numerical analysis of historical timber frame structures

Eirini Markella Psalti

Numerical Analysis of historical timber frame structures.

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Eirini Markella Psalti

Numerical Analysis of historical timber frame structures.

Numerical Analysis of timber frame structures

Erasmus Mundus Programme

ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS i

DECLARATION

Name: Eirini Markella Psalti

Email: [email protected]

Title of the

Msc Dissertation:


Supervisor(s): Luca Pelà, María Belén Jiménez

Year: 2017

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: Universidad Politécnica de Cataluña

Date: 15/07/2017

Signature: ___________________________



ii ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS



ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS iii

ACKNOWLEDGEMENTS

Firstly, I would like to thank my supervisors, Professor Luca Pelà and María Belén Jiménez

for their continuous help and guidance.

My sincere thanks to all the SAHC professors, tutors and to the administration staff for all the

knowledge and experience shared, the dedicated time and the given support.

I would like also to thank the SAHC Consortium for their financial contribution.

Then, I am very grateful to all my classmates for the time we have spent together during this

past year and all the happy moments.

Finally, a big thank you and love to my family.



iv ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS



ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS v

ABSTRACT

Timber frames have historically proven to be resilient structures when subjected to seismic

hazard. Their design and construction techniques are based on the principles of vernacular

architecture regarding sustainability and adaptation to the special local environmental

conditions and seismic activity. Testimonies of this technique can be found across the world.

In the historic city center of Valparaiso at Chile, an area with extremely high seismicity,

timber frame structures had been widely used in buildings with heritage and cultural value

between the late eighteenth and early nineteenth centuries. This diffusion combined with their

traditional design contributed to the development of several typologies, resulting in a great

diversity of structural arrangements and typologies. Nowadays many of these constructions

are still preserved and represent an important part of the heritage and cultural value of the city

which was listed on the World Heritage Site by UNESCO in 2003. However, due to the

permanent exposition of these buildings to the seismic hazards, the evaluation of their seismic

capacity became a necessity.

Assessment of the response of Valparaiso’s vernacular timber frame structures under lateral

loading is based on the proposal of numerical models suitable for an urban scale structural

evaluation of these typologies. Contribution of carpentry connections and different

morphological configuration, such as the bracing and opening ratio, the alteration in height

and the row-house phenomenon, are chosen as the main examined parameters of this study.

Moreover, redistribution of the forces and the occurring load path at the post-elastic section of

the static analysis is a studying point. Nonlinear static analysis is used for the definition of the

capacity of the varied typologies and comparison between the different models results to a

range of values of deformation and load bearing capacity.

The results obtained from this thesis represent a starting point for the further research on

seismic assessment of the timber frame structures at the historic quartier of Valparaiso.



vi ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS



ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS vii

RESUMO

A lo largo de la historia los sistemas de entramado de madera han demostrado ser estructuras

de gran rendimiento y resiliencia frente al peligro sísmico. Sus diseños y técnicas

constructivas se basan en los principios de la arquitectura vernácula, considerando factores

como la sostenibilidad y la adaptación de estas tipologías a las condiciones locales de los

territorios, tal como los escenarios ambientales, sísmicos y los recursos disponibles. Las

estructuras de entramado de madera fueron ampliamente propagadas en el pasado, existiendo

múltiples variaciones entre los ejemplares que aún son preservados en muchas ciudades

alrededor del mundo. El centro histórico de la ciudad de Valparaíso (Chile) se presenta como

un relevante caso de estudio al estar situado en un territorio altamente sísmico donde las

estructuras de entramado tuvieron un importante auge entre finales del siglo XIX y comienzos

del XX. El uso de estas estructuras fue enérgicamente influenciado por la población

inmigrante asentada en la ciudad en aquella época -principalmente británicos y alemanes- sin

embargo, sus sistemas tradicionales foráneos fueron combinados con las técnicas

constructivas y recursos locales que ofrecía la ciudad. El resultado se ve reflejado en la gran

diversidad de formas y configuración estructural de los edificios, muchos de las cuales aún se

conservan en la actualidad. Debido al permanente estado de exposición de los edificios a la

peligrosidad sísmica, evaluar la capacidad estructural de las construcciones históricas de

entramado en Valparaíso se ha vuelto una necesidad.

En la presente tesis se abordó el estudio del comportamiento de las estructuras de entramado

sometidas a cargas laterales a través de modelos numéricos. Se analizaron tipologías

representativas con el fin de establecer una comparación entre las variaciones existentes en el

centro histórico de Valparaíso. Los principales parámetros de evaluación fueron las uniones

carpinteras y las posibles configuraciones de los muros de carga, considerando las relaciones

de arrostramiento y abertura de vanos, número de pisos, y la configuración en fachada

continua de los edificios. Análisis estáticos no lineales fueron aplicados con el fin de definir la

capacidad de las tipologías propuestas y comparar los resultados según sus valores de

deformación y capacidad de carga. Los resultados obtenidos representan un análisis

preliminar para futuras investigaciones en el campo de la evaluación del riesgo sísmico en el

centro histórico de Valparaíso.



viii ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS

TABLE OF CONTENTS

1. Introduction .......................................................................................................................................... i

1.1. Motivation ............................................................................................................................... 1

1.2. Objectives ................................................................................................................................ 2

1.3. Methodology ............................................................................................................................ 3

1.4. Thesis outline ........................................................................................................................... 4

2. State of the Art ..................................................................................................................................... 5

2.1. Numerical Analysis of Timber-Frame structures with infill under seismic loading – A multi-

scale approach ..................................................................................................................................... 6

2.2. Analytical Micro-Modelling of Traditional Composite Timber-Masonry Walls .................... 7

2.3. Seismic Performance of Dhajji Dewari. The detailed and the simplified modelling

approaches ........................................................................................................................................... 9

2.4. Analytical iterative approaches for seismic evaluation of old masonry buildings ................ 12

2.5. Experimental evaluation and numerical modelling of timber-framed walls ......................... 13

2.6. Comparison between an analytical and a simplified non-linear model ................................. 14

2.7. Seismic Analysis of a Pombalino timber frame and of a Heritage Building Compound in the

Old Town of Lisbon .......................................................................................................................... 18

2.8. Detailed modelling approach for quincha typology .............................................................. 22

2.9. Final Remarks ........................................................................................................................ 23

3. Vernacular Architecture and Timber Frame systems ........................................................................ 25

3.1. The Pombalino Building ........................................................................................................ 29

3.1.1 Morphology .......................................................................................................................... 29

3.1.2 Structural Behaviour ............................................................................................................. 30

3.2. Casa Baraccata ....................................................................................................................... 32

3.2.1 Morphology .......................................................................................................................... 32


3.3. Traditional typology at Lefkada, Greece ............................................................................... 35

3.3.1 Morphology .......................................................................................................................... 35


3.4. The Balkan typology ............................................................................................................. 37

3.4.1 Morphology .......................................................................................................................... 39


3.5. The Quincha typology ........................................................................................................... 41

3.5.1 Morphology .......................................................................................................................... 42


3.6. Valparaiso timber frame typology ......................................................................................... 45

3.6.1 Morphology .......................................................................................................................... 45


3.6.3 Urban Development of Valparaiso ....................................................................................... 49

3.6.4 Definition of Vernacular Timber Frame Typologies at Valparaiso Historic Quarter ........... 51

3.6.5 Carpentry Joints characterization ......................................................................................... 54

4. Numerical Analysis of Timber Frame Typologies in Valparaiso ...................................................... 57



ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS ix

4.1. Experimental campaign at Pombalino cage ...........................................................................57

4.1.1 Geometry and Materials ........................................................................................................57

4.1.2 Test setup & Results ..............................................................................................................59

4.2. Numerical Model of Pombalino cage .....................................................................................62

4.2.1 Geometry &Material properties ............................................................................................62

4.2.2 Loading Conditions ...............................................................................................................66

4.2.3 Boundary Conditions .............................................................................................................67

4.2.4 Structural Analysis ................................................................................................................67

4.2.5 Calibration of the models ......................................................................................................67

4.3. Numerical Analysis of Vernacular Valparaiso Typologies ....................................................77

4.3.1 Geometry of a Valparaiso typical timber frame wall ............................................................77

4.3.2 The effect of the Bracing Ratio .............................................................................................79

4.3.3 The effect of the Opening Ratio ............................................................................................85

4.3.4 Influence of the multi-storey configuration ...........................................................................88

4.3.5 Influence of the ‘row-house’ phenomenon ...........................................................................91

4.4. Discussion of the results .........................................................................................................93

5. Conclusions ........................................................................................................................................99

5.1 Summary ......................................................................................................................................99

5.2 Final Remarks ............................................................................................................................100

5.3 Further Developments ................................................................................................................102

TABLE OF TABLES

Table 1: Results of the survey at the historic quartier of Cerro Concepcion (Molen 2013). .................53

Table 2: Timber material properties (Poletti 2013) ................................................................................59

Table 3 Calibration of the linear response of MOD3 .............................................................................72

Table 4: Storey displacement and storey drift for the 2storey and 3storey facades ...............................89

Table 5: Correlation between bracing and opening ratio and the impact to the global response. ..........95

TABLE OF FIGURES

Figure 1: Multi-scale approach (Vieux-champagne et al. 2014). ............................................................ 7

Figure 2: Finite element micromodels of the examined composite timber-masonry wall (left) and

deformed shape and distribution of effective stresses within masonry at load step 100 (right)

(Doudoumis 2010). ................................................................................................................................. 9

Figure 3 :Final building condition with (left) and without nails (right) after earthquake time histories

(Hicyilmaz 2012). ..................................................................................................................................10

Figure 4: Mathematical modelling of Dhajji wall for nonlinear static pushover analysis. From top to

bottom Dhajji wall, complete equivalent frame idealization, type of elements for analysis and detail of

frame element connectivity (Ahmad et al. 2012). ..................................................................................11

Figure 5 :a) Diagonals elements, b) Vertical and horizontal timber frame elements, c) Model of the

masonry wall, d) Connection between the masonry and the timber wall, in the model developed by

(Goncalvez A. M., Ferreira J.G. , Guerreiri L. 2014). ............................................................................14

Figure 6: Modelling of the specimen with the detailed and the simplified beam elements (the bullets

represent the plastic spring) (Kouris and Kappos 2012). .......................................................................16

Figure 7: The axial plastic hinge of the diagonals (Kouris and Kappos 2014). .....................................17

Figure 8: Studied models for timber frame wall with elastic no-tension (ENT) material, an elastic-

perfectly plastic gap and the available at OpenSees SAWS material (Lukic 2016). .............................19



x ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS

Figure 9: Studied models for timber frame wall with applied of nonlinear link elements at the

diagonals and at the main frame elements (Ciocci 2015). ..................................................................... 19

Figure 10 :Summary of the capacity curves obtained from the modelling of the timber frame wall

(Ciocci 2015). ........................................................................................................................................ 20

Figure 11: Numerical model of the full building compound (left) and compressive stresses for vertical

loading, in the complete block (right) (Ramos and Lourenço 1999). .................................................... 21

Figure 12: Timber species in Frame A and in Frame B (Quinn and Ayala 2016). ............................... 22

Figure 13: Wheel of environmental, socio-cultural and socio-economic sustainable principles(Mariana

Correia, Letizia Dipasquale 2014). ........................................................................................................ 26

Figure 14 : Mediterranean Seismic Hazard map. Vernacular timber typologies: Pombalino Cage

(green), Casa Baraccata(pink), Lefkada building typology(black) and Balkan typology(white)

(Dipasquale and Mecca 2015). .............................................................................................................. 27

Figure 15: Pombalino blocks at Lisbon (left) & details of the buildings: structural scheme, gaiola

Pombalina and typical cross section- connection with the underground sanitation

network(right)(Ortega et al. 2015). ........................................................................................................ 31

Figure 16 : Vivenzio anti-seismic prototype building, façade (left) and plans (right). (Vivenzio1783).

............................................................................................................................................................... 33

Figure 17 : a) Inside view of the ground floor of a traditional building in Lefkada. b) The wooden

frame of the upper storey. c) Detail of the wooden joint elements. d) Inside view of the upper storey.

The wooden frame with masonry infill(Vintzileou and Touliatos 2005). ............................................. 36

Figure 18: Partial collapse mechanism(Vintzileou and Touliatos 2005). .............................................. 37

Figure 19: Traditional Balkan houses in the historical centre of the city of Xanthi. ............................. 38

Figure 20: Plan views of a typical Balkan typology, Building cross section, Front view, Arrangement

of timber laces (Pantazopoulou 2013). .................................................................................................. 40

Figure 21: Reconstruction after the fire of 2014 at Valparaiso, using contemporary quincha building

technology (Shelterprojects.org 2016). ................................................................................................. 42

Figure 22: Variations of quincha typology, used at the upper storeys(Quinn et al. 2015). ................... 44

Figure 23: Timber frame typologies in Valparaiso, Chile, facades and internal partition walls(Molen

2013). ..................................................................................................................................................... 47

Figure 24: Vernacular timber frame typology in Valparaiso, Chile(Jimenez 2015). ............................ 48

Figure 25: Growth of Valparaíso on reclaimed lands (Indirli et al. 2010). ........................................... 49

Figure 26: Limits of the UNESCO area in Valparaíso(Hurtado 2007) ................................................. 51

Figure 27: Map of vernacular buildings at the historic quartier of Cerro Concepcion ,1:2500 (Molen

2013) ...................................................................................................................................................... 53

Figure 28: Map of Materials used at the historic quartier of Cerro Concepcion, 1:2500 (Molen 2013).

............................................................................................................................................................... 54

Figure 29: Joints Configuration at a typical vernacular typology of Valparaiso(Jimenez 2015). ......... 55

Figure 30: a) Vernacular timber frame at Carrer Urriola 495, b) mortice-tenon joint at Lautaro Rosas,

c) Cross half lap at Paseo Dimalow at the ceiling level (Jimenez 2015). .............................................. 56

Figure 31: Geometry of the real scale specimen (Poletti 2013). ........................................................... 57

Figure 32: Geometry of half-lap joint specimen tested (left) & connection dimensions (right) (Poletti

2013). ..................................................................................................................................................... 58

Figure 33: Timber frame wall with lower (left) and higher (right) vertical load levels (Poletti 2013). 60

Figure 34: Damages in the central connection at timber frame walls and half-timbered walls (Lukic

2016). ..................................................................................................................................................... 61

Figure 35: Behaviour of the wall during the test: rocking of walls for lower vertical load level: half-

timbered wall (left) and timber frame wall (right) (Lukic 2016) ........................................................... 62

Figure 36: Geometry of the numerical model. ...................................................................................... 63

Figure 37: Linear elastic force–deformation for axial (left) and shear (right) spring introduced in MOD

2(Poletti 2013). ...................................................................................................................................... 64

Figure 38: Force – Deformation diagram assigned at a pushover hinge(Computers and Structures Inc.

2016). ..................................................................................................................................................... 65



ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS xi

Figure 39: (a) Non-Linear force-deformation diagram assigned at the axial nonlinear Hinge 1, (b)

Non-Linear force-deformation diagram assigned at the shear nonlinear Hinge 2 and (c) Non-Linear

moment - rotation diagram assigned at the rotational nonlinear Hinge 3. .............................................66

Figure 40: Deformed shape (up), moment diagram (left) and axial forces diagram (right) at MOD0. ..68

Figure 41: Deformed shape (left) and moment diagram (right) at MOD1. ............................................69

Figure 42: Deformed shape (left) and moment diagram (right) at alternative MOD1. ..........................70

Figure 43: Force–displacement for the half–lap connection(Poletti 2013). ...........................................71

Figure 44: Moment-rotation diagram for the half-lap connection..........................................................71

Figure 45: From top to bottom: Assigned axial, shear and rotational plastic hinge at the edges of the

diagonals for the numerical model analysed f Fy =21 kN. ....................................................................73

Figure 46: Parametric analysis of the capacity of the connections between the diagonals and the main

frame elements. ......................................................................................................................................74

Figure 47: Pushover diagram for the numerical model with connection capacity of diagonals Fy=29

kN(left) and initial state of response (right). ..........................................................................................75

Figure 48: Timber frame response for the different stages of the pushover analysis. ............................76

Figure 49: Timber frame response for point E (left) and final step (right). ...........................................77

Figure 50 : Geometry of the elementary cell at vernacular Valparaiso typology(Jimenez 2015). .........78

Figure 51: Geometry of the timber frame wall at vernacular Valparaiso typology(Jimenez 2015). ......79

Figure 52: From top to bottom, geometry of the Model_A, Model_B, Model_C and Model_D timber

frame walls at vernacular Valparaiso typology (Jimenez 2015). ...........................................................80

Figure 53: Capacity curves of Valparaiso models with varied bracing ratio. ........................................81

Figure 54: Influence of the rotational stiffness for Bracing Ratio = 0.17. .............................................82

Figure 55: Results for Model_A. a. Deformed shape, b. first hinges created, c. formation of hinges at

step 62, d. final step of the analysis. .......................................................................................................83

Figure 56: a) Pushover curve for Model_D and characteristic points of the global response, b)

Deformed shape of Model_D for points A and B at steps 9 and 31 of the analysis respectively. .........84

Figure 57: Deformed shape of Model_D for points C and D at steps 55 and 62 of the analysis

respectively. ...........................................................................................................................................85

Figure 58: Deformed shape of Model_D for point E of the push over curve. .......................................85

Figure 59: Comparison between Model_C, Model_C* and Model D* in terms of load and

displacement capacity. ...........................................................................................................................86

Figure 60: Deformed shape of Model_D* and hinge formation at ultimate step. ..................................87

Figure 61: Deformed shape of Model_C* and hinge formation at ultimate step. ..................................87

Figure 62: Deformed shape of Model_C and hinge formation at ultimate step. ....................................87

Figure 63: Capacity curves for the different storey configuration at Model_D. ....................................88

Figure 64: Deformed shape of Model_D for last step of the analysis. ...................................................89

Figure 65 : Hinges formation (left) and deformed shape with displacement contour (right) of the two-

storey model for early and late step of the analysis. ..............................................................................90

Figure 66: Deformed shape with displacement contour of the three-storey model (right) and the four-

storey facade at late step of the analysis.................................................................................................91

Figure 67: Capacity curves for the different storey configuration at Model_D. ....................................92

Figure 69: Progressive failure of the connections at the bottom part of the openings. ..........................93

Figure 70: The effect of bracing ratio at the vernacular timber frame typologies at Valparaiso. ..........94

Figure 71: The effect of opening ratio at the vernacular timber frame typologies at Valparaiso. ..........95

Figure 72: Deformed shape of the four basic models at the final step of the analysis. ..........................96



xii ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS

NUMERICAL ANALYSIS OF HISTORICAL TIMBER FRAME STRUCTURES


ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS 1

1. INTRODUCTION

1.1. Motivation

Timber-frame structures, part of local vernacular architecture have always been used

for residential structures across the world. Their efficient seismic capacity has be proven

several times throughout the years and although theirs design and construction was not based

on rigid regulations, these structures can withstand significant amounts of lateral load with no

collapsing. Theirs resilience is based on Local Seismic Cultures1, a continuous process of trial

and error defines the evolution of vernacular architecture and the creation of what is known as

the Local Seismic Culture defined at the areas with extended seismic activity. Local builders

taking advantage of the available materials and considering both the environmental and

special local conditions evolved their building technology always considering the urgent need

of safety. Thus, sophisticated carpentry timber frame systems can be found in historical

buildings, incorporating the advantages of these light weighted and flexible structures.

