Transparent Restoration by Lida Barou

RESTORATION

TU DELFT

STUDIO

MENTORS

EXTERNAL EXAMINER

STUDENT

PUBLICATION DATE

MSC ARCHITECTURE, URBANISM & BUILDING SCIENCES [BUILDING TECHNOLOGY TRACK] SUSTAINABLE DESIGN GRADUATION STUDIO

IR FAIDRA OIKONOMOPOULOU [1st] IR TELESILLA BRISTOGIANNI [2nd]

DR IR ANDREJ RADMAN

LIDA BAROU . 4414942

JUNE 2016

Fig i . The Lab team

AKNOWLEDGEMENTS Working on this project, for the last seven months, has been a unique experience for me; from the long days at the laboratory to the even longer often sleepless - nights, I have enjoyed and appreciated every single moment. However, this would not be possible if it wasn’t for the contribution of so many people.

This thesis would not have been completed if it was not for the collaboration of Ms Ioanna Aggelopoulou, the archaeologists in charge of the monument that I studied. During my on-site visit, she heartily welcomed and guided me in the area, trusting me with all the necessary data for the elaboration of my design.

Foremost, I would like to express my gratitude to my two mentors, Faidra Oikonomopoulou and Telesilla Bristogianni, who have been both very helpful throughout the entire process in so many different ways. Faidra, my first mentor, has been encouraging from our very first meeting to our last, being always there to share her knowledge, advice, support and innovative ideas. She did not only introduced me to the topic, but managed to make me passionate about it through her enthusiasm and positive energy.

I would, also, like to thank Dr. ir. Fred Veer for his help and contribution during the experiment,as well as, Prof. Rob van Hees, Eric van den Ham, Christian Louter, Ate Snijder, Peter Eigenraam, Foteini Setaki and Dora Chatzi Rodopoulou for their time and input in multiple aspects of the project. Moreover, I would like to thank Mark van Erk, Remko Siemerink, Louis den Breejen and Kees Baardolf for their help regarding the mock-ups and prototype manufacture, as well as, Simon Luitse for his programming skills.

I am especially grateful to Telesilla, my second mentor, for her commitment during the manufacture of the prototype, providing guidance and practical help. Her knowledge and input has been valuable, but also her company during the hard work.

I would like to thank Eugenia and Ali for their contribution and advice, as well as, my friends and roommates Ioanna and Natalia, for their input, ideas, encouragement and, most importantly, their patience through this entire period. Konstantinos’ practical help has also been of great importance in a critical time.

iii

Robert Akerboom, or as I like to call him “my partner in crime” is the person that I spent most time with during the final phase of my thesis - the manufacture of the prototype. Having similar topics, we worked together, helping each other not only practically but mentally too. He has been a great support and a good friend.

Finally I would like to thank my family, Glykeria Gounaropoulou and Takis Barous, as well as, Marios for their caring and emotional support throughout my studies in TU Delft and for believing in me.

Fig ii . Illustration of the transparent restoration approach

ABSTRACT key words: cast glass, transparency, restoration, dry connections, interlocking geometry

The importance of preserving our built heritage for future generations is indisputable, and, nowadays, architectural conservation is assumed to be an integral part of our national identity. Restoration practices have evolved through the time, always imbued with the spirit of the era. However, there is a question that still remains unanswered: How can one intervene in anotherâ&#x20AC;&#x2122;s work, maintaining its significance and authenticity? [Stanley-Price, 2009] On the one hand, the treatment should be efficient enough to protect the monument, while on the other hand, it should be as discrete as possible. Aspects of materialization and aesthetics are still part of the on-going debate between restoring and preserving. This fine line could, possibly, be articulated with gestures that seem existent and nonexistent, material and immaterial, visible and invisible, in other words, transparent solutions [Lefaki, 2007]. Transparency, by means of structural glass, is introduced in order not only to safeguard the structure, but also allow for the perception of both the original and the ruinous state of a monument. The current research investigates how restoration treatments, using structural glass elements, could be feasible, by examining the potential case study of a historic tower in Greece. When the historic materials have decayed due to time and nature, glass is used as a protective measure against the elements, not only by sealing the vulnerable areas, but also by stabilizing and consolidating the entire structure. The main focus is the restoration of a facade located right next to the sea, which is the primary reason of weathering. In an attempt to respect the existing setting and aesthetics, the intervention suggests a masonry made of cast glass blocks, which resembles the texture and appearance of the original.

A versatile approach has been followed, in order to address the arising challenges. Thus, aspects related to restoration guidelines, manufacture specifications, assembly and construction feasibility, mechanical behaviour of the materials, as well as, climatic conditions, have been investigated through the conduct of this thesis and have been a constant reference point. However, the innovative contribution of such a cast glass masonry lies in the development of an interlocking system in combination with dry connections between the glass units; by rejecting the idea of any permanent solutions [e.g. adhesives], the approach aims to comply with the principle of reversibility, as suggested by the Venice Charter. Due to the abrupt failure that occurs when glass is subjected to pick stresses, often because of imperfections on its surface, the hard contact between glass elements is avoided. Instead, a transparent plastic interlayer is used to transfer the loads in a uniform way, while the overall stability is attained by the interlocking geometry of the glass units, as a physical constraint against movement. The manufacture of a 1:2 scale cast glass masonry prototype, as part of the research, has provided an insight concerning the requirements and complexity of such process. Apart from the literature study and detailing, the validation of the design is accompanied by an experiment to test the strength of the interlocking connection. The first indications show that such a system has potential for further development, displaying a good performance against shear loading. The aim of this thesis is to investigate and present the common ground between restoration and structural glass technology, as a new methodology to exploit our built heritage; a distinguishable but at the same time discreet restoration approach.

CONTENTS 00 RESEARCH FRAMEWORK 00.1 00.2 00.3 00.4 00.5 00.6 00.7

PROBLEM STATEMENT CASE STUDY OBJECTIVES RESEARCH QUESTION METHODOLOGY RELEVANCE TIME PLANNING

01 CONSERVATION THEORY 02 04 05 05 06 06 06

01.1 01.2 01.3 01.4 01.5 01.6

INTRODUCTION WHY CONSERVE? HISTORIC BACKGROUND GUIDELINES CONSERVATION METHODOLOGY REDEFINING THE MATERIALS . WHY GLASS? 01.7 TRANSPARENT RESTORATION 01.8 REFERENCE PROJECTS 01.9 CONCLUSIONS

12 13 14 20 22 29 31 34 46

02 GLASS TECHNOLOGY 02.1 02.2 02.3 02.4 02.5 02.6 02.7

INTRODUCTION MATERIAL PROPERTIES SAFETY PRODUCTION TECHNIQUES CONNECTIONS STRUCTURAL CONFIGURATIONS GLASS APPLICATION IN RESTORATION

52 54 58 62 70 74 76

03 MONUMENT ASSESSMENT 03.1 03.2 03.3 03.4 03.5 03.6 03.7 03.8

INTRODUCTION HISTORICAL BACKGROUND LOCATION & CLIMATE STRUCTURE MATERIALS PATHOLOGY CONSOLIDATION TREATMENTS SIGNIFICANCE ASSESSMENT

80 80 82 84 85 85 87 88

04 DESIGN RESEARCH 04.1 04.2 04.3 04.4 04.5 04.6 04.7 04.8 04.9 04.10

RESTORATION DEGREE DESIGN CRITERIA CONCEPT GENERATION & EVALUATION FOCUS AREAS PRELIMINARY DESIGN GLASS MASONRY RESEARCH DESIGN LIMITATIONS DESIGN STRATEGIES INTERLOCKING SYSTEM DRY CONNECTIONS

08 CONCLUSIONS 92 93 94 96 96 97 100 102 104 111

05 FINAL DESIGN 05.1 05.2 05.3 05.4 05.5 05.6 05.7

FINAL SYSTEM STRUCTURAL PRINCIPLES CAST GLASS UNITS CONNECTIONS OTHER DETAILS CLIMATE PERFORMANCE AESTHETICS

TEST SET-UP PROTOTYPE MANUFACTURE SHEAR TEST RESULTS & OBSERVATIONS

120 126 131 133 140 147 148

154 154 166 168

07 FEASIBILITY 07.1 07.2 07.3 07.4 07.5 07.6 07.7 07.8

METHODOLOGY MATERIAL TREATMENT 3D SCANNING TECHNOLOGY GLASS MANUFACTURE INTERLAYER MANUFACTURE CONSTRUCTION DISASSEMBLY MAINTENANCE

DESIGN EVALUATION COMPATIBILITY ASSESSMENT CONCLUSIONS & RECOMMENDATIONS REFLECTION

198 199 200 204

09 REFERENCES 09.1 BIBLIOGRAPHY 09.2 FUGURES

208 211

10 APPENDICES

06 VALIDATION TESTS 06.1 06.2 06.3 06.4

08.1 08.2 08.3 08.4

174 176 178 182 190 192 194 195

10.1 10.2 10.3 10.4 10.5

APPENDIX APPENDIX APPENDIX APPENDIX APPENDIX

1 2 3 4 5

vii

218 219 220 221 226

Fig 00.1 Ghostly reconstruction of the destroyed basilica of Santa Maria Maggiore di Siponto church by Edoardo Tresoldi . Puglia . Italy

00.

RESEARCH FRAMEWORK

“With the term “transparent restoration” I intend to embody all the possible interventions applied on a historic building, which aim to prolong its life and include mainly glass elements to substitute the original ones that are missing. These interventions range from merely protective measures against the elements to more drastic solutions in a structural level. Transparency sets a fine line between the old and the new allowing for a simultaneous perception of the monument in its damaged and original form”

TRANSPARENT RESTORATION

Our built heritage is an integral part of our collective memory and forms our national and cultural identity. Architectural conservation encompasses all those aspects that should be taken into account and applied in the form of small or large interventions, in order to prolong the life of historic monuments of substantial value. “Having lived” at another era and context, buildings that have survived over time are imbued with cultural, historic, scientific and aesthetic values that need to be acknowledged and respected. They are expressed through the design and material integrity of the monuments, thus any intervention to preserve them has to be thoroughly examined and evaluated, so as not to undermine them.

00.1 PROBLEM STATEMENT “The demands on those charged with the repair and conservation of our built heritage continue to expand in many and conflicting directions. On the one hand, there is this growing perception that all repair or intervention should be kept to an absolute minimum. On the other, increased expectations of performance, safety and longevity ... coupled woth those restraints and concerns over professional indemnity” Robert Demaus [Feilden, 1982 p.xi]

However, how can one determine how and to what extent an intervention is viable and not harmful? How can one intervene in another’s work, maintaining its significance and authenticity? [Stanley-Price, 2009] These questions are difficult to answer, as there are no strict rules to clearly define what is acceptable or not. Conservation principles, though, can be found in several Charters and conventions providing some main guidelines that have been established through the years and form the contemporary conservation strategies. Yet, there is an on-going debate between “restoring” and “preserving”. How can the balance between a monument’s maintenance for future generations and historic significance embedded in its ruinous state be achieved? [Karron 2015]

00 RESEARCH FRAMEWORK

Materialization is the main aspect that encounters this dilemma. Compatible materials [to the original ones] should be used in such way, so as to not cause conjecture and “bear the contemporary stamp”, in order to “preserve and reveal the aesthetic and historical value of the monument” [Venice Charter]. Recent conservation works seem to express rather conservative approaches, involving materials that resemble to the old ones giving the sense of addition and not providing the opportunity to perceive the building in its current context. Transparent solutions, by means of structural glass, could be one of the answers to this debate. Glass components replacing the missing parts of a monument could, at the same time, show its current state revealing its stratification and protect it against the elements and its natural deterioration. It can give the impression of the original form in a rather subtractive than additive way. However, the great significance of such an approach lies in the fact that structural glass could provide the necessary reinforcement due to its mechanical properties. This can ensure not only the preservation of the monument but also a possible rehailitation. Restoration works using glass have so far been realized but not as an extensive and researched conservation methodology. The statement, however, in most of these is the same: to reveal the authenticity of the monument and reinstate its image.

TRANSPARENT RESTORATION

The current research on an innovative restoration approach using structural glass is based on the case study of an old tower, as a starting point for the design elaboration.

00.2 CASE STUDY

Bemboâ&#x20AC;&#x2122;s Tower is part of the old castle of Methoni located in SW Peloponnese, in Greece. The castle was built by the Venecians around 14th -15th century and, for many centuries, served as a fortify due to its strategic location at a peninsula separated from the land by an artificial moat. Until recently, the tower has suffered from severe damages [the reasons are explained in Chapter 03.6] and has been in danger of total collapse. For the period 2011-2015, the structure became part of a restoration project funded by the EU and today the tower is no longer under threat. This restoration approach suggested the reconstruction of the missing parts using the same technique and materials, so that the tower could regain its structural integrity.

Regardless the measures taken to prevent further deterioration, this case study is a great example of a monument in need of immediate restoration treatments to enhance its structural integrity. A transparent restoration approach, as suggested in the current thesis, could stand as a contrast to the current solutions and arise an interesting comparison. It is also my intention to explore how glass could confront such a challenge on a structural level and not merely as an architectural intervention, for aesthetic reasons.

Fig 00.2 Location of Methoni

Fig 00.3 Bemboâ&#x20AC;&#x2122;s Tower after the restoration

Fig 00.4 Aerial view of the castle and the remaining structures in the south: Bourtzi [left], Porta di san Marco [middle] and the semicollapsed Bemboâ&#x20AC;&#x2122;s Tower [right], before the restoration.

00 RESEARCH FRAMEWORK

00.3 OBJECTIVES

The objectives of the current research, as suggested by the title itself, aim at two directions: transparency and restoration. Regarding the transparency, the glass type, the arrangement of the glass elements and the joining methods should be carefully examined. The goal is to use glass in such way so as to: 01 . be as less intrusive as possible 02 . show the original and current state of the monument simultaneously Concerning the restoration part, the connection of the old and the new structure as well as the structural analysis of the new hybrid system should be examined, so as to: 01 . protect the monument from its gradual natural deterioration 02 . enhance the structural performance 03 . ensure reversibility

00.4 RESEARCH QUESTION

According to the aforementioned observations and demands of a transparent conservation approach, the research question can be formed as followed: â&#x20AC;&#x153;In what ways can structural glass elements be used for the restoration of historic buildings instead of conventional materials?â&#x20AC;? The research question can be further broken down to subquestions such as: 01 . What restoration degrees of intervention permit the use of glass components? 02 . What kind of joining methods can enhance maximum transparency? 03 . What kind of joining methods should be employed at the connections of the glass components with the existing structure to ensure reversibility? 04 . In what ways does the design enhance the structural performance of the existing building and ensure its future structural integrity? 05 . What is the methodology one should follow in order to achieve a transparent restoration?

TRANSPARENT RESTORATION

The structure of the research is organised in three phases as shown in Fig 00.5. The 1st phase is based on literature studies from various sources [books, articles, internet, reports] that provide a deeper knowledge on glass technology [fabrication, applications etc] and in what ways it could be incorporated in a restoration practice. The 2nd phase focuses on self-observation of the chosen case study [site visit, photographs, interviews], which provides a solid background for further analysis. An assessment of the current situation is essential to form the main conceptual design in combination with the restoration guidelines and the limitations imposed by glass as a material. The design strategies try to address to the main aspects of transparency, compatibility, aesthetics, structural consolidation and reversibility. In the 3rd phase, the final design is thoroughly explained in terms of manufacture, construction, assembly and detailing. A prototype and a validation test help to reach some first results and estimations concerning the feasibility and structural performance of the system as well as indications for future research. Drawings, illustrations and details are part of the 4th phase and finalization of the proposal as well as the overall evaluation on the chosen system according to the main aspects.

00.5 METHODOLOGY

The current research could set a basis on how to approach restoration works aiming at transparent solutions, by means of structural glass. This field is yet to be explored and established as an acknowledged restoration technique, thus there are no guidelines or scientific references we could address to. The findings and results of this research could become a future reference for architects, archaeologists and engineers who are involved in this discipline. The content of this research aims to analyse the two aspects that restoration practices encounter: a way to highlight the historic monument and a way to ensure its survival. The contribution of this research lies on the argumentation of the chosen technique, always in accordance to the theory of conservation, as well as the methodology on how to restore actual structural problems with a new glass structure.

00.6 RELEVANCE

Table 01 shows where each part of this research is located in the general time framework given for the conduct of this thesis.

00.7 TIME-PLANNING

00 RESEARCH FRAMEWORK

GLASS TECHNOLOGY PROPERTIES GLASS TYPES PRODUCTION TECHNIQUES GLASS CONFIGURATIONS

RESTORATION CONSERVATION THEORY GUIDELINES METHODOLOGY WHY GLASS ? REFERENCE PROJECTS

LITERATURE

TRANSPARENT

BACKGROUND PATHOLOGY SIGNIFICANCE

DESIGN RESEARCH FOCUS AREA RESTORATION DEGREE DESIGN CRITERIA CONCEPT GENERATION DESIGN LIMITATIONS

OBSERVATION & ANALYSIS

CASE STUDY ASSESSMENT

DESIGN STRATEGIES

GLASS-STONE CONNECTION ASSEMBLY SAFETY MECHANISM DETAILING

INTERLOCKING SYSTEM UNIT DESIGN ASSEMBLY DRY CONNECTIONS DETAILING

VALIDATION UNIT MANUFACTURE SC. 1:2 SHEAR TEST

DESIGN

COMPATIBILITY

STRUCTURAL CONSOLIDATION TRANSPARENCY REVERSIBILITY COMPATIBILITY

RECOMMENDATIONS & CONCLUSIONS Fig 00.5 Methodology diagram

EVALUATION

TRANSPARENT RESTORATION

NOVEMBER ACTIVITY / WEEK

DECEMBER 4

JANUARY 8

LITERATURE STUDY: CONSERVATION REFERENCE PROJECTS SCOPE OF RESEARCH CASE STUDY INVESTIGATION RESTORATION METHODOLOGY DEGREES OF RESTORATION LITERATURE STUDY: TRANSPARENT RESTORATION LITERATURE STUDY: GLASS TECHNOLOGY GLASS STRUCTURAL CONFIGURATIONS GLASS IN RESTORATION APPLICATIONS SELF-OBSERVATION & INTERVIEW MONUMENT DATA ACQUISITION PRELIMINARY DESIGN APPROACH MONUMENT ASSESSMENT DESIGN CRITERIA CONCEPT GENERATION PRELIMINARY DESIGN 08

LITERATURE STUDY: CAST GLASS MASONRY DESIGN LIMITATIONS DESIGN STRATEGIES LITERATURE STUDY: INTERLOCKING TECHNOLOGY UNIT INVESTIGATION ASSEMBLY HAND CALCULATIONS INTERLAYER INVESTIGATION LITERATURE STUDY: 3D SCANNING TECHNOLOGY CONNECTIONS INVESTIGATION PROTOTYPE MANUFACTURE SHEAR TEST RESULTS PROCESSING 3D MODEL DRAWINGS . ILLUSTRATIONS . VISUALISATIONS MOCK-UPS REPORT PRESENTATION

Table 01 . Time-planning

00 RESEARCH FRAMEWORK

LITERATURE REVIEW

EDITING

JUNE

DESIGN PROCESS

MAY

BRAINSTORMING

APRIL

DATA COMBINATION

MARCH

HANDS-ON EXPERIENCE

FEBRUARY

Fig 01.1 Restoration of Parthenon . Athens . Greece

01.

