesalign.

For the steel plate reinforced samples, in order to avoid slipping of the top anchorage part of the post

duetothehighstressesinvolved,anadditionalmeasurewastaken,i.e.placing4screwsof8x80mlaterally,

twoundereachrodsituatedinthemiddleoftheprofile,asadditionalreinforcementtopreventbendingof

the threaded rods and tearing of the post.

5.3 Test setup procedure and instrumentation

Pull-out tests were performed to test the uplifting capacity of the unreinforced and retrofitted

connections.

Thebeamoftheconnectionwasanchoredtoasteelprofilewhichwaslinkedtothereactionfloor

(Figure 58). The post was pulled-out by means of a hydraulic actuator which was linked through a hinge at

thetopofthepostbymeansofaUprofilegrippingthepostwithfour12mmdiameterthreadedrods.Notice

that, in order to prevent failure at the top gripping device, GFRP sheets were glued to strengthen the zone

as described in Subchapter 5.2. Similar testing setups have been realized by Poletti (2013) and Koukouviki

(2013).

Figure 58: Pull-out test setup (Poletti, 2013)

The actuator used had a load capacity of 250kN and a displacement range of 200mm. The same

procedure adopted for the sound specimens was used for the specimens subjected to wetting/drying cycles

Test setup procedure and instrumentation


andtofloodconditions.Twodifferentprocedureswereadoptedforunreinforcedandretrofittedspecimens,

consideringtheirdifferentcapacityandinitialstiffness(Figure59)(Poletti,2013).

Figure 59: Pull-out test procedures adopted: (a) unreinforced connections (b) reinforced connections

All specimens were monitored with linear variable displacement transducers (LVDTs) in strategic

positionsinordertorecordthemostsignificantdeformationoftheconnections.

For the pull-out tests of the unreinforced connections, LVDT V1 measures the vertical uplift at the

back of the connection, i.e. the separation between beam and post, LVDT OOPR measures the out-of plane

opening of the connection on the right side and LVDT OOPL measures the same opening on the right side

asseeninFigure54.Additionally,theupliftofthebeamfromthesteelprofiletowhichitwasanchoredwas

monitored through LVDT UP.

Figure 60: Instrumentation used during the unreinforced connections pull-out tests

62



For the pull-out tests of the double threaded screws reinforced connections, LVDT V1 measures the

vertical uplift at the back of the connection, i.e. the separation between beam and post, LVDT V2 measures

the vertical uplift at front of the connection, LVDT OOP measures the out of plane opening of the connection,

theupliftofthebeamfromthesteelprofiletowhichitwasanchoredwasmonitoredLVDTUP(Figure61).

Figure 61: Instrumentation used during the double threaded screws reinforced connections pull-out tests

For the pull-out tests of the perforated steel plates reinforced connections, LVDT V1 and LVDT V2

measures the vertical uplift of the post in relationship to the beam on the right and left side of the post, the

upliftofthebeamfromthesteelprofiletowhichitwasanchoredwasmonitoredLVDTUP(Figure62).No

out of plane opening was measured in this case, since it was prevented from the strengthening adopted.

Figure 62: Instrumentation used during the steel perforated plates reinforced connections pull-out tests

Results and comparison of the pull out test


5.4 Results and comparison of the pull out test

5.4.1 Unreinforced connections

From the results of the pull-out tests carried out on unreinforced connections, it was observed that

bothconnections,previouslysubmittedtofloodsandwinddrivenrain,behavedinasimilarway(Figure

63). The response is characterized by an out-of-plane opening when the post was pulled out and the

deformationofthenailwhenreleased.Theconnectionstoppedworkingwhenthenailwasnoteffective,as

it pulled out completely from the beam (Figure 63 centre).

Figure 66 presents a typical force-displacement diagram characterizing the pull out response of the

connection.Itisseenthatthediagramischaracterizedbyahighinitialstiffnessandanearlynon-linear

behaviour. In the unloading branch, the connection has an immediate loss of strength and then acquires

compression forces. This is associated to the reaction to the re-entering of the post to its original position in

the beam, due to the plastic deformation developed in the nail. On the other hand, the reloading branches

present a high amount of pinching, caused by the crushing of the wood surrounding the nail and consequent

increasing gaps. Important strength degradation is observed during the tests. This phenomenon is not only

observed between two successive steps, but also in the stabilization cycles.

Figure 63: Damage patterns of the unreinforced connections

64



Duringunloading,duetothedifficultyfortheposttoreachitsoriginalpositionbecauseoftheplastic

deformationofthenailanditsimpossibilitytore-enterthebeam,theconnectionexhibitsincreasingopening

values for increasing vertical uplift levels, and thus for a higher deformation of the nail (Figure 64).