At the historic city centre of Valparaiso, a high seismicity territory, timber frame

typologies have been widely used in buildings with heritage and cultural value. Preservation

of these structures is promoted firstly by UNESCO that inscribed Valparaiso as a World

Heritage Site(Unesco 2002). Moreover, their sustainable and environmental friendly character

and their seismic capacity combining with the scarce information regarding their response and

structural configuration are the main reasons for further research and evaluation of theirs

response.

1 Local Seismic Culture: The entirety of knowledge, both pragmatic and theoretical, that has built up in a

community exposed to seismic risks through time (Homan et al 2001).



2 ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS

1.2. Objectives

The aim of this study is to define an appropriate numerical model that can be used at

an urban level analysis. When applied upon relevant and appropriate assumptions, numerical

analysis captures the global response and it has proven to be a useful and accurate tool for

simulation of buildings models. For these reasons, numerical analysis of vernacular timber

frame typologies will be developed at this study. The historic city centre of Valparaiso is used

as a case study. The vernacular structures at the area, are characterized by a wide variety of

configurations in terms of geometry, materials and connection types. Moreover, it is not

always possible to determine the mechanical characteristic of these variations in each building

due to limitations in terms of testing and time. Suitable structural models should incorporate

the most common and influential parameters and comparative analysis should be made in

order to detect the range of theirs values. The final model should balance between the

requirements of feasibility and accuracy. Moreover, it should be able to be applied at different

structures with no need for recalibration.

Recent researches have depicted the importance of the timber carpentry connections

(Kouris and Kappos 2012)(Quinn and Ayala 2016)(Poletti 2013). Their complexity affects

global response and most of the times, they are indicative of a region, a period of time and

even the carpenters' know-how. The conception of joints has always been the most complex

task to be carried out and simulation can be proved a challenging issue. The thesis is focused

on the numerical description of carpentry joints connections between the different elements of

a vernacular timber frame façade.

In particular, different stiffness configurations are going to be examined at the joints

level. These areas are the most vulnerable parts of the structure and for this reason, definition

of these local failures is an objective of the thesis. Moreover, redistribution of the forces and

the occurring load path at the post-elastic section of the static analysis is a studying point. The

impact of different kind of connections at the global behaviour of the wall façade is an

important step for the definition of the structural capacity. Final step of analysing the response

of vernacular timber frame typologies at Valparaiso, is the proposal of appropriate

simplifications regarding the stiffness and capacity of the joints. Preservation and restoration




decisions of historic monuments and of buildings with cultural value, can be based on the

results of this kind of analysis.

1.3. Methodology

First step of the work is the study of the recent research and bibliography concerning

numerical analysis of historic timber frame structures. Different approaches and

methodologies are examined before deciding upon the simulation of the case study

typologies. Then, definition of the main structural parameters is done. Results of a field urban

survey in an historic quartier of the city of Valparaiso are used(Molen 2013). The aim is to

extrapolate data regarding categorization of the used materials, structural typologies and

characterization of the vernacular buildings. The decision upon the representative timber

facades that are going to be analysed is also based on the findings of architectural analysis and

extended inspection at both the level of the carpentry connections and at the global level of

existing historic vernacular buildings at the city of Valparaiso(Jimenez 2015).

For the analysis of the defined typologies, calibration of the nonlinear response of the

carpentry connections is done according to a relevant experimental campaign (Poletti 2013).

Although, Valparaiso’s common typologies have yet to be examined at an experimental level,

data upon behavior of Pombalino timber frame walls are chosen as a suitable correlation for

this thesis context. Imitation of the test setup and conditions results in acquiring the nonlinear

response of both the timber joints and of the elementary structure.

Finally, different models are used in order to test the response of the commonest

vernacular Valparaiso timber facades. Different morphological variations in shape and height

are tested such as the opening ratio, the bracing ratio, the effect of multi-storey facades and

the row- house phenomenon. Parametric analysis is run in order to define the impact of each

alteration at the local level and also the range of values of the ultimate displacement and load

bearing capacity at the global response of the structure. The results of this analysis can be

used as a preliminary step for conducting an experimental campaign at these typologies or for




further research and implementation at an urban level analysis at the historic city centre of

Valparaiso.

1.4. Thesis outline

The work is organized at five chapters.

Chapter 1 presents the topic, the main objectives as well as the organization of

the thesis.

Chapter 2 includes the relevant state of the art in terms of modelling

approaches and experimental campaigns. The results can be used for both

comparison and development of the numerical models of the Valparaiso

typologies.

Chapter 3 provides morphological and structural details for the different

vernacular timber typologies across the world. An introduction to the case

study of Valparaiso is made, followed by the study of recent urban surveys at

the historic quartier of Cerro Concepción and definition of the dominant

typologies.

Chapter 4 presents the results of linear and nonlinear analysis of timber frame

typologies according to experimental tests. Analysis of different parameters is

made in order to expand the use of the results.

Chapter 5 includes the final remarks, conclusions and further development of

the work.




2. STATE OF THE ART

Existing literature regarding the timber frame mixed typologies of Valparaiso is

limited. Scarce number of research studies is available regarding the structural

characterization, the materials characteristics, the connections capacity and the pathology of

these structures. Also, relevant experimental campaigns focusing on the different

morphologies of the historic structures in Valparaiso are not available.

However, extensive surveys were conducted in the past and information systems

regarding the urban plan and the general architectural characteristics of the structures were

developed in the context of ‘Mar Vasto’ project(Indirli and Apablaza Minchel 2009) and also

by researchers such as (Molen 2013), (Hurtado 2007),(Hurtado et al. 2016)(Jorquera

2014)(Jimenez 2015). As a result, definition of the main typologies in terms of geometry and

material configuration is possible.

Although detailed numerical models have not been developed for the historical

structures of Valparaiso, a significant number of studies have been carried out on the

simulation of typologies of traditional infilled timber constructions and also bare timber frame

structures found across the world. In many cases, masonry is the main infill of the timber

frame structures. Additional timber cross bracing, resulting to a stiffer global response, is also

amongst the main alterations of the studied Valparaiso models. At this part of the study, the

different approaches in terms of modelling and analysis are examined in order to find the most

appropriate one for our purpose. Micro and macro modelling models, linear and non-linear

elements and dynamic and static analysis all developed for historic timber frame are presented

and compared. The aim is to define amongst the existing methodologies, a suitable technique

applicable to the developing of a numerical model for the vernacular Chilean structures




2.1. Numerical Analysis of Timber-Frame structures with infill under

seismic loading – A multi-scale approach

A multi-scale approach is used from Vieux-Champagne, Grange, Daudeville and al in

order to predict the seismic response of traditional timber frame structure (Vieux-champagne

et al. 2014). A specific study case of Haitian timbered masonry construction ‘Kay Peyi’ is

analysed numerically based on experimental results at different stages as presented at Figure 1.

At the first level, joints behaviour is captured using experiments. The connections are tested

through monotonic and cyclic tests, both in tension and shear and the relevant constitutive

model is calibrated. Then at the level 2, the presence and the kind of the infill as well as the

presence and type of bracing is studied in a parametric analysis. Assessment of the impact of

these parameters is crucial for validating the finite element model and for this reason analysis

of an elementary shell is conducted. The results of this analysis depict that global behaviour is

only governed by lateral stiffness and energy dissipation capacity. A macro-element finite

element model of the elementary cell is used for simulating the structure. Experimental data

are also extrapolated at the next level, at the analysis of the shear wall. At the proposed finite

element, a simplified model is constructed by the combination of macro-elements.

Specifically bars are used for representing the bracing system while posts are simulated by a

continuous beam. Then, at the building level, a dynamic test is performed in order to

demonstrate seismic behaviour. Mode shape and evolution of the fundamental period of the

building are amongst the main aims of the tests.

In conclusion, nonlinear dissipative phenomena in the structure are tested at the joints

level. The final model of a shear wall or an entire house by combining macro-elements is

based at the constitutive law as defined at the previous level. Thus, an accurate and tool for

the assessment of the seismic vulnerability of timber framed houses with infill is developed.




Figure 1: Multi-scale approach (Vieux-champagne et al. 2014).

2.2. Analytical Micro-Modelling of Traditional Composite Timber-

Masonry Walls

The response of the composite timber-masonry walls to any static or dynamic loading

is mainly non-linear. This is mainly due to friction developed at the contact area between the

timber structure and the infill material. Varied load conditions result to the creation of a

frictional contact interface. Moreover, slipping or relaxation are quite possible occurring




phenomena at the connection joints. Finally, in case of dynamic loading inelastic material

behaviour is also a possibility. Therefore, a reliable and effective structural model, taking into

consideration the sources of non-linear behaviour is necessary for the analysis, design,

strengthening and retrofitting of these structures. A micro-modelling approach is proposed by

Doudoumis for representing with sufficient accuracy the complex non-linear structural

behaviour of the composite timber-masonry wall(Doudoumis 2010).

Inelastic frame elements with bilinear elastoplastic material law and predefined

locations of possible plastic hinges are used for the simulation of the timber frame. The infill

is represented with inelastic plane-stress or shell elements with pressure-depended material

strength (Drucker-Prager, etc.) or low-strength concrete law. Local discontinuities are

modelled by incorporating release-end conditions at the ends of the timber elements. Two

alternative elements are used in order to represent slipping possibility between the timber

frame. The first one is the introduction of linear spring with proper slip modulus Ks while

special gap elements which prohibit penetration but allow separation with “slip modulus” Ks

are also included at the simulation model. The capacity of the connections is modelled by

elastoplastic link elements. Finally, the boundary conditions between the timber frame and the

masonry infill are captured by the Coulomb’s law of dry friction (Doudoumis and

Mitsopoulou 1998) (Doudoumis and Mitsopoulou 1998).

The final model represents a façade of a one-storey building of 3m height and 5m

length. For the proposed micromodel 337 frame and 422 shell elements are created at the

numerical model presented at Figure 2. The results of the research depict the significance of

the contact boundary conditions at the timber-masonry interface, the arrangement and

orientation of the timber diagonal bracing and the construction details at the joint connections.

These parameters affect considerably the global response of the structure under quasi-static or

dynamic loading. However, uncertainties regarding the material laws and the construction

details of these composite walls are the most challenging issues while modelling a structure

according to this approach. The influence of the connections at the structural behaviour is far

more than critical than any other parameter tested at this sophisticated micromodel. Moreover,

one main disadvantage of this approach is that it is computationally demanding and time

consuming particularly if frictional contact between the frame and infill is considered.




Figure 2: Finite element micromodels of the examined composite timber-masonry wall (left) and deformed

shape and distribution of effective stresses within masonry at load step 100 (right) (Doudoumis 2010).

2.3. Seismic Performance of Dhajji Dewari. The detailed and the

simplified modelling approaches

The performance of dhajji dewari construction, a timber frame masonry system is

checked by Hicyilmaz and al.(Hicyilmaz 2012) The aim of the research is to validate the

analytical models of this kind of structures and to assess their response to large earthquake

loads. This type of vernacular typology presents many similarities with the timber-frame

structures we can find at typologies at the Mediterranean and Latin America territories. LS-

DYNA computer software is used for the analysis. Both timber frame structure and masonry

blocks are simulated through solid elements and frictional behaviour is taken into account at

the contact surfaces. The roof system is represented by beam and shell elements with no

diaphragmatic action. As for the nailed connections is concerned, non-linear material

properties are assigned to the discrete elements. Finally, for simplification reasons and also

due to the high level of uncertainties regarding the material characteristics, the mortar made of

mud is not modelled. The assumptions of infinite compression strength for the masonry and

ideal elasticity for the timber is adopted.

A building typology with no nailed connections is also checked as the main alteration

of this typology in order to assess the performance and the failure mode of the joint

connections. Nonlinear time history and also nonlinear static analysis are conducted. As

expected, the presence of nailed connections prevents the out-of-plane failure of the walls.

Interlocking between the masonry infill and the timber frame is proved to have significant




impact at the global behaviour. According to the detected load path, infill at the top level is

the first component to dislodge and fail in the case of no nailed connections. When timber

frame cannot provide any more confinement to the infill, failure occurs. However, the

structure without nailed connections is able to withstand greater forces. Its flexibility results

to a longer period of vibration and thus to application of lower accelerations. According to the

analysis, at the model with the nailed connections only minor local damages occur, since infill

and timber frame remain well attached throughout loading.

In conclusion, the impact of the connections at the global behaviour is highlighted at

this research. Modelling these structures through extensive analytical models based on

experiments is the proposed methodology. Qualitative results show the mechanisms of

collapse of these structures under seismic loads and are presented at Figure 3. On the other

hand, quantitative results are produced in consistency with the specimens and taken into

account the differences in geometry and connections.

Figure 3 :Final building condition with (left) and without nails (right) after earthquake time histories (Hicyilmaz

2012).

A simplified engineering tool for seismic analysis of traditional Dhajji-Dewari

structures, is developed by Ahmad et al (Ahmad et al. 2012). Concentrically braced timber

frame with masonry infill, are tested within the context of vulnerability assessment of existing

stock. Strengthening and restoration of historical heritage and feasibility analysis of future

construction projects are the main objectives of the research. First step is the conduction of an

experimental investigation. In-plane quasi-static cyclic test is applied on three full scale Dhajji

walls. Additionally, tension and bending tests are performed on the mortice and tenon joints

connections. The results depict the influence of the timber frame at the global behaviour. The

lateral force-deformability of these traditional structures is found heavily depended on the

lateral force-displacement response of the timber-braced frame. On the contrary, the




contribution of the infill is relevant only in the elastic state whereas it could be considered as

negligible factor in the inelastic state.

At the next step, simplified analytical models are derived based on the experimental

findings, using SAP2000 as showed at Figure 4. Omission of the masonry infill and

compression and zero tensile capacity of horizontal and diagonal braces are the main

assumptions in the mathematical models. Equivalent frame modelling approach is followed.

Elastic bending elements are used for modelling the posts and beams, whereas diagonal and

horizontal braces are simulated through trusses elements working only in compression.

Moreover, moment releases are applied at the ends of bracing elements in order to simulate

the free rotation of connections. Lumped plastic hinges are included at the ends of the

elements. The assigned hinge behaviour is calibrated using the force-deformation constitutive

law of the connections. In conclusion, the results of this macro modelling approach is found

in a fair agreement with the experimental campaign. However, calibration of the models is

made according to the specific experimentally tested walls. Therefore, the use of this model is

restricted to this specific type of walls.

Figure 4: Mathematical modelling of Dhajji wall for nonlinear static pushover analysis. From top to bottom

Dhajji wall, complete equivalent frame idealization, type of elements for analysis and detail of frame element

connectivity (Ahmad et al. 2012).




2.4. Analytical iterative approaches for seismic evaluation of old masonry

buildings

A simplified model based mainly on the elastic behaviour of timber frame structures is

developed by Cardoso.(Cardoso et al. 2005) Nonlinear iterative analysis is performed and at

each step the failed connections and even the stiffness changes due to cracking or yielding are

removed from the model of a Pombalino building. In that way, the main sources of

nonlinearity are defined. SAP2000 is used for simulation and analysis of seismic response is

held by response spectra. Shell elements represent the exterior masonry walls, taking into

account bending deformations for in and out-of-plane action.