CONSERVATION THEORY

â&#x20AC;&#x153;Memory is what defines who we are and who others are in our own minds. Memory shapes our intellectual and moral personality [...] Indeed, it would be impossible to live as one person, with an individual history, or to possess our being in a continuous fashion, without the memory threads that constantly link our present to our past and prospective futureâ&#x20AC;? [Bourtchouladze, 2003: 172]

TRANSPARENT RESTORATION

History is an inseparable part of our living environment and its traces are visible in multiple aspects of our every day life. These traces from past civilization contribute radically to our cultural identity today and it is our duty to maintain them for present and future generations. This action or, even better, a set of actions that aim to ensure the survival of our cultural heritage can be referred to as conservation and its scope is very wide. Conservation can be about natural resourses, archaeological sites, cultural artifacts, movable items, energy and generally anything of acknowledged value for the future. Architectural conservation deals with measures taken in order to prolong the integrity of our built heritage; and by integrity we mean all those characteristics that contribute to the general significance of a building or a place, such as the materials, the design and its history. Our built heritage encompasses ruins, archaeological sites, monuments, vernacular buildings, palaces, castles settlements and urban areas. The protective measures can range from minimal repairs to larger modifications, even the demolition of parts of a building to allow a new function. However, as each building bears different characteristics â&#x20AC;&#x201C; built in a different era, under different historic and social contexts and with different building techniques â&#x20AC;&#x201C; there is no pattern or secure approach when proceeding with a conservation plan. Thus, architectural conservation is a unique and creative process. The starting point, in any case, is first to understand the existing structure with respect to all the previous layers, usually of materials from different historic periods. Conservation is the process of managing change. [Orbasli 2008]

01.1 INTRODUCTION

Conservation [kon-ser-vey-shuh n] 1. the act of conserving; prevention of injury, decay, waste, or loss; preservation: conservation of wildlife; conservation of human rights. 2. official supervision of rivers, forests, and other natural resources in order to preserve and protect them through prudent management. 3. a district, river, forest, etc., under such supervision. 4. the careful utilization of a natural resource in order to prevent depletion. 5. the restoration and preservation of works of art. Origin: 1350-1400; Middle English conservacioun < Latin

-ion [www.dictionary.reference.com]

MATERIAL

01 CONSERVATION THEORY

›

CONSERVATION

REHABILITATION ADAPTIVE RE-USE

›

MAINTAINANCE

KEEP

Fig 01.2 Terminology often used for conservation practices: “Consevation” expresses the whole idea of protection of our built legacy, however there are more terms that describe and adress to specific aspects such as the materials, the usage of a monument, its general significance or the building as a structure itself.

› USE

CHANGE

REPAIR ANASTYLOSIS RESTORATION PRESERVATION RECONSTRUCTION

01.2 WHY CONSERVE ?

Monuments that embody values such as history, culture, aesthetics and trigger our emotions are assumed to be of great significance and thus worthy of been conserved. Such buildings contain embedded messages shaped throughout the multiple layers of time and reveal historical, social and political information. The Burra Charter provides an adequate theory on the concept of cultural significance:

“The places that are likely to be of significance are those which help an understanding of the past or enrich the present

”

It is our obligation not only to protect the historic fabric as part of our past and our collective memory, but also as an important scientific testimony. As constant reminders of the cultural background, monuments are today in close relation to the national identity and pride, adding an emotional value to their significance. However, apart from the

TRANSPARENT RESTORATION

romantic perception of â&#x20AC;&#x153;buildingâ&#x20AC;? a bridge between the past and the future, conservation has a significant impact on much more practical aspects. Historic buildings can promote national integrity and stimulate domestic and international tourism. The Covent Garden [see Fig 01.3] in London is a great example of how a historic district does not only contribute to the character but also the economy of a city. It has acted radically for the regeneration of the entire area as a major retail and entertainment quarter. [Orbasli, 2008] Furthermore, conservation contributes to the sustainability of our building stock. From an environmental and economic point of view, it is more practical to use available resources rather than waste them. People often presume that maintenance needed for old buildings is a disadvantage compared to the one needed for the new structures. Yet all buildings need maintenance and especially for the latter, it is often underestimated. In the long term, this in not sustainable and exploiting the current recourses with sufficient care can prove more efficient.

Fig 01.3 Covent Garden, London

Conservation represents an entire philosophy, which has been evolved during the centuries, through the different mindsets of each era, before it receives the meaning it has today. A brief flashback will enhance the deeper understanding of the theory of conservation as this was developed from the reconstruction in need of infrastructure to the conscious preservation of entire historical ensembles. The practice of restoration can be traced back to the 6th century, at the Time of Theodoric the Great king of the Romans and the Goths [493-526], who repaired aqueducts, public baths and city walls, as well as, restored palaces into centers of administration in a variety of cities in Italy. Even earlier, the adaptive change of use was also a common practice when Christianity was established [around 100] resulting in the transformation of Roman temples and basilicas into churches. On the other hand, there are recordings that ruins were often used as quarries in order to eliminate the transportation costs, especially by the Venetians. [Orbasli 2008] At this time, there was no awareness and particu-

01.3 HISTORIC BACKGROUND

01 CONSERVATION THEORY

lar interest for the antiquities as part of our cultural background and the survival of certain buildings was a result of other factors e.g. religious or meerly practical purposes to house certain uses.

Fig 01.4 Leonardo da Vinci, “Studies for the tiburio of Milan Cathedra”, c. 1487 [Codex Atlanticus, Biblioteca Ambrosiana, folio 851, Milan, Italy]

Fig 01.5 Notre-Dame, Paris. Jean-Baptiste-Antoine Lassus and Eugène Viollet-le-Duc were responsible for the main restoration plan of the cathedral after its partial demolition due to French Revolution. The restoration lasted twenty five years and included a taller and more ornate reconstruction of the spire, as well as the addition of the chimeras on the Galerie des Chimères.

A more systematic interest on historic buildings and awareness of the cultural heritage of the building fabric can be stretched back to the Renaissance [13th - 17th century]. The main focus was on classic monuments [Romans and Greeks] rather than mediaeval architecture; however, the spirit of the time towards a general respect for the achievements of the past generations, supported by Leon Batista Alberti, prevented the demolition of such structures. This spirit encompassed a general praise to the ruins of the past from different representatives, such as humanists, poets and painters. However this interest was limited among the popes and small groups of intellectuals. It was then when extensive studies and recordings on historic buildings started as well as the first repair suggestions [see Fig 01.4]. In the early 16th century, in Rome, for the first time a person was appointed responsible for the overseeing of the activities concerning the ancient ruins under the title of “Commissioner of Monuments”. Moving on to the Enlightment, restoration gained ground and it became a matter of wider public interest having as a result the first legislation for the protection of heritage “Act Concerning the Monuments and Antiquities of our Nation” [1779], of Friedrich II. [Jokilehto, 2002] However, it was only after the French Revolution [1789] when an extensive wave of conservation work was observed, in France. That emerged from the desecration and demolition of a great deal of historic building fabric during the revolution. Back then, restoration aimed to bring the monuments to their former state; it was mainly synonymous to reconstruction of monuments, mostly based on assumptions of what they used to be, often applying arbitrary actions in order to express the architect’s style. The evolution of nationalism and Romanticism in Europe as concrete evidence of a nation’s history had been of great influence for the conservation philosophy of that time. Monuments were treated in a way so as to reveal the glory of the initial architectural concept and not in respect to all the layers of history that it could incorporate. The most important advocate

TRANSPARENT RESTORATION

of this movement was Viollet-le-Duc [1814-1879], in France, who “frequently combined historical fact with creative modification”.

The lack of use of proven evidence has led to falsified interpretation of what was authentic and the development of an “anti-restoration” movement did not take long to oppose to these practices. The basis of the argumentation against this school of restoration was that it was impossible to reproduce a missing part with the same significance in another cultural and historical context. The new restoration treatments recommended additions in contemporary style and form. This new theory on conservation authenticity initiated in England and was expressed in William’s Morris “Manifesto of the Society for the Protection of Ancient Buildings” [SPAB] in 1877. Its significance lies in the fact that even today it forms the basis for the Society’s philosophy. Another great proponent and founder of the society was John Ruskin, who supported repairs rather than stylistic replacements and replaced the word “restoration” with “conservation”. Despite the fact that theory and practice were not always compatible, a significant number of conservation approaches of the 20th century derived from the debates and practices of the 19th century. With the dawn of 20th century conservation concept had already been broadened. The idea of additions far from the imitations of the past was, by then, well established as a conservation practice and had many supporters such as Alois Giegl [18581905]. Furthermore the publication of “City Planning according to Artistic Principles” by Camillo Sitte [1843-1903], in 1889, set the ground for the consideration of urban locations as worthy of conservation. [Giebeler, Krause et al. 2009] During the two devastating World Wars the bombs destroyed a lot of European historic cities and buildings. Thus, after the wars it was essential for the nations to restore the “lost” dignity in a symbolic way and the conservation concept associated to the national identity. The historic center of Warsaw was rebuild from scratch after WWII based on pre-war documentation and has since then been inscribed on the UNESCO World Heritage List [see Fig 01.7]. At the second half of the century the modern urban

Fig 01.6 Study of medieval plazas by Camillo Sitte

Fig 01.7 85% of buildings in Warsaw were destroyed during WWII

01 CONSERVATION THEORY

INTERNATIONAL CONSERVATION CHARTERS: [APPROVED BY ICOMOS] -

movement suggested the mitigation from the historic centers to the suburbs as a higher life quality model in the expense of the historic fabric, for example by creating car-friendly cities. It was during the 20th century when an international effort was made in order to establish the basic principles of conservation. The very first meeting â&#x20AC;&#x201C; of mostly European representatives â&#x20AC;&#x201C; was held in Athens [Athens Charter], in 1931, and was the basis for some primary recommendations, which were further elaborated at the, more important, Venice Charter, in 1964, which is assumed to be a milestone of the conservation movement. The latter set some ground guidelines extending the understanding of historical monuments to urban areas. It constitutes, until today, a guidance of national conservation policies. Since then a great number of additional Charters and Conventions have taken place on multiple restoration concepts. The Nara Document, in 1994 is also of particular importance as it provides an insight on the idea of authenticity and how it can be preserved.

GUIDELINES: -

ARCHITECTURAL CONSERVATION ORGANIZATIONS

Today, each country can follow their own principles according to their unique architectural heritage, but all in respect to the charters and international guidelines. Furthermore, several organizations have been created aiming to raise public awareness of the necessity of preservation. Apart from promoting and protecting the cultural properties, they contribute to restoration projects in terms of funding. As a general outcome of this brief flashback, we conclude that each era affects significantly the identity of architectural conservation, whose boarders have started, more and more, expanding. Especially after periods of war, restoration practices seemed to flourish as an attempt to preserve and regain what was lost. Living in an era of scientific and technological advancements in the fields of architecture and engineering, gives us great opportunities regarding the solutions that can be achieved. It enables us to reinterpret the values and the significance embedded in each monument or historical place, and at the same time make them functional and useful to the community.

TRANSPARENT RESTORATION

ONLY SURVIVAL OF MONUMENTS AS A RESULT OF APPROPRIATE CIRCUMSTANCES

AWARENESS OF CULTURAL HERITAGE

EARLY RENAISSANCE Ancient ruins start becoming a topic of interest for humanists, poets, painters

600

1200

1300

1400

6th CENTURY First restoration practices for the reuse of historic buildings by Theodoric the Great in Italy

15th CENTURY Architectural treatises Extensive studies and first reconding of monuments Repair suggestions and criteria for the protection of historic structures [Leon Battista Alberti . Leonardo da Vinci . Filarette . Francesco di Giorgio Martini]

Fig 01.8 Brief timeline of the evolution of Architectural Conservation through history

1500

01 CONSERVATION THEORY

AUTHENTICITY REINSTATEMENT CONSERVATION A MATTER OF

IMAGE REPRODUCTION

NATIONAL IDENTITY 1994 Nara Document

1814-1879 Violet-le-Duc expresses a restoration philosophy based on the exact reproduction of the monument’s former state in France 1600

1700

1800

1931 Athens Charter 1900

2000 19

1779 First legislation for the protection of heritage “Act Concerning the Monuments and Antiquities of our Nation” by Friedrich II EARLY 16th CENTURY “Commissioner of Monuments”as responsible for the overseeing of the activities concerning the ancient ruins

1877 “Manifesto of the Society for the Protection of Ancient Buildings” by William Morris as an “anti-restoration” movement philosophy

1964 Venice Charter to form the conservation principles

1889 “City Planning according to Artistic Principles” by Camillo Sitte

TRANSPARENT RESTORATION

The aforementioned Charters embody the main principles that should be observed in every conservation work today. They are also known as the ethics of conservation and contain information on different aspects and stages of this process. These guidelines are primarily recommendations and function as a starting point for the conservation philosophy of our time in an international level. However, each nation decides their own conservation strategy according to their historical and cultural background, having as a result buildings, of the same architectural style or era, to be treated differently according to the respective context. Rarity plays an important role on that as it adds value to the monuments.

AUTHENTICITY Authentic does not imply a replica of the original structure. According to the cultural context it can be associated with different information, such as the design, the materials, the techniques, the general setting or location and the function. The interpretation of this information and the respect of the evidence are responsible for the revealing of the authenticity and heritage value of the monument without falsifying the truth.

01.4 GUIDELINES

“Conservation of cultural heritage in all its forms and historical periods is rooted in the values attributed to the heritage. Our ability to understand these values depends, in part, on the degree to which information sources about these values may be understood as credible or truthful. Knowledge and understanding of these sources of information, in relation to original and subsequent characteristics of the cultural heritage, and their meaning, is a requisite basis for assessing all aspects of authenticity.” [Article 9, The Nara Document on Authenticity, 1994]

INTEGRITY Physical, structural, design, aesthetic as well as the integrity of a building fabric within its context should be respected in every conservation work. For example, maintaining all the components of the historic fabric at their initial setting shows a respect to its integrity. The surroundings of historic monuments are as significant as the building themselves. Conservation approaches should not isolate a building or its components from their setting. This respect on historic integrity has multiple extensions. Integrity could also refer to physical, structural and aesthetic characteristics.

“A monument is inseparable from the history to which it bears witness and from the setting in which it occurs. The moving of all or part of a monument cannot be allowed except where the safeguarding of that monument demands it or where it is justified by national or international interest of paramount importance.” [Article 7, Venice Charter, 1964]

NO CONJECTURE The new additions should exist in harmony with the historic monument but in no case mimic it. It is important that the different layers of materials and, by extension, the different time of interventions are easily distinguished. Every restoration practice should reflect its own age.

“… Its aim is to preserve and reveal the aesthetic and historic value of the monument and is based on respect for original material and authentic documents. It must stop at the point where conjecture begins, and in this case moreover any extra work, which is indispensable must be distinct from the architectural composition and must bear a contemporary stamp ...” [Article 9, Venice Charter, 1964]

01 CONSERVATION THEORY

“The valid contributions of all periods to the building of a monument must be respected, since unity of style is not the aim of a restoration. When a building includes the superimposed work of different periods, the revealing of the underlying state can only be justified in exceptional circumstances and when what is removed is of little interest …” [Article 11, Venice Charter, 1964]

UNDERSTANDING THE LAYERS Over time, multiple changes are likely to have occurred to historic buildings. Each of these layers, however, is an important part of its history even if it is not accepted by the contemporary conservation principles and practices. They inform us about their own time – the techniques and materials – and have been integrated in the stratification of the historic fabric. The removal of these additions should be thoroughly examined, but in some cases – if they damage the structure in any way or detract from the cultural significance – could be justified.

“Conservation is based on a respect for the existing fabric, use, associations and meanings. It requires a cautious approach of changing as much as necessary but as little as possible.” [Article 3.1, The Burra Charter, 1999]

MINIMUM INTERVENTION The protection of the existing fabric should be of priority at any conservation concept. The intervention should be kept as minimum as possible in order not to undermine its significance or any other value. After all, the intention of the conservation is primarily to safeguard the old and not to take advantage of it. When the larger part of a historic building is missing then conservation should not be the option. 21

“Where traditional techniques prove inadequate, the consolidation of a monument can be achieved by the use of any modern technique for conservation and construction, the efficacy of which has been shown by scientific data and proved by experience.” [Article 10, Venice Charter, 1964]

MATERIALS Using traditional materials and methods should be the first option. The use of traditional materials may also ensure that the structure will continue to behave in the same way. In many cases new solutions may answer to old problems and be, at the same time, compatible. However, the new materials should be used only if they have proven to be effective and not damage the historic fabric. [Orbasli 2008] The development of technology provides us with a great number of new advancements that could be used in the restoration practices.

“Changes which reduce cultural significance should be reversible, and be reversed when circumstances permit.” [Article 15.2, The Burra Charter, 1999]

REVERSIBILITY It is essential that the new intervention has the possibility of being removed either because new technologies may be discovered in the future or in case it proves inadequate and fails. However, in many conservation practices, this principle is often discarded when more permanent solutions are needed for the survival of the structure, or by using modern materials in combination to adhesives and resins.

TRANSPARENT RESTORATION

There is no clear line between wrong and right in conservation works – always in respect to the conservation ethics. However, history has shown that “brave” interventions in their own time were judged “wrong” and treated as threats, while later they were considered valuable [e.g. Franco Minissi’s protective shelter of “Villa del Casale”, in Sicily]. The key is to balance the conservation principles with the main concept and desired result. After defying the main objectives, the embedded values of the historic building should be identified in order to establish the conservation approach. These values need to be examined and analyzed so as to define the “significance” of the structure. Some are more important than others and, consequently, in priority to be preserved. This values – based approach illustrates the essence of the historic fabric and enables concrete and justified solutions in terms of decision-making during the design. Sometimes, it is not forbidden to overlook some of the principles in favor, for example, of a new function, important on a social and cultural level. These values can be classified under four headings [see Fig 01.9]

01.5 CONSERVATION METHODOLOGY

Aesthetic

Age & Rarity

Artistic

Historic

Cultural 22

Architectural

Symbolic

Associative

The main steps of the design process one should follow when dealing with conservation projects are the following: First of all, we need to collect all the relevant and available data in order to understand the greater value and significance of the place, as well as, its current situation; when there is not enough information, assumptions could be made. The next step is to assess the data and continue with the main concept in full respect of the general guidelines. During the conservation plan, both the degree of intervention and the materials should be decided, while records should be kept regularly during the implementation. Finally, some general considerations concerning the evaluation and the maintenance needed are necessary in order to ensure the survival of the conservation plan. This process however is reversible when the final result is not satisfying and assessment of every previous step should be made. [see Fig 01.10]

Landscape Townscape

Scientific Research & Knowledge

Educational

Technical

Social

Economic Political Religious

Public

Emotional

Fig 01.9 Values of a bulding heritage that can atribute significance to a historic monument. According to the corresponding context and time, one or more values can be considered more important than the others. These can form the main concept of the conservation approach and therefore influence the desicions taken and the degrees of intervention. In some cases, sacrifices can be acceptable for a greater purpose.

01 CONSERVATION THEORY

The approach of a conservation plan demands the collaboration of a great number of professionals, from different disciplines. According to the ICOMOS Guidelines [1993] the architect, the landscape architect, the conservator, the surveyor and the curator are these who are actively involved, without exception, to every step and decision making. Aditionally, the part of the approach that demands the involement of all the professions is the deeper understanding and careful application of all the regulations and guidelines of the charters and conventions. [see Table 02]

ADMINISTRATOR . OWNER ARCHAEOLOGIST ARCHITECT ART . ARCHITECTURAL HISTORIAN BUILDER . CONTREACTOR CONSERVATION OFFICER CONSERVATOR ENGINEER

ENVIRONMENTAL ENGINEER LANDSCAPE ARCHITECT MASTER CRAFT WORKER MATERIALS SCIENTIST BUILDING ECONOMIST SURVEYOR TOWN PLANNER CURATOR A . Read a monument, ensemble or site and identify its emotional, cultural and use significance B . Understanding the history and technology of monuments, ensembles or sites in order to define their identity, plan for their conservation and interpret the results from this research C . Understand the setting of a monument, ensemble or site, their contents and surroundings, in relation to other buildings, gardens and landscapes D . Find and absorb all available sources of information relevant to the monument, ensemble or site being studied E . Understand and analyse the behaviour of monuments, ensembles and sites as complex systems F . Diagnose intrinsic and extrinsic causes of decay as a basis for appropriate action G . Inspect and make reports intelligible to non-specialist readers of monuments, ensembles or sites, illustrated by graphic means such as sketches and photographs H . Know, understand and apply UNESCO conventions and recommendations and ICOMOS and other recognised Charters, regulations and guidelines

I . Make balanced judgements based on shared ethical principles and accept responsibility for the long-term welfare of cultural heritage J . Recognise when advice must be sought and define the areas of need of study by different specialists, e.g. wall paintings, sculpture and objects of artistic and historical value and or studies of materials and systems K . Give expert advice on maintenance strategies, management policies and the policy framework for environmental protection and preservation of monuments and their contents and sites L . Document works executed and make them available M . Work in multi-disciplinary groups using sound methods N . Be able to work with inhabitants, administrators and planners to resolve conflicts and to develop conservation strategies appropriate to local need, abilities and resources

Table 02 . Skills matrix for the different professions involved in conservation based on ICOMOS Guidelines for Education and Training in the Conservation of Monuments, Ensembles and Sites [1993].