Figure 64: Outofplanedisplacementoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood

Figure 65: Upliftoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood

Residual or permanent out-of-plane displacements can be observed for very high values of

displacement as well as important nail deformation. At the end of the test a permanent opening was

observed in the connections, being usually higher at the bottom of the post and lower at the top of the post,

indicatingitsrotation.Thevalueofopeningwasapproximately28mmforU2.ForthesampleU3wecan

observe a horizontal rotation of the sample, the recorded opening on the left side of the post was 42 mm

and on the right side of the post 27 mm (Figure 64).

The recorded values for the vertical uplift of the sample were of 0.02 mm for U2 and 0.04 mm for U3

(Figure 65).



The nail presented signs of rust, also the wood area surrounding it presented signs of colouring due

to this process as the result of the wetting cycles.

Itappearsthatthesampleswhichunderwentfloodingandwinddrivenrainweatheringcyclespresent

avaluesofstiffnessandstrengthsituatedbetweentheminimumandmaximumvaluesobtainedforsound

wood connections by Poletti (2013). The values for wind driven rain samples are lower than the ones

forflood.Thefatiguedconnectionsstoppedworking(fullextractionofthenailfromthebeam)atalower

displacement rate than the ones of the sound specimens (Figure 66).

Figure 66:

-8

-6

-4

-2

0

2

4

6

-10,00 0,00 10,00 20,00 30,00 40,00 50,00 60,00

Load

[kN]

Vertical uplift [mm]

Sound sample max

Sound sample min

U2 (W.D.R.)

U3 (Flood)

Cyclic pull-out force-displacement diagrams for the unreinforced connections

Thefasterextractionofthescrewmaybearesultofthegapspresentinthejoint(seeChapter4.3),

thus in the unloading parts of the cycle the nail and the post had a wider space to slide back through in the

joint thus accelerating the formation of the plastic hinge formed in the nail. This defect was also present for

the sound specimens, and thus it is feasible that the reduction of the strength and displacement capacity

in theweatheredspecimenssubmittedtowetting/dryingcyclescanbeattributedtosomeextent tothe

degradation of the wood and the rusting of the nail.

Theresponseoftheexposedconnectionsissomewhatsimilar,whichtoacertainextentvalidatesthe

differentbehaviouritshownincomparisontothesoundconnections.Theclearreductionontheultimate

66



displacementcurvecanindicatethattheweatheringexposureoftraditionalconnectionscandeterminea

lower level of performance under cyclic loads.

IthastobealsopointedoutthatspecimensU2(subjectedtoWDR)showedalowerinitialstiffness

thanall unreinforced specimens, either soundor subjected to flood, appearing that thewetting/ drying

cycleshadaninfluenceonthisparameter(Figure66).

5.4.2 Double threaded screws reinforced connections

Regarding the double threaded screws reinforced connections, it was seen that due to the small

distance of the screws positioned in the front at 30° (beam-post-beam) to the beam, they crushed the wood

and broke out at a relative low displacement rate. Regarding the screws that were inserted through the

post at the back (post-beam), due to their threads and upwards and downward movement they crushed the

wood grain resulting in wood dust and pieces, thus weakening the connection (Figure 67).

After the dismantling of the connection it was found that the screws had been deformed, although

notsignificantly.

Figure 67: Damage patterns of the double threaded screws reinforced connections

It appears that the major difference between the samples which were subjected to weathering

conditionsandthesoundonesisintheinitialstiffnessoftheconnection.Itisobservedthatbothconnections

thatweresubmittedtoweatheringcyclespresentedlowerstiffness,andtheconnectionsubjectedtothe



floodcyclespresentthelowestvaluesforinitialstiffness.Itisalsoseenthatthepulloutstrengthisalso

lower in case of specimens submitted to weathering, particularly in case of the specimens submitted to a

periodofflood.ThelowerdifferenceinstrengthobtainedinthespecimensubmittedtoWDRcanbejustified

bythepositionof thescrewswhichunderthewinddrivenraincycleswerenotexposedtoasignificant

variationofwettinganddrying.Ontheotherhand,nodifferenceswerefoundamongthedistinctspecimens

in the post-peak regime, and in particular with respect to the ultimate deformation.

Figure 68: -30

-20

-10

0

10

20

30

40

-5,00 0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00

Sound sample

S2 (W.D.R.)

S3 (Flood)

Cyclic pull-out force-displacement diagrams for the screws reinforced connections

Figure 69: Outofplanedisplacementoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood

68



Table 10: Upliftoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood

5.4.3 Steel plates reinforced connections

Also in the case of the specimens subjected to wetting and drying cycles, as in the case of the sound

specimens (Poletti 2013), the joints reinforced with perforated steel plates were able to provide the highest

gainintermsofstiffnessandstrength.Itisimportanttomentionthatduringthepull-outtest,boththebolt

at the overlapping connection and the vertical plate at the back of the specimen, which provides continuity

between the beam and post members, prevented the uplifting. The rest of the strengthening elements are

meant for a better distribution of the stresses and anchorage.