The infill of the ‘gaiola’ timber frame structure is not included in the analysis. Only

the wooden elements are simulated through bars and as for connections, they are free to

rotate. Diagonal struts are assumed pinned at the connections and able to only carry

compression forces. These assumptions are made according to experimental data. Floors are

considered as flexible diaphragms and truss bars with no restrains in rotation are used for

theirs simulation. In terms of interlocking between the masonry and the timber frame,

resistance only to axial forces is considered. Moreover, nailed connections are neglected

because of the high level of uncertainties regarding their presence in the buildings. The roof is

not included in the model and its self-weight load is transmitted at the joints of the upper

storey. Rigid diagonal bars represent the masonry vaults of the ground floor. Finally, even

though masonry mechanical behaviour in compression is non-linear, in this research the

assumption of a constant secant Young’s modulus is adopted. This is a reasonable decision,

considering the wide variety of available material properties and also the requirement for an

effective and easy tool for assessment of these structures. In conclusion, the progressive

removal of the failed elements of the model is not appropriate for an accurate definition of

displacements. Moreover, the iterative steps and the multiple runs with alternate models

complicate the analysis. On the other hand, this methodology can be followed in case of

uncertainties regarding the mechanical characteristics and when a proper non-linear model is

not required.




A methodology based on the same assumptions is proposed by Vintzileou et al. for the

assessment of Lefkada’s traditional building (Vintzileou and Touliatos 2005). The aim of the

study is to identify the main damages and collapse mechanisms. Two distinctive categories

for timber connections are studied. Connections between timber posts and beams are

considered totally rigid whereas diagonals are taken as pinned connections to the main timber

frame. The assumptions of this methodology are the outcome of an excessive survey and

experimental results that defined the main pathologies of the structures. A precise estimation

of displacement is not favoured by this approach. However, it has the advantage of an

accurate and effective tool for the seismic assessment of this building typology.

2.5. Experimental evaluation and numerical modelling of timber-framed

walls

Ferreira et al, (Goncalvez A. M., Ferreira J.G. , Guerreiri L. 2014) propose also a

similar methodology for evaluation of gaiola timber frame structures. Beams, struts and shell

elements are used and carpentry joints are considered rigid everywhere besides the free –to-

rotate diagonals. An experimental campaign is held and reinforcement by means of iron plates

is studied as well. The tested walls consist of Four Saint Andrew’s crosses. The presence and

the impact of the masonry infill is analyzed. Two of the walls are made of the bare timber

structure whereas two identical walls with masonry infill are constructed. ABAQUS software

is used for the numerical analysis and the analyzed models are showed at Figure 5. Calibration

to the experimental data is the first step at the modeling and analysis procedure. Diagonals are

assumed to act only in compression and cross-halving joints are represented by link elements.

Moreover, vertical and horizontal timber frame elements are connected through an

elastic-plastic joint having both tension and compression response (fig.2.5). Wood mechanical

properties, sections and connections are all calibrated respectively to the tested wall models.

As far as the connection between the timber frame and masonry is concerned, in this numeric

model, the connection assumed to have only compression behaviour (Fig.2.5). Imitation of the

test conditions in terms of loads and boundary conditions is held. Hexahedral elements with




eight nodes (element C3D8R from ABAQUS library) are used for the meshing of the models.

The interaction properties between the different parts are defined in the assembled model.

Figure 5 :a) Diagonals elements, b) Vertical and horizontal timber frame elements, c) Model of the masonry

wall, d) Connection between the masonry and the timber wall, in the model developed by (Goncalvez A. M.,

Ferreira J.G. , Guerreiri L. 2014).

As a conclusion, defining the mechanical properties of the link elements is a

challenging issue but yet has a significant impact at the global behaviour. In cases of no

experimental campaign, links are more difficult to take into account due to wide variables.

2.6. Comparison between an analytical and a simplified non-linear model

Elastic analysis can be used for the identification of the most vulnerable areas of a

structure. However, redistribution of stresses and the definition of the collapse mechanism is

only possible through a nonlinear analysis. The different approaches of a nonlinear model of a

masonry building with embedded timber frame structure is analysed by Kouris and

Kappos(Kouris and Kappos 2012). Firstly a detailed model is developed. The assumption of

orthotropic material is followed for the wooden elements. Mechanical characteristics are




defined through a trilinear constitutive law σ-ε under monotonic axial loading. Plastic

deformation begins at 40% of the uniaxial ultimate load and a generalisation of von Mises

yield criterion, Hill’s yield criterion is adopted for representing anisotropy in ductile region.

The required values of the mechanical characteristics are the ultimate strength in

tension and compression parallel and normal to the fibres of wood (fxx, fyy), the modulus of

elasticity parallel and normal to the fibres (Exx, Eyy), the ultimate shear strength (fxy), and the

shear modulus (Gxy). Definition of all these parameters through tests is not feasible and since

destructive tests are not allowed at historical structures, the values are obtained through

relationships described at the standard EN338.

The next step for the development of the proposed model is the definition of the

contact capacity between the diagonals and the surrounded timber frame. These connections

although are mainly nailed, the decay of the material due to the natural corrosion should be

taken into account. For this reason, the connections are modelled as having zero tensile

capacity. Contact elements are used in order to simulate these joints connections, according to

the Mohr-Coulomb criterion. Validation of the proposed model is made through experimental

data from a campaign held at Lisbon in Pombalino building. Simulation of the specimens is

developed with the ANSYS software.

Contribution of the masonry infills at the post-elastic stage is negligible since it is

completely disengaged from the surrounding timber members. For this reason, also at this

methodology the infill is not included at the analysis as showed at Figure 6. This first model,

accurate it may present is not appropriate for testing a building or a relevant complex

structure. For this reason, research is focused on a simplified model. Lumped plasticity

approach is followed and implementation of hinges is the main difference between the two

models. Linear-elastic beam element are used when simulating the posts and beams and link

elements pinned at the end for the diagonals elements. These link elements include a plastic

axial spring and for the definition of the relevant constitutive law, an elastic preliminary

analysis is held.




Figure 6: Modelling of the specimen with the detailed and the simplified beam elements (the bullets represent

the plastic spring) (Kouris and Kappos 2012).

A correction factor ks is used in order to adjust the elastic stiffness of the diagonals

and take into account the sliding effect that occurs at the elastic range. This model is validated

using the results of the experimental tests of Pombalino building. At the final step of the

research, the response of the simplified model is tested in a seismic analysis of the main

façade of an historic timber-frame masonry building in Lefkada, Greece. The analysis is

conducted in steps. First, a linear elastic analysis is held so to catch the response of the

masonry of the ground floor. Timber frame of the upper storeys remain inactive. Then a non-

linear analysis is used and each individual frame is independently modelled using the detailed

approach.

A new practice-oriented non-linear macro-model is also studied (Kouris and Kappos

2014). Timber frame masonry structures are simulated based on the diagonal strut approach

with nonlinear hinges in the struts. The research aim to derive a simple model appropriate for

many case studies of timber frame buildings with diagonals where level of knowledge is low.

According to the established methodology, calibration of the hinges is held according to the

results of experimental campaign. Moreover, the previously developed micro-model by the

authors is a useful tool for definition of the parameters to be checked at the analysis.

Relationships response parameters are derived after considering independently the impact of

each parameter at the global response. As a result, empirical expressions are developed. Only

the necessary for describing the kinematics of the timber frame panels terms are used for these

equations that define the nonlinear constitutive law for plastic hinges. Specifically, only

geometric characteristics of the timber panels and the timber strength are included at the




calculations. Summarizing the main steps of the procedure, the macro-modelling approach

consists of the following steps:

1. Discretization of the building into individual timber frame panels.

2. Calculation of the equivalent vertical load in each timber frame panels.

3. Application of the proposed empirical formulas in order to define the constitutive

load of each panel in terms of horizontal shear vs. displacement.

4. Correction of the elastic stiffness of the diagonals.

5. Definition of the nonlinear law of the plastic hinges in the diagonal struts in terms

of axial load vs. deformation, showed at Figure 7.

6. Pushover analysis of the of the braced timber frame panels defined in the previous

steps.

Figure 7: The axial plastic hinge of the diagonals (Kouris and Kappos 2014).

This research propose a methodology for the definition of the constitutive law of the

nonlinear hinges. Another result refers also to the impact of the infill as well as the impact of

connections between the posts and the beams. As in many researches, contribution of the infill

is found negligible. On the contrary, the influence of the connections between posts and

beams is proved to be significant especially in terms of the ultimate displacement. The main

advantages of this approach is the combination of accuracy and simplicity. It has applications

in a wide variety of cases in engineering projects and it is useful for cases where level of

confidence is generally low. Finally, it can be used to assess the seismic behaviour of timber

frame masonry buildings in terms of their pushover curves as well as for seismic vulnerability

and risk analyses.




In conclusion, both the simplified and the detailed models are calibrated using cyclic

loading tests on timber framed masonry-infilled panels. The results depict a fair correlation

between the analytical models and the experimental data. The gradual softening of the walls

can be captured from the detailed model whereas the outcome pushover of the simplified

model is mainly of bilinear form. Nevertheless, in case of a building or a façade seismic

evaluation, the simplified model can be adopted since it proved to be appropriate for seismic

fragility assessment.

2.7. Seismic Analysis of a Pombalino timber frame and of a Heritage

Building Compound in the Old Town of Lisbon

Pombalino timber frame cells have been the focus of many researchers. Detailed

experimental campaign and various numerical approaches have been made. (Lukic

2016),(Ciocci 2015). These macro modelling differ firstly in terms of modelling the wooden

elements. A nonlinear approach of the timber material is followed from Lukic while Ciocci

includes nonlinearity only at the connection level. Calibration of the models is made at both

cases using the results of the experimental campaign held by (Poletti 2013). In the first case

study, three timber frame models with different uniaxial material definitions and

configurations at the connections are studied and are presented at Figure 8. An elastic no-

tension (ENT) material, an elastic-perfectly plastic gap and the available at OpenSees SAWS

material that provides the implementation of a one-dimensional hysteretic model are added at

the connections in order to achieve calibration.

At the second case study, nonlinearity is introduced only at the connection level and

nonlinear link elements are used at SAP2000 in order to imitate the response of the joints

according to the relevant experimental data. Four different models are studied (Figure 9),

starting from the basic elementary cell where connections are considered rigid and adding

additional stiffness (axial, shear and rotational) to the diagonals and to the main frame

elements. Then, parametric analyses is carried out and the influence of the timber connections

is studied in terms of pushover analysis Figure 10. Final step of the research is the selection of




the critical joints. The aim of the study is to incorporate the most important nonlinear

connections in terms of global response in order to study Ica cathedral at Peru.

Figure 8: Studied models for timber frame wall with elastic no-tension (ENT) material, an elastic-

perfectly plastic gap and the available at OpenSees SAWS material (Lukic 2016).

Figure 9: Studied models for timber frame wall with applied of nonlinear link elements at the diagonals and at

the main frame elements (Ciocci 2015).




Figure 10 :Summary of the capacity curves obtained from the modelling of the timber frame wall (Ciocci 2015).

Protection of architectural heritage is a key aspect for a sustainable development of

modern societies. Besides monuments and historic structures, building compounds and urban

districts of significant cultural values are also listed and preserved. As a result an efficient tool

for quick yet accurate assessment and a suitable retrofitting strategy is required. At Lisbon in

Portugal, the Pombalino compounds gain research attention and a restoration methodology is

proposed by Ramos and Lourenco.(Ramos and Lourenço 1999)

For this purpose, a building compound at the downtown of Lisbon is selected as a case

study. Mechanical characterization of the materials is obtained through experimental testing

on specimens. Horizontal loads proportional to the weight of the structure are used so to

simulate seismic action on the building compound. Several simplifications are made in terms

of the numerical analysis. Firstly, internal walls are not modelled and this assumption

conservative as it is, fulfil the safety requirement. Moreover, the hypothesis of rigid

diaphragms is not followed. For this reason, timber floors contribution is omitted and only the

relevant static loads are used at the model. A homogenized material (Fig.2.7) is used for

simplification reasons. The analysis is focused on spotting the vulnerable sections of the

compound in terms of compressive stresses and the results are presented at Figure 11. Risk

maps are developed and vulnerable zones to seismic actions are distinguished in order to help

the authorities in case of emergency or for strengthening and retrofitting purposes.




Figure 11: Numerical model of the full building compound (left) and compressive stresses for vertical loading,

in the complete block (right) (Ramos and Lourenço 1999).

After the study of the specific building compound, a general methodology is proposed

for the study of structural blocks or for an urban level analysis in seismic areas. Firstly, a

thorough survey of the existing structures should be held. Material characterization,

architectural and technical details and development of relevant drawings and technical reports

should be conducted in this first step. Then, a classification of the existing structure according

to the proposed main typologies could be occur. Analytical model of the compound could be

developed under special circumstances whereas and retrofitting strategies should be proposed

either based on the findings of this analysis or based on the existing risk maps and the

relevant results of the typologies.

In case of an urban level analysis, the main challenges to be confronted are the

complexity and the time consuming process of surveying, modelling and numerical analyzing

the buildings. Diversity in terms of both materials and building details and technology

complicate more the procedure. When searching for a feasible solution simplifications should

be made without jeopardizing the need for accurate representing structural behavior. Detailed

models of walls and connections should be avoided both because of the uncertainties

regarding material characterization but also due to time and economy constraints (Lourenco,

2014). Thus, the use of a single one homogenized material is proposed for urban level

analysis. This methodology succeeds in representing complex geometry but is not suitable for

studying failure of timber elements or connections since stress distribution is based on the

assumption of the homogenized material.




2.8. Detailed modelling approach for quincha typology

Assessment of historic quincha typology found in Peru has been studied recently and a

methodology is proposed for this mix structure (Quinn and Ayala 2016). The proposed

methodology consists of three stages: data collection, detailed model, and simplification of

the model.

An experimental campaign had been held by university of Bath and according to the

elaboration of the results numerical models are analysed. Comparison of different geometrical

configuration as well as between bare timber frame and infilled is made and showed at Figure

12. Connection’s influence at the structural response is critical and thus parametric analysis is

held in order to estimate the sensitivity of the model to a variety of rotational stiffness of the

top tenons. Sensitivity analysis is also essential for simplifying the model for wider

applications. As far as modeling is concerned, timber frames are represented by linear elastic

beam elements while nonlinear springs were used for carpentry joints in Autodesk ©

Simulation Multiphysics software. The infill of canes and mud is modelled as a homogenised

shell element with a material bilinear constitutive law and a Von Mises failure domain with

isotropic hardening. Compression-only contact elements are used for modeling the interaction

between the frame and the infill. Moreover, a bare timber frame wall is analysed using beam

elements with contact elements between the canes and posts. At the concluding findings of the

research, the significance of large-scale experiments is mentioned always in correlation with

small scale experimental tests & material testing. Finally, the most vulnerable part of the

quincha structure is found to be is in the interactions between macro-elements.

Figure 12: Timber species in Frame A and in Frame B (Quinn and Ayala 2016).




2.9. Final Remarks

Timber frame constructions are structures whose behavior is highly influenced by the

carpentry joints connection type. As a result, a rigorous approach while testing the behavior of

these structures is to study the geometry of a specific joint, reproduce it in the laboratory as

faithfully as possible and test it experimentally in order to determine behavior, capacity and

stiffness. In terms of modelling, the most complex approach adopted in literature in terms of

computational effort is to model the timber frame and the infill in detail. Micro-element

approach although no suitable for analysis of an entire structure, it can be used for validation

of a prime substructure and then to be incorporated into the global model.

A usual and accurate simplification proposed by bibliography is the use of simplified

macro models based on beam elements with springs or hinges at their ends, experimentally

calibrated, to model the behavior of the carpentry joints. In this way, a useful insight into the

global behavior of the structure with a relatively low computational effort is possible. One

limitation of this method is the difficulty in discretizing the interaction between the infill and

the timber. Moreover, local failures and cracks are difficult to advert from this method. When

simplified models are followed, sensitivity analysis is essential to run in order to define the

impact of the variations of the response to the global structure. Alterations in geometrical or

mechanical characteristics of the frame should be done only after recalibration of the model.

Use of homogenized material is proposed for analysis of building compounds and also for an

urban level analysis. Moreover, a thorough study of seismic behaviour of a traditional

structure should follow the multi-scale approach. Analysis and validation of the model begins

from the joint scale, moves to the elementary cell and to the shear wall by combining the

basic elements and then finally the study is focused on the building level.

In deciding about the modeling methodology, a number of parameters are to be taken

into account. The most significant factors are the aim, the time and the means of research. In

case of analysis of historic vernacular typologies in urban centers, the selected models should

be as simplified as possible in order to avoid recalibration of the elements that concentrate the

nonlinear behavior of the structure. As a result, balance between accuracy and feasibility of

the analysis should be kept.




3. VERNACULAR ARCHITECTURE AND

TIMBER FRAME SYSTEMS

The timber-frame structures are part of local vernacular architecture. "Vernacular

architecture can be said to be the architectural language of the people with its ethnic,

regional and local 'dialects,'" writes Paul Oliver, author of The Encyclopaedia of Vernacular

Architecture of The World’(Oliver 1996). However, fast paced technological development

combined with the innovation of new construction materials resulted in a growing disregard

for traditional architectural language. This phenomenon besides the fact that endangers the

global heritage and cultural values, it also contributes to the creation of far less sustainable

structures.