TRANSPARENT RESTORATION

DATA AQUISITION OFF - SITE DOCUMENTARY ORAL PHYSICAL [E.G. LABORATORY TESTS

ON - SITE VISUAL INSPECTIONS MEASUREMENTS

›› ASSUMPTIONS [WHEN NOT ENOUGH OR TOTALLY RELIABLE DATA EXIST]

SIGNIFICANCE HISTORY AESTHETICS SCIENTIFIC SOCIAL

STRUCTURE MATERIAL BUILDING METHODS STRUCTURAL SCHEME PREVIOUS PROTECTIVE ACTIONS PATHOLOGY

ASSESSMENT SIGNIFICANCE ARCHITECTURAL CONCEPT PRIORITY IN VALUES THAT MUST REMAIN INTACT

STRUCTURE DIAGNOSIS STRUCTURAL CONCEPT

››

UNDERSTAND THE CASE STUDY

FOLLOW THE ICOMOS RECOMMENDATIONS EXAMINE SIMILAR CASE STUDIES STATE OF THE ART IN MATERIALITY & TECHNIQUES

01 CONSERVATION THEORY

CONSERVATION PLAN DEGREE OF INTERVENTION PROTECTION FROM THE ELEMENTS STRUCTURAL REINFORCEMENT FILLING THE FORM ADAPTIVE RE-USE

MATERIALS STONE MARBLE WOOD CONCRETE MASONRY STEEL OTHER

IMPLEMENTATION RECORD OF WORK SURVEYS DRAWINGS VISUAL MATERIAL

GENERAL CONSIDERATIONS 25

EVALUATION OBJECTIVES FULFILLMENT TECHNIQUES USED STRUCTURAL PERFORMANCE VISUAL RESULT

MAINTENANCE TYPE FREQUENCY

Fig 01.10 Conservation Approach. It is a back-and-forth process where every step should be thoroughly examined and evaluated.

TRANSPARENT RESTORATION

DEGREES OF INTERVENTION PROTECTION FROM THE ELEMENTS TREATMENT OF THE MATERIAL

e.g. vegetation control e.g. laser cleaning

Fig 01.11 Thick growth of vegetation at Sri Ayravadeswarar Temple . Tiruchi . India

Fig 01.12 Laser treatment of the Parthenon marbles

STRUCTURAL REINFORCEMENT SIMPLE REINFORCEMENT

Fig 01.15 Punched lead cast in a Venice bridge wall fixing the hard-metal connecting bar 26

FILLING OF THE FORM ANASTYLOSIS

3rd

ABSTRACT . MODERN

Fig 01.17 Detail of the materials at Valletta Walls in an abstract restoration work by Renzo Piano

Fig 01.16 Missing parts of Parthenon are reproduced at the exact original shape

ADAPTIVE RE-USE NEW USE = OLD USE

NEW USE

OLD USE

Fig 01.18 Church restored in to a brewery . Haarlem

4th

01 CONSERVATION THEORY

1st

PROTECTIVE SHELTER partly covered

fully covered

Fig 01.13 Partial shelter over the Bishopâ&#x20AC;&#x2122;s Palace . South England

Fig 01.14 Fully covered archaeological site . Ephesus . Turkey

2nd

REINFORCEMENT & FILLING THE FORM

RARITY

REALISTIC

ABSTRACT

ERECTION YEAR

REALISTIC

ABSTRACT

Fig 01.19 Qualitative graphs . Relation between erection time - restoration approach and rarity - restoration approach

GENERAL OBSERVATIONS Apart from the first case, of merely protective measures, it appears that for older structures, e.g. the Parthenon, more conservative solutions are followed so as to keep the original image as intact as possible. As age is often related to significance, when it comes to historic buildings, we can conclude that the older the monument, the more realistic the intervention is. Thus, the age factor indicates what kind of approach will be chosen for a monument. Abstract forms are usually used in more recent buildings e.g. industrial complexes, while more accurate, in terms of form, interventions are applied in older structures. Another important factor is the rarity of a structure. If a monument is assumed rare and worthy of preservation in respect of the original form and materials, a more conservative approach is followed. However, rarity relates directly to the location of the structure; a structure that in one place is tradition, in another place may be unique and valuable.

TRANSPARENT RESTORATION

CONVENTIONAL MATERIALS STONE

MARBLE

BRICK

Fig 01.20 New stone combined with the old one at Bemboâ&#x20AC;&#x2122;s Tower . Greece

Fig 01.21 Marble supplement adapted at the capital of the north colonnade . Parthenon

Fig 01.22 Brick restoration

WOOD

STEEL

28 Fig 01.23 Broletto arcades . Como

Fig 01.24 Steel reinforcement of the arches

CONCRETE

OTHER

MORTARS

GLASS FIBER REINFORCED CONCRETE [GFRC] CAST ALUMINUM CAST STONE FIBER REINFORCED POLYMER [FRP] EPOXY GLASS Fig 01.26 Cast aluminum columns

Fig 01.25 Pointing with mortar

INJECTIONS

Fig 01.27 Epoxy injection

01 CONSERVATION THEORY

01.6 REDEFINING THE MATERIALS WHY GLASS ?

A brief analysis of the current conservation practices reveals the contemporary view on this discipline, which seems rather conservative in the 21st century. The concerns, regarding the deeper understanding of the historic fabric, expressed at the recent charters and conventions, set a lot of restrictions if we take a look at the regulations and the bureaucratic procedures. The minimum desired interventions are juxtaposed to the aim for an essential protection of the historic fabric in more practical ways. On the one hand, the interventions should respect and leave untouched the existing structures but on the other hand they should safeguard them; as Lefaki has, aptly, pointed out:

“interventions asking for non-interventions” [Lefaki, 2013] This fine line can be articulated by gestures that appear visible and invisible, material and immaterial, existent and non-existent, in other words transparent solutions. Concidering the fact that materialization in historic building restoration is an ongoing debate, where issues concerning the nature and colour of materials or the coherent connection to the surroundings are of great importance, glass being “neutral” can confront such challenges.

Fig 01.28 Detail from the reconstruction of Basilica di Santa Maria Maggiore di Siponto by Edoardo Tresoldi, in Italy. The steel wireframe allows for the perception of the original form, but at the same time establishes, through transparency, aconnection with the current setting.

Glass is a well-known material for its transparent properties and has been widely used in conventional constructions to satisfy the demands for more “open” spaces, defined by natural light and airiness, while, at the same time, provide a functional indoor environment. In restoration practices of today, however, glass is not encountered as a building material, with the exception of restoring parts previously made by the same material, such as stained or glass panes. The recent technological advances in structural glazing have set the ground for using glass in a structural way considering its load-bearing capacity and creating large transparent structures with minimal supportive elements. Thus, why not exploit these huge loads of knowledge with respect to the conservation theory in order to reinstate the image of the monuments? Below are shown some advantages of glass as possible primary restoration material.

TRANSPARENT RESTORATION

01 . FOLLOWING THE NORMS Taking into account the theoretical background of conservation and the general guidelines, glass meets the requirements as a restoration material, as it is easily distinguishable in order not to falsify the historic evidence and create conjecture. It also â&#x20AC;&#x153;bears the contemporary stampâ&#x20AC;? [Venice Charter, 1964] as a material of our era given the general architectural interest and effort optimizing the material possibilities. Furthermore, the Venice Charter does not exclude any material as long as it provides scientific proof that it will not damage the existing structure.

04 . DURABILITY It is not new that glass can satisfy the demands for protection from the elements, as it appears in many past and recent structures, e.g. glasshouses. This could be the case in a restoration concept as well; when the desire for a new function arises but there is also need to protect the historic fabric when its survival is threatened.

02 . LESS IS MORE The transparent quality gives the idea of subtracting rather than adding to an existing structure, which is the goal in many conservation concepts. When the purpose is to keep the structure as intact as possible, transparent solutions can provide the minimal perception of the missing parts. Glass offers the opportunity to create the ideal image of the monument in a minimally intrusive way, by merely outlining the original geometry, revealing at the same time its historic and aesthetic significance.

05 . INDOOR COMFORT In relation to the previous advantage, when a new function is aimed there are also demands for an adequate indoor climate in accordance to the new use. Protective measures are available in order to mitigate effects such as overheating and visual discomfort, e.g. low-e coatings, fritted glass etc.

03 . STRUCTURAL PERFORMANCE The latest developments show that glass can contribute not only aesthetically, but also structurally to the restoration design. This would be an asset in contrast to the conventional materials as it offers potential for large transparent repairs with a small visual impact.

06 . NOVELTY Glass appears to be an innovative material, considering the recent architectural designs [e.g. the Apple Glass Cube 2.0], but underestimated in conservation practices with very few applied examples. It is still an unexplored field worthy of further research in order to unfold, in full extent, its potentials.

01 CONSERVATION THEORY

01.7 TRANSPARENT RESTORATION

As already mentioned, the examples of restoration works that involve glass as the main material are few to minimal. The first attempts to combine glass interventions with old structures date back to the modern movement, with the Maison du Verre in Paris [1928-1932], a landmark for the 20th century architecture. The metal-glass structure replaced the three out of total four floors of a building, having the latter kept in place and used independently. Twenty years later, the new Memorial Church in Berlin [1959-1963] made of glass blocks was erected as a reminder of the WWII and in order to reinterpret the ruins of the old one. However, the title of pioneer in the use of â&#x20AC;&#x153;transparentâ&#x20AC;? restoration strategies should be attributed to the Italian architect Franco Minissi [1919-1996]. His main guiding principle was to create a distinguishable architectural language in order to reveal the historical stratification of the monuments. He aimed at this contrast between the old and the new in an attempt to reinstate the authentic image of the historic fabric. He considered transparency as a variable element in order to intensify the preexisting historic structure and outline its absolute and permanent character. Through his work is evident the sensitivity with which he treated the ancient ruins, applying different approaches according to the age of the respective structure.

Fig 01.29 The original Memorial Church was built in 1890s and was badly damaged in 1943 in a bombing raid. The New Memorial Church was designed by Egon Eiermann. The initial design included the demolition of the spire of the old church but following pressure from the public, it was decided to incorporate it into the new design.

Fig 01.30 Maison du Verre, Paris

TRANSPARENT RESTORATION

His critical view was obvious from the beginning of his career, in his work at the Walls of Capo Soprano at Gela, Sicily in 1950-54. He created an innovative protective system composed by tempered glass plates, which statically pressurized the walls in a similarly as it has been subjected for centuries by earth when buried, preventing in this way their collapse. [see Fig 01.31] The slight movement of the structure caused water-infiltration between the glass plates, which was moderated by a light covering on the restored walls. While the aim for the walls protection was achieved, the microclimate created in between the elements of the new structure in combination with the poor maintenance resulted in its removal in 1994. The Etruscan Museum of Villa Giulia was another case where Minissi treated with fineness the historic material, in a different context this way. Apart from designing and organizing the entire space of the museum, his proposal for simple transparent Plexiglas pedestals allowed for a clear promotion of the exhibit’s objects.

An intervention on a larger scale was proposed for the Roman “Villa del Casale” at Piazza Armerina in Enna, Sicily: a transparent canopy made of glass and Plexiglas to provide protection against wear, rain and direct sunlight [see Fig 01.32]. The choice of material, once again, aimed to communicate to the visitors the authentic image of the ancient ruins undistracted, as much as possible. By 2004, the structure was also removed because of the greenhouse microclimate and the degradation of the materials. The new building not only casted the archaeological site into shade but cut the connection to the landscape [see Fig 01.33]. This choice was assumed to diminish its historic value, showing little respect to the surroundings and its general context. In the Greek Theatre of Heraclea Minoa in Agrigento, Sicily Minissi decided to consolidate the ruins in transparent cases filling the original form, while at the same time be protective, colorless and resistant to water, wind and temperature changes. [Vivio, 2015] he interpreted the remains “through their virtual evocation” [Vivio, 2014]. The Plexiglas encases over the bleachers were anchored through metal pivots, which later eroded and threatened

Fig 01.31 Timoleonte’s Greek Wall at Capo Soprano . Implementation phase of the drilling tract in raw land through special rotating equipment, without hammering effect.

Fig 01.32 “Villa del Casale” at Piazza Armerina . Suspended ceilings on the roof of the “basilica”

Fig 01.33 The new arrangement of the rooms in “Villa del Casale” with the interior obscured by wooden roofs and opaque materials. Photograph . G. Meli . 2006–12

01 CONSERVATION THEORY

the original stone. They were replaced by aluminum coatings with semi-translucent polycarbonate sheets. In the end, the natural deterioration of Plexiglas resulted to an image not as transparent as intended, altering the general concept aiming in the search of authenticity. [see Fig 01.34]

Fig 01.34 Greek Theatre of Heraclea Minoa in Agrigento . Breaking laminate and greenery infestation

Fig 01.35 Church of S. NicolĂ˛ Regale at Mazara del Vallo . System vaulted into panels of translucent plexiglas

Fig 01.36 Initial proposal for S. Maria dei Greci . Fondo Minissi . drawing of 1970

Similar strategies were followed at the church of San Nicolo Regale [1960-66] and his proposal for the church of S. Maria dei Greci. In the former, he used a modular metal frame filled with Plexiglas elements in respect of the volumetry of the vaulted ceiling [see Fig 01.35], while in the latter he suggested a transparent floor in order to reveal the archaeological remains inside the church [see Fig 01.36]. Compatibility, reversibility, critical interpretation and minimum intervention were some of the principles that Minissi embodied in all his restoration projects. He aimed to a conceptual restoration rather than a literal one, which, in many cases, was considered too modern for his time. He outlined the importance for a deeper connection between the historic building and its setting. Transparent solutions offered that advantage in a discreet and fine way. The pattern of decline in his structures is defined by the lack of climate considerations, poor maintenance, bad choices for the bonding materials and the natural optical deterioration of Plexiglas. Contemporary technologies, however, could give solutions to these problems, putting structural glass in the foreground. The general spirit of MInissiâ&#x20AC;&#x2122;s transparent restorations, in respect of the conservation guidelines, is an attempt to invoke the cultural heritage of the past and enable its narrative to the present.

TRANSPARENT RESTORATION

After Minissi’s introduction to transparent solutions for restoring missing parts, little has been done in that direction. Some of the most representative examples will be analyzed in the following section, in order to have a deeper understanding on what has been implemented so far and what is the general view of this entire philosophy.

01.8 REFERENCE PROJECTS 1960–66 The Church of S. Nicolò Regale at Mazara del Vallo Trapani . Sicily

1940

1950

1960

1970

1950–54 Timoleonte’s Greek Wall Capo Soprano . Sicily

Fig 01.40

1960–63 Greek Theatre at Heraclea Minoa Agrigento . Sicily

1958–63 The Roman Villa del Casale at Piazza Armerina . Enna . Sicily

Fig 01.54 Timeline of the case studies in restoration using glass

Fig 01.39

Fig 01.37

Fig 01.41

Fig 01.38

1950–1960 Etruscan Museum of Villa Giulia

01 CONSERVATION THEORY

Fig 01.51 Fig 01.46

Fig 01.43

1990

2000

2010

2005 Esma Sultan Geraki . Greece

2020

2013 Church of Corbera d’ Ebre Terra Alta . Tarragona . Spain

Fig 01.53

Fig 01.44

Fig 01.47

1992 Reichstag Berlin . Germany

2014 [on-going project] Menokin Glass Project . USA

2001 Roman bath ruins Badenweiler . Germany

Fig 01.52

1991 Coop’s Shot Tower Melbourne . Australia

2011 Glass Tea House Kyoto . Japan

2011 Church of St Francis Convent Santpedor . Spain

Fig 01.50

Fig 01.42

1989 Museum Courtyard covering Hamburg . Germany

2007 Flourmill Geraki . Greece 1998 Juval Castle Schnals Valley . Italy

Fig 01.49

Fig 01.45

Fig 01.48

2009 Victoria Memorial Museum Ottawa . Canada

TRANSPARENT RESTORATION

MUSEUM COURTYARD COVERING YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

1989 VOLKWIN MARG HAMBURG . GERMANY GLASS . STEEL FRAME SHELTER ROOF NEW USE

Fig 01.55 3D view of the lattice shell structure

36 Fig 01.56 Plan [not in scale]

Fig 01.57 Section [not in scale]

Fig 01.58 View of the glass roof from the couryard

The proposal of a glass protective shelter aimed to allow fuller use of the L-shape courtyard of the Hamburg City History Museum built in 1914-1926. The structure consists of a lattice shell in the form of two arched vaults linked at the point of their intersection by a dome-like element. The geometry is a result of optimization so that the loads can be transfered to the ground through the form of a membrane-shell compression forces, avoiding bending stresses. The load-bearing structure is a network of orthogonal identical cells of 60x40 mm flat steel sections [the minimum dimensions required to support the glass covering]. These are connected with pivoting

bolts at the nodes. Diagonal cables in both directions were also applied to ensure the rigidity of the shell structure. The glazing consists of sheets of 10 mm toughened safety glass laid on the steel frame and held in place by point fixings over the nodes. The new roof is connected to the main building by an I-section beam through its entire length. The beam is set 70-90 mm above the existing roof and is point-fixed through it to the reinforced concrete slabs and walls within. To prevent condensation, a heating wire was placed between the edge bearing of the glazing and the supporting bars. There are also ventilation flaps to exaust the warm air. [Schittich, Staib et al. 2007)

01 CONSERVATION THEORY

COOP’S SHOT TOWER YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

1991 UNKNOWN MERBOURNE . AUSTRALIA GLASS . STEEL FRAME SHELTER ROOF NEW USE

REICHSTAG YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

1992 FOSTER + PARTNERS BERLIN . GERMANY GLASS . STEEL FRAME ROOF NEW USE

Fig 01.60 The glass dome with the spiral ramp

Fig 01.59 View from the interior of the glass cone

The tower was completed in 1888 and is 50 metres high. The historic building was saved from demolition in 1973 and was incorporated into Melbourne Central complex in 1991 underneath an 84 m-high conical glass roof. The heavy steel framework of the new roof does not enhance the vision and connection with the exterior. [en.wikipedia.org]

The original dome of the building, built by Paul Wallot in 1894, was destroyed on a fire in 1933. While the building was partially reconstructed in the ‘60s, the dome was not until 1992. The design was made by the architect Norman Foster and was built to symbolize the reunification of Germany. The distinctive appearance of the dome has made it a prominent landmark in Berlin. The dome offers a 360 degree view of the surrounding Berlin cityscape. A mirrored cone in the center of the dome redirects sunlight into the building to the lower chamber and decreases significantly the carbon emissions of the building. [en.wikipedia.org]

TRANSPARENT RESTORATION

JUVAL CASTLE YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

1998 ADALBERT WIETEK SOUTH TYROL . ITALY GLASS . STEEL BEAMS ROOF PROTECTION . RE-USE

Fig 01.61 The discreet supporting structure provides unobstracted view to the exterior

Castle Juval was built around 1250. As the castle repeatedly changed hands in the course of time it started deterriorating. In 1913 the Dutchman William Rowland purchased the castle and refurbished it under the direction of the architext Adalbert Wietek. In 1983 the alpinist Reinhold Messner acquired the castle of the 13th century and restored it in a substantial manner. Since then Castel Juval is a museum, vineyard, biologic farm and a socalled â&#x20AC;&#x153;Buschenschankâ&#x20AC;? wine restaurant, all in one. The glass roof was a protective measure against the deterioration of the walls and created an internal space available for sculpture exhibitions. The form of the roof is simple following the lines of the

original construction. It is fixed at only a few points and extends by 250-400 mm at the edges so that it seems to hover above the historic ruins. The structure consists of main steel beams, which run parallel to the ridge by means of point fixings and balance arms. The panes of glass are trussed on the underside in the direction of the slope and connected to the beams. The trapezoidal plan form of the building resulted in a radial layout, thus all the glass panes have different dimensions. The process of cutting the panes to size and drilling them was performed electronically. [Schittich, Staib et al. 2007]

01 CONSERVATION THEORY

ROMAN BATH RUINS YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2001 UNKNOWN BADENWEILER . GERMANY GLASS . STEEL FRAME SHELTER ROOF PROTECTION

ESMA SULTAN YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2005 ISTANBUL . TURKEY GLASS . STEEL FRAME INDIPENDENT STRUCTURE NEW USE

Fig 01.63 Longitudinal section

Fig 01.62 View of the ruins in juxtaposition to the glass shell

The Badenweiler complex was excavated by Margrave Carl Friedrich von Baden in 1784. In the late 19th century, the ancient spa received a more contemporary counterpart: marble neoclassical style baths that were extensively extended during the subsequent decades. The natural springs, with temperatures up to 26.4°C, were enjoyed in Roman times and form the basis for Badenweiler’s status as a spa town today. Since 2001, a spectacular, multiple award-winning glass roof, designed by Stuttgart engineers Schlaich, Bergermann und Partner, has protected the historical site. The permanent exhibition at the bath ruins offers an insightful look at the Roman culture of bathing and provides fascinating facts about the entire complex. [www.badruine-badenweiler.de]