Itwasobserved thatmostof thescrewheadsusedwereshearedoffbetween theplateand the

timber beam. As seen in Figure 70 the steel plate underwent plastic deformation, but no rupture was

recorded, as in the tests performed by Poletti (2013). This should be attributed to the fact that the strength

reachedduringthetestwassignificantlylower.Thisimpliesalsothatthefinalcollapseisnotconditionedby

thetensilestrengthofthesteelplate,whichjustifiesthelowerstrength.Inthiscase,forbothWDRandflood

subjected specimens, the failure occurred due to the crushing of the wood by the steel bolts.

Figure 70: Damage patterns of the steel plates reinforced connections



Figure 71:

-60

-40

-20

0

20

40

60

80

100

120

140

160

-5 0 5 10 15 20 25 30 35 40 45

Load

[kN]

Vertical uplift [mm]

sound specimen

P2 (W.D.R.)

P3 (Flood)

Cyclic pull-out force-displacement diagrams for the steel plates reinforced connections

The samples subjected to wind driven rain and flooding cycles have similar characteristics. It

appears(Figure71)thattheinitialstiffnessoftheconnectionissimilartothatofthesoundspecimen,as

the steel plates are able to guarantee such a behaviour. The overall response though becomes plastic for

deformationshigherthan10mm,pointingoutthatthewooddegradedandthemaximumcapacityofthe

strengthening technique was not reached. The bolts were crushing the wood without stressing the plates.

Figure 72: Upliftoftheunreinforcedconnections:leftU2W.D.R.;rightU3flood

70



As see in Figure 72 the bottom uplift for the specimen U3 is 0.4 mm, partially due to the crushing of

the wood. For the specimen U2 the LVDT has not been connected appropriately.

As can be observed in Figure 73 for the WDR specimen, the bolts deformed greatly and both bolts and

screws were crushing the wood and creating progressively larger holes that would allow the deformation of

thejoint.Themaximumstrengthofthesteelplateswasnotreached,asinthiscasethewoodwasweaker;

this could be attributed either to a lower quality of wood or to a loss of capacity due to the cycles to which

it was subjected.

Figure 73: Failure modes of the specimen P2

Forthefloodspecimen(Figure74),thesameobservationcanbemade;plasticdeformationofthe

bolts was observed and both bolts and screws were crushing the wood. In this case, it can be additionally

observed a cracking line connecting the two bolts of the post with the screws present in the post, additionally

weakening the post. The crack goes all through the base of the post and it could have been facilitated by

somedryingfissureinthepost.



Figure 74: Failure modes of the specimen P3

Therefore, it is apparent from these preliminary tests, that the failure now is not governed by the steel

plates, as it happened for sound joints and timber framed walls (Poletti 2013), but by the wood itself, which

presents a weakened state.

72




CONCLUSION AND FUTURE DEVELOPMENT


6. CONCLUSION AND FUTURE DEVELOPMENT

This experimental programme has highlighted a number of quantitative relationships between

extremeweatherconditionsandtheirimpactuponthestructuralintegrityoftraditionalhalflapconnections.

From the comparison of the pull-out tests results carried out on sound and weathered connections it

canitbestatedthattheextremeweatherconditionscauseadecreaseinthestiffnessandoverallstrength

of both unreinforced and reinforced connections.

Inthefutureitishopedthatamorethoroughunderstandingoftherelationshipbetweentheexposure

ofhistoricstructurestoextremeweatherconditions,andthesubsequenteffectsontheintegrity,strength

and durability of structures is attained.

Aiming at better characterizing the effects of extremeweather conditions on the performanceof

timber connections, further developments can include:

• Experimentalstudywithmoreaccurateextremeweatherconditions,asdynamicfloodparameters;

• Experimentalstudytakingintoconsiderationtheinfillmaterial;

• Indepthstudyofthematerialpropertiesandgeometricconfigurationsregardingwatersorption

anddesorption;

• Experimentalstudyforinplanecyclictesting,orothers;

• Experimentalstudytakingintoconsiderationdifferenttypesofprotectivelayersforthewood;

• Thetestingofalargernumberofsamplestobeabletostartdevelopingafragilitydiagram/index

forthistypeofconnection;

• Experimentalstudyregardingthepossibledamagegeneratedbyfungalgrowth;

• Experimentalstudyforrealscalehalf-timberwalls;

• The development of a risk methodology.

74




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