numerical analysis of historical timber frame structures
TRANSCRIPT
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:
Numerical Analysis of timber frame structures
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: ___________________________
Numerical Analysis of timber frame structures
Erasmus Mundus Programme
ii ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS
Numerical Analysis of timber frame structures
Erasmus Mundus Programme
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.
Numerical Analysis of timber frame structures
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Numerical Analysis of timber frame structures
Erasmus Mundus Programme
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.
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Numerical Analysis of timber frame structures
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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.
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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
3.2.2 Structural Behaviour ............................................................................................................. 34
3.3. Traditional typology at Lefkada, Greece ............................................................................... 35
3.3.1 Morphology .......................................................................................................................... 35
3.3.2 Structural Behaviour ............................................................................................................. 36
3.4. The Balkan typology ............................................................................................................. 37
3.4.1 Morphology .......................................................................................................................... 39
3.4.2 Structural Behaviour ............................................................................................................. 40
3.5. The Quincha typology ........................................................................................................... 41
3.5.1 Morphology .......................................................................................................................... 42
3.5.2 Structural Behaviour ............................................................................................................. 44
3.6. Valparaiso timber frame typology ......................................................................................... 45
3.6.1 Morphology .......................................................................................................................... 45
3.6.2 Structural Behaviour ............................................................................................................. 47
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
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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
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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
Numerical Analysis of timber frame structures
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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
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NUMERICAL ANALYSIS OF HISTORICAL TIMBER FRAME STRUCTURES
Erasmus Mundus Programme
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).
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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
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ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS 3
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
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4 ADVANCED MASTERS IN STRUCTURAL ANALYSIS OF MONUMENTS AND HISTORICAL CONSTRUCTIONS
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.
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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
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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.
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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
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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.
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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
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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
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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).
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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.
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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
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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
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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.
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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
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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.
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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 non- linearity 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
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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).
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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.
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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.
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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).
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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.
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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.
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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
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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
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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
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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.
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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
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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,
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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
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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
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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).
3.2.2 Structural Behaviour
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.
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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
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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).
3.3.2 Structural Behaviour
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
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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
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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.
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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).
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Figure 20: Plan views of a typical Balkan typology, Building cross section, Front view, Arrangement of timber
laces (Pantazopoulou 2013).
3.4.2 Structural Behaviour
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
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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).
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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
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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.
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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).
3.5.2 Structural Behaviour
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
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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
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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).
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Figure 23: Timber frame typologies in Valparaiso, Chile, facades and internal partition walls(Molen 2013).
3.6.2 Structural Behaviour
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
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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).
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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).
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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.
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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.
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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.
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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)
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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
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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.
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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).
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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).
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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).
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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.
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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.
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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).
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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
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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
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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.
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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
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=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
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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.
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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.
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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.
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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.
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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.
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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
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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
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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.
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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.
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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
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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.
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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.
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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
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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.
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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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