39 Fig 01.64 View from the interior

The building was erected approximately 200 years ago for Esma Sultan, an Ottoman Sultan’s wife as a summer palace. Destroyed by fire over a century ago, the exterior brick walls are all that remain of the building. In 1999 it was decided to reuse this land-marked ruin as an event and exhibition venue. The adaptive design suggests an indipendent structure; a thin but strong stainless steel and glass box that is suspended within the brick structure. The existing brick walls inadvertently create a shelter for the transparent glass box from the sun, rain and wind. The glass box is tethered to the brick walls with suspension rods, which ensures the two separate structures remain equidistant from each other and can therefore withstand extreme weather conditions and earthquakes. Through the design the building encourages a comparison between modern construction methods with those of 200 years ago. [www.gadarchitecture.com]

TRANSPARENT RESTORATION

FLOURMILL YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2007 COSTAS VAROTSOS GERAKI . GREECE GLASS ROOF FILLING THE FORM

VICTORIA MEMORIAL MUSEUM YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2009 PKG JOINT VENTURE ARCHITECTS OTTAWA . CANADA GLASS . METAL FRAME TOWER NEW USE

Fig 01.65 Exterior view of the flourmill

This work was developed for the First Environmental Art Festival Laconia: Arthumanature Topos 2007. The glass installation on an old flourmill is the result of a sculptural restoration of its ruined part. In respect to the local architecture the artist uses glass to state his signature. He uses layers of float glass stacked horizontally to abstractly resemble to the original structure. [www.costasvarotsos.gr]

Fig 01.66 Front exterior view of the glass lantern

This massive stone structure is an excellent example of early 20th-century architecture in Ottawa, and was built by the architect David Ewart to house the collections of the Geological Survey of Canada. Unfortunately, because of the presence of unstable Leda clay in the geology of the site, a tall tower that was situated at the front of the building had to be taken down in 1915 due to settling and the concern that the foundation could not support the weight. A major renovation of all parts of the building began in 2004 and was completed in 2010, including a lighter-weight glass “lantern” taking the place of the tower removed in 1915. The lantern structure was christened the “Queens’ Lantern” in honour of both Elizabeth II, who visited the building on her 2010 royal tour, and Queen Victoria. [en.wikipedia.org]

01 CONSERVATION THEORY

KOU-AN GLASS TEAHOUSE YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2011 TOKUJIN YOSHIOKA KYOTO . JAPAN GLASS . STEEL FRAME NEW USE

CHURCH OF ST. FRANCIS’ CONVENT YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2011 DAVID CLOSES SANTPEDOR . SPAIN GLASS . ALUMINUM ENTRANCE NEW USE

Fig 01.68 Sketch of the new adaptive glass entrance of the church

Fig 01.67 Exterior view of the teahouse

The Japanese designer attempts to translate the traditional teahouse to a modern total glass structure. It juxtaposes to the Shoren-in Temple built in 794-1185. The choice of glass aims to connect the tea ceremony with nature and to the visual setting of picturesque gardes, the Kyoto cityscape and the Higoshiyama Mountains. The teahouse’s roof is made up of overlapping glass panes, supported by a slender steel framework featuring a mirrored surface that camouflages with the glass. Chunky slabs of glass make up the floor and have a gently rippled surface that helps it to catch the light. [www.dezeen.com]

St Francis convent, built in the 18th century, was almost demolished in 2000, except for the church which was standing in ruinous condition. The project aimed to convert the church into an auditorium and multifunctional cultural facility. The intervention has consolidated the church without deleting the process of deterioration and collapse that the building had suffered. The project has maintained the dimensions of the church interior space and, also, the unusual entries of natural light produced by partial roof collapses. Rather than reconstructing the church, the intervention has just consolidated the old fabric distinguishing clearly the new elements executed of the original ones. The external staircases wind up from the entrance through the walls of the building, overlooking the auditorium in the former nave. The existing vaulted ceiling remains damaged, but a new roof overlaps and shelters it. [www.dezeen.com]

TRANSPARENT RESTORATION

CHURCH OF CORBERA D’EBRE YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2013 FERRAN VIZOSO TERRA ALTA . TARRAGONA . SPAIN ETFE . STEEL FRAME ROOF REUSE . PROTECTION

Fig 01.70 3D illustration of the new construction part

Fig 01.71 The roof made from single ETFE cusions stretched along a steel frame

Fig 01.69 Detail of the discreet reinforcement of the arches

Fig 01.72 Interior view of the transparent roof

The main purpose of the work was to restore the old temple, transforming it in a new and secure multifunctional public room. The challenge was to do it without changing its appearance, a great symbol and expression of the Spanish Civil War. In the third phase of the works the structural consolidation was completed and a new transparent EFTE plastic roof was introduced. This new cover stops the deterioration of the construction, due to rain and wind, and greatly improves its habitability conditions. Known for their impressive durability, thermal efficiency and light properties, ETFE panels

create a protective transparent film over the entire ruin. A primary load bearing structure was necessary as ETFE cannot bear loads. The final result, with a discreet white colour chosen for the steel structure, fits harmonically to the existing building. Since the beginning of the works one thing was clear, the restoration had to preserve the subtle balance in between nature and construction (exterior and interior) that all runes have. The perception of still being outside when “entering” in the old church had to be kept. [www. divisare.com]

01 CONSERVATION THEORY

MENOKIN GLASS PROJECT YEAR ARCHITECT LOCATION MATERIAL RESTORATION PART PURPOSE

2014 [IN PROGRESS] MACHADO AND SILVETTI ASSOCIATES WARSAW . VIRGINIA . USA GLASS PANES . STEEL FRAME SHELL [FACADE + ROOF] REUSE . PROTECTION

Fig 01.75 Elevations that show the original and the new structure

Fig 01.73 3D visualization of the glass structure

Fig 01.74 3D section of the proposal

Fig 01.76 Illustration of the interior of the museum

The Menokin residence originally constructed, in 1769, as the house of Declaration of Independence signer Francis Lightfoot Lee; the site was later named a National Historic Landmark. Over the years the building has been slowly and gradually making its way to complete and utter ruin. Approximately 80 percent of Menokin’s original materials have survived but the building is in bad shape. The initiation for its reconstruction started in 2011 and the proposal suggests structural glass to recreate an abstract memory of an 18th-century house as it once stood while protecting what remains of it

today. By showcasing the intricate details of the house, the architect’s goal is to connect the past to the future. The exterior is partially encased in glass. Indoors, glass is used in some areas to provide a catwalk and a transparent floor. [www.menokin.org]

TRANSPARENT RESTORATION

PROJECT

YEAR

MATERIAL

RESTORATION PART

Timoleonte’s Greek Wall

1950-54

glass & stainless aluminum alloy ties

wall

Roman Villa del Casale

1958-63

plexiglas & steel frame

shelter

Greek Theatre at Heraclea Minoa

1960-63

plexiglas & metal pivots

bleachers

S. Nicolò Regale Church

1960-66

plexiglas & steel frame

vaults

Museum Courtyard covering

1989

glass & steel frame

roof shelter

Coop’s Shot Tower

1991

glass & steel frame

roof shelter

Reichstag

1992

glass & steel frame

roof

Juval Castle

1998

glass & steel frame and connections

roof

Badenweiler Roman bath ruins

2001

glass & steel frame

shelter

Esma Sultan

2005

glass & steel frame

indipendent shelter

Flourmill

2007

glass

facade & roof

Church of St Francis Convent

2011

glass & steel frame

entrance

Victoria Memorial Museum

2012

glass & steel

facade

Church of Corbera d’ Ebre

2013

ETFE & steel frame

roof

Menokin Glass Project

2014

glass & steel frame

facade & roof

Table 03 . Overview and evaluation of the case studies

01 CONSERVATION THEORY

VISUAL IMPACT*

RESTORATION PRINCIPLE

STRUCTURAL PRINCIPLE

protection from the elements reinforcement

glass panels fixed on the historic fabric

protection from the elements

plexiglas panes in load-bearing steel frame

protection from the elements

plexiglas case fixed on the historic fabric

reproduction of missing parts

plexiglas panes in load-bearing steel frame

filling the openings new use

rectangular flat glass panels in lattice shell structure

new use

rectangular flat glass panels in steel frame structure

reproduction of missing parts new use

rectangular flat glass panels in steel frame structure

protection from the elements reproduction of missing parts new use

glass panes fixed with bolted connections in cable structure

protection from the elements

rectangular flat glass panels in lattice shell structure

new use

glass - steel structure

reproduction of missing parts

stacked float glass panes

new use

plexiglas panels in steel loadbearing structure

new use

suspended structural glass panels by steel truss frame

protection from the elements

single ETFE foils on steel frame

protection from the elements reproduction of missing parts new use

glass panes point-fixed on steel frame

â&#x20AC;ş *small visual impact

â&#x20AC;ş big visual impact

TRANSPARENT RESTORATION

Having an overview on different aspects of architectural conservation, it is evident that everything old, regarding our architectural heritage, can be interpreted in more than one ways. There is still space to revaluate past methods so as to reveal the authenticity embedded in each monument. As theories over conservation practices have so far

01.9 CONCLUSIONS

Fig 01.77 Intervention at an old slautery house by Arturo Franco . Madrid . 2006

01 CONSERVATION THEORY

provided, more or less, the main guidelines, the key-decisions have to do with the materials; these are to highlight or doom a monument. In theory, glass as a transparent material can be used in restoration practices as it stands for transparency causing minimum visual impact on the existing structure. In such way, the visitor can clearly distinct the old and the new, having at the same time the general image of the original form. Furthermore, glass technology can provide safe glass components able to withstand loads, giving solutions even to buildings with extended damage. “Transparent restoration” can be divided in two main categories, as resulted from the case studies review: indirect and direct approaches. The former deals with interventions aiming to shelter and protect the monuments in an invisible way, such as showcases or glass floors. The direct approach, as implied by the name, deals with the use of glass in direct relation to the monument. Glass could reinforce, ensuring the structural integrity, fill the form, e.g. by reproducing the missing parts or serve an adaptive re-use, e.g. by closing the space. As shown in Fig 01.82 traditional and transparent restoration result in common intervention strategies. As minimal impact is one of the initial reasons of choosing glass, it is crucial to ensure its proper use in order to reveal the desired qualities. The case studies have provided a wide range of solutions sometimes successful, sometimes not. We can conclude that ratio of glass and framing is important, as the “heavier” the supporting structure is, the more the visual obstacles [see Table 03]. In conclusion, glass speaks for authenticity; it has the unique ability to provide a complete image of the original form, by exposing the traces of time and ageing, while introducing a distinct line between the old and the new. It provides the advantage of perception, a material and immaterial result that tricks the eye but at the same time relates the structure to the setting of the present time.

TRANSPARENT RESTORATION

TRADITIONAL RESTORATION PROTECTION FROM THE ELEMENTS

MATERIAL TREATMENT

SHELTER

[E.G. SHOWCASE OR SHELTER]

STRUCTURAL REINFORCEMENT

SIMPLE REINFORCEMENT

REINFORCEMENT & FILLING THE FORM

[STRUCTURAL INTEGRITY]

Fig 01.78 Juval Castle

Fig 01.79 Timoleonteâ&#x20AC;&#x2122;s Greek Wall

PROTECTION

REINFORCEMENT

INDIRECT

GLASS USE TRANSPARENT RESTORATION Fig 01.82 Relation between traditional & glass restoration regarding the degrees of intervention

01 CONSERVATION THEORY

DEGREES OF INTERVENTION FILLING OF THE FORM

ABSTRACT

ADAPTIVE RE-USE

ANASTYLOSIS

NEW USE = OLD USE

[E.G. ABSTRACT REPRODUCTION OF MISSING PARTS]

NEW USE

OLD USE

[E.G. CLOSING THE SPACE]

Fig 01.81 Museum courtyard covering Fig 01.80 Flourmill

FILLING OF THE FORM

DIRECT

ADAPTIVE RE-USE

Fig 02.1 2.5-meter PyrexÂŽ mirror blank for the Palomar Observatoryâ&#x20AC;&#x2122;s Hale telescope . 1910

02.

GLASS TECHNOLOGY

“What interests me about the transparency is the idea of evaporation. Ever since man became man, he has fought against fate, against the elements, against matter. He started off building stone by stone, then made windows with small pieces of oiled paper, then learned how to do other things. There is a kind of architectural “Darwinism” at work, which is an evolutionary process through which man attempts to cover the maximum amount of space, the largest surface, insulate the most but with the least amount of material, without looking like he did anything. There’s been a tremendous push forward that still isn’t over and never will be. We can summarize it as follows: how can we resolve the most material problems with the greatest amount of elegance? It evolves the domination of matter”. Jean Nouvel [Baudrillard and Nouvel 2005, 63]

TRANSPARENT RESTORATION

Glass is a man-made material, widely know for its transparent property, which redefines the interrelation between exterior and interior. In its architectural expression it is often related to openness and lightness, creating at the same time, an honest relation to the surroundings. Glass responds to elementary human need for sunlight and a close attachment to the nature, in the broader sense.

02.1 INTRODUCTION

Pure transparency has not been always the case though, and that is mainly because of the glass fabrication techniques, which have gradually evolved in time offering new possibilities. The oneway transparency concept of the Middle Ages, being responsible for the semi-lighted gothic cathedrals, was replaced by the two-way transparency, establishing the interaction of indoor and outdoor spaces having a broader impact. By the 17th century, glass was assumed a vital and indispensable element of the architectural design. A new aspect, associated with the presence or non-presence of a glass surface, led the way to structures that expressed the potential of spatial transparency as a new architectural style. Palm House [1848] [see Fig 02.3] and Crystal Palace [1851] embodied the spirit of the time, as two of the first industrial achievements of mass production, which functioned as milestones in glass constructions. [Rice and Dutton, 1995)

“The word glass is derived from glaza, the Germanic term meaning “amber”, “glare” or “shimmer”” (Balkow 1999)

Fig 02.3 Palm House at Royal Botanic Gardens . Kew

Fig 02.2 Glass Cube House . Bad Driburg

02 GLASS TECHNOLOGY

This “craving” for transparency is more than obvious in the contemporary architectural achievements. The Apple Glass cube 1.0 and 2.0 are the perfect examples, reflecting the intentions towards the constant optimization of the “absolute transparent image”. However, this could not have been possible without the recent advancements in fabrication and treatment technologies, which have turned glass into a respectable structural element, among concrete, steel and timber. Glass is not anymore applicable solely at the building envelope; instead, glass load-bearing components are becoming more common nowadays. The challenge in this case is to manage and mitigate its brittle nature, which is responsible for its unpredictable failure behavior. Nevertheless, the emerging technologies have given solutions for the safe use of glass components.

Fig 02.4 Corrugated glass facade at MAS Museum . Antwerp

While in the previous centuries, elements such as beams, floors, columns and bricks made of glass were probably beyond our imagination, now they are more than real. Structures such as the MAS Museum [see Fig 02.4], the Laminata House, the Glass Cube House [see Fig 02.2], the Atocha Memorial, the Willis Tower Glass Balconies and the new interior of the town hall of Saint-Germain-en-Laye [see Fig 02.5] show some of the potentials in glass innovative constructions.

Fig 02.5 Glass columns at the town hall of Saint-Germain-en-Laye . France

TRANSPARENT RESTORATION

Glass, in its most familiar to us form, is a mixture of silicon oxides, alkaline oxides and alkaline earth that is heated to temperatures higher than 1100°C. It is an inorganic product of fusion, which has been cooled down resulting in a solid state without undergoing crystallization [without developing any crystal bonds between the molecules]. [see Fig 02.7] This rather amorphous chemical composition is the reason why glass does not have a fixed melting point. Its structural state can be compared to that of liquids and molten materials, thus it does not possess any direction-oriented properties. (Weller 2009) The glass widely used today in the building industry is a soda-lime-silica glass [SLSG], but other types are also available. (Schittich, Staib et al. 2007) The typical properties of the main glass types are shown in Table 04.

02.2 PROPERTIES “There are two things everybody knows about glass: it is transparent... and it breaks!” [Bos, 2009]

sand 72.6% 54 limestone 13.0% soda 8.4% other 6.0%

Fig 02.6 Proportions of the raw glass materials

Fig 02.7 Molecular structure of soda lime glass [left] and quartz [right]

Fig 02.8 The color of glass may be changed by adding metallic oxides: iron [green], copper [light blue], manganese dioxide [decolorize], cobalt [dark blue] and gold [deep red]

02 GLASS TECHNOLOGY

Fig 02.9 The transition of the light rays through multiple media in a hollow glass block results in more distortion compared to a solid glass block

TRANSPARENCY Optical properties depend on thickness, chemical composition and applied coatings. The most evident of them is the very high transparency within the visible wavelength [ cal bonds are responsible for transmitting, reflecting and absorbing the radiation making glass a highly permeable material. For even more transparent result, anti-reflection treatments or lowiron, extra-clear glass [see Fig 02.8] to reduce its absorptance can be used. Moreover, the structure of the glass component can influence the degree of transparency, as shown in Fig 02.9.

Fig 02.10 Stress / strain graph of glass compared to steel [brittle vs ductile behavior]

BRITTLENESS Glass is a brittle material, which means that it does not yield plastically, like materials such as steel [see Fig 02.10]. On the contrary, the maximum elongation it reaches is in the area of 0.1%. There is no plastic-behavior zone, so it is not possible to anticipate its failure. (Weller 2009)

Fig 02.11 Scratches on glass surface invisible to human eye

TRANSPARENT RESTORATION

The intact atomic bonding forces, on the molecular scale, suggest a glass surface perfectly smooth that can undergo high mechanical strength. However, this is just in theory because tensile strength, which is of concern for brittle materials such as glass, is very much dependent on mechanical flaws on the surface of the material. Minimal damages [see Fig 02.11] can occur even during the fabrication process [through e.g. cutting, grinding, drilling].

ALUMINO SILICATE GLASS

BOROSILISODA LIME QUARTZ GLASS LEAD GLASS CATE GLASS GLASS

While in compression, flaws do not affect the overall structural behavior, when subjected to tension they display very high local stresses, according to the “Griffith Flaws”. (Balkow 1999) Cracks grow with the time when loaded. The higher the load, the longer the load duration and the deeper the initial surface flaw, the lower the effective tensile strength. (Haldimann, Luible et al.) Fig 02.12 gives an overview of typical strength values according to the flaw depth.

Fig 02.12 Rough estimated ration between tensile strength and effective flaw depth

DENSITY [kg/m3]

PRICE [€/kg]

YOUNG’S MODULUS [GPa]

HARDNESS [kg/mm2]

2170-2200

5.140-8.580

68-74

450-950

2440-2490

1.160-1.370

68-72

440-485

2200-2300

3.430-5.150

61-64

84-92

3950-3990

3.300-5.100

53-55

472-525

2490-2300

1.170-1.370

85-89

68-75

Table 04 . Typical properties of different glass types [Construction Manual, 2007]

02 GLASS TECHNOLOGY

It is, also, important to outline that tensile strength is not a constant value. It depends on a lot of factors such as: duration of load size of pane glass type surrounding medium [air moisture content] age of pane

< 0.01 mm . 45 MPa 0.01 mm . 40 MPa 0.02 mm . 35 MPa 0.05 mm . 30 MPa 0.10 mm . 25 MPa >0.10 mm . 20 MPa Fig 02.13 Distribution of surface damage and margin of strength. New glass [top], weathered glass [middle], damaged glass [bottom]

TENSILE STRENGTH [MPa]

COMPRESSIVE STRENGTH [MPa]

THERMAL EXPANSION COEFFICIENT [10-6/K]

POISSONâ&#x20AC;&#x2122;S RATIO [-] 57

41-155

1100-1600

0.55-0.75

0.15-0.19

30-35

360-420

9.1-9.5

0.21-0.22

22-32

264-348

3.2-4

0.19-0.21

23-24

232-244

8.82-9.18

0.23-0.24

40-44

400-440

4.11-4.28

0.23-0.24

TRANSPARENT RESTORATION

The crack propagation mechanisms driven by the tensile stresses that occur on the glass surface constitute glass an unsafe and inappropriate material for construction. However, there are methods that can strengthen the glass components regarding the tensile strength and ensure a safe fracture pattern. The measures can be taken either for the primary product or the final glass component.