According to the main definition of vernacular architecture, it is composed of

traditional buildings, which represent a morphological response to both environmental and

climatic constraints(Mariana Correia, Letizia Dipasquale 2014). From the design phase till the

final construction of the building, the specific socio-economic and also cultural characteristics

of an area are taken into consideration. Materials and architectural components are all chosen

in order to be compatible with the local circumstances. As a result, the final outcome is

adapted to local environmental and also to seismic conditions. Due to this fact, these

structures are until today considered to be seismic resistant and environmental friendly

structures. The main aspects of vernacular architecture that enhance its sustainable character

can be described from the wheel of sustainability presented at Figure 13 defined during the

“VERSUS: Heritage for Tomorrow” project.




Figure 13: Wheel of environmental, socio-cultural and socio-economic sustainable principles(Mariana Correia,

Letizia Dipasquale 2014).

Resilience of the vernacular buildings has always been a topic of research interest. It

has been noted that the interaction between building technology, climate change and changing

socio-cultural conditions are the main reasons for the endurance of these structures through

natural hazards. Through centuries, different civilizations have been trying to create

comfortable, steady and practical building shapes using materials of the local region. In areas

of high seismicity, this continuous process of trial and error defines the evolution of

vernacular architecture and the creation of what is known as the Local Seismic Culture. The

definition has been stated by Homan as ‘the entirety of knowledge, both pragmatic and

theoretical, that has built up in a community exposed to seismic risks through time’ (Homan

et al 2001).

Different vernacular strategies have been developed in order to counteract seismic

vulnerability taken advantage of available materials, local building cultures and also the skills

of the builders. In Europe, these systems can be found across the Mediterranean area, the most




seismic active zone of Europe. Across the world, resistant timber frame structures have been

adopted also in Latin America and in Asia. 1) the “Pombalino cage”, a structural system

developed in Lisbon Portugal, 2) the “Casa Baraccata”, found in southern Italy, 3) a building

type spread in North Greece, as a typical Balkan system 4) the “pontelarisma” a vernacular

construction system, found in Lefkas Greece, 5) the Quincha timber frame structure

developed in Peru and Chile and 6) the mixed timber frame structure of Valparaiso in Chile.

The four different European regions are all seismic prone areas and so aseismic structural

systems have been evolved there as displayed at Figure 14. Moreover, climate conditions and

availability of resource materials present not significant variations. As a result local wood,

stone and bricks are the main building materials. Their similar structural systems attracts the

attention and proves that one of the main reasons of theirs seismic resilience is the interaction

between timber and masonry. These two materials respond as primary and secondary bearing

structure and vice versa, depending on the specific loading conditions. Finally, these building

typologies have all been developed around the same era (between 18th and 19th century),

indicating the cultural connections between the Mediterranean communities.

Figure 14 : Mediterranean Seismic Hazard map. Vernacular timber typologies: Pombalino Cage (green), Casa

Baraccata(pink), Lefkada building typology(black) and Balkan typology(white) (Dipasquale and Mecca 2015).

Across the Atlantic, Latin America regions although similar in terms of intense and

often seismic hazards, differ significantly in both territorial conditions and social

circumstances. Their connections with Spain and Portugal and other European countries and

also their rapid economic growth due to the trade development resulted in the creation of




aseismic building structures that have similarities with the European ones. In Valparaiso, a

port city in Chile, adobe, masonry and timber have been used in order to increase the lateral

loading capacity of the buildings. During the 19th century, large amounts of wood were

imported from the northern hemisphere and a new typology combining the timber with an

earthen infill, the adobillo block, had been created (Jorquera 2014). At the end of the 19th

century, another typology was developed and spread at Valparaiso mainly by a local architect

Harrington (Hurtado et al. 2016). Harrington’s buildings besides their high aesthetical and

historical value survived through extreme earthquakes and for this reason attract research

attention. The main common characteristic of these buildings is the joint bracing technique

between the brick masonry and a light weighted timber frame. Although the unquestionable

differences in geographical and climate conditions, the social and economic links with the

Mediterranean countries allowed the creation of a similar aseismic local culture in building

technology.

Across the globe, two main categories of timber frame typologies can be identified:

the hooping and the frame systems (Dipasquale and Mecca 2015). At the hooping system,

wooden beams of circular or rectangular cross section are horizontally disposed within the

load-bearing masonry. In many regions, timber beams are used at both the inner and outer

sides of the wall, enhancing a ‘box-behavior’ of the building. These ring beams are regularly

distributed along the height of the wall always taking into consideration the level of the

storeys as well as the openings and the lintels. Brick or stone is used upon availability for

filling the gap between the timber elements and nailed connections contribute to an efficient

interlocking system. At the second category, a more sophisticated system is created, consisted

of both horizontal and vertical timber elements embedded at the masonry. This three-

dimension wooden frame structure may be formed by rectangular, round or square section

beams and pillars as well as by diagonal braces. Locally available materials are used as filling

materials and nailed corners offer additional reinforcement to the wall. It is also a common

strategy to also combine these systems in order to create an anti-seismic structure.

All these typical vernacular strategies of using timber frame typologies as a

reinforcement system of the brick masonry or earthen wall have been proved to be seismic

resistant (Ruggieri et al. 2015). The main reason for this is that these typologies combine




mechanical characteristics of different materials. The great elastic properties of wood, its

flexibility, tension capacity, lightness and deformability without reaching failure added to the

adequate compression behaviour of the load-bearing wall result to an effective seismic

behaviour and holistic response. It has been noted that timber frame enables the dissipation of

substantial amounts of energy. Another advantage of these systems is that timber elements

divide the structure into subsections. In this way, local cracks occurring in masonry are not

spread and their influence in the global response of the structure is restricted. Nevertheless, a

critical issue for the performance of these structures is the geometry, quality and the

mechanical characteristics of the connections used to tie the different elements and improve

the resistance to shearing, bending and torsion forces.

3.1. The Pombalino Building

The most representative example of the Portuguese Local Seismic Culture is the

Pombalino building, a sophisticated three-dimensional braced timber frame structure

embedded into the masonry walls. Also known as gaiola Pombalina, the technique is said to

be linked with the wooden structure of ships, a significant part of history and heritage of

Portuguese seafaring people. The term “Pombalino” derives from Marquês de Pombal, who

was king Joseph I’s prime minister, responsible for Lisbon reconstruction after the disastrous

earthquake that occurred in the city in 1755.

3.1.1 Morphology

Pombalino constructions are block buildings and according to the original urban plan

ground floor was used for commercial reasons while residences could be found at the upper

storeys. Each storey had one or two flats and the disposition of the blocks, streets and

pavements can be described as regular. Regularity is also applied at the block level where a

strict and schematic pattern is followed. Each block has usually 7 or 8 buildings, with size of

70 x 25 m. The inner part of the block usually includes a small common courtyard, or a patio,

accessed only from the interior of the dwellings. Pombalino houses have up to four storeys.

At the ground level, the presence of arcades benefit the commercial uses of the local shops.

The facades are shaped in a simple neoclassical style.




However, scarce classical elements typical of that era can be found in Pombalino

buildings. This may be due to the lack of funds for the reconstruction as well as to the

personal architectural rationality and soberness of Pombal. Decorations are applied inside and

outside of the dwellings in a reduced measure, with limited use of “azulejo” tiling, very

common in the area (Bonavita et al. 2016). As expected decorations layout depend on the

importance of the building and as a result residential blocks are characterized by theirs simple

facades. Openings at the main facade are distributed in a rigid and repetitive pattern, always

aligned in both vertical and horizontal direction. Moreover, depending on the building

dimensions the number of openings can be altered from three to six. Ground floor openings

are mainly doors, while at the first storey bigger openings such as balconies can be found. A

distinctive characteristic of the fourth storey at Pombalino buildings is a continuous balcony

at the main facade. As far as the roof is concerned, ceramic tiles are used for decoration of the

final layer and openings are also widely used (Cardoso et al. 2003).

3.1.2 Structural Behaviour

As already stated, the most distinctive aspect of Pombalino structures is their mixed

timber-masonry system. The construction of these buildings was carried out in phases. Firstly,

a self-stable three-dimensional wooden cage (usually made of pine or oak), named gaiola, was

constructed and then embedded in the external masonry walls of the upper storeys. The

resulted heterogeneous wall had significant shear resistance capacity. The typical frame of the

gaiola is composed by vertical and horizontal struts, and even cross struts, disposed in St.

Andrew’s cross shape in order to form bracing and to increase the rigidity of the cage.

Connections between timber struts were realized in different ways: the most common ones

were mortise and tenon, half-lap and dovetail. The interior partition walls are wooden and

mortar panels (tabiques), without bearing function. The ground floor walls are made of stone

masonry on which lay stone arches and vaults of ceramic masonry. Fire prevention and

protection from the saturated ground due to the proximity of the Tagus River dictated the

absence of timber frame at that level. All the exterior masonry walls have an 80 cm thickness,

and are made of irregular blocks of calcareous stone, clay bricks, gravel and lime mortar, with

scarce mechanical characteristics. A special mortar, prepared in place with clayish sand,

quicklime and tallow, guaranteed efficient waterproof properties. The infills of the gaiola cage




consist of stone rubble from previously in-place collapsed buildings or clay bricks similar to

those ones used at the ground floor vaults. Both types of masonry can be found in the interior

walls (Bonavita et al. 2016). The floors are made of wooden boards laid on timber joists. The

foundations consist of small-diameter wooden piles connected with a wooden grid. The roof

tiles are also supported by timber trusses. Thick masonry walls without any openings are used

in order to connect the different buildings creating the effect of the building row house.

Wooden elements are avoided at the intersections in order to prevent the propagation of fire

(Ortega et al. 2015). Structural details and Pombalino blocks at the urban level are presented

at Figure 15.

Figure 15: Pombalino blocks at Lisbon (left) & details of the buildings: structural scheme, gaiola Pombalina and

typical cross section- connection with the underground sanitation network(right)(Ortega et al. 2015).

Pombalino buildings unconsciously satisfy many anti-seismic laws of the

contemporary knowledge; first of all regularity in plan and in vertical section. This induces

regular distribution of mass and stiffness. Block buildings are also of the same height, that

allows a “row” behaviour and as a result structures benefit from this confinement. Moreover

the careful execution of the wooden elements connection, provides an effective global

response behaviour. Despite having a brittle behaviour if considered separately, timber and

masonry combined demonstrate a certain ductility. In fact timber nodes are not too rigid,




therefore they can cause energy dissipation, working together with friction inside mortar

joints between bricks and stones. In case of moderate displacements, timber frame’s

flexibility allows the wall to return to its original position and prevent from plastic

deformations (Correia et al. 2014). Lastly, this way of mixing materials reduces the total mass

of the building. In comparison with a full masonry technique, these lighter constructions

receive reduced seismic forces and thus seismic demand is significantly lower in comparison

with bare masonry constructions. By lowering the centre of gravity and concentrating their

mass closer to the ground, the construction demonstrated increased stability in case of a

seismic hazard(Ruggieri et al. 2015).

3.2. Casa Baraccata

A crucial date for the development of Local Seismic Culture in Italy is the 5 February

1783, when a destructive earthquake struck Calabria region. On 1784 Ferdinando IV

Bourbon, ruler of Southern Italy, released “Istruzioni per la ricostruzione di Reggio”

(Guidelines for rebuilding Reggio Calabria). These guidelines are considered to be the first

building European code and both scientific methods of the age of the Enlightenment and local

building traditions were combined to that purpose. Firstly, a survey campaign had occurred

led by the Neapolitan Academy of Science and Letters throughout the territories affected by

the earthquake. Its findings were used for the restoration phase and the development of the

guidelines. An anti-seismic building system focused on the structural use of wooden framed

elements was introduced. The Bourbon system, is also known as “Casa baraccata”, coming

from “baracca” a kind of hut made of timber and smashed earth. Typically these huts were

utilized as temporary shelters in case of an emergency. Then they spontaneously became

permanent refuges as timber framed structures annexed to the main masonry building, already

before the 18th century(Tobriner 1983).

3.2.1 Morphology

Similarly to the Pombalino buildings, the main common principle applied at casa

Baraccata buildings is the response of the whole building as one unit. Thus the volume is as

compact as possible and all the elements have to be reciprocally well connected in order to




withstand horizontal forces in a box-like manner (Bonavita et al. 2016). Aiming to this

purpose, regularity of the plan, moderate development in height and reduction of the mass are

required. The prototype of casa baraccata as originally suggested by the architect Vivenzio is

a symmetric organism composed by three prismatic bodies in a perfect square plan and is

showed at Figure 16. According to the guidelines, two-storey courtyard houses were

developed.

Figure 16 : Vivenzio anti-seismic prototype building, façade (left) and plans (right). (Vivenzio1783).

The choice of introducing timber as the main building material has been determined

not only due to its good tensile strength and lightness, but also in order to limit the use of bad

quality materials such as river stones and sun-dried adobe blocks. At the Vivenzio’s building

models the whole structure is made of timber from the foundation level where piles were

properly treated so to be prevent deterioration, to the light roof which substituted the

previously used tiled roof. A massive wooden skeleton was created and the walls were

reinforced with diagonal braces and then infilled with fastened and cemented stones(Tobriner

1983). According to the Borbon code, basement is consisted of masonry walls of 130 cm

while there is applied a cross section reduction in relevance with the height. At upper storeys,

the walls made of small stones, bricks and mortar, are at least of 65 cm thickness and wooden

tie-rods are applied on the top of the walls. The elements of the timber frame are not visible

from the outside and are thus protected from the deterioration caused by biological and

natural attack. The cross section of beams and columns is square of 10/12 cm wide and they




are arranged in perimeter walls. The masonry, is mainly made of stones and in some cases, of

raw earth bricks. Collaboration between the inner wooden frame and the masonry wall

provide a resistant behaviour against both horizontal loads and horizontal seismic

forces(Bonavita et al. 2016).


The structural behaviour of the casa baraccata presents many similarities with the

Pombalino buildings. All the advantages of the combination of the high compressive strength

masonry with the lighter and tensile resistant timber frame are applied at this typology.

However, several contingent factors such as the urgent need for fast rebuild the demolished

towns, the lack of awareness about the seismic behaviour of some workers and the non-

strictly defined guidelines of the Instructions, led to the development of a wide variety of the

casa baraccata typology. In some cases, the St. Andrew’s cross braces are used so to increase

the in-plan stiffness of the walls(Bonavita et al. 2016).

Connections are of critical importance for the global response of the structure. Weak

or even non-existent connections between the wood framework and the masonry can be found

at historical casa baraccata buildings disfavouring their seismic resistance capacity. Another

significant parameter affecting the global response, is the presence of transversal ties. When

existent, these diatonic elements prevent the out-of-lane mechanism during a seismic event.

In 1908 another devastating earthquake occurred between Calabria and Sicily regions.

(Ruggieri et al. 2015)This event proved that despite of its limits, the casa baraccata system

proved to be an effective defence from the complete collapse in case of earthquake. The

buildings although suffered few significant damages, limited portions of masonry collapsed.

In the following decades the baraccata system has not been implemented with the original

layout and technical and architectural aspects. The high level of uncertainties concerning

mainly the timber connections resulted to a gradual disregard and finally abandonment of this

typology.




3.3. Traditional typology at Lefkada, Greece

Lefkada is a Greek island, located in the Ionian Sea in one of the highest seismicity

areas of Greece and in Europe. Due to the frequent and destructive earthquakes, local seismic

awareness was high and sophisticated building construction techniques were widely used. The

structural system, called “pontelarisma”, emerged from a long traditional practice. More

specifically, after the 1825’s destructive earthquake, the system “proved” it’s satisfactory

behaviour and the English government, who occupied the island at that time, imposed it for

the any new building. Thus, a prime building code was established in 1827, providing the

local workers with instructions about the choice of the materials, the walls thickness and the

floor height. Moreover, according to them a minimum distance between the buildings was

required so to avoid a possible spread of fire. Nowadays, a lot of traditional buildings

constructed with this structural system have been survived through time and are in use.

3.3.1 Morphology

The traditional buildings, consist of one, two or rarely three storeys. Each storey has

height between 2.8 m to 3.0 m. The plan layout is usually shaped as a perfect rectangular and

some common used dimensions are 4.0-5.0 m along the one axis and 7.0-15.0 m along the

other. The openings of the buildings are few, small in dimensions with their width to be less

than 1 m. A symmetric pattern is followed both in plan and elevation. The ground floor is

made of stone masonry, while the upper floors are made of timber frame with masonry infill.

The floors and the roofs are also made of wood. The buildings are based upon foundations,

consisting of tree logs that form a large wooden grill. In order to increase their resistance, the

logs were left for a period of time in a lake of mud near the city. Then, they were placed in the

foundations and covered with a mixture of fine sand, stones and a pozzolana cement. This

foundation system could prevent differential settlements and also increase the stability and

provide a uniform movement to the whole structure in case of a seismic event(Vintzileou et

al. 2007). The stone walls of the ground floor are double-leaf, constructed from local stones

(sedimentary rock and limestone) and have a width of 0.5-1.2 m. Moreover, quoins are placed

at the corners to ensure bracing between the perpendicular walls. At the ground floor level, a

secondary structural system of wooden columns with cross-section of 0.15-0.20 m2, parallel

to the walls exists. The columns are arranged at the inner perimeter of the walls at a distance




of 0.1-0.5 m and are placed on stone bases, secured into them with steel ties. Structural

configuration and architectural details of this typology are showed at Figure 17. Their

presence allows independent movement of the two systems. Thus pounding effects during a

seismic event are avoided. Finally, the buildings lack of plentiful decorative elements. Scarce

decorations of neoclassical architecture style can be found at the openings and at the

corners(Bonavita et al. 2016).