01 . THERMAL TREATMENT . TEMPERING The main principle of tempering is to create a favorable field of residual stresses, tensile stresses in the core and compressive stresses near and on the surfaces. This will prevent the growing of cracks and flaws in the glass surface [they grow if subjected to tensile stress]. (Haldimann, Luible et al.) Annealed glass is the raw product that comes out the fabrication process; it has low residual stresses that allow for cutting drilling or grinding. This is then reheated to approximately 620-675°C and then rapidly cooled down. That thermal treatment results in a hard outer skin and a still very hot core. When the outer skin cools down, at the same time it shrinks, “pulling” the core. Thus, the outer layer is under compression while the interior is under tension. This results in an overall higher tensile strength. Depending on the airflow rate of the heating and cooling temperatures, fully tempered or heat-strengthened glass can be produced. The different treatments result in different internal stress distribution.

cleaning

02.3 SAFETY

Fig 02.14 The principle of glass tempering

heating > 600°C

Fig 02.15 The manufacturing steps for tempering flat glass

cooling

02 GLASS TECHNOLOGY

Tensile Strength [max] 20 MPa [45]

40 MPa [70]

80 MPa [120]

Fig 02.16 Beak patterns for annealed [left], heat-strengthened [middle] and fully tempered glass [right]

FULLY TEMPERED GLASS [TOUGHENED GLASS] It has the highest level or residual stress and thus the highest tensile strength [up to 120 MPa]. It is also known as “safety-glass”, because of its fracture pattern. It breaks into small pieces reducing the risk of injury. However, exactly because of that, it is considered inappropriate for load-bearing components if not laminated, as the small fragments do not allow for integrity after breakage. HEAT-STRENGTHENED GLASS It is produce by heating in temperatures around 650°C and has a lower tensile strength than fully tempered glass [max 40MPa]. Its fracture pattern is similar to this of annealed glass, it breaks into larger fragments, capable of transferring the forces after breakage.

Fig 02.17 Principle of ion exchange in chemical strengthening

Fig 02.18 Stress distribution according to the toughening method. [left: fully tempered safety glass . middle: heat strengthened glass . right: chemically strengthened glass. Near the surface glass is in compression and in the middle under tension.

02 . CHEMICAL STRENGTHENING The glass panels are immersed in a bath of potassium salt [typically potassium nitrate] at 300°C, while pre-stressing is realized by ionic exchange [the small sodium ions in the glass surface are exchanged for the larger ions in the molten salt, which leads at compressive stresses in the glass surface]. Chemical strengthening results in a strengthening similar to toughened glass [see Fig 02.18]. The advantage of this type of strengthening is that glass is not subjected to extreme variations of temperature, so is has little or no bow or warp, optical distortion or strain pattern, compared to toughened glass. Chemical strengthening is primary applied in thin glass panels, because the compressive zone in the surfaces is smaller than this of tempered glass.

TRANSPARENT RESTORATION

03 . LAMINATION Laminated glass is a glass unit that consists of at least 2 layers of glass panels bonded together using foil or resin interlayer. This facilitates the over-dimensioning and prevents the component to collapse upon failure. In the case that a single glass panel is subjected to stresses higher than the allowed ones, a failure occurs. In contrast, by laminating the glass component, this failure occurs to the outer, “sacrificial” layers, leaving the middle panel intact to bear the loads. Upon cracking, the outer layers will remain bonded to the inner layer. As interlayer materials can be used either foils or resins. Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered [overhead structures].

positioning and layering

prelamination by calender

Fig 02.19 Post breakage behaviour of laminated glass made of different glass types

autoclave

finished laminated safety glass

Fig 02.20 Float Glass manufacturing process. The manufacturing steps of PVB-laminated safety glass. First the individual sheets are washed, the film is layered between them and the assembly is heated and pressed before the full surface bond is created in an autoclave using high pressure and temperatures of about 140°C. POSSIBLE MATERIALS FOR INTERLAYER IN LAMINATED GLASS UNITS

Fig 02.21 Prelamination using vacuum bag process [usually applied in case of bent sheets]

Fig 02.22 The dimensions of a laminated glass sheet can be up to 3.2 x 15 m [www.Sedak.com]

02 GLASS TECHNOLOGY

04 . STEEL REINFORCEMENT This measure minimizes the consequences of glass failure as, upon fracture, it can still transfer the tensile forces allowing the component to carry the loads. It is applied in glass beams, as part of the lamination, providing a controlled ductile failure. [Louter, 2007] Fig 02.23 Cross-section designs developed by C. Louter at TU Delft U-section . Box-section . T-section . Full-section [from left to right]

Fig 02.24 4000 mm long prototype for an aquarium, studied by Dr. F. Veer, with two stainless steel profiles bonded to the bottom plate

05 . MECHANICAL PRESTRESS It aims to enhance the strength of glass in tensile stress by overcompressing the surface cracks beforehand. This can be achieved by applying dead load or using springs to overcompress the entire cross-section. When glass is subjected in tensile force, this initially leads to a decrease in the precompressive force and, after that has been neutralized, a tensile stress occurs.

Fig 02.25 Atrium facade with concentrically prestressed glass tubes in Tower Place . London

TRANSPARENT RESTORATION

The production of glass depends on multiple factors: the raw materials, the heat energy required to melt these materials, the technical conditions of a glassworks or factory and the highly experienced personnel. (Weller 2009) The basic products can be either float, cast or extruded glass, however float glass is the most common type and worldwide available in building industry.

02.4 PRODUCTION TECHNIQUES Additional production lines for glass sheets are:

O1 . FLOAT GLASS Pilkington Company developed float glass method between 1952 and 1959, which is currently the dominant manufacturing procedure, accounting for the 90% of today’s flat glass production worldwide. The main advantages of this method are its low cost, its wide availability, the high optical quality of the glass and the large size of panes that can be produced.

ROLLED GLASS This process is used for the production of patterned, wired or Uprofiled glass. When the molten glass leaves the melting tanks, at 1200°C, it passes between two water-cooled contra-rotating rollers, one above the other. [see Fig] The distance between the rollers can vary between 3-15 mm in order to control the thickness of the glass ribbon. The glass is then transported on rollers to the annealing lehr. The light permeability of rolled glass is inferior to that of float glass and depends on thickness and surface texture. (Weller 2009)

The process is as follows [see Fig 02.27]: Once the main ingredients are melted all together in a tank at approximately 1550°C, the molten glass is poured at 1050°C onto a large bath of mirrorlike molten tin where it slowly spreads to reach the desirable thickness. It exits the float bath at

DRAWN GLASS This production method is not widely use in the building industry because of the significantly lower optical qualities. In this case, the glass ribbon is drawn vertically out of the melt. This optical quality is usually encountered in historical glasses, which constitutes, therefore, drawn glass suitable for restoration purposes.

Fig 02.26 The glass ribbon being formed by a pair of rollers

02 GLASS TECHNOLOGY

600Â°C to move on to the annealing lehr, where it floats over a length up to 150 m; a process that helps the hot glass to relieve internal stresses by cooling it down slowly to a temperature of 100Â°C. While being inspected by automated machines to ensure the highest quality, glass is cooled down to room temperature so that the further treatment processes can begin. [www.pilkington.com]

Fig 02.27 Float glass manufacturing process 63

TRANSPARENT RESTORATION

O2 . CAST GLASS This method is suitable when larger glass volumes or perplex shapes are required [see Fig 02.28]. It has been so far applied for the manufacturing of glass bricks [or glass blocks] in the building industry; however, the same principle is followed in glass sculpture or ornaments fabrication, providing high flexibility of the form. Glass casting is the process which involves a mold in order for the glass to take the desirable shape. This can be achieved by two methods: hot pour and kiln casting.

Fig 02.28 Glass sculpture by Karen La Monte

HOT POUR Hot pour involves molten glass poured directly into a mold at around 1200째C. The mold should be heated beforehand and after the glass is poured in, at around 850째C, the glass can be released from the mold and put into the kiln for the annealing process. It is known as sand casting, a method used frequently by artists, where the mold is formed in sand. Alternatively, for commercial manufacturing, steel molds could be used [see Fig 02.29]. 64

KILN CASTING In kiln casting the mold is in the kiln during the whole process [heating-cooling-annealing]. The mold [usually made from materials with resistance in high temperatures] is placed into a kiln at temperatures around 1200째C [760-870째C for fusing] and is filled with glass pieces that slowly melt and fill the space [see Fig 02.30]. Once the mold if full of liquid glass the kiln is slowly cooled down to avoid cracking [annealing]. Once the kiln reaches room temperature the mold should be carefully taken out and destroyed to reveal the cast glass form. MOLD PREPARATION Molds can be prepared in two ways. There are the disposable and the permanent ones. Disposable molds are made out of soft materials [e.g. plaster] which can withstand high temperatures and are destroyed so as to reveal the glass form. In order to shape these type of molds we can have either a permanent or disposable model, which is usually made by wax in order to be malleable. The permanent molds are made from harder materials such as steel and are used when a series of glass components are to be manufactured.

Fig 02.29 Manufacturing process of glass bricks [hot pour]

Fig 02.30 Glass pieces melt and are poured into the mold in kiln casting

02 GLASS TECHNOLOGY

Despite the design potential that comes with cast glass there are considerable limitations in practice. Glass casting is a very perplexed process and especially with larger objects, the process of annealing is extremely slow [see Fig 02.32]; that can be timeconsuming and increase the manufacturing cost. Additionally, heavy glass elements are difficult to handle, thus at the present they are commercialized up to the size range of standard ceramic masonry bricks. [Oikonomopoulou et al, 2015]

Fig 02.31 Crystal House . Amsterdam. Cast glass brick were used to create this total glass facade, designed by MVRDV and Gietermans & Van Dijk, in collaboration with the Glass and Transparency Lab of TU Delft

Fig 02.32 â&#x20AC;&#x153;Ten Liquid Incidentsâ&#x20AC;? by Roni Horn. Her work was exhibited in the 19th Biennale of Sydney, 2014. Ten cylindrical cast glass units, of 45.5x91.5 m were created in a period of two years [2010-2012]. Every unit weights approximately 800 kg and required 9 months of controlled cooling to avoid the formation of bubbles and cracks due to residual stresses.

TRANSPARENT RESTORATION

03 . EXTRUDED GLASS This method can be used to produce glass profiles such as [thin wall] tubes, rods or products with other than circular cross section [see Fig 02.33]. Products like these provide solutions in several fields such as architecture, art, design and lighting [see Fig 02.35]. Extruded glass products have high thermal shock resistance, tight geometrical tolerances and high optical quality, as well as, a wide geometrical dimension range [SCHOTT, 2015]. Extruded glass is typically borosilicate. By using laminate extrusion methods, two or three types of glass can be combined to produce, for example, components sheathed with chemically resistant glass. [Pfaender, 1996) The most common production process is the Danner process [see Fig 02.36], named after Edward Danner in 1912. Glass flow falls onto a rotating mandrel. Air is blown down a shaft creating a hollow space in the glass as it is drawn oof the end of the mandrel by a tractor mechanism. The diameter and thickness are controlled by regulating 66

Fig 02.33 Large variety on profiles for extruded glass products

Fig 02.34 Thermal prestressed tubes smooth and with fine break pattern similar to tempered safety glass

Fig 02.35 Arquia - Caja de Arquitectos . Barcelona . Spain. Eduardo Arroyo used borosilicate glass tubes to create a continious tow of transparent walls that separate the public area from the office spaces. Due to their cylindrical form, the tubes transmit light slightly distorted and also have sound insulating effects. 300 tubes, 3 m high with a dimateter of 150 mm were installed.

02 GLASS TECHNOLOGY

the strength of the air flow and the speed of the drawing machine [thicknesses up to 10 mm]. The more recent centrifuging process the glass is fed into a steel mold that rotates. When the glass has cooled sufficiently, rotation stops and the glass is removed. This process allows for large sections but is expensive. [Haldimann, Luible et al., 2008] Fig 02.36 Principle of Danner process for glass tubing manufacturing

Fig 02.37 Rendered cross-section of the Kiln Cartridge 1. crucible 2. heating elements 3. nozzle 4. thermocouple 5. removable feed access lid 6. stepper motors 7. printer frame 8. print annealer 9. ceramic print plate 10. z-driven train 11. ceramic viewing window 12. insulating skirt

04 . 3D PRINTED GLASS Recently, Mediated Matter Group, in collaboration with MIT’s Department of Mechanical Engineering and MIT’s Glass Lab, developed a Glass 3D Printing method for optically transparent glass [G3DP]. The platform is based on a dual heated chamber concept. The upper part, which acts as a Kiln Cartridge, operates at approximately 1040°C and through a nozzle pours the molten glass and forms the shape to a lower annealing chamber [see Fig 02.37]. This process has so far been used for the production of decorative objects. [John Klein, 2015] [matter. media.mit.edu]

Fig 02.38 Conceptual design for a compressive shell structure with 3D printed custom glass components

TRANSPARENT RESTORATION

After the primary fabrication, the glass product can be processed into subsequent treatments, which aim to modify it for functional reasons. These processes are displayed in order as follows:

SURFACE TREATMENT SAND BLASTING [MATTE SURFACE]

MECHANICAL WORKING

Fig 02.44 Sandblasted Michelle Ivankovic

vessels

ACID ETCHING [TRANSLUCENT SURFACE]

CUTTING TO SIZE

Fig 02.45 Translusent glass at the Apple Store stairs . NY

ENAMELLING & PRINTING Fig 02.39 CNC automatic cutting glass table

Fig 02.40 Water jet cutting

GRINDING & POLISHING THE EDGES

MITRE

ARRISED

BEVEL

GROUND

ROUND

FINE GROUND

HALF-ROUND

POLISHED

Fig 02.41 Edge work and bevelling

Fig 02.42 Edge types and finishes

Fig 02.46 P r i n c i p l e of roller-applied colour coating

Fig 02.47 40% white ceramic frit helps control heat gain and diffuse light [sunscreen]

COATINGS & SEALING THE EDGES DRILLING HOLES

CYLINDRICAL HOLE

CONICAL HOLE

UNDERCUT HOLE

Fig 02.43 Differrent hole shapes

Fig 02.48 Pyrolitic haed coating for self-cleaning glass

Fig 02.49 I n s u l a t i n g glass unit

OPTICAL CHARACTERISTICS

STOCK SIZES [MM]

THICKNESS [MM]

FLOAT GLASS

SMOOTH . TRANSPARENT TEXTURED

MAX 3210 X 6000

2.3.4.5.6 8 . 10 . 12 . 15 19 . [25]

CAST GLASS

SMOOTH . TRANSPARENT

NOT IN STOCK

UNLIMITED [THEORETICALLY]

EXTRUDED GLASS

SMOOTH . TRANSPARENT

600-10000 [LENGTH]

3 - 460 [OUTER Ã&#x2DC;]

GLASS TYPE

Table 05 . Overview of the glass fabrication methods

02 GLASS TECHNOLOGY

FORMING

STRENGTHENING

HOT BENDING

TEMPERING

Fig 02.50 In hot bending, glass sheet is heated up to 580600Â°C and bends under its own weight or by applying load on it, to the desirable mold. Ties can be used to hold it into place while it slowly cools down to room temperature. [Appelqvist 2015]

Fig 02.53 During the tempering process the outer surfaces are in compression and the core is in tension to increase the strength of the glass

CHEMICAL STRENGTHENING

COLD BENDING

Fig 02.51 In cold bending, the glass sheet is mechanically pressed and fixed directly into the desired frame in room temperature. 69

FUSING [TEXTURED GLASS]

Fig 02.54 Structural Glass Dome with 2 mm laminated chemically strengthened glass: . Stuttgart

LAMINATION

Symmetric build-up Fig 02.52 Wood pattern on glass

Asymmetric build-up

Fig 02.55 Build-ups of laminated glass

ADVANTAGES

DISADVANTAGES

HIGH QUALITY MASS PRODUCTION PRECISE MANUFACTURE

LIMITED DESIGN POSSIBILITIES [SHAPE + DIMENSIONS]

BIG VOLUMES PERPLEX SHAPES

TIME-CONSUMING ANNEALING PROCESS EXPENSIVE

WIDE RANGE OF PROFILES

LIMITED DESIGN POSSIBILITIES [SHAPE + DIMENSIONS] EXPENSIVE

Safety glass

TRANSPARENT RESTORATION

The use of glass as a structural element suggests that it allows the loads to be transmitted in a predictable way from the loaded surface to the ground. These elements are usually very slender with a cross-section that tends to deflect laterally under load [see Fig 02.56]. Connections play a critical role to the safe failure mode of the system as they are responsible for transfering the loads among the glass structural members even in their fracture state [residual load-bearing capacity of glass].

BUCKLING

LATERAL TORSIONAL BUCKLING

PLATE BUCKLING

Fig 02.56 The three basic stability conditions of linear and planar structural elements made from flat glass

The form of loading transfer has great effect on the stress distribution on the glass. The structural elements can be supported on their edges, corners or surface, linearly or at points. The design and detail must be such that glass does not come into contact with harder materials or damaging mechanical actions. Restraint stresses due to unintentional loads should be avoided. Connections should also ensure a sufficient level of robustness, durability and weather resistance. [Weller, 2009]

02.5 CONNECTIONS

CLAMP CONNECTIONS 01 . Out-of-plane loads are transfered by mechanical interlock 02 . In-plane loads [e.g. self weight] are transfered by friction forces through brackets and blocks 03 . The larger the clamped surface are and glass embedment, the greater the residual load-bearing capacity 04 . Clamp connection are applied either on the edges or the corners and can be linear, point fixing or a combination of both POINT FIXED

Fig 02.58 Individual clamp fixing for safety barrier glass

LINEAR SUPPORT

Depending on their force-transfer mechanism glass connections can be classified as mechanical interlock, friction or adhesive connections [see Fig 02.57]. The connections currently used in the build industy can be clamps, bolts, adhesives, and embeded connections. Fig 02.59 Stages at the development of clamping linear support

Fig 02.57 Force-transfer mechanisms in glass connections [top] mechanical interlocking [middle] friction [bottom] adhesive forces

Fig 02.60 Linear support with patent glazing bar

02 GLASS TECHNOLOGY

MATERIAL BONDED CONNECTIONS

SILICONES

POLYURETHANES

EPOXY RESINS

TRANSPARENCY

JOINT THICKNESS

STRENGTH

01 . Loads are transfered by mechanical interlock 02 . The glass needs to be tempered 03 . Too high local stresses are developed around the holes because this area is difficult to be tempered [see Fig 02.61] 05 . Hinged point fixings can reduce the restraint stresses in the glass pane. Articulation in the bolt prevents the glass from cracking. [see Fig 02.64]

TEMPERATURE RESISTANCE

BOLTED CONNECTIONS

MOISTURE UV-RESISTANCE

01 . Loads are transfered by the adhesive forces developed in molecular or atomic level 02 . The layer needs to have the right thickness in order to have optimum strength

ACRYLATES

Fig 02.65 Qualitative comparison of different adhesives

ALL GLASS ADHESIVE CONNECTIONS

Fig 02.66 U V - c u r i n g acrylate colourless adhesive for the bonding of the glass brick masonry in Crystal House . Amsterdam Fig 02.61 Stress distribution around the holes of a glass Fig 02.62 Possible hinge positions for point fixings a. hinge positions with minimal eccentricity b. rigid support c. hinge position with large eccentricity d. hinge roughly in line with the pane of the glass

HYBRID ADHESIVE CONNECTIONS [EMBEDED] 01 . An extension of adhesives are embeded connections [inserts]. Strong laminating foils can also be applied to metal inserts. 02 . Nature of the metal does not matter, it can be stainless steel, aluminum or titanium

Fig 02.67 Cross-section of linear adhesive connection

Fig 02.63 Button fixing [left], countersunk fixing [middle] and undercut fixing [right]

Fig 02.64 Countersunk point fixing

Fig 02.68 Apple Glass Cube 0.2

TRANSPARENT RESTORATION

The use of glass in restoration practices as explained in the previous section [see chapter 01] aims at a minimal visual interference. Despite the fact that glass is transparent, frequently, the connections and support frames used are acting in a negative way to this desirable transparency. An evaluation of the aforementioned connection methods is necessary, in terms of visual obstruction and reversibility [according to the restoration guidelines], two of the most important qualities that need to be attained in a transparent restoration design. However, despite these two parameters [visual obstruction and reversibility] the overall structural stability of the glass stucture should be primarily ensured. The challenge in a restoration project with structural glass is to achieve a delicate system of connections that will not outshine the existing structure.

Fig 02.69 Detail of cruciform node connection of the glass roof at TU Dresden . 2006

CONNECTION TYPE CLAMPED BOLTED ADHESIVE EMBEDED Table 06 . Overiview of the connection types

UNOBSTRUCTED VIEW

REVERSIBILITY

02 GLASS TECHNOLOGY

Fig 02.70 Pre-stressed aramide cables allow for a frameless glass facade at the Polytechnic School INHolland . Delft . 2009

NOTES SUSCEPTIBLE TO PANES SLIPPING OUT OF FIXING PEAK STRESSES DUE TO DRILLING AND POINT SUPPORTS UNIFORM DISTRIBUTION OF LOADS UNIFORM DISTRIBUTION OF LOADS

OVERALL EVALUATION

TRANSPARENT RESTORATION

Glass can be fabricated with specific production lines [see chapter 02.4] and are connected together in different ways according to the respective stuctural system. As the case study for this graduation project involves the restoration of the collapsed part of the walls of a tower, an analysis of the possible geometries for vertical structures with glass will be conducted.

02.6 STRUCTURAL CONFIGURATIONS

Float, cast and extruded glass are the possible final glass products that can be fabricated. For each we will examine how they can be arranged in order to replace parts of a vertical structure, such as walls, beams and columns.

EXTRUDED GLASS

CAST GLASS

BUNDLE

MASONRY

Fig 02.73

Fig 02.71 Glass column by welded rods

ARRAY Fig 02.74

ONE CROSS-SECTION ELEMENTS

Fig 02.72 The Walbrook . Foster + Partners . London . 2010

Fig 02.75 “Library of Water” . Roni Horn . 2007

02 GLASS TECHNOLOGY

FLOAT GLASS

STACKED PANELS VERTICAL ARRANGEMENT HORIZONTAL ARRANGEMENT

Fig 02.76 Laminata House . Kruunenberg van der Erve Architects . Leerdam . 2002

CONFIGURED GLASS GLASS FINS

CURVED GLASS

PROFILES

PLANE

SINGLE CURVED

DOUBLE CURVED

Fig 02.77 Entrance to the underground . Glasgow . 2003

Fig 02.78 Casa di Musica . OMA . Porto . 2005

TRANSPARENT RESTORATION

Below there is an overiew of the possible applications that glass can have in restoration projects. According to the different fabrication techniques, the respective parts of a building that can be replaced by glass elements are outlined. In general, float glass can stand for more abstract restoration concepts as the past building techniques did not include purely flat surfaces. For example, float glass planes could be used to shape

CAST GLASS EXTRUDED GLASS

FLOAT GLASS

WALL

02.7 GLASS APPLICATION IN RESTORATION

FLOOR

ROOF

Fig 02.79 Obelisk . Washington

Fig 02.80 Iron staircase in a medieval castle . Italy

Fig 02.81 Japanese Pagoda

MASONRY

STAIRS

ROOF TILE

VAULT

Fig 02.83 Chand Baori stepwell . India

Fig 02.84 Byzantine roof tiles

Fig 02.85 BasilicaCistern . Istanbul

Fig 02.82 Puebloan masonry . Hovenweep National Monument . San Juan County

[NOT FEASIBLE]

Table 07 . Overview of the applications of glass in restoration according to the fabrication technique

02 GLASS TECHNOLOGY

the outline of a massive wall. Cast and extruded glass, on the other hand, can represent more accurately a specific shape [even a complex form] and could be applied in order to represent the exact original form of parts of a monument. The latter types of glass can form even the most delicate details in decorative elements that need to be replaced. It should be outlined, though, that extruded glass is not that easily feasible due to its linear shape.

LINEAR ELEMENTS COLUMN

DECORATIVE ELEMENTS

BEAM

Fig 02.86 Rectangular shaped Fig 02.87 Wooden roof beams of industrial building . columns . Palmyra Greece

Fig 02.88 Recessed ceiling panel

COLUMN

COMPLEX SHAPE ORNAMENTS

ARCH

Fig 02.92 Corinthian order column Fig 02.93 C o l u m n capital . Greece

Fig 02.89 Columns made by Fig 02.90 Winery of Pinell de Brai Fig 02.91 Arch types stacked massive blocks of stone . Catalonia

COLUMN

TRUSS

LINEAR ORNAMENTS

Fig 02.94 Twin columns in early gothic style . Cloister of S. Giovanni in Laterano

Fig 02.95 Truss configurations

Fig 02.96 Gothic architecture ornaments

Fig 03.1 North-east faรงade of the tower . Methoni . Greece

03.

MONUMENT ASSESSMENT

TRANSPARENT RESTORATION

Based on the methodology that emerged from the literature review concerning the theory of conservation [see chapter 01.6], the assessment of theexisting condition of chosen case study is essential for the further elaboration and design. Thus, this chapter includes all those characteristics that I assume to be of great importance in order to give me an insight and better understanding of the structure. This is a vital step in every restoration practice, which enables and ensures a safe path towards the final concept and implementation. Inputs that could prove useful are the history, the location, the climate, the structure and pathology of the monument as well as previous restoration treatments.

03.1 INTRODUCTION

As already mentioned, Bemboâ&#x20AC;&#x2122;s Tower has already undergone restoration and is in this state since December 2015. Visiting the site and having the chance to interview the archaeologist responsible for the project, Ms Ioanna Aggelopoulou, has been of great help in critical issues concerning the structure. She also provided me with the relevant archaeological and structural documentation, which was my main source of information [see Aggelopoulou I. et al, 2015]. Additionally, external literature has also been reviewed where this information was insufficient. Methoniâ&#x20AC;&#x2122;s castle, where the tower is located, has been a fortress since the 4th century BC and served as an important harbour since then also during the Byzantine times. The Venetians occupied the city in 1206, under Geoffrey de Villehardouin Empire and fortified it with the existing castle. It was developed as an important trade centre with great prosperity as it was the middle station between Venice and the Holy Lands, a stop for every traveler on their way to the East. After 300 years, in 1500, Methoni passed to the hands of the Turks. During the 16th and 17th centuries its decline was very obvious in all sectors but it only became complete around the 18th century having the population being reduced, the harbour becoming shallow while the most important trade being the one of slaves. In 1829 the French freed the town, which is since then part of the Modern Greek State. [www.kastra.eu] Today, the castle functions as an archaeological site, open to the public and hosting a great number of tourists every year.

03.2 HISTORICAL BACKGROUND

03 MONUMENT ASSESSMENT

1686-1715 2nd Venetian Occupation

1500-1686 1st Turkish Occupation

1206-1500 1st Venetian Occupation

1715-1828 2nd Turkish Occupation

Fig 03.3

late 17th century

1686 illustration by Vincenzo Maria Coronelli

Fig 03.2

Fig 03.4

before 1572 oldest color illustration made for Georg Braun & Franz Hogenberg

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000 81

Fig 03.5

June 15th & 16th 1483 illustration by Eberhard Reuwich

Fig 03.6

1828-1833 engraving by the Scientific Exhibition of Morea

Fig 03.7

2015 view of the east part of the fortress

Fig 03.8 Brief historic timeline of the Castle of Methoni

TRANSPARENT RESTORATION

Methoni’s castle is located at the southern edge of Peloponnese’s west coast and occupies the entire peninsula, since the ancient times. As already mentioned, in the past the castle was inhabited and assumed to be an important economical, commercial and transportation hub. The relative tower is actually a bastion, part of the southern fortress, and stands at the east of the southern gate [Porta di san Marco], which leads to Bourtzi [see Fig 03.10]. The erection time of the tower was recently estimated thanks to the coat of arms found at the site after excavation works. The features of the coats of arms [three roses and a shape] are attributed to six Venetian families [Bembo, Damian, Fradello, Priuli, Ragusio, Spineta]. However, according to paintings and illustrations [see Fig 03.8] there were two coats of arms placed at the south-east facade, which indicate a dual government of the castle. That dual government occured in the period 1308-1460, which places the tower chronologically at the 1st Venetian Occupation.

03.3 LOCATION & CLIMATE

Fig 03.9 Coat of arms found after excavation in the site

Fig 03.10 Bourtzi relatively to Bembo’s Tower as it was before the restoration [right]. Bourtzi is a two-floor octagonal tower with bastions built at an islet and connected to the main castle with a bridge and Porta di san Marco.

03 MONUMENT ASSESSMENT

Fig 03.11 Francesco Grimani’s plan of the castle. The tower and piazza grante d’ armi are highlighted in red.

According to Francesco Grimani’s archive of 1701, the detailed urban planning of the castle [see Fig 03.11] indicates a close relation of the tower with both the old port and a large square [piazza grante d’armi]. The construction of a building just on top of the main city’s port illustrates an emblematic role as well as a possible connection with social, economical, commercial and defensive activities during the 1st Venetian Occupation. 83

Fig 03.12 The Hellenic arc or Aegean arc is an arcuate tectonic feature of the eastern Mediterranean Sea related to the subduction of the African Plate beneath Sea Plate. It consists of an oceanic the Aegean trench, the Hellenic Trench, on its outer side; two arcs; and a marginal sea on its inner side.

Concerning the climatic conditions of the surrounding area, Messinia County, has a mild and temperate climate [apart from the mountains] and is assumed to be one of the places with the highest percentage of sunshine in Greece. The annual temperature fluctuates between 13°C and 19°C, while humidity is quite high due to the close proximity to the sea. Winds are also very common in the wider area of the castle and the coast as it faces directly the mediterranean sea [see Appendix 1]. It should, also, be outlined that the entire area of southern-west Peloponnese shows a high seismic activity since antiquity, as it is located at the borders of the Hellenic Arc [see Fig 03.12]. That is also the main source of earthquakes in Greece [see Fig 03.13].

Fig 03.13 Map illustrating the most destroying earthquakes in Messinia County from antiquity until today [see Appendix 1]

TRANSPARENT RESTORATION

The architecture of the tower is simple but includes features of high aesthetics and well-constructed detailing. The bastion is of rectangular shape with its one side directly related to the sea while being part of the fortress wall. The only access was through a path along the outer walls of the castle. The NW faรงade faces the acropolis and has two large openings shaped as pointed arches [see Fig 03.15]. There were originally two levels, which were connected though an L-shape staircase [see Fig 03.16], however the upper floor is currently collapsed. The upper part of the tower was shaped as a battlement. The ground floor is divided in two chambers connected through a pointed arch opening and covered by two barrel-shaped vaults.

Given the fact that it is a masonry structure, which shows brittle behaviour, large cross-sections are a common design principle; the wall thickness fluctuates from 1.40m to 2.25m. Some of the special architectural features that reveal the aesthetics of the structure are the corner stones, the arches, which in some cases are constructed as interlocking pieces [see Fig 03.17], as well as the mouldings at the northwest faรงade at the base of the arches. Excavation works prove the presence of stonepaved floor, which maintains a patchy limestone mortar covering.

03.4 STRUCTURE

Fig 03.14 Plan of the tower

Fig 03.15 NW faรงade

Fig 03.16 Remainings of the staircase adjacent to the outer wall

Fig 03.17 The pointed arches of the openings. The interlocking system of the stones indicates a later construction phase as no mortar is introduced to bond the pieces together.

03 MONUMENT ASSESSMENT

03.5 MATERIALS

The tower in its largest part is constructed with rubble masonry; sandstone and limestone of local origin are the primary building materials. The core consists of [partially] rough stones bonded together with lots of mortar, while the outer surface consists of carved stones placed irregularly or in rows, having smaller ones vertically filling the joints. The typical stone dimensions vary from 5 cm to 50 cm. The corner stones are made of limestone and have dimensions of 50 x 30 x 20 cm. Similarly, the outer and inner arches of the openings, the moldings and the staircase are also made from limestone. The properties of these material are shown in Table 17, chapter 05.2.

Fig 03.18 Masonry corner detail

03.6 PATHOLOGY

Fig 03.19 SE faĂ§ade

It is evident that the abandonment of the monument for so many years and the exposure to the elements have greatly affected its current state and pathology. From a materials point of view, the monument suffers from material loss, precipitation, material detachment, mortar weathering, cavities and black crust. The main damages that affect its mechanical behaviour are cavities of the inner masonry body at the lower part of the SE wall [see Fig 03.19], the collapsed roof of the northern chamber and the reduction of the cross-section at several parts of the masonry, which favours buckling. Masonry is a multistage and â&#x20AC;&#x153;indisciplineâ&#x20AC;? structure arising from the diversity of the raw materials [stones and mortars]. Therefore, the exact specification of its mechanical properties is not feasible because of the inhomogeneity of the materials.

TRANSPARENT RESTORATION

Generally, the damages are related to natural, environmental, chemical, biological and man-made factors in combination with neglect for long periods of time. The reasons of collapse & material deterioration are the following:

The close proximity of the monument to the sea is assumed to be the principal cause of deterioration. The momentum of the waves, especially during winter, damages the structure constantly. Sea salt penetrates the stones and accelerates their weathering. The presence of salt in combination with humidity and low temperatures result in the crystallization of stones and mortars. Because of the porosity of the materials [mortar, sandstone & limestone], salt enters into the cavities, crystallizes, because of the temperature decrease, and increases its volume; consequently, hydraulic stresses are developed from the inside resulting in cracking. Thus, the cross-section of the stone is decreased and similarly its mechanical resistance. Moreover, the constant exposure to wind and sandblasting weathers the surface of the masonry.

As earthquakes are a very common natural phenomenon in the wider area, they have greatly affected the monument for centuries. Especially after a large part of collapsed areas the structure have become more vulnerable to seismic activities. The good reaction of a building to this kind of lateral loads is highly depended on the existence of horizontal connective elements. The collapsed roof and SE wall result in the walls acting as cantilevers, moving independently.

The critical location of the tower and the fact that it served as a bastion put it on the front line of every act of war. The empire alternation between Venetians and Turks has probably damaged the tower; however, the collapse of the entire upper level is attributed to bombing during WWII.

Fig 03.20 The unobstructed exposure of the monument to the sea

Fig 03.21 The tower after the final restoration in December 2015

Fig 03.22 Detail of the tower after the final restoration

Fig 03.23 Distinction of the materials

03 MONUMENT ASSESSMENT

03.7 CONSOLIDATION TREATMENTS

Concerning the previous restoration treatments, photograph archives reveal consolidation works of the northern part of the walls to take place during the period 1950-1960. More recently, in 2007, there was a more consistent restoration of the monument with a partial reconstruction of the masonry core and missing parts mainly at the southern part of the structure. In 2011, due to the danger of total collapse, the tower became part of a restoration project funded by the EU for the period 2011-2015 and today the tower is no longer under threat. The restoration approach suggested the reconstruction of the missing parts using the same masonry technique, so that the tower could regain its structural integrity [see Fig 03.24]. The coexistence of the old and new materials is evident in most areas creating no conjecture [see Fig 03.23].

Fig 03.24 View of the restored tower from the adjacent breakwater

TRANSPARENT RESTORATION

Given the historical background, it is evident that the monument has been in the front line of continuous alterations regarding the economical, social and political activities. Thus, its role is assumed to be not only symbolic, as a building of great importance for each era, but also an integral part of the landscape of the castle. Its architecture may not be unique, in the wider area, but is a result of a solid structure, with high aesthetics and detailing in relation to the time of erection. The fact that the castle of Methoni has been the “apple of discord” between various conquerors over the years attributes an exta historical value to the monument.

03.8 SIGNIFICANCE ASSESSMENT

Two of the most important parameters that influence the restoration approach and further treatment are the age and rarity of the monument [see chapter 01.5]. In this case, the building is assumed not very old but also not very recent, so it is an in-between state. Moreover, this type of structure is not rare especially at the wider area of Messinia County, as during the Venetian Occupation a variety of towers and castle were built there, with similar architectural qualities. A great number of them have been rehabilitated and are now being used, for example, as touristic accommodations. In our case, the specific location of the monument makes it part of the landscape of the east side of the castle and a place frequently visited by tourists. The evaluation of the significant values embed-

AESTHETIC

HISTORIC

SCIENTIFIC

SOCIAL

AGE & RARITY

CULTURAL

RESEARCH & KNOWLEDGE

ECONOMIC

ARCHITECTURAL

SYMBOLIC

EDUCATIONAL

POLITICAL

ARTISTIC

ASSOCIATIVE

TECHNICAL

RELIGIOUS

LANDSCAPE

PUBLIC

TOWNSCAPE

EMOTIONAL

Table 08 . Assessment of the possible values that can attribute significance to a monument

03 MONUMENT ASSESSMENT

ERECTION YEAR

REALISTIC

ABSTRACT

ded in the monument reveals that an innovative transparent restoration could be indeed realistic [see Fig 03.25]. A more abstract restoration using structural glass elements to consolidate the tower could result in a pioneering treatment. This new attraction would be an integral part of the cultural, social, touristic and development activities of the wider area but also an important source and demonstration of the latest restoration technologies.

RARITY Fig 03.25 Diagram that relates age and rarity to the restoration approach

Fig 04.1 3D printing of interlocking units in scale 1:10 as a design tool for the investigation of the interlocking units

04.

DESIGN RESEARCH

TRANSPARENT RESTORATION

In the previous chapter the main reasons of damage and collapse are analyzed in order to understand the pathology of the monuments and proceed with adequate treatments in the restoration plan. On the one hand, the materials show significant deterioration due to age, negligence but most importantly the proximity to the sea, which allows salt and humidity to wear down the masonry. On the other hand, man-made factors, such as bombings, have resulted in several parts of the building to collapse. Consequently, not only the mechanical properties of the materials have been decreased, but also the overall structural integrity of the structure is under dispute. The hazards of total collapse are constantly amplified due to the frequent seismic activity in the surrounding area. Without vital connective structural elements [walls and roof], the monument cannot behave as a monolithic structure as it should, and is less resilient to earthquakes.

04.1 RESTORATION DEGREE

The concept of transparent restoration through the use of structural glass components can address to specific degrees of restoration [see Chapter 01.9]. Glass can be used as shelter, reinforcement by filling the form or in the context of adaptive re-use. It is evident that in our case an integral part of the restoration scheme should encompass the improvement and treatment of the materials [crystallization occurred in the stones and mortar because of the penetration of sea salt]. However this investigation will not be included in the current research; what we will focus on in the following chapters is how glass can play the role of consolidating medium between the remaining parts of the monument and, in such way, reinforce the structure by filling the form. The SE faรงade and the northern vault are the two most severely damaged parts of the monument, where glass can be used to both fill the form and enhance the structural integrity of the entire building. The SE faรงade [see Fig 04.3], adjacent to the sea seems to be the most interesting case, as more than half of it is missing, which is the most critical aspect in terms of structural performance. This fact raises great challenges and potentials, at the same time, for the concept of transparent restoration.

Fig 04.2 Conceptual impressions of glass as the main restoration material filling the missing parts of the roof and the SE faรงade

04 DESIGN RESEARCH

04.2 DESIGN CRITERIA

Previous research on multiple glass configurations [see Chapter 02.6] and possible ways of application as a missing part in a monument [see Chapter 02.7] are very useful for the next step of the thesis: to decide what will be the primary glass structure. In Table 07 [see Chapter 02.7], it appears that float and cast glass are the most promising products that could be applied at a wall or a masonry showing an abstract or realistic restoration approach respectively. According to the conservation guidelines, minimum visual impact and compatibility with the existing structure are two indisputable factors that one should consider from the first steps of the design process. Furthermore, the principles, in terms of aesthetics and architecture, are the ones to generate the main concept and the general feeling that one wishes to trigger through the design. These factors â&#x20AC;&#x201C; minimum visual impact, compatibility and concept â&#x20AC;&#x201C; are the criteria taken into account during this first phase of preliminary design, and are analyzed as followed:

Fig 04.3 SE facade as the main area of focus for the transparent restoration approach

The concept can be identified as the outcome of the personal desire of the architect in combination with the respect to the values embedded in the monument. The assessment of the case study has revealed that there is a strong relationship between the building and its setting, as well as a great symbolic, historical and social value being in the front line of important events during the last six centuries [see Chapter 03.8]. Nevertheless, one of the most critical relationships is that of the monument with the natural environment. More specifically, the water element has been of great influence for the materials and, by extension, the entire structure as it appears today; with the largest impact on the aforementioned SE faĂ§ade. This fact in combination with the rough texture of the masonry discloses a sense of gradual disintegration, which is a quality I would like to incorporate in the final design. It is also chosen to maintain the rectangular shape of the monument in order not to cause any conjecture.