Figure 17 : a) Inside view of the ground floor of a traditional building in Lefkada. b) The wooden frame of the

upper storey. c) Detail of the wooden joint elements. d) Inside view of the upper storey. The wooden frame with

masonry infill(Vintzileou and Touliatos 2005).


The double structural system at the ground level, introduced at traditional building in

Lefkada provides the structures with additional resistance and it is presented at Figure 18 .

The loads from the upper storeys are carried out by both the timber beams and columns and

masonry walls. In a seismic event, the stiffer stone walls will limit the global displacement

until the time that they will collapse. At the same time the wooden columns will remain intact

due to their different deformation capacity. Moreover, due to the presence of the interior

columns, masonry walls will fall towards the exterior part of the building, preventing from

additional life losses. After the failure of the stone walls, the wooden columns will then carry




the upper floors. Therefore, the people on both ground and upper floors will be protected and

as a result the most important aseismic criterion of life safety is satisfied. Afterwards, the

masonry walls can be easily and rapidly repaired(Bonavita et al. 2016).

Furthermore, efficient aseismic behaviour is achieved by certain structural details.

Firstly, the lightweight upper floors keep the gravity centre low. Secondly, the regular plan

and the small-dimensioned openings prevent torsional effects. Moreover, the stone walls and

the diagonal braced frames ensure adequate stiffness. At the same time, the joints provide

additional stiffness and ductility behavior by absorbing energy. Lastly, the quoins at the

corners of the walls, the steel ties of the floor and the beams and the roof’s stiffness improve

the “box behavior” of the building(Vintzileou and Touliatos 2005). Finally, since an aseismic

structural system can prove its performance only in real earthquakes, it should be noted that

since their construction these buildings have survived many destructive earthquakes.

Figure 18: Partial collapse mechanism(Vintzileou and Touliatos 2005).

3.4. The Balkan typology

Throughout history, the Balkan Peninsula has always been the meeting point of

different civilizations. The character of the area is dominated by its unique geographical

position; between East and West, South and North, Balkans area is historically seen as a

crossroads of cultures. It was there where Latin and Greek bodies of the Roman Empire




united to a new empire, where pagan Bulgars people and Slavs decided to settle down after a

massive influx. The region has been a juncture between Orthodox and Catholic Christianity as

well as the main meeting point between Islam and Christianity.

All these different civilizations and influences had a major impact on the building

environment. Since architecture reflects the way that man understands and interacts with his

surroundings, the local cities were very much affected from these mixture of lifestyles. A

unique example of joint local traditions, showed at Figure 19, can be found at the old city of

Xanthi, a North-eastern small city of Greece, in the Balkans area. There a certain structural

system comprising timber-laced masonry that dominated at the whole region, remains a vivid

witness of the past history. In 1976 the Greek Nation declares the old town of Xanthi as a

protected region because of its cultural value. Nowadays more than 1,200 structures are

considered as listed and due to their recognized importance, systemic efforts have been made

in terms of recording, restoring and centering attention and awareness on them

(Pantazopoulou 2013).

Figure 19: Traditional Balkan houses in the historical centre of the city of Xanthi.




3.4.1 Morphology

The shape of the constructions was the result of the specific knowledge and technical

ability of the builders, the availability of the materials, the lack of place and of course the

religious lifestyle. Every single house is unique in terms of design but at the same time it

remains harmoniously connected with the whole urban plan of the city. Made by common and

widely available materials of the region, wood and stone, these characteristic types of

vernacular architecture aimed to serve the needs of everyday life while exaggerating and

impressive details were totally avoided. Their dependence on the sun through wide windows

and openings as the main source of energy is apparent and so is their social style; the majority

of the main facades always look to the main road. During the mid of 19th century, the

construction plan changed. Prosperity and openness to European civilization because of

commerce had an immediate impact on traditional buildings. Neoclassical elements are

introduced while some other morphological elements were abandoned(Bonavita et al. 2016).

The typical building model consists of timber-laced stone masonry with lacing at

regular intervals throughout the exterior walls as depicted at Figure 20. The south side of the

building consists of a timber-laced frame that is set out, in the corner relative to the supporting

masonry walls of the first storey in a so-called “bay-window” or “erker” or “sahneshi”

formation. The timber-laced infilled frame walls – ‘tsatmas’ of the protrusion are supported

on the perimeter beam and floor. Interior divisions both in the first and second storeys

comprise timber infilled frames which are integrally functioning with the overall structure to

secure its characteristic resilient earthquake behaviour. The building has an orthogonal plan

arrangement, 9 m × 11 m in the x, y-directions. Total height is around 9 m, while basement’s

height is typically 3 m with 1.8m is above the ground and ground floor’s height is 3.2m. As

for the foundation is concerned, it follows the geometry of the load bearing walls and is made

of stones of thickness 0.85m. The thickness of the masonry walls is decreased at the upper

storeys. Floors and roof are also made of wood (Pantazopoulou 2013).




Figure 20: Plan views of a typical Balkan typology, Building cross section, Front view, Arrangement of timber

laces (Pantazopoulou 2013).


During the last decades, it was noted that timber-laced masonry constructions at the

Balkan area when well-maintained and well-tied perform surprisingly well and their resilience

is impressive. However, since construction practices were not the identical even for buildings

built in the same period, their seismic resistance varies widely. In some cases, the strength of

the connection depends only on the friction between the materials. For an accurate assessment

each construction should be examined separately. The aim should be to identify the internal

load path and the most vulnerable points of the construction. Maximum deformations are

always occur at the upper storey, at the bearing walls that are verticals to the main direction of

the seismic load(Bonavita et al. 2016). There is where the phenomenon of out-of-plane

bending takes place. Critical areas are the ones located at the middle of the upper storey, the

edgy ones, the ones that connect different type of wall, the ones near the windows and doors,

as well as the ones at the foundation of the construction (Pantazopoulou 2013). Moreover,

timber-filled walls, ‘tsatmas’ have a direct impact at the flexibility of the construction. Due to

a step change in stiffness and the unilateral behaviour of connections, its presence and its area

increase the maximum deformations of the buildings and the whole construction is more

bendable. The uneven quality of the original masonry or the construction of different walls




also lead to poor strength and stiffness properties. The expected collapse mechanisms due to

earthquake actions are the overturning of facades (out-of-plane) or shear failure at the plane of

the walls at ground floor level (global shear mechanism), leading to a global collapse

mechanism.

3.5. The Quincha typology

Quincha is a traditional construction system where wood and cane or giant reed are

combined in a simple and easy to build way. Nevertheless, the resultant structure is

considered as an earthquake-resistant system. Its origin is a Spanish term widely known in

Latin America and means "fence, wall, enclosure, corral, animal pen". Historically, this type

of construction has been utilized in the Spanish and Portuguese colonies throughout the

different regions of the Americas. Quincha technique is widely spread in historic buildings in

towns and cities along the coast of Peru but also in rural and urban areas of Chile(Mariana

Correia, Letizia Dipasquale 2014). The timber frame is filled with a weave of canes and it is

covered with mud and plaster. Even though quincha is an ancient technique, it was further

developed to its ultimate stage after the Spanish conquest. Spanish settlers preferred more

distinguished materials such as masonry and stone. However, the extensive lack of these

materials combined with intense and frequent earthquakes led them to abandon their common

building technology. Adapting the local environmental and natural conditions, the

development of the quincha technique was finalized between 16th and 19th centuries. After

the 1687 earthquake a law was passed according to which the use of quincha for the upper

storeys of any building greater than a single storey in height was mandatory.

Nowadays, quincha remains an alive building technology in the seismic countries of

Latin America. Characteristic examples of this typology can be found at the rural areas in

northern Chile. Half-timbered structures, a secondary reed structure and a fill of mud and

straw are widely used. In urban areas the technique has been reinterpreted. In Valparaiso, a

seaport city in central Chile local awareness and seismic culture led to the adaptation of

quincha typology in case of emergency (www.mingavalpo.cl).




After the destructive fire that hit the city in 2014, local population choose to recycle

the huge amount of material waste from the fire and use it to rebuild their houses and the

reconstruction process of this project is shown at Figure 21. Wooden pillars have been used

for the main structure, while wires or wooden panels, for the secondary structure. Clayed soil

and recycled burnt adobe walls have been served as filling material. This contemporary form

of quincha, easy and quick to build, as well as a fair anti-seismic structure, favours

sustainability and local culture. The whole reconstruction project has been a fine example of

how vernacular architecture can even nowadays provide excellent opportunities regarding the

three fundamental aspects of the construction process. Environmental, economic and socio-

cultural aspects were promoted since best thermal conditions were applied through the

application of adobe and wood, local materials were re-used and collaboration and

involvement between the population occurred respectively (Mariana Correia, Letizia

Dipasquale 2014).

Figure 21: Reconstruction after the fire of 2014 at Valparaiso, using contemporary quincha building technology

(Shelterprojects.org 2016).

3.5.1 Morphology

Three are the main and distinctive components of a typical quincha frame. Although

many variations do exist, the vertical load bearing frame, the lateral bracing system, and the

infill are always present. A series of vertical timber posts compose the load-bearing frame.

Horizontal beams at each ends are used for connectivity reasons. The most common




connection joints at this level is cylindrical mortice and tenon joints. The posts are arranged in

a space of 0.6 to 1.2m and the typical height of the storey is approximately more of 4m

(Quinn and Ayala 2016).

As far as the lateral bracing system is concerned, two distinct arrangements can be

spotted in historical construction of quincha. The first, found usually on the second story, is

the use of short diagonal struts. In this way bracing of the lower portion of the frame is

possible. Adobe blocks or small fired bricks, are used to fill the space lying at the lower part

of the frame. In that way a fair increase in stiffness occurs and additional weight mass is

added. The second alteration can be found at the third story and instead of consisted of struts

or bricks, a large bracing member is used. This element extends across several bays.

The last typical component is the infill, usually consisted of 25 mm diameter

horizontal canes passing through holes in the vertical posts. These canes are inserted in pairs

of four and sometimes five and they are arranged evenly at the vertical direction of the posts.

Then another set of tightly packed canes weaves vertically through them and the result can be

described as compact and united. The canes usually have a layer of mud mixed with straw

while lime plaster is applied as the last layer, covering everything.

Regarding the basic dimensions, as showed at Figure 22, a quincha wall is usually

between 3.2-5m tall. Posts are spaced every 0.45-1 m. The openings do not interrupt the

continuity of more than two posts. Their width is usually 1.0-1.4m and the height/width ratio

can be varied from 1.2 to 3.5. It is highly impossible to find a quincha façade without any

opening in its total length of 6m but according to general construction rule in a single section

of a wall no more than three openings can exist. Another characteristic aspect of quincha

configuration is the varied cross section of the timber elements. Due to the lack of diagonal

braces, the higher vertical loads and also their increased height, posts used on the second

storey are larger. In this way, the need for lateral restraint is satisfied. Floors and roofs are

made by wood and according to research they cannot be considered as rigid

diaphragms(Quinn 2017). A wide variety of connections can be found as it is expected at any

type of vernacular architecture.




However, the most common one is the simple mortice and tenon connection.

Depending of the area and the specific construction date, different wooden materials were

used and defining theirs elastic properties is of high importance for the vulnerability

assessment of the structures. Similar to the European timber frame structures, quincha

buildings combine wooden elements at the upper storeys with a ground floor made of adobe

or fire brick masonry.

Figure 22: Variations of quincha typology, used at the upper storeys(Quinn et al. 2015).


As it has been stated there are several typologies of quincha walls. The general pattern

consists of vertical timber posts connected together by a top and a bottom beam. The main

alteration that has also major impact at the global behaviour is the bracing system. It can be

timber diagonals or timber struts limited only at the lower part of the quincha wall. In any

case, the walls are filled with cross linked cane and mud. An additional layer of mud and

gypsum is applied as a top coat.

Recent research is focused on this variation in stiffeners and also at the presence and

quality of the infill. According to their results, the quincha walls are characterized by their

high flexibility. Considerable deformations can be sustained by this typology without

reaching failure. The presence of the infill increase the global stiffness of the frame by around

2.3 times and the yield strength is more than six times greater. In case where diagonal braces

exist oly at the bottom of the quincha, it has been noted that adobe blocks remain undamaged.

This may be due to prevention of rotation of bottom tenon. Accordingly where diagonal




braces cover all the height of the quincha, the timber frame is stiffer in compression than

tension but buckling of diagonal occurs. Moreover, connections between the diagonal braces

and the posts are vulnerable to relative rotation. Axial movement is also a possibility of

failure at the connection level. Even after the failure of the connections, the wall is still

capable of supporting significant lateral loads relying on the contribution of the infill(Quinn

2017).

3.6. Valparaiso timber frame typology

In the city harbour of Valparaiso, the high amounts of imported wood allowed the

development of a mixed timber frame system. Taking into consideration the local

environmental and social conditions as well as the intense need for seismic resistance due to

the many earthquakes a local anti-seismic culture had been developed. The colonial character

is apparent in the majority of the buildings. However, the rapid economic growth because of

the trade and the influence of different civilizations and culture also affected the vernacular

architecture of the area. This flourishing period ended with the opening of the Panama

channel and the sudden reduction of ship traffic. Nowadays, Valparaiso’s unique heritage

value is recognized and protected by UNESCO(Unesco 2002).

3.6.1 Morphology

In Valparaiso of Chile, timber frame structures are widely spread and many variations

exist regarding their morphology and even the materials in use as noted at Figure 23.

Different construction era as well as local availability in materials and builder’s capacity led

to the development of many typologies. Composite typologies can be spotted: masonry and

balloon, or platform frame. In Valparaiso, the balloon and platform frame are mainly used for

residences, especially in the area of the hills. Brick masonry, on the other hand, was used for

commercial and public buildings within the flat area of the city(Molen 2013).

Royal Hotel is an example of this second type and a characteristic project of the

famous local architect, Harrington. It is built mainly in masonry whereas there is also fair

contribution of wood at the upper storeys, iron at the connection and stone at the basement. It




has a regular compact volume with a trapezoidal layout with an average width of 28 meters.

Its height is 21 m and amongst its facades there is also a firewall facade bordering the hotel

with another building in order to prevent form fire expansion. Historic buildings of

Harrington attracts until today research interest. He used to construct major buildings

appropriate for commercial use as well as residences for the upper class of the area. His

buildings besides their cultural and aesthetic value, survived several disastrous earthquakes

that hit the area (Hurtado et al. 2016).

Moreover, in terms of vernacular architecture a daubed earth-timber building system

was introduced. It is also known as adobillo system and it changed the traditional use of adobe

masonry through an extensive use of a mixed wood-earthen building system. This new

typology can easily adapt to the local peculiar topography of the hills of Valparaiso. Its

building system consists of a wooden frame composed by logs. Their arrangement is held in a

systematic pattern every 60 cm and an earthen block is used as an infill. Although variations

exist a typical earthen block is of 60x15x10cm in size. A small piece of wood is used in order

to fix the block into the wooden logs. This type of connection prevents the façade overturning

in case of an earthquake and due to its efficiency, the technique was widely spread at

Valparaiso. However, the metal plates used as external layer have hidden for many years this

configuration and as a result no extensive research has been held at this typology(Jimenez

2015).




Figure 23: Timber frame typologies in Valparaiso, Chile, facades and internal partition walls(Molen 2013).


Different building typologies can be found in Valparaiso in Chile. At the first

category, the historic buildings constructed by Harrington can be described by their regular

and symmetric plan. Anti-seismic behavior is guaranteed by the effective tying system

between the different materials in elevation and also the good diaphragmatic function of the

floors. Lastly, stiff basements and lighter storeys provide better response in case of

earthquakes sine the mass centre is closer to the ground. Due to these advantageous features,

these buildings survived many earthquakes hazards.

As far as the response of buildings with the adobillo block is concerned, existing

bibliography is limited. One result of recent research showed that their response is mainly

correlated with the quality and state of conservation of the used materials and of the

connections. Similarly to any vernacular construction typology, variations do exist and are

plenty in terms of materials, connections and shapes at the balloon and platform timber

structure. Definition of the main patterns should be done after inspection and thorough




analysis of the alterations and also taking into account the bibliography. The aim of this study

is to define the impact of several aspects of timber frame structures presented at Figure 24 in

Valparaiso at the global response of the building. To this term, analysis should be held in a

joint, an elementary cell and a shear wall level.

Figure 24: Vernacular timber frame typology in Valparaiso, Chile(Jimenez 2015).




3.6.3 Urban Development of Valparaiso

Located on central Chile’s Pacific coast, the colonial city of Valparaíso with its

historic quarter, is a vivid testimony of late 19th-century urban and architectural evolution in

Latin America. During the late 19th and early 20th centuries, the augment of the international

sea trade and its association with the harbour of Valparaiso, transformed the city into the first

and most important port of the Pacific coast of South America. Foreign influences, mix

cultures and pioneering technology were the main results of this growth, all adjusted to the

Valparaiso development. Three are the main factors contributing in the unique character of

the city. Firstly, the particular geographical location with the steep hills and the ravines,

favours an amphitheatre city layout. Then, its vernacular forms and the multicultural impact

contribute to a peculiar urban ensemble. Evolution of the city plan through ages is presented

at Figure 25.