TRANSPARENT RESTORATION

Compatibility of the new structure with the existing one deals with multiple aspects; it can refer to the construction techniques [aesthetics, form, design] but also the structure itself [material properties, failure behavior]. As glass, as material, differs from stone in many levels, the latter aspect of compatibility is not relevant at this point and will be discussed in the following chapters. The degree of compatibility in terms of the construction technique, through the masonry pattern, the texture, the rhythm and the modulus, can determine the appearance and the configuration of the glass components, and consequently the aesthetics of the new design.

Minimum visual impact can be translated as maximum transparency in terms of glass quality. The setting and the view to the sea are an integral part of the monument in its current state and are worthy of preservation. Thus, apart from the transparency of the material, the different configurations, shapes and surface treatments can result in different degrees of transparency. The idea is to achieve an optical result that will not block the visual connection of the visitor to its surroundings but, at the same time, will resemble to the existing structure.

The concepts regarding the glass façade are based on different configurations of float and cast glass. The preliminary design process examines first the concept of float glass fin-plane configuration, which is mostly applied in buildings today and has the advantage of simplicity, transparency and verified performance. However, in an attempt to create a more “texturized” façade two cases of vertical and horizontal float glass stacking are examined. These configurations provide a larger degree of freedom; the former creates a gradual transition from few to multiple stacked layers when reaching the edges of the existing building, while the latter shows a high degree of compatibility with the original structure in terms of construction technique. In order to enhance the optical quality of this last configuration instead of float glass [which is transparent when looking at the large surface, but translucent when looking at the side] we use cast glass units. The cast glass masonry option seems the more promising according to the design criteria [transparency, compatibility, concept] and is the one chosen to further elaborate on. Table 09 shows an overview and evaluation of each proposal according to the design criteria.

04.3 CONCEPT GENERATION & EVALUATION

04 DESIGN RESEARCH

GLASS FINS

CONCEPT

DETAIL

EVALUATION

transparency

compatibility

VERTICAL STACKING

concept

transparency

compatibility

concept

CAST GLASS MASONRY

HORIZONTAL STACKING

Table 09 . Preliminary concept overview and evaluation

transparency

compatibility

concept

transparency

compatibility

concept

TRANSPARENT RESTORATION

The main focus of the current thesis in the following phase is the detailed design of the cast glass units, the connection between them as well as the connection between glass and the existing masonry. Other aspects that will also be investigated and analyzed are the manufacture and assembly of the components. The connections of glass and the existing structure are especially challenging, as this is the most crucial part of the restoration concept, which aims to enhance the structural integrity of the monument.

04.4 FOCUS AREAS

In order to create a more texturized effect on the new glass faĂ§ade, the first approach was to address to reference projects that deal with parametric masonry systems. Grammazio and Kohler provide a very wide range of examples as for the last 15 years they have been investigating additive robotic fabrication. Projects such as the Winery Gantenbein [see Fig 04.5] and the Resolution Wall [see Fig 04.6] can give an idea on how this system works. The patterns and possibilities of such a concept are numerous and rely on parametric digital design tools in combination with self-assembly construction technology.

04.5 PRELIMINARY DESIGN

Fig 04.4 Flight Assembled Architecture by Gramazio & Kohler and Raffaello dâ&#x20AC;&#x2122;Andrea . 2012

04 DESIGN RESEARCH

Fig 04.5 Winery Gantenbein . Gramazio & Kohler + Bearth & Deplazes Architekten . Switzerland . 2006

Based on this concept, the initial idea for the cast glass masonry is to design it parametrically so as to adjust and “embrace” the irregularities of the remaining masonry. Variations in the size and length of the bricks, as well as translation, rotation and spacing of the units were incorporated in this preliminary design; the basic principles are shown in Fig 04.7. The most important aspect of this design is maybe its flexibility to meet the boundary conditions of the irregular surface of the existing masonry. With the use of grasshopper plug-in for Rhinoceros software, a set of experimental algorithms is developed in order to address to most of these principles. However, the complexity that such a system sets, as well as the construction and assembly constraints result in the critical review of the restoration approach we are applying in our monument. As a next step, it is decided to extend our research more towards the glass, its properties, manufacture, construction and assembly in order to have a clear view of the possibilities in terms of feasibility and not only conceptual design.

Fig 04.6 Resolution Wall . Gramazio & Kohler Research . ETH . 2007

97 E

Fig 04.7 Principles of parametric masonry. Distinct corner stones according to original structure [A], variation in scale to adjust to the uneven surface of the existing masony [B], rotation of units when reaching the existing masonry [C], recess of units to create a texturized effect [D], spacing of units to reduce the overall weight [E].

04.6 EXTENDED RESEARCH

After having concluded to a cast glass masonry wall in order to replace the missing parts of the SE façade, a further investigation of reference projects, which introduce cast glass components, is critical at this point. As cast glass technology for structural applications is relatively new, there are few realized examples so far. For each case, according to the structural requirements, the location and the concept, different design strategies have taken place. Table 10 gives a brief overview of each case, highlighting interesting information that could prove useful in my case.

TRANSPARENT RESTORATION

ATOCHA MEMORIAL

PROJECT

STRUCTURE

Fig 04.9 Plan

The shape of the outer shell is elliptical and it is the geometry itself that provides robustness. Additionally, the roof creates a rigid connection for the upper free edge and prevents the ovalisation of the section. In order to avoid high shear stresses at the lowest glued joints, the glass blocks were placed on a total of 200 elastomer pads. [Knut et al., 2007]

Fig 04.8 Atocha Memorial . Estudio FAM . Madrid . 2007

OPTICAL HOUSE

Fig 04.13 Structural scheme

Fig 04.12 Optical House . Hiroshi Nakamura & NAP . Hiroshima . 2013 4 buttresses 5.5 m tall are introduced in the design to reinforce the flat glass wall against buckling and counteract for the lateral wind loads. The glass blocks of the buttresses interlock with these of the faรงade, thus forming a continuous relief faรงade envelope. [Oikonomopoulou et al., 2014]

CRYSTAL HOUSE

The necessary stability is provided though mechanical supports structured as threaded metal dowels hanging from a pre-tensioned beam above the 8.6 m2 faรงade, to guide the glass bricks into perfectly aligned rows. Stainless steel flat bars help the faรงade resist the lateral wind forces. [www.designboom.com]

Fig 04.16 Crystal House . MVRDV and Gietermans & Van Dijk . Amsterdam . 2016

Fig 04.17 Faรงade principles

Table 10 . Overview of the 3 case studies that introduce a cast glass masonry system

04 DESIGN RESEARCH

GLASS BLOCK 15.600 blocks [200 x 300 x 70 mm] of 8.4 kg, were produced in total. The concave and convex opposed sides facilitate the easy adjustment of the blocks to the cylindrical shape of the structure. Due to strict tolerance requirements [±1 mm] the blocks were manufacture in special molds under pressure to ensure maximum uniformity. Moreover, they were cooled down in controlled conditions for more than 20 hours in order to avoid any internal stresses. [Christoph & Knut, 2008)

CONNECTIONS A UV-curing acrylic adhesive was used to glue together the glass blocks. The average thickness of the adhesive layer was 2.5 mm, which permits a good structural performance, while at the same time absorbs the manufacture tolerances. [Knut et al., 2007]

IMPORTANT NOTES

The climate of Madrid and the high temperature differences that often occur [e.g. rain on a sun-heated glass block] resulted in the use of borosilicate glass. Its low thermal expansion coefficient of 4.3x10-6 K-1 results in relatively lower thermal stresses compared to conventional soda-lime glass. [Knut et al., 2007]

Fig 04.10 Cast glass block

Fig 04.11 Bonding of the cast glass masonry

Because of the adhesive layer the structure is permanently bonded and does not facilitate reversibility and disassembly.

6000 borosilicate glass bricks [50 x 253 x 50 mm] with holes were constructed in total. [www.designboom.com]

Embedded connections were used to connect the glass blocks to the support frame. The flat bar is seated within the 50mm-thick glass block to render it invisible, and thus a uniform 6mm sealing joint between the glass blocks was achieved. [www.dezeen. com]

The mechanical supports and connections have the great advantage of reversibility and fast construction due to the dry assembly process.

However, the vertical and horizontal supports create a visual obstacle to the glass facade.

Fig 04.14 Granite mold

Fig 04.15 Embedded T-shape connection

Precision molds were used to produce the soda-lime glass blocks of 3 different dimensions [210 x 210 x 65 mm, 105 x 210 x 65 mm, 157.5 x 210 x 65 mm]. The strict tolerance requirements [±0.25 mm] demanded the post processing of the units in order to achieve uniformity in dimensions, rectangularity and flatness. [Oikonomopoulou et al., 2014]

A one-component UV-curing acrylic adhesive layer of 0.3 mm was used to bond the glass structure and create a monolithic system. [Oikonomopoulou et al, 2015] All blocks meet the ±0.25mm tolerance, resulting in an even spread and thus homogeneous bonding with an optimum visual result. [Oikonomopoulou et al., 2014]

Fig 04.18 Manufacture of glass blocks by Poesia

Fig 04.19 PURE mold for the precise application of the adhesive layer

High levels of transparency

In order for the adhesive to be efficient, it requires flat surfaces and strict tolerances. An inconsistent spread of the adhesive can result in visible gaps and bubbles. [Oikonomopoulou et al., 2014] Thus, a very complex fabrication and construction process is necessary, resulting in the post-processing of the glass blocks as well as a meticulous bonding process. Also, the permanently bonded façade does not allow for reversibility.

TRANSPARENT RESTORATION

The design limitations that we need to take into consideration deal, on the one hand, with the manufacture and construction of the cast glass structure and, on the other hand, with the principles of restoration and general concept.

04.7 DESIGN LIMITATIONS

The aforementioned case studies provided an important input of basic knowledge concerning the cast glass technology. Thus, three of the most important factors to take into account regarding the fabrication and assembly are the size, the annealing process and the manufacture tolerances. To begin with, the size of the units is of great importance, as the blocks need to be lightweight in order to be easily handled during the construction. It is assumed that a maximum of 10 kg should be the limit when designing such cast glass units in order to ensure a fast and safe assembly process.

100

The annealing process is a vital procedure that helps the glass component being relieved from any internal stresses that can affect its mechanical properties. Rapid cooling of the molten glass is necessary in order to avoid crystallization; however, this results in the generation of internal stresses. The relaxation of these constraints is called annealing and should be realized very carefully in a controlled environment. Annealing relates also to glass viscosity and can be obtained in a relatively narrow range of temperatures [see Fig 04.20]. Between the annealing and strain point, glass should be cooled down gradually in order to remove the already formed internal stresses, due to temperature gradients [see Fig 04.21]. [Hubert, 2015] The permanent stresses are affected by the cooling rate, the glass properties and the shape of the unit and can be calculated by the following formula:

Fig 04.20 Temperature VS viscosity rate for different types of glass

Fig 04.21 Different steps during the annealing process. Step 3 is the most important process as it ensures that no permanent stresses will remain in the glass block after the strain point.

= M * h * d2 * b [Pa]* Generally the annealing is a long process, which can be time-consuming, increase the overall manufacture costs and consequently jeopardize the marketability of the product. [Oikonomopoulou, 2015]

* = M * h * d2 * b [Pa] M = (E * aex)/(1-μ) * ( * cp)/ h = cooling rate unit d = characteristic dimension characteristics b = shape factor = thermal conductivity

[annealing = heating = energy consumption = costs]

glass properties

[K/s] [m] [-] [W/(m*K)]

= density [kg/m3] cp = specific heat [J/(kg*K)] aex = thermal expansion coefficient [K-1] E = Young’s modulus [Pa] μ = Poisson’s ratio [-]

04 DESIGN RESEARCH

Fig 04.22 Shrinkage at the right part of glass due to temperature difference when cooling down

Glass type

aex 0-300 °C [K-1]

Tg [°C]

Soda-lime-silica Borosilicate E-glass Vycor [97 SiO2, 3 B2O3] Vitreous Silica

92 x 10-7 33 x 10-7 60 x 10-7 8 x 10-7 5 x 10-7

520-580 565 670 910 1100

Table 11 . Thermal expansion coefficient values for various types of glass [Hubert, 2015]

Tolerances seem to play an important role especially in the case of an adhesively bonded façade [e.g. Atocha Memorial and Crystal House]. As it cools down, glass shrinks, which can result in different dimensions between the units and uneven surfaces [see Fig 04.22]. Shrinkage is influenced by the glass properties and more importantly by the thermal expansion coefficient [the higher the value, the more the shape is affected by temperature difference]. When the design requires strict tolerances, as in the case of Crystal House [±0.25], the units need to be further treated in order to ensure uniformity among the glass units [see Fig 04.23]. Post-processes can increase the overall cost of the manufacture process. The last but most important limitation that derives from the conservation guidelines is reversibility. Optical House is the only case study that introduces the use of mechanical dry connections to bond the glass blocks instead of adhesive connections. However, mechanical supports decrease the transparency of the glass wall, thus for our design an innovative dry assembly system should be investigated in order to achieve reversibility, transparency and structural integrity at the same time.

Fig 04.23 Prototypes constructed during for Crystal House. The first mock-up [left] was made with tolerances of ±0.5 mm and resulted in open joints and a significant offset in both height and width. The second mock-up [middle] resulted in bubbles, gaps and low optical quality due to unflatness of the bonding surfaces. The final mock-up [right] with tolerances of ±0.25 mm resulted in a uniform distribution of the adhesive layer and an optimum visual result. [Oikonomopoulou, 2014]

101

TRANSPARENT RESTORATION

This chapter provides an insight in critical issues that affect the design process and determine the main strategies incorporated in the suggested restoration plan. Various constraints are introduced in order to cover different aspects that deal either with glass as a material, the principles of restoration or the concept. A cast glass masonry is proposed as it combines transparency, compatibility with the original structure in terms of aesthetics, form and construction techniques, as well as the concept for a texturized faรงade that resembles the disintegration of the monument.

102

The manufacture limitations of cast glass show that the best option is to use borosilicate glass instead of the widely used soda-lime glass. The reason is that the former has a much lower thermal expansion coefficient [approximately 1/3 of the latter], which not only facilitates a faster annealing process, but also results in less shrinkage and consequently minimizes the post processing of glass units. Moreover, the high temperature differences that can occur in the glass surface during the summer [heat coming from the sun alternated with the cold coming from the waves pounding the faรงade] suggest a glass with low thermal expansion coefficient in order to avoid thermal shock. On the other hand, the high working temperature that borosilicate glass demands and the higher cost compared to soda-lime glass can make it a less favorable option; however, the overall benefits of a fast fabrication process counteract these disadvantages, decreasing the construction and labor costs. The limitation for a reversible structure that addresses to the restoration guidelines is the most important parameter that forms the main design strategy. So far, the glass masonry concepts have introduced either adhesively bonded connections or reversible solutions, which however sacrifice the transparency of the faรงade using mechanical connections. These findings lead the way to dry connections that can ensure safe disassembly without harming the monument. The brittleness of glass suggests that the slightest flaw on its surface can cause abrupt failure. This is the main reason why glass units cannot be in direct contact to each other and an interlayer should be used instead,

04.8 DESIGN STRATEGIES

04 DESIGN RESEARCH

such as a foil or sheet. Also, in order to achieve a minimum visual obstruction this interlayer should be transparent. The absence of any bonding material or substructure may jeopardize the structural integrity of the glass masonry. The design strategy chosen to deal with the structural aspects is an interlocking system, where the geometry of the glass units in combination with the overall weight of glass can provide the necessary stability.

CRITICAL DESIGN ASPECTS GLASS CONFIGURATION

HORIZONTAL STACKING

CONCEPT

VERTICAL STACKING

COMPATIBILITY

TRANSPARENCY

GLASS FINS

CAST GLASS

CAST GLASS MASONRY

BOROSILICATE GLASS

DRY CONNECTIONS + INTERLAYER

INTERLOCKING SYSTEM

DESIGN & RESTORATION CONSTRAINTS

CLIMATE

WEIGHT

POST PROCESSING

SODA-LIME

ANNEALING TIME

GLASS TYPE

BOROSILICATE

CONNECTIONS MECHANICAL

REVERSIBILITY

MANUFACTURE & CLIMATE CONSTRAINTS

TRANSPARENT FOIL

ADHESIVE

SYSTEM

STRUCTURAL INTEGRITY

RESTORATION CONSTRAINTS

MOTION RESTRAINTS DUE TO GEOMETRY

STRUCTURAL CONSTRAINTS Fig 04.24 Overview of the design process, the constraints and the final strategies

103

TRANSPARENT RESTORATION

SYSTEM PRINCIPLES In order to address to the restoration guidelines that suggest a reversible design, a dry masonry wall is suggested as the main structural design strategy. In general, this type of construction technique makes no use of mortar or any binding material between the blocks, which makes the disassembly also possible, as the units are not permanently bonded together. The structural integrity of the masonry is ensured by the geometry, which introduces a mechanical interlocking mechanism between the units. [RogĂŠrio Pave et al., 2010]

104

This concept of interlocking masonry can be traced back to the ancient Inca structures [see Fig 04.25], which have allowed for stable, self-aligning structures. The parameter of fragmentation in such structures, in comparison to monolithic structures, provides another important advantage: their ability to dissipate vibration energy and as a result the high seismic resistant [self-adjusting property]. That probably underpins the longevity of such structures even in seismic zones. Enhanced stability derives from the ability of fragments to undergo limited displacements or rotations [within the limitations of kinematic constraints imposed by interlocking]. Moreover, while mortars or other mechanical connectors can act as stress concentrators, risking the overall strength of the structure, interlocking geometries can provide flexibility and tolerance to local failures. [Y. Estrin et al., 2011] Mortarless construction has gained popularity during the last years as it provides fast construction, reduced labor and consequently reduced costs.

LOCKING METHODS The geometry of the interlocking unit plays, maybe, the most critical role at a successful interlocking system; it sets the necessary constraints so that each fragment stays in place and does not endanger the stability of the structure. There are 4 different locking methods that can be identified in such systems: tongue and groove, protrusions and depressions, topological non-planar contact [Kintingu, 2009] and recursive interlocking. [Peng Song et al., 2012]

04.9 INTERLOCKING SYSTEM

Fig 04.25 Inca ashlar masonry

Fig 04.26 Unidirectional interlocking units

Fig 04.27 Bamba interlocking system

04 DESIGN RESEARCH

The first two types are the most common and widely used in construction, especially where there is a large demand of fast and affordable housing solutions, such as Tanzania and the rest developing countries in Africa. Multiple designs have been developed so far to address to such structures [see Fig 04.27]. [Kintingu 2009] Fig 04.28 Tetrahedron topological interlocking assembly

Fig 04.29 Osteomorphic interlocking blocks

Topological interlocking, on the other hand, introduces assemblies, where no internal block can be removed while being held in position by kinematic constraints from the neighbouring blocks. In that case, the overall structural integrity depends on the constraining force provided by a peripheral constraint. This can be achieved either by self or dead weight, or by constraining frames, pre-tensioned tendons or cables. The shapes of blocks that allow for such interlock are convex polyhedral, such as all five platonic solids [see Fig 04.28], and their truncated derivatives, as well as special engineered shapes, such as osteomorphic blocks [see Fig 04.29]. [A. V. Dyskin et al., 2012]

105

Fig 04.30 In a recursive interlocking puzzle after the key element P is removed then the following units can also be removed in the correct order: P > Q > R

Fig 04.31 Schematic illustration of the key block concept. The two key blocks can move freely in the direction indicated by the arrows. As long as the key blocks are held in place, all other blocks are locked.

The last joining method has derived from interlocking puzzles, which introduce only one specific sequence of assembling or disassembling [see Fig 04.30]. This system is based on the key block theory [see Fig 04.31], which suggests that as long as the key block stays in place, all other blocks are locked. [Arcady V. Dyskin et al., 2001] Such models can be produced using computational methods and recursive algorithms. [Peng Song et al., 2012] The subdivision of the model can be controlled resulting from larger to smaller units. The complexity of such system, though, is very high, not only because it eliminates multiple joining options but also because each unit is different. Thus, the higher the fragmentation degree, the higher the complexity of the system.

TRANSPARENT RESTORATION

DESIGN CONSIDERATIONS Another crucial issue, concerning the design of the units, is to what degree their movement is constrained due to the neighbouring units; the more the constraints, the better the connection and general integrity of the structure. The structural element is what determines what kind of constraints is necessary [e.g. wall, column, arch, pavement]. In the current research, the case we are studying is a wall, free from both edges, so the units should be restricted in both x and y axes [x as the axis parallel and y as the axis vertical to the structural element], assuming that self-weight of the structure is a constraint for the z axis. The aforementioned joining methods address to different degrees of interlocking: tongue and groove system restraints in x and y axes; protrusions and depressions system interlocks along the y axis; topological interlocking has constraints in all axes as long as the boundary constraints are held in place; recursive interlocking also interlocks in all x, y and z axes. The considerations we should take into account when designing such a system deal, basically, with the shape and the arrangement of the units and are explained as follows. 106

01 . Physical characteristics As described in chapter 04.7, glass has limitations concerning the manufacturing process, which suggest a lightweight unit in order to be easily handled. Moreover it is preferable that the unit has a homogeneous mass distribution so that the shrinkage during cooling is also homogeneous in order to avoid internal stresses due to temperature differences. Thus, when using glass we should carefully design the locking features [protrusions/ depressions or tongues/grooves] in order not to create areas susceptible to stress concentration or cracking. Very slender protrusions can result in weak locking constraints and risk the integrity of the structure. 02 . Self-alignment Self-alignment suggests a unique way of the units to interlock in each other. Distinct orientation is important in order not to cause confusion during the assembly and ensure a fast construction. [Kintingu, 2009] The number of special units is equally important, as the simplicity of the system contributes greatly in aspects such as the manu-

Fig 04.32 Constraints due to neighbouring blocks in a tetrahedron configuration

04 DESIGN RESEARCH

facture, the assembly and the overall costs of the construction. 03 . Pattern The way the blocks are laid on top of each other determines the structural integrity of the wall [see Fig 04.33]. Overlapping blocks perform better under loading, as the loads are distributed in a uniform way to the lower rows. Such system suggests only one type of unit for the main masonry, which is beneficial, as well as, a symmetric design of the locking joints.

Fig 04.33 Failure modes in different masonry configurations

107

Fig 04.34 3D printing of diamond units in sc. 1:10

Fig 04.35 3D printed interlocking units sc. 1:1

UNIT INVESTIGATION Different interlocking systems have been investigated in an attempt to find an efficient one that suits best in our design. The systems are evaluated according to transparency, stability and complexity in terms of manufacture and construction. It appears that the number of basic units affects greatly the assembly mode and complexity, while at the same time increases significantly the number of special components needed. As one of the big advantages of an interlocking system is the fast construction, it is important that the units are kept simple and do not complicate the assembly mode. Another vital parameter is the overall stability of the masonry, which is affected by the degree of interlock and the physical constraints due to the geometry of the units [constraints in x,y,z axes and rotation around z axis are taken into account]. The investigation of the units has been achieved first by digital design and later with the fabrication of 3d-printed and laser-cut models in scale 1:10, 1:5 and 1:4.

TRANSPARENT RESTORATION

LOCKING PRINCIPLE

CHESSBOARD

PROTRUSIONS & DEPRESSIONS

TETRIS

TONGUE & GROOVE

[-]

DIAMOND

TONGUE & GROOVE

PROTRUSIONS & DEPRESSIONS

ZIG-ZAG

LEGO 1

ASSEMBLY MODE

LEGO 2

BASIC UNIT[S]

PROTRUSIONS & DEPRESSIONS

108

Table 12 . Overview of the glass units examined for the masonry wall

04 DESIGN RESEARCH

MOTION CONSTRAINTS

ASSEMBLY EASE*

TRANSPARENCY*

MANUFACTURE EASE*

109

› *small visual impact . easy assembly/manufacture

› big visual impact . complex assembly/manufacture

TRANSPARENT RESTORATION

LEGO 2 is the system chosen to implement in the design of the glass masonry [see Table 12, chapter 04.9]. On the one hand, it incorporates a simple interlocking mechanism, which results in just one unit for the main structure, decreasing the degree of complexity regarding the assembly. On the other hand, it provides satisfying optical results. The mechanism of the well-known LEGOÂŽ bricks is adjusted and applied to the design of the units in order to meet the manufacture requirements.

110

Fig 04.36 LEGO chandelier by Tobias Tostesen . Milan Design Week 2013

04 DESIGN RESEARCH

04.10 DRY CONNECTIONS

The principle of dry connections that derived from the design limitations and responds to the aspect of reversibility is based on the use of an intermediate foil between the structural members. Thus, the new structure has the advantage of easy disassembly. The research focuses on two parts of the design that need dry connections: between the cast glass units and between the glass and the existing masonry. GLASS-TO-GLASS Glass is a brittle material, so any flaws in the surface can result in peak stresses and failure [see chapter 02.2]. The main purpose of such intermediary layer is to stabilize the structure by carrying the variations in thickness and flatness of the glass units, while transferring the forces between the elements in a homogeneous and uniform way; the glass bricks are loaded in both compression and shear. The leading criterion in our choiceof the appropriate interlayer is the degree of transparency. The material families that meet this criterion are glasses, plastics and some technical ceramics [according to CES EduPack 2015]. It appears that plastics are the most prominent for further investigation in our research. The degree of transparency of a plastic is dependent on its molecular structure and can be categorized according to Table 13 [Bos et al, 2007]. The main properties we need to take into account are explained as follows according to Heugten [Heugten, 2013]. Table 14 shows an overview of the main properties of plastics that could be used as interalyers. The selection has been made based on transparency [transparent, optical quality], Youngâ&#x20AC;&#x2122;s modulus [min of 2 GPa], glass temand UV radiation [acceptable,excellent] and possible forming methods [thermoforming, injection molding]. PET,PETG,PMMA and PVC seem possible for application as an interlayer, but need further investigation at the next step.

DEGREE OF TRANSPARENCY

VISIBLE LIGHT TRANSMISSION [ ]

DESCRIPTION

Opaque Translucent Transparent Optical quality

Material does not transmit any visible light Material transmits a little light, in a diffuse way Material transmits enough light to see through it Material transmits light almost perfectly. Images transmitted through it are clear and not distorted.

< 70% , < 85% ,

Table 13 . Degrees of transparency [Bos et al, 2007]

111

TRANSPARENT RESTORATION

COMPRESSIVE STRENGTH Compression is also introduced in the connections, so according to the maximum compressive stress [provided by the proper structural calculations] this value should be taken into account.

TRANSPARENCY For the sake of transparency the interlayer should not pose any visual intrusions. The level of transparency of the glass block is actually what determines the level of transparency of the interlayer [see Table 13].

POISSON’S RATIO The poisson’s ratio is the ratio between the transverse strain and the axial strain. When a load is applied on a material it is axially compressed and expands in the direction perpendicular to the load. The higher the poisson’s ration, the larger the expansion is. When the material expands, tension forces are introduced in its surface, which are unwanted as glass is not resistant in tensile stresses.

SHEAR MODULUS Shear forces are introduced by lateral forces [wind, earthquakes]; the higher the shear modulus is, the higher the resistance of a material against shear. According to the maximum shear stress that occurs in the connections [provided by the proper structural calculations], this value should fullfill the required values.

HARDNESS The harder a material is the more its resistance to plastic deformation. This property is important in a similar way as Young’s Modulus, but in this case refers to the point where plastic deformation begins and depends on the ultimate strength of the material.

112

PROPERTY

PA [AMORPHOUS,

PEI [UNFILLED]

PPSU [UNFILLED]

LOW TG]

DENSITY

1030-1050

1260-1280

1290-1300

PRICE

7.86-9.04

12.6-13.9

20.6-23.7

HARDNESS - VICKERS

20.7-22.8

22.1-24.3

15.9-17.5

MODULUS OF ELASTICITY

1.74-2.16

2.89-3.04

2.29-2.04

POISSON’S RATIO

0.39-0.40

0.38-0.4

0.392-0.407

COMPRESSIVE STRENGTH

63.8-70.6

144-159

63.6-70.2

SHEAR MODULUS

0.67-0.71

1.04-1.09

0.81-0.85

Klc

FRACTURE TOUGHNESS

3.5-3.87

1.99-4.03

2.65-6.08

ELONGATION

124-178

55.8-64.5

THERMAL EXPANSION COEFFICIENT

79-81

84.6-101

51-61

TRANSPARENCY

TRANSPARENT

REFRACTIVE INDEX

1.56-1.58

1.65-1.67

1.66-1.68

Table 14 . Main properties of plastics suggested as an interlayer for the dry connections between the glass blocks [CES EDUPack 2015]

04 DESIGN RESEARCH

YOUNG’S MODULUS The stiffer a material is the lower the [elastic] strain is at a given force, meaning that the material deforms less. The ability of an intelayer to adjust to the microprofile of the glass, in terms of flatness and thickness, is crucial in order to avoid stress concentrations. On the other hand, a higher Young’s modulus results in a higher bending stiffness.

SALT WATER-RESISTANCE Despite the fact that the interlayer is sealed in between the glass components, salt water is an “enemy” due to the location of the tower especially at the lower part, which is in close proximity to the sea.

FRICTION COEFFICIENT Friction expresses the resistance of two materials sliding against each other. The coefficient of friction describes the ratio of the force of friction between two bodies and the force pressing them together. The higher this value is, the higher the friction and the higher the tesnile forces introduces in the surfaces of the materials. [the coefficient for glass elements is 0.9-1.0]

UV-RESISTANCE The interlayer is exposed to solar radiation, so a good performace against it is crucial to ensure both the good structural properties and avoid discoloration.

THICKNESS The thickness of the interlayer can affect its performance: higher thickness can ensure the homogeneous transfer of the loads, but lower thickness ensures a higher bending/axial stiffness. It also depends on the manufacture and thermal expansion tolerances of glass.

GLASS-TRANSITION TEMPERATURE The softening point of the interlayer is important, as high temperatures can occur due to the climate. A high glass temperature can ensure that the material remains in a solid state and with the desirable mechanical properties.

113

PET [UNFILLED,

PETG [UNFILLED]

AMORPHOUS]

PMMA [MOLDING

PVC [RIGID, HIGH IMPACT,

AND EXTRUSION]

MOLDING AND EXTRUSION]

1290-1390

1260-1280

1170-1200

1290-1460

kg/m3

1.59-1.75

1.87-2.06

2-2.21

2.23-2.46

EUR/kg

2-5

14.4-15.9

16.1-21.9

11.3-12.4

2.8-3

2.01-2.11

2.24-3.24

2.2-3.1

0.381-0.396

0.395-0.411

0.38-0.40

0.395-0.405

50-60

57.5-63.5

72.4-124

37-44.3

0.99-1.49

0.71-0.75

0.8-1.16

0.75-1.1

4.75-5.22

2.11-2.54

0.7-1.6

3.63-3.85

280-320

102-118

2-5.5

40-80

115-119

120-123

90-162

65-81

% strain/°C

OPTICAL QUALITY

TRANSPARENT

1.57-1.58

1.57

1.49-1.5

1.53-1.54

MPa*10-1 GPa MPa GPa MPa*m1/2

TRANSPARENT RESTORATION

GLASS-TO-STONE The initial goal when restoring a historic building is to safeguard it and prolong its lifetime. This means that any intervention should not harm or burden the existing structure and materials. Consequently, the connection between new – existing, glass – stone in our case, is the most critical aspect of the design.

114

As glass is a much stiffer material compared to historic masonry, the connection between these two systems is what provides the necessary compatibility; thus, it should be designed as the weakest link, which acts as a warning mechanism in case of overloading. While we want to preserve the historic fabric, glass is the material we want to fail in case of overloading. Additionally, the connections should be capable to carry any deformations occur due to loading or thermal expansion of the materials. In order to achieve that, it is preferable to design them less rigid and more flexible, making use of ductile materials. Very rigidly joined structures do not allow for movement and can result in cracks. The choice of the intermediate layer, as well as the force transfer mechanism, are two factors that influence the behaviour of the connection. While in the case of glass-to-glass dry connections a plastic interlayer is chosen, in this case, where glass is in contact to the existing masonry, a more flexible solution should be suggested. Rubber foils are usually applied in restoration projects at the joints as they are flexible and can take the necessary tolerances. Additional point fixings should be added along the contact faces in order to stabilize the foil and the glass elements. Neoprene [Polychloroprene rubber] is a material widely applied in restoration treatments as an indermediary; some of its basic properties are shown inTable 15.

PROPERTY

POLYCHLOROPRENE [CR, UNREINFORCD]

PRICE

3.97 - 4.42

€/kg

DENSITY

1230-1300

kg/m3

YOUNG’S MODULUS

0.00165 - 0.0021

GPa

TYPICAL COMPRESSIVE STRENGTH

14.4 - 28.8

MPa

TYPICAL TENSILE STRENGTH

12 - 24

MPa

ELONGATION

750 - 950

% strain

POISSON’S RATIO

0.48 - 0.495

[-]

THERMAL EXPANSION COEFFICIENT

202 - 245

TRANSPARENCY DEGREE

TRANSLUCENT

[-]

WATER [SALT] DURABILITY

EXCELLENT

[-]

UV RADIATION RESISTANCE

FAIR

[-]

FLAMMABILITY

SELF-EXTINGUISHING

[-]

Table 15 . Typical properties of Polychloroprene/Neoprene

04 DESIGN RESEARCH

The optimum thickness of the rubber foil is determined by calculating the thermal expansion of the materials. The worst case scenario of a tempera* The existing masonry consists of a combination of limestone and sandstone, so the actual value of thermal expansion coefficient is much lower than the one used for the calculations. Sandstone has a higher linear thermal expansion coefficient than limestone [8 x 10-6 K-1] meaning that it expands more and shows the maximum possible length change.

for summer] is assumed. The mean linear thermal expansion coefficients for borosilicate glass and sandstone* are 3.6 x 10-6 K-1 and 11.6 x 10-6 K-1 respectively. The following formula is used to calculate the change in length for both cases: =L*a*

[m]

Again the worst case scenario is chosen for both cases of sandstone and glass. For Lglass=13.23 m and Lsandstone=12.45 m the length change is 5.7 mm and 1.9 mm respectively. Taking into account that materials expand in both sides, a joint of minimum 4 mm is required.

Due to the uneven surfaces of the ruined parts of the monument, the suggested glass blocks do not fit to the existing structure. Thus, an intermediate zone should be created to bridge the glass and the stone masonry. Different options for the critical connections are examined always in respect to the restoration principles [transparency, reversibility, structural integrity] and design complexity. Table 16 shows an overview of the advantages and disadvantages of each system.

Fig iii . Conceptual connection of existing masonry to glass masonry

The final design introduces stacked float glass components, which are fabricated according to the exact imprint of the existing structure in order to directly fit in. The small thickness of float glass can easily adjust to the uneven rough surface of the monument, just with a proper cutting process [water-jet cut]. Generally, it is a material widely available, causing the least complexity to this already demanding design. These components are prefabricated and transferred to the site where, they are assembled. The system is elaborated in chapter 05.4. The third option of 3d-printed units is also very promising, as it leads the way to a wide range of possible transparent materials, even to customized glass units, achieving a fully transparent result. However, due to the large area we want to cover, this system is not efficient in our case.

115

TRANSPARENT RESTORATION

TRANSVERSE SECTION

POINT FIXINGS

LONGITUDINAL SECTION

3D PRINTED UNITS

FLOAT GLASS

116

Table 16 . Overview of the connections examined between the glass units and the existing masonry

MATERIALS

Special cast glass units to accomodate the embedded connections Protective foil Steel rods

Stacked float glass bonded with adhesive interlayer and shaped to accomodate embedded connections Intermediary Steel rods

3d printed unit by transparent | translusent materials: glass, plastic Intermediary Steel rods

04 DESIGN RESEARCH

COMPLEXITY*

IMPORTANT NOTES

Simple and minimum treatment, which is already used as a consolidation technique in restoration practices

Material - cost - construction time efficiency

Non uniform distribution of loads

Distinguishable connections [steel rods] that undermine the sense of transparency

117

â&#x20AC;ş *less complex

Uniform distribution of loads

Tolerance differences cast and float glass

Large variety of materials and 3d printing methods

Limitations in size due to existing 3d printers.

Uniform distribution of loads

Different materials set multiple parameters concerning the connections, possible reinforcement and structural performance.

â&#x20AC;ş more complex

between

Fig 05.1 Photo of the final model in sc. 1:100

05.

FINAL DESIGN

TRANSPARENT RESTORATION

The suggested restoration treatment addresses primary to the consolidation of the SE faรงade, the corner with the eastern part of the SW facade and a small part of the NE faรงade. The shape that needs to be restored is not uniform because of the irregularly collapsed parts; the maximum dimensions of the SE facade are 17.5 m height and 13.25 m width. The parts that have remained are some rows and cornerstones at the lower part and a large area approximately at the level of the ground which is merely connected to an even larger part above it. We can assume that the new glass facade is divided in two large parts, given the large existing masonry in the middle of the wall, which covers almost the entire width. These two parts are treated in a different way in order to respond to the respective needs.

120

The lower part of the existing masonry is assumed to be the part that suffers the most dut to the humidity and the sea salt have resulted in the decay of the materials and consequently the structural behaviour of the masonry. As long as this part is exposed to the sea the decay continues and affects also the upper parts of the monument. The restoration treatment suggests that this part of the wall [which is also part of the exterior wall of the fortress] is completely sealed with the cast glass masonry in order to prevent further deterioration and provide a more permanent solution to this decay. As glass is a durable material against salt water, it can sufficiently protect the limestone and sandstone which are not. The upper part stands 10 meters above the sea and covers the two chambers of the towers; in other words this is what the visitors see when they enter the monument. The collapsed parts have created openings at the SE faรงade towards the sea and this perception is something the new design aims to maintain as part of the current setting. As the consolidation of the monument using structural glass does not intervene in the existing materials, special treatments, proper cleaning and application of coatings should take place beforehand. These aspects are thoroughly discussed in chapter 07.2.

05.1 FINAL SYSTEM

Fig 05.2 Part of the faรงade to be restored with glass

05 FINAL DESIGN

121

SE FAÃ&#x2021;ADE

TRANSPARENT RESTORATION

9.14 m

13.23 m

122

PLAN

16.70 m

9.50 m

05 FINAL DESIGN

SECTION

123

TRANSPARENT RESTORATION

124

05 FINAL DESIGN

Glass is the only structural material used in the transparent restoration approach, however due to the specific demands of the consolidating parts, different glass configurations have been applied and are discussed in the following chapters.

LAMINATED FLOAT GLASS For the horizontal connections of the glass masonry to the monuments, namely the roof and the corner at the ground floor, where the ground has partially collapsed, we choose to use laminated float glass. As there is no substructure or physical constraints to hold this parts, the use of interlocking glass blocks is not directly feasible.

CAST GLASS UNIT The SE and SW facades are made of solid cast glass units, as the primary restoration elements, which interlock together to form a masonry.

STACKED FLOAT GLASS The connection between the cast glass blocks and the existing structure is critical and challenging due to the uneven surfaces of the latter. For this reason the use of glass units along the edges is impossible because this would lead to a high level of complexity in both manufacture and assembly. Float glass is once again chosen as a solution, because once we have the exact imprint of the existing surface, it can be easily cut into the desirable shape. These panes are stacked and bonded together and assembled on site.

125

TRANSPARENT RESTORATION

The structural integrity of the new composite structure is determined both by the structural behavior of the monument in combination with the one of the restored part. The evaluation of the monument affects greatly the design and form of the new addition.

05.2 STRUCTURAL PRINCIPLES

TENSILE STRENGTH [MN/m2]

800 600 400 200

COMPRESSIVE STRENGTH [MN/m2]

0 200 400 600 800

DENSITY [mg/m3]

8 6 4 2 0

200

STIFFNESS [GN/m2]

126

150 100 50 0

Fig 05.3 Strength, density and stiffness of old and modern materials compared [courtesy: Allen Lane and Penguin Books]

ALUMINIUM ALLOY

STRUCTURAL STEEL

WROUGHT IRON

CAST IRON

TIMBER

CONCRETE

1800 1930 1970

BRICK [BRICKWORK ABOUT 1/3]

up to

STONE

Structural analysis enables a better understanding of the original structure, however, the high level of complexity that characterizes the historic structures suggests a difficult structural assessment process. Computational methods can be used, nowadays, to simulate the stresses that occur in the building. An accurate structural analysis is necessary in order to avoid either over-strengthening the monument, resulting in unnecessary

05 FINAL DESIGN

loss of both material and cultural value, or insufficiently intervening on it, and generate unacceptable risks on people and heritage. [Pere Roca, 2010] Fig 05.3 shows a comparison of old and new materials in terms of density, stiffness and strength. However, structural members such as masonries are often non-homogeneous and show complex internal structures, such as