Figure 25: Growth of Valparaíso on reclaimed lands (Indirli et al. 2010).




Urban development at Valparaiso is characterized by this spontaneous economic and

trade growth. The port played a decisive role to this increase, gathering the majority of the

commercial activities, public and administrative services. However, at the north oriented bay,

free space was inadequate to accommodate all the necessary residential facilities. As a result,

the first settlement was located in the west side of the bay in the area called “El Almendral”

and the urban uses were completely divided in terms of geography. Moreover, this

configuration prevented the development of the city in a regular square network, a typical

planning in Hispanic-American cities. The main pattern followed was the requirement of

adaptation at the specific topographical features implied by the limited flat ground and the

hills. During the years of the intense trade activities, these limitations were the main problem

for the city evolution. In addition, there was also urgent need for transportation and

connectivity between the port and the city. To this end, a network of longitudinal streets

parallel to the sea was created by systematic stuffing of the bay. Irregular shapes were

incorporated to the resulting blocks. (Hurtado 2007)

The city is until now well preserved and it represents a fine example of industrial

heritage. UNESCO recognized its value by including Valparaiso in the list of the protected

World Heritage Sites according to Criterion iii.2

Nowadays Valparaiso’s historic quarter as showed at Figure 26lies on the coastal font

and up the surrounding hills, consisting of five neighbourhoods. Firstly, la Matriz Church and

Santo Domingo Square, is located between the hills and the plain and characterized by the

19th-century buildings typical of the seaport architecture. Then, Echaurren Square and

Serrano Street is a commercial region with intense street trade. It is followed by Prat Pier and

Sotomayor and Justicia squares, where the largest public spaces are located. The majority of

the monumental sites can be found at the Prat Street and Turri Square area around the foothill.

Lastly, there are the two hills of Cerro Alegre and Cerro Concepción, where German and

English immigrants settled. This last neighbourhood is dominated by squares, viewing points,

promenades, alleyways, stairways and the top stations of some of Valparaíso’s distinctive

funicular elevators.(Unesco 2002)

2 Criterion (iii) Valparaíso is an exceptional testimony to the early phase of globalisation in the late 19th century,

when it became the leading commercial port on the sea routes of the Pacific coast of South America.




Figure 26: Limits of the UNESCO area in Valparaíso(Hurtado 2007)

3.6.4 Definition of Vernacular Timber Frame Typologies at Valparaiso Historic Quarter

Building shapes and architectural style at Valparaiso were influenced by the trade

boost. Different techniques, knowledge and patterns with both an academic and a spontaneous

origin were combined. Buildings designed by professional architects, highly influenced by

European aesthetics and building technology, are until now a significant part of the cultural

value of the city. However, the urban building stock consists also of traditional structures

made from skilled craftsmen, lacking formal education.




Identifying these vernacular structures in historic quartier of Valparaiso is the first step

for analysing and preserving them. Materials and building technology were the main aspects

to be considered for this categorization. Extensive building survey at historical quartier of

Cerro Concepcion by ICOMOS revealed the main characteristics of vernacular residential

structures. Regarding the materials of the structural system, adobe, adobe-wood (Adobillo),

Quincha, masonry, or just wood have been used from local builders. Foundations were

usually made of rock and the base was made of masonry or bricks. Façades were cladded with

plancha ondulada or metal sheets, adobe-stucco, Chilean or concrete-stucco (reinforced) or

wooden cladding. Moreover, distinctive colours were used as a final protective layer of these

cladding giving a unique character at each building block. According to the findings of the

survey, vernacular typologies in Cerro Concepcion represent more than the 45% of the

existing building stock as shown at Figure 27 (Molen 2013).

Amongst all, the “Adobillo” system is the most common building technique found at

the historical quartier of Cerro Concepcion, found in more than 70% of the surveyed

structures according to the Table 1. On the contrary Quincha pattern was the least popular

typology found at Cerro Concepcion since it was distinguished in only two cases as depicts

Figure 28. As far as the materials used at the facades is concerned, besides wood, metal sheets

are also common feature in vernacular typologies. They are used as final layer of wall

cladding and according to surveys more than 75% of the vernacular building stock include

this feature (Molen 2013). Detailed configuration regarding materials and building technology

are presented at the following pictures and table.




Table 1: Results of the survey at the historic quartier of Cerro Concepcion (Molen 2013).

Figure 27: Map of vernacular buildings at the historic quartier of Cerro Concepcion ,1:2500 (Molen 2013)




Figure 28: Map of Materials used at the historic quartier of Cerro Concepcion, 1:2500 (Molen 2013).

3.6.5 Carpentry Joints characterization

The dominant timber frame vernacular typologies at the historic region of Valparaiso

are characterized by the carpentry joints. The stability of timber structures depends mainly on

the connections.Timber elements are connected without any dowel type fasteners and forces

are transferred within the joints via contact pressure and friction. These examples of the

developed building technology at the area consist the most complex task to be carried out on

timber structures (Feio and Lourenço 2008).

Mainly, three different joint connections can be found at the vernacular adobillo

typology of Valparaiso as showed at a typical wall at Error! Reference source not found..

Connection by contact, notched joints and mortice and tenon. Although variations exist in

both dimensions, morphology and location, the most common configuration is presented

(Jimenez 2015). The mechanism of transmission of forces is via contact, pressure and friction.

As a result, the cutting of the joint by the carpenter create notches and contact surfaces

between the connected members. Within the connections, there is an interaction in terms of




stiffness and strength between the different pathways in which the forces are transferred

(Quinn et al. 2015). Eccentricities are inherent in this kind of connections and thus it should

be included in calculations.

Figure 29: Joints Configuration at a typical vernacular typology of Valparaiso(Jimenez 2015).

Amongst the different connections found at vernacular typologies of Valparaiso, the

mortice and tenon can be found at the bottom and top edges of the posts. Its function is based

on a geometric assumption. The posts where wider than the horizontal wooden elements

incorporate the smaller ‘tenon’ part. The tenon can be centred or be flush with the layout face

of the post. Rounded, rectangular and also square configuration of this type can be found at

vernacular buildings. The simplest and thus a very common connection, is the notched one. In

Valparaiso it is used mainly for connecting the diagonal elements with the posts. Finally,

connection by contact is used for tying non-structural elements and also at the upper part of

the braces. The different joint configuration of vernacular typologies is presented at Figure 30.




Finally, all connections are nailed but due to natural material decay, neglecting the nail

elements and their contribution to the joint resistance is a usual approach while studying this

typologies.

Figure 30: a) Vernacular timber frame at Carrer Urriola 495, b) mortice-tenon joint at Lautaro Rosas, c) Cross

half lap at Paseo Dimalow at the ceiling level (Jimenez 2015).




4. NUMERICAL ANALYSIS OF TIMBER

FRAME TYPOLOGIES IN VALPARAISO

4.1. Experimental campaign at Pombalino cage

Analytical models of typical vernacular Valparaiso timber frame structures are

validated using experimental data from an extensive experimental campaign carried out at the

University of Minho (Poletti 2013). Real scale specimen were tested in order to study the

seismic response of traditional timbered walls and final calibration of numerical model is

obtained through comparison between numerical and experimental curves, similarly to the

approach followed by Ciocci 2015.

4.1.1 Geometry and Materials

Common dimensions of existing historic buildings were used for the construction of

the real scale specimen of the timber frame wall without infill. Four braced cells with

dimensions of 840x860 mm2 and of 236m height composed the timber frame wall. The cross

section of the main frame was 160x120mm2 whereas cross sections of posts, beams and

diagonals were 80x120 mm2 and the schematic feature is presented at Figure 31.

Figure 31: Geometry of the real scale specimen (Poletti 2013).




The influence of masonry was neglected. According to results of testing on full-scale

walls, masonry confinement effect favours the global response since it adds stiffness and

strength to the frame. On the contrary, a timber frame without infill represents the most

unfavourable condition.

Three different carpentry joints connections can be found at the tested elementary cell

of the Pombalino buildings.

1. Half–lap tee halving connection between the post and the beam of the main frame,

presented at Figure 32.

2. Half–lap halving connection between the diagonal elements.

3. Connection by contact between the diagonal elements and the main frame.

All of them are nailed connections of a square cross section.

Figure 32: Geometry of half-lap joint specimen tested (left) & connection dimensions (right) (Poletti 2013).

Maritime Pine (Pinus pinaster) was the material used for the wooden elements and its

properties are presented at the Table 2. Probabilistic model code was used in order to derive

the properties not acquired from the experimental results (Poletti 2013).




Table 2: Timber material properties (Poletti 2013)

4.1.2 Test setup & Results

A steel profile was connected to the three posts and the reaction floor and the

specimen was located on the top of it. Cyclic displacements were imposed to the top of the

wall and out-of-plane displacements were avoided through the use of punctual steel rollers at

the top timber beam. As for the boundary condition is concerned, the bottom timber beam was

connected to the steel profile and was confined laterally in order to prevent any kind of

movement. A vertical load was applied by means of vertical hydraulic actuators on the three

posts of the wall. Moreover, a horizontal displacement was applied to the top timber beam

through a hydraulic servo–actuator.

Overall, the experimental campaign was developed according to ISO 21581 (2010)

and it was consisted of:

1. Preliminary monotonic tests, aiming at the calculation of the displacement capacity of the

wall. Moreover, prevention of the out-of-plane movement was validated movement of the

wall and to calculate the displacement capacity of the wall;

2. Quasi–static in–plane cyclic tests occurred in the following steps:

i) Simulation of pre-stressed conditions b applying vertical loads of 25 kN and 50 kN on the

top level of the posts of the wall

ii) Cyclic application of a horizontal displacement history on the top timber beam.

For the case of the 25kN applied as pre-stressed load, the ultimate displacement was

found to be equal to 101mm and these values are going to be used in the studied models of the

typical Valparaiso typologies.




The resulted force–displacement hysteresis diagrams presented at Figure 33 indicate

the shear resisting mechanism of the timber frame. Pitching behaviour can be spotted at the

flat area of the curve and the evolution of the vertical displacements depict an uplift of the

posts. As expected, application of higher pre-compression vertical loads result to an increase

in terms of load capacity and stiffness.

Figure 33: Timber frame wall with lower (left) and higher (right) vertical load levels (Poletti 2013).

As far as failure modes is concerned, significant deformation capacity was noted until

the failure. Braces could move independently from the posts gathering high shear stresses on

the central connection. Then after the cracking of this connection (Figure 34) elongation of the

braces occurred through detachment in one direction. Upon application of tensile forces the

posts and the braces moved separately. After failure, diagonals elongation was increased and

all connections crushed. Another aspect analysed by the experimental campaign was the load

path. After the failure of the central connection, stress redistribution occurred. As long as

displacement remained lower than 70.8 mm, timber frame wall had the ability to regain

strength due to this phenomenon.




Figure 34: Damages in the central connection at timber frame walls and half-timbered walls (Lukic 2016).

The main defined damage pattern was the bending mechanism of the posts as well as

the failure of the nailed connections. At half-lap connections, as stated before, central

connection was the first element to crash due to the augmented lateral compression applied by

the braces. Then redistribution of loads was noted and the right connection was the next

element to fail. At this experimental campaign the response of infill wall was also checked.

In short, the main results revealed a rocking mechanism of failure with a higher value of uplift

(Figure 35). Load capacity and global stiffness were increased in comparison with the bare

timber frame, pitching effect was less significand and damages were spread more

progressively at the connection level. The identified locations of nonlinearities at the

connections within the frame could be used for the development of a working numerical

model. Further details on their set-up can be found in (Poletti 2013).




Figure 35: Behaviour of the wall during the test: rocking of walls for lower vertical load level: half-timbered

wall (left) and timber frame wall (right) (Lukic 2016)

4.2. Numerical Model of Pombalino cage

A numerical model is developed at SAP2000 structural and earthquake engineering

software in order to simulate the response of the timber frame wall tested at the experimental

campaign under the pre-compression load of 25 kN. Frame elements were used while for

including non-linearity effects concentrated hinges were applied at the proper joints. Final

calibration of numerical model is obtained through comparison between numerical and

experimental curves. However, only the positive values of the experimental diagram is taken

into account since during tests the load was applied only at one side, resulting to an

asymmetrical response.

4.2.1 Geometry &Material properties

The analysed model consists of four braced elementary cells (Figure 36).

Simplifications are made at the dimensions size of each cell following a regular pattern. The

final configuration is 0.95m x 0.95m. Assumption of linear elastic isotropic homogeneous

material is followed for the timber elements. The values of modulus of elasticity and the

Poisson’s ratio are retrieved from the experimental data equal to 1 ∙ 107 KN/m2 and 0.3

respectively.




Figure 36: Geometry of the numerical model.

According to the results of the experimental campaign, connections were the most

vulnerable points and theirs nonlinear behavior influence the global response of the structure.

Different assumptions at the joint level of the connection are checked in order to identify the

most suitable one for calibration with the tests results. Starting from the rigid assumption,

which is one of the commonest approaches adapted from bibliography, stiffness was

progressively added at the diagonals and at the main frame elements.

In total, four models are checked and are presented at in Fig.4.7, using a nomenclature

similar to that adopted by Ciocci 2015.

1. MOD0 consists of perfectly rigid connections

2. MOD1 includes hinged connections between the braces and the main frame elements

3. MOD2 where connections between the braces and the main frame are considered as

semi-rigid.

4. MOD3 has semi-rigid connections at both between the braces and main frame

elements and the main frame elements.




Half-lap connections in the diagonals are not modelled. According to the experimental

results their contribution to the global behaviour is not significant and it can be omitted.

Frame elements are used for the beams of the main and internal frame, the posts and

the diagonals. For simulating the linear behavior of the connections, partial fixity springs are

used appropriately at the frame elements. In order to calibrate the stiffness of the connections

with the experimental data, a spring stiffness value is introduced at the suitable DOF for the

frame partial fixity springs. Axial and shear partial fixity is introduced at MOD2 and

rotational partial fixity for the linear analysis of MOD3, following the diagrams presented at

Figure 37 and Figure 39.

Figure 37: Linear elastic force–deformation for axial (left) and shear (right) spring introduced in MOD 2(Poletti

2013).

For the nonlinear analysis of the semi-rigid assumption, concentrated nonlinear hinges

are introduced at the frame elements in order to simulate post-yield behavior. This kind of

hinges are suitable for pushover analysis since hinge state may be displayed graphically for

each pushover increment. Theirs properties are entered manually capturing costumed

behavior. All over the frame elements’ length deformation remains within the elastic limits.

Inelastic behavior occurs entirely within the hinges modelled at the edges of the elements.

This is achieved by integration of the plastic strain and plastic curvature at a user-defined

hinge length.

By definition, hinge’s plasticity may be associated with force-displacement behaviours

in case of axial and shear displacement or moment-rotation for torsion and bending. Thus the




appropriate nonlinear hinges are used for each model. CSI Software automatically limits

negative slope to 10% of elastic stiffness, though overwrite options are also available. Limit

states may be specified. More specifically, the acceptance Criteria IO (Immediate

Occupancy), LS (Life Safety) and CP (Collapse Prevention) values are deformations

normalized by the same deformation scale factors used to specify the load deformation curve.

As shown at diagram of Figure 38 these intermediated stages are located between points B

and C on the curve. They serve at the indication of the state of the hinge at the display of the

results of the analysis. However, they do not affect the behavior of the structure.

Figure 38: Force – Deformation diagram assigned at a pushover hinge(Computers and Structures Inc. 2016).

Similarly to the spring elements, hinges may be assigned to any of the six degree of

freedom of the elements. Post-yield behavior is thus described by the general backbone

relationship shown to the Figure 38.

In this study, three nonlinear hinges are considered: Hinge 1 (Axial Hinge), Hinge 2

(Shear Hinge) and Hinge 3 (Rotational Hinge). Hinge 1 and Hinge 2 are located at each

connection between the main frame and the diagonal elements in MOD 2 and MOD 3. In

MOD 3 in addition to these two hinges, Hinge 3 is also used. It is located at each beam–post

connection. Due to the planar nature of the developed models, only axial, shear and pure

bending stiffness are considered for the element deformational DOFs. As a result, properties

of Hinge 1, Hinge 2 and Hinge 3 are assigned according to the axial, the shear and the

rotational stiffness respectively. The properties of the nonlinear hinges are defined according

to the force-displacement and the moment-curvature diagrams presented at Figure 39.




Figure 39: (a) Non-Linear force-deformation diagram assigned at the axial nonlinear Hinge 1, (b) Non-Linear

force-deformation diagram assigned at the shear nonlinear Hinge 2 and (c) Non-Linear moment - rotation

diagram assigned at the rotational nonlinear Hinge 3.

4.2.2 Loading Conditions

The exact conditions followed at the experimental campaign are simulated

numerically. Thus, the applied loading conditions are:

Vertical load equal to 25 kN at the top-level joints of the posts in order to imitate the

pre-stressed conditions.

Application of a horizontal displacement equal to 0.10 m at the top beam of the main

frame.




4.2.3 Boundary Conditions

The three bottom joints of the beams are restrained in vertical and horizontal

directions. Moreover, a local restraint is applied at the horizontal direction at the left corner of

the top beam, in order to be possible to apply the displacement. In addition in MOD1, the

connections of the braces are simulated as pinned and for this purpose all the rotational degree

of freedom of the diagonals are released.

4.2.4 Structural Analysis

Linear and nonlinear analysis are used in order to define the capacity of the timber

frame wall. MOD0, MOD1 and MOD2 only linear analysis are checked in linear static

analysis since no nonlinearity exists at that models in terms of geometry, material loading and

boundary condition. Nonlinear analysis in MOD3 is used in order to check the capacity of the

timber connections through the introduction of the plastic hinges. It is applied in two steps:

Application of the self-weight and the pre-stressed vertical loads.

Application of 0.1 m displacement and displacement control at the left top corner.

Relationship between the base shear and displacement at the top left joint are

presented at the capacity curve of the model.

4.2.5 Calibration of the models

At the experimental campaign, initial and secant stiffness and the secant stiffness of

the timber frame wall were calculated for the initial cycle according to ISO 21581 (2010).

Secant stiffness indicated an initial nonlinear behaviour of the structure. An initial adjustment

of the connections resulted to a very small value of the lateral drift. The origin and the point

corresponding to 40% of the maximum load were taken into account so to calculate the secant

stiffness K1,+. According to the results for the lower pre–compression load level of 25kN,

average values of 2.14 kN/mm and 2.60 kN/mm were obtained for the initial and secant

stiffness, respectively(Poletti 2013). The value of the secant stiffness is used in order to

validate the results from the rigid and pinned assumptions as well as so to define the axial,

shear and rotational stiffness of the timber connections at MOD3.




Model with rigid connections - MOD0

The first assumption adapted at the analysis was to consider the connections rigid. At

MOD0 no stiffness is added and all nodes behave rigidly. The resulted deformation of the

timber wall, presented at Figure 40 is mainly due to the application of the horizontal

displacement at top joint. Impact of the self-weight is no significant. Different behavior is

observed at the braces regarding theirs location. The diagonal elements inclined against the

applied displacement are found in compression while the ones along are in tension. The value

of the stiffness of the timber frame wall of MOD0 is 36.22 ∙ 103 kN/m, much higher than the

experimental result. Thus, the rigid assumption is not considered accurate enough. The

moment and axial diagrams of the Pombalino cage are presented at the Figure 40 in a

qualitative way since it’s the distribution of the forces and moments that is studied at this

stage of the study.

Figure 40: Deformed shape (up), moment diagram (left) and axial forces diagram (right) at MOD0.




Model with pinned connections – MOD1

Next assumption in modelling the timber frame structure is to consider the connection

between the diagonals and the main frame as pinned. To this term, the rotational degree of

freedom is released. The global stiffness, calculated from the ratio between the displacement

and the force at the left top joint, is 36.17 ∙ 103kN/m. The value is still significant higher from

the experimental outputs and really close to the rigid assumption. This indicates that the

impact of the rotational stiffness between the diagonals and the main frame could be

neglected. Timber structures are generally characterized by their low bending stiffness.

Moreover, Pombalino timber frames present an almost rigid triangular configuration. The

resulted deformation and the qualitative diagram of the moment at the timber frame is

presented at Figure 41.

Figure 41: Deformed shape (left) and moment diagram (right) at MOD1.

Finally, in order to assess the impact of the direction of diagonals, an alteration of

MOD1 is also checked. At MOD1_ALT, only one brace exists at each elementary cell and the

resulted stiffness is almost half of the original one of MOD1. The value is equal to 17.91∙ 103

kN/m and this confirms that when in the elastic area, contribution of braces is similar

regardless being in tension or compression. The resulted deformation and the qualitative

diagram of the moment at the timber frame is presented at Figure 42.




Figure 42: Deformed shape (left) and moment diagram (right) at alternative MOD1.

Model with semi–rigid connections of the diagonal elements - MOD 2

A MOD2 additional stiffness is added at the connections between the main frame

elements and the braces. As described at the section 4.2.1 axial and shear springs are applied

at the diagonal elements at the relevant degree of freedom. The force-deformation relationship

assigned to the springs follows the linear elasticity assumption. The first attempt is to assume

similar response of the axial springs for both tension and compression diagonal elements. In

other words, stiffness in tension k+ is assumed to be equal with the stiffness in compression k-.

Inverse fitting method is used in order to define the value of the stiffness of the connections in

tension and compression.

For stiffness equal to k+= k- =4.21∙103 kN/m assigned at the axial springs, global

stiffness of MOD2 is equal to 2.6∙103 kN/m which is the value of the global stiffness of the

specimen calculated experimentally. Similarly, calibration of the shear springs occurs. For the

shear springs values of k+= k- =8.72∙103 kN/m are assigned. As for the axial springs, only

contribution of compression elements is taken into account and for k- =8.72∙103 kN/m and

k+=0 kN/m global stiffness of the structure is equal to the experimental output.

Model with semi–rigid connections of the diagonal elements and elements of the

main frame - MOD 3

At this final model, contribution of connections between the main frames is also

studied. Rotational stiffness of the horizontal elements of the main frame is extrapolated from

the results on in–plane cyclic tests on half-lap joints with a pre–compression vertical load of




25 kN of the experimental campaign (Poletti 2013). A tri-linear curve is derived from the

average force-displacement diagram shown at Figure 43. It is used for the numerical model

and it is presented in Figure 44. The values of the rotational stiffness are calculated equal to kin

= 171kNm/rad and kfin = 47 kNm/rad.

Figure 43: Force–displacement for the half–lap connection(Poletti 2013).

Figure 44: Moment-rotation diagram for the half-lap connection.

Calibration of the values of the stiffness of the axial and shear springs occurs in

similarly way with the previous models and the results are presented at the Table 2.

According to the results, shear stiffness contribution to the linear elastic response of the

timber frame model is not so significant.




Table 3 Calibration of the linear response of MOD3

MOD3 Stiffness A B C D E F G H Final

k+ [kN/m] 0 0 0 0 0 0 0 0 0

k- [kN/m] 11000 10000 10100 10200 10250 10255 10255 10280 10300

k+ [kN/m] 10000 10000 10000 10000 10000 10000 10000 10000 10000

k- [kN/m] 10000 10000 10000 10000 10000 10000 10000 10000 10000

kin+ = kin

- [kNm/rad] 171 171 171 171 171 171 171 171 171

kfin+ = kfin

- [kNm/rad] 47 47 47 47 47 47 47 47 47

Numerical Model Kglobal (kN/m) 2696,742 2506,02 2525,3 2544,527 2554,124 2555,083 2556,041 2559,876 2563,709

Experiment Kglobal (kN/m) 2600 2600 2600 2600 2600 2600 2600 2600 2600

Convergence 3,72 3,61 2,87 2,13 1,76 1,73 1,69 1,54 1,40

Axial spring

Shear spring

Rotational spring

After calibrating the linear response of the numerical model, nonlinearities are

introduced at the connections of the diagonals with the main frame and at the connections of

the main frame elements. Axial (Hinge 1) and shear hinges (Hinge 2) are applied at the edges

of the braces while rotational hinges are applied at the edges of the main frame elements

according to the described force-displacement and moment-rotation diagrams presented at

Figure 39: (a) Non-Linear force-deformation diagram assigned at the axial nonlinear Hinge 1,

(b) Non-Linear force-deformation diagram assigned at the shear nonlinear Hinge 2 and (c) Non-

Linear moment - rotation diagram assigned at the rotational nonlinear Hinge 3.. Capacity of

the connections can be calculated from (1).

Fy= fc90 * A, (1)

Where,

fc90: compressive strength perpendicular to the grain

A: contact area for each connection

Then the yield displacement dy can be computed by (2).

dy =Fy /k, (2)

Regarding the ultimate displacement of the connections, experimental data are used.

At the half-lap connections of the main frame, ultimate displacement is reached for rotation

equal to 0.07rad, as shown at Figure 44: Moment-rotation diagram for the half-lap connection.




For the connections of the braces with the main frame elements ultimate displacement is 0,05

m. When these values are reached, the capacity of the connections assumed to be zero.

Experimental tests do not define the yield capacity of the brace’s connections.

Parametric analyses have been carried out to define this value and to better understand the

influence of the stiffness of this type of connection. Different fc90 compressive strength values

perpendicular to the grain are considered and from the relationships (1) and (2) yield forces

and displacements are calculated. The first consideration is made for the value fc90= 4,4 MPa.

Then yield force is calculated, Fy = 21kN and this value is assigned at the axial and shear

hinges. The defined force-displacement and moment-rotation relationships for Fy=21kN

assigned to the plastic hinges are presented at the Figure 45. The hinges are applied at 1% and

99% of the total length of the braces elements and overwrite command is used.




Figure 45: From top to bottom: Assigned axial, shear and rotational plastic hinge at the edges of the diagonals

for the numerical model analysed f Fy =21 kN.

The response of the numerical model is checked under nonlinear static analysis.

Definition of the capacity of the connections is done by comparison between the pushovers

curves obtained from the analysis with the experimental output. The resulted curves of the

different numerical models are shown at the Figure 46.

0

10

20

30

40

50

60

70

0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1

Ba

se S

he

ar

(kN

)

Displacement (m)

Experiment

Fy=21kN

Fy=23kN

Fy=25kN

Fy=27kN

Fy=29kN

Figure 46: Parametric analysis of the capacity of the connections between the diagonals and the main frame

elements.

From the comparison of the different models, the best fitted values of the connection

capacity of the diagonal elements are 27 kN and 29 kN. Each change at the slope of the curves

indicates the creation of a plastic hinge at an element or the transmission from one limit state




to another. Different stages of the global response are examined for the yield force of the

diagonal connections equal to Fy=29kN. The main changes at the slope of the pushover curve

are shown at the Figure 47 and the relative response of the timber frame wall are presented for

points A,B,C,D and E. Starting from step 1 at Figure 47 when all elements correspond

linearly and moving towards collapse steps 6, 23,44 and 92 are examined respectively.

Formation of hinges can be checked by the different colour configuration which corresponds

to a state of deformation starting from initial unloaded state until the local failure of the

connections defined by parametric analyses. Global response in terms of maximum

displacements is assessed at Figure 49.

Figure 47: Pushover diagram for the numerical model with connection capacity of diagonals Fy=29 kN(left) and

initial state of response (right).

According to the results showed at Figure 48, nonlinear response starts at stage 6 when

the first nonlinear hinges are created. Most vulnerable point of the structure is proved to be

the central connection where 2 nonlinear hinges are noted early at stage 6 of the analysis-point

A of the diagram. The same pattern is followed at the next steps. Between points A and B,

corresponding to steps 6 and 23 of the analysis, the diagonals in tension concentrate stresses

and as a result hinges near the failure level are obvious.

Rotational hinges at the main frame edges are the last to be created at step 44 - point

C. Then, the response of the structure is governed by theirs behavior and a plateau is created

where the load remains relatively constant. Between points C and D additional nonlinear

hinges are noted. After point D, redistribution of forces occurs and nonlinear hinges are

developed at all the elements of the timber frame wall. At the bottom of the elementary cell,

redistribution of forces occurs through the diagonal in tension.




A. B.

C. D.

Figure 48: Timber frame response for the different stages of the pushover analysis.

After the failure of the connection at the upper edge of the brace occurring at point D –

step 62, load is transferred to the bottom edge of the diagonal taking advantage of the

remaining capacity. The additional load is transferred at the bottom end where the nonlinear

hinge status ‘proceeds’ at the next safety level. At the final step of the analysis, failure occurs

at the central connection and at the bottom edge of the central post as shown at the figure

Figure 49. By the default software settings, intermediate hinges are created between points B

and C. Although they do not affect global response, comparison in terms of hinge’s colours

should not be correlated with the displacement contours.




Figure 49: Timber frame response for point E (left) and final step (right).

4.3. Numerical Analysis of Vernacular Valparaiso Typologies

After the definition of the response of the carpentry joints at a Pombalino timber frame

wall numerical models of typical Valparaiso timber facades are created. The effect of the

bracing system in correlation with the opening ratio is examined. Moreover, different models

in height are analysed in order to define the impact of the number of storeys. Finally, the row-

house effect at the global response of each building’s façade is examined.

4.3.1 Geometry of a Valparaiso typical timber frame wall

Vernacular Valparaiso buildings at the historic quartier have been examined through

inspection and detailed surveys(Jimenez 2015). Consequently, typical typologies of the timber

frame frontal walls can be derived. Although variations exist, regularity in plan and shapes is

followed. Usually, seven to nine elementary cells are used so to create the façade timber wall.

Commonly, elementary cells are of 3.5-4.0 m height and are consisted of three posts located

at a 0.5-0.6 m distance. Dimensions of the elementary cells are presented at the Figure 50 and

a typical geometrical configuration of a vernacular timber wall at Figure 51.




Figure 50 : Geometry of the elementary cell at vernacular Valparaiso typology(Jimenez 2015).

Horizontal beams can be found only at the bottom and at the top level of each cell. At

the level of the openings, wooden lintels can be found limited however, to the opening’s

width. According to a traditional building technology of the area, cross sections of all

elements are similar. Thus, cross section of the beams, posts and braces can be considered

equal to 0.1m *0.15m. In terms of materials, many different wood species can be found at the

Valparaiso historical structures. Besides the local materials, imported wooden elements were

also used for the construction of the buildings. Alterations through years are many due to

natural decay of the material. For consistency reasons with the experimental campaign,

maritime pine is used at the analysis.




Figure 51: Geometry of the timber frame wall at vernacular Valparaiso typology(Jimenez 2015).

4.3.2 The effect of the Bracing Ratio

As proved by the analysis of the Pombalino walls, the impact of the diagonals at the

global response of the structure is significant. Moreover, in Valparaiso vernacular buildings

no strict rules regarding the structural configuration were applied. For these reasons, four

models are checked with varied bracing ratio in an attempt to model the most common

typologies and also derive conclusions regarding this parameter.

The bracing ratio is defined by dividing the number of the braces at the wall with the

number of the resisting cells. To this end, cells with openings are not included at the

calculations. Basic model, Model_A is a wall consisting of nine elementary cells, six of which

are resisting, while no braces exist. Even though this case cannot be considered as a

representative typology, it is checked in order to serve as the initial model at the comparative

analysis. Then, Model_B with one brace and bracing ratio equal to 0.17, Model_C with two

braces and B.R.=0.33 and Model_D and B.R.=0.67 with four braces are analysed and

compared as shown at Figure 52.




Figure 52: From top to bottom, geometry of the Model_A, Model_B, Model_C and Model_D timber frame

walls at vernacular Valparaiso typology (Jimenez 2015).

Nonlinear incremental static analysis in steps is applied at the models of the

Valparaiso walls. Firstly, self-weight and the vertical loads of the roof are applied. Then

ground- acceleration load is applied at the x direction with displacement control at the top left




joint. Nonlinear rotational hinges (Hinge 3) are introduced at the posts elements where the

connection with the braces occurs according to the dominant geometry of the elementary cell.

Moreover, braces are designed to have nonlinear axial (Hinge 1) and shear hinges (Hinge 2).

Hinges properties are assigned according to the force-deformation and moment-rotation

diagrams obtained from the calibration with the experimental campaign and described at the

section 4.3. Application of the hinges at the edges of each element follows the auto-merge

tolerance of 0.01m and overwrite option is checked. Comparison of the results is done in

terms of push over capacity curve showed at Figure 53.

0

30

60

90

120

150

180

210

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

Base S

hear (

kN

)

Displacement (m)

Model_A

Model_B

Model_C

Model_D

Figure 53: Capacity curves of Valparaiso models with varied bracing ratio.

As expected, presence of the braces increase the lateral capacity of the Valparaiso

walls. Model_A, the facade with the no brace elements could resist until a load of 146 kN,

while the four-braced model presents an increased bearing capacity by 18.4% corresponding

to a load equal to 173 kN.




Moreover, another assumption regarding the hinges application is tried. Braces are

considered to have semi-rigid rotational stiffness and thus rotational hinge 3 is applied at the

diagonal elements at the Model_B* where B.R.= 0.17. Model_B* has exactly the same

geometrical configuration with and Model_B. The resulted diagram at Figure 54, depicts a

high impact at the initial linear stiffness. However, as displacements are increased the effect

fades out and the nonlinear response follows the pattern of all the other models already

analyzed. Changing the stiffness affects significantly the initial stiffness of the structure,

while the global capacity changes slightly.

0

30

60

90

120

150

180

210

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

Base

Sh

ear

(kN

)

Displacement (m)

Model_A

Model_B

Model_B*

Figure 54: Influence of the rotational stiffness for Bracing Ratio = 0.17.

In order to better understand the response of the different braced models of the

Valparaiso typology, detailed deformation shape and hinges formation is presented. Starting

from the wall with no braces, modal analysis is used so to check the deformation shape as

shown at Figure 55. Then, nonlinear static analysis indicates the most vulnerable elements of

the wall. Firstly, nonlinear hinges are created at the joints just under the opening’s level,

followed by the bottom joints located near the door. The same applies also at the last steps of




the analysis, just before failure. Openings areas concentrate forces and nonlinear hinges occur

signing the capacity failure of the connections at these points.

Figure 55: Results for Model_A. a. Deformed shape, b. first hinges created, c. formation of hinges at step 62, d.

final step of the analysis.

Similarly, results of Model_D, the four-braced wall, are presented in detail since this

was found to be the most resistant model in terms of loading and displacement capacity. As

the lateral load imposed at the structure is increasing, slope of the curve is changing defining

the characteristic points for the global response. Point A at the capacity curve of Figure 56 is

where nonlinearity is introduced for the first time at the model at early step 9. From the

deformed shape of the wall presented at

Figure 59, nonlinear hinges at the upper edges of the braces occur. Then at point B at

step 31, redistribution of the loads has already happen and more hinge have been created at

the bottom part and also at the windows level. Between points C and D, three drops in the

value of the base shear are noted at the pushover diagram. Comparing the deformed shapes of




the relevant steps 55 & 62 of the analysis at Figure 57, there are three areas of the wall where

significant change at the hinge’s formation occur; at the two bottom parts of the windows and

at the upper part of the door as well as at the intermediate brace.

a.

b.

.

Figure 56: a) Pushover curve for Model_D and characteristic points of the global response, b) Deformed shape

of Model_D for points A and B at steps 9 and 31 of the analysis respectively.




Figure 57: Deformed shape of Model_D for points C and D at steps 55 and 62 of the analysis respectively.

At the final steps of the analysis, connections at the down areas of the openings fail

and the same applies for the connection between the posts and the first brace. Overall as

shown at the Figure 58 almost all elements display nonlinear hinge and since there is no

additional loading capacity, redistribution of the loads is no possible and failure occurs.

Figure 58: Deformed shape of Model_D for point E of the push over curve.

4.3.3 The effect of the Opening Ratio

Even though, the influence of the infill at the Valparaiso typologies is neglected,

opening ratio is checked in correlation with the bracing ratio. This parameter expressed as the

ratio between the area of the openings to the overall area of the wall is checked through the

analysis of three different models, Model_C as defined at the section 4.4.2 with Opening

Ratio = 0.207, Model_C* with Opening Ratio = 0.24 and Model_D* with Opening Ratio




=0.175. When compared at the linear part, difference at the initial stiffness is significant.

Load and displacement capacities of the Model_C are higher while the hinge formation is not

expanded across the wall. As showed at the diagram of the

Figure 59, the impact of this parameter at the global structure is decreased naturally

along the failure part. When displacement reach the ultimate displacement of the wall,

response of Model_C and Model_C* is similar.

0

30

60

90

120

150

180

210

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18

Base

Sh

ear

(kN

)

Displacement (m)

Model_C

Model_C*

Model_D*

Figure 59: Comparison between Model_C, Model_C* and Model D* in terms of load and displacement

capacity.

Amongst the three walls, façade of Model_D* has the less opening area and also the

most braces. As it can be seen from hinge formation and deformed shape at Figure 60,

combination of a small opening ratio with an increased bracing ratio results to an increased

bearing capacity and also deformation tolerance. The deformed shape and the detailed

response of the Model_C* at the last step of the pushover analysis is presented at the Figure

61. In comparison with the respective shape of Model_C as showed at Figure 62, differences

in hinges formations exist at the bottom area of the increased in width window and also at the




upper edges of the posts located at the left part of this window. This indicates the

unfavourable influence of the opening ratio to the global response.

Figure 60: Deformed shape of Model_D* and hinge formation at ultimate step.

Figure 61: Deformed shape of Model_C* and hinge formation at ultimate step.

Figure 62: Deformed shape of Model_C and hinge formation at ultimate step.




4.3.4 Influence of the multi-storey configuration

The impact of multiple storeys is checked at the four-braced wall, Model_D. Besides

the variation of the height, all the other elements in terms of materials, geometry, hinge

definition and analysis process are kept constant. Lateral drift is calculated at Error!

Reference source not found. for assessment of the models response. According to the results

of the nonlinear static analysis of the three models apparent at capacity curves of Figure 63,

increase in height influences negatively the global response of the Valparaiso façade. As

distance between the ground and the centre of mass and weight is increased, overall

vulnerability is increased and load capacity is dropping. However, displacement capacity at

the multi-storey façade is higher in comparison with the one storey model.

0

20

40

60

80

100

120

140

160

180

0 0,05 0,1 0,15 0,2 0,25 0,3 0,35

Ba

se S

hea

r (k

N)

Displacement (m)

1 storey

2 storeys

3 storeys

4 storeys

Figure 63: Capacity curves for the different storey configuration at Model_D.




Table 4: Storey displacement and storey drift for the 2storey and 3storey facades

Storey

Height

(m)

Total

Height

(m)

Storey

Displacement

(m)

Storey

Drift % 4 s

tore

ys

faça

de Ground

Level 0 0 0,0007 0,00

1st Storey 3,7 3,7 0,21288 5,73

2nd Storey 3,7 7,4 0,2786 1,78

3rd Storey 3,7 11,1 0,32157 1,16

4rth Storey 3,7 14,8 0,33959 0,49

3 s

tore

ys

faça

de

Ground

Level 0 0 0,0007 0,00

1st Storey 3,7 3,7 0,1811 4,88

2nd Storey 3,7 7,4 0,2392 1,57

3rd Storey 3,7 11,1 0,263187 0,65

2 s

tore

ys

faça

de

Ground

Level 0 0 0,0005 0,00

1st Storey 3,7 3,7 0,1654 4,46

2nd Storey 3,7 7,4 0,199207 0,91

The deformed shape of the Model_D at Figure 64 indicates the distribution of forces

along the wall as well as the vulnerable elements that are located at the main opening and at

the first brace.

Figure 64: Deformed shape of Model_D for last step of the analysis.




The deformed shape and mechanism of failure for the two-storey and three-storey at

Figure 65 and Figures 66 respectively, depict that global response is governed by the local

collapse of the brace elements. The braces at the top levels are implied to intense loads and

even at first steps their resisting capacity is lost. Loads are transferred at early stages at the

bottom part of the structure and they are redistributed until the final failure that occurs for a

lower load in comparison with the one storey wall facade.

Figure 65 : Hinges formation (left) and deformed shape with displacement contour (right) of the two-storey

model for early and late step of the analysis.

Although the role of the braces in connecting the different elements fails at these

occasions, their early failure results to concentration of higher loads at these elements,

allowing the rest of structure to sustain further displacements. The load path is limited to the

failing elements and its late impact at the wall section allows further deformation without the

development of the final mechanism of collapse.




Figure 66: Deformed shape with displacement contour of the three-storey model (right) and the four-storey

facade at late step of the analysis.

The results are indicative of the main assumption made at the analysis. The critical

role of the connections and the introduction of nonlinear behavior at these joints is also

noticeable while checking geometrical parameters.

4.3.5 Influence of the ‘row-house’ phenomenon

Finally a typical urban development pattern followed at Valparaiso is the row-house

phenomenon. Timber frame vernacular typologies are linked one each other creating a whole

compound. Masonry walls are used at the union joints in order to prevent a possible fire

expansion. In order to preliminary assess the structural response of this phenomenon, a façade

created by the union of three basic walls is analysed. At Figure 67 comparison between the

pushover curves of the two alterations of the Model_D is made in terms of pushover capacity

curves. According to the results, union of multiple timber frame buildings has a favourable

contribution to the global lateral stiffness and load capacity.




Figure 67: Capacity curves for the different storey configuration at Model_D.

The whole compound has the ability to sustain higher lateral loads without failing.

This is mainly due to the cooperation between the different timber frame buildings and their

holistic final response. Their similarities in terms of mechanical and geometrical

characteristics, allows the redistribution of the loads within the wooden elements taking

advantage of the flexible wooden connections and elements. Load path can be tracked through

hinge’s formation at Figure 68. As far as the deformed shape of the compound is concerned,

similarities between the Figure 68 and the basic Model_D at figure 64, confirms the holistic

response of the compound when imposed to a lateral load.

Figure 68: Deformed shape of the row-house alteration of Model_D. is concer




The most vulnerable points of the structure can be defined by the deformation shape at

the last step of the analysis. Failure occurs for the connections joints at the bottom part, below

the openings and also at the upper part of the braces. Between steps 80 and 83 of the analysis,

hinges at these points progressively reach their ultimate capacity and fail as it showed at

Figure 69. This transmission affects the global behavior and at the pushover curve of Figure

67, load drop can be spotted at this point of the analysis. Moreover, location and orientation

of the braces influence their response and as a result the connections of the diagonal elements

at the beginning of each façade designed towards to the loading fail at the late steps of the

analysis.

Figure 70: Progressive failure of the connections at the bottom part of the openings.

4.4. Discussion of the results

The main parameters that were assessed was the bracing and the opening ratio. These

alterations are easily noted when surveying and for this reason, defining the capacity in

correspondence to them is preferable for a large scale analysis. Moreover, their impact at the

vernacular typologies of Valparaiso response was found significant




According to the results of the analysis presented at Figure 70, increase of the bracing

ratio favours the response of the façade. The model D with the four braces could sustain a

172.95 kN lateral load. The same applies for the displacement capacity. As the number of the

braces gets higher, flexibility of the structure is augmented and load path allows a further

displacement of the wall. However, direction and location of the braces in this monotonic

incremented analysis seems to have a slight effect on global displacement. The Model_B has

only one brace designed in compression at the second elementary cell. The total displacement

is 2 mm higher in comparison with Model_C, where two braces exist at elementary cells four

and six. However, for higher bracing ratio, displacements are also increased as shown at

Fig.71.

Figure 71: The effect of bracing ratio at the vernacular timber frame typologies at Valparaiso.

Alterations at opening ratios were also checked and ass expected increase of

opening areas has disadvantageous results at the global response. As shown at Figure 71,

when more windows and doors exist, the façade is more vulnerable in terms of lateral load

capacity.




Figure 72: The effect of opening ratio at the vernacular timber frame typologies at Valparaiso.

Since the infill was neglected, opening ratio was studied as dependent parameter of the

bracing ratio. The comparative results of these correlated parameters are presented at Table 5.

Table 5: Correlation between bracing and opening ratio and the impact to the global response.

Finally, deformed shape and hinge formation is used for defining the vulnerable areas

of the structures and the possible local failures. As showed also at Figure 72, the distribution

of the loads is favoured by the presence of the braces. Comparison of the deformed shape

between models A and D indicates that phenomenon by development of nonlinear hinges at

various stages of the analysis.




Figure 73: Deformed shape of the four basic models at the final step of the analysis.

Most vulnerable areas are found to be at lintels and at the bottom area of the openings

were connections failed at the majority of the models. The upper part of the wall, has to

sustain to the maximum of the global displacement but due to the light weight of the

elements, flexibility is increased. In terms of connections behavior, the assumption of the

rotational stiffness assigned at the braces of the variation of Model_B proved to have a

significant impact at the linear part of the analysis. As it is showed at Figure 54, stiffness and




load capacity are increased in comparison with the basic models. However, this impact fades

away as further loading and deformation of the structure occurs.

Multi-storey configuration reveals the expected increased vulnerability for the upper

storeys. However, lateral load capacity of the three storey façade was found increased

according to the results presented at Figure 63 and Figure 64.

Finally, the row-house effect a common architectural pattern followed a historic

quartier of Valparaiso was checked by an alteration of Model_D. Three facades were united in

one model and according to the results showed at Figure 68, ignoring the impact of the linked

walls and considering only one façade seems to be a conservative approach that favours the

need for safety. This approach is commonly used for accurate and quick seismic assessment at

an urban level.




5. CONCLUSIONS

5.1 Summary

The aim of this thesis is to assess the response of vernacular timber frame typologies

under lateral loading at Valparaiso and to propose suitable numerical models for an urban

scale analysis of these typologies. To this context after studying the relevant bibliography, the

contribution of carpentry connections and different morphological configuration, such as the

bracing and opening ratio, the alteration in height and the row-house phenomenon, are chosen

as the main examined parameters.

First step of this approach, is the calibration of the joints connections according to

results of an experimental campaign held at the vernacular typology of Pombalino cage

(Poletti 2013). The assumption of rotational nonlinear hinges at the posts and axial and shear

nonlinear hinges at the braces is adapted. Their properties are extrapolated from the

calibration of the Pombalino model, studied at section 4.1. Moreover, preliminary check of

the impact of rotational nonlinear hinges at both the posts and the braces is tried.

Even though differences between the real scale specimen and the vernacular timber

frame typologies at Valparaiso exist, the developed numerical models are appropriate for a

preliminary check of the response of the buildings as well as for an urban vulnerability

assessment of different timber frame typologies at the protected by UNESCO historic quartier

of Valparaiso(Unesco 2002). Urban scale analysis already held by researchers at district Cerro

Concepción (Molen 2013) were used in order to define the dominant structural typology.

Then different facades configurations are developed and evaluated according to the results of

extended surveys at the field from(Jimenez 2015).

In total four vernacular timber frame facades Model_A, Model_B, Model_C and

Model_D with different bracing ratio are analysed. Moreover, response of seven alterations of

the basic models in terms of opening ratio, multi storey and row-house configurations are

examined and the results were showed at the section 4.5 and 4.6.




5.2 Final Remarks

According to the results of the experimental campaign at Pombalino timber frame,

nonlinear hinges are assigned at the edges of the timber elements in order to simulate the

nonlinear response of the carpentry connections. Axial and shear stiffness are provided at the

braces and rotational stiffness at the posts of the typical Valparaiso models through relevant

constitutive law. Load path is determined through the study of the global response at different

stages of the nonlinear analysis and the progressive transmission of the hinges status from

initial conditions till failure. Most vulnerable point of the structure is proved to be the central

connection where nonlinear hinges are noted at early stage of the analysis and also

progressively reach the status of failure. The diagonals in tension concentrate also stresses and

as a result, hinges near the failure level are obvious. Finally, rotational hinges at the main

frames are the last to be created but their increased capacity governs the response of the

structure. As it showed at Figure 46, a plateau is noted at the pushover curve. The load

remains relatively constant similarly with the introduced moment-rotational diagram of the

rotational hinges.

At the analysis of the Valparaiso timber frame typologies, different assumptions are

used in order to simulate the nonlinear response of the carpentry connections. Firstly,

nonlinear axial and shear hinges are applied at the edges of the braces and rotational hinges at

the posts. Then rotational stiffness is assigned also at the braces. This assumption seems to

have a direct impact at the stiffness and load capacity at the linear early phase as depicted at

Figure 54. This effect however fades away when nonlinearities are appearing at the structure

and finally the failure pattern and the global response is relatively the same at both examined

models.

Amongst all examined parameters, the alteration of the bracing ratio, defined as the

ratio between the existing diagonal braces and the resistant cells that do not have openings,

has the major influence in terms of load bearing and displacement capacity. Moreover, in this

one direction incremented analysis location of the braces in correspondence with the openings

seems to have a slight impact at the global response as it showed at Table 5. Finally, for




different bracing ratio from 0.00 to 0.67 the bearing capacity is ranged between 146kN and

180Kn and all the detailed results are showed at Figure 68, Figure 69 and Table 5.

The infill of the adobillo system is neglected and as a result, the opening ratio is

examined only as dependant parameter in correspondence with the number of the braces. As

expected, its increase has a negative impact for the global behavior. Most vulnerable areas are

found to be at lintels and also at the bottom area of the openings. It was there where

connections fail, a pattern noted at the majority of the models. The upper part of the wall, has

to sustain to the maximum of the global displacement but due to the light weight of the

elements, flexibility is increased.

According to the results of the multi-storey configuration, rise in height influences

negatively the global response of the Valparaiso façade. As distance between the ground and

the centre of mass and weight is increased, the structure becomes more vulnerable under

lateral loading. The resulted storey drift ratio presented at Table 4, can be used for further

assessment and identification of damage state at these typologies. The deformed shape and the

capacity curve at Figure 63 shows that the three-storey model presents an increased

displacement capacity even though the load bearing capacity was substantially lower than the

single and two-storey models.

Finally, the usual approach in analysis of building compounds or blocks following a

row-house pattern is to isolate one building. In order to preliminary assess, the row-house

widely spread Valparaiso, a relative alteration of Model_D is analysed based on the

assumption of neglecting the impact of the linked walls. The outcome of the analysis depicts

the ability of collaboration between the different elements and their impact at redistribution of

the loads after local failure occurred. The effect increases the global capacity and as a result,

focusing on only one building of a compound proved to be conservative method that can be

applied, fulfilling the requirement of safety.




5.3 Further Developments

This study followed the assumption of Pombalino vernacular connections for

feasibility and accuracy reasons. The development of a numerical model suitable for use to an

urban level seismic assessment does not require sophisticated micro-modeling approaches. On

the other hand, global impact of each connection, seems very important factor for timber

frame typologies. Alterations between the Pombalino and Valparaiso typical typologies exist

in both geometrical terms and also in types of the joints connections. For further research, a

real scale specimen of the Valparaiso typology could be developed and then assessed

numerically. Thus, accurate representation of the commonest carpentry joints could be made

and numerical model would be more representative of the response of vernacular timber

frame buildings. Contribution of the infill could also be checked in a refined analysis in order

to measure its impact at the lateral load capacity. Then assessment of other parameters as the

opening ratio could be checked. Overall, according to the results of this research project and

given the conclusions, interesting subjects are identified for future works.

Specifically topics for investigation could be:

Seismic assessment of timber frame structures at the historic quartier of

Valparaiso.

Global assessment of a typical real scale adobillo typology could be checked so

to evaluate the capacity of this unique aseismic typology and also be used for

further research of the existing variations.

Improvement of knowledge level regarding materials, joint configurations, and

existing damage levels at the historic quartier of Valparaiso.

Structural analysis of the numerical model of the combined model with

quincha configuration.

Definition of existing listed buildings that can be used and assessed as case

studies. Definition of materials and mechanicals characteristics and analysis.

Simulation of the lateral walls and of the interior timber frame walls and

definition of the load path. In this way, generalized conclusions could be made,

used and applied at a wide variety of analysis of relevant structures.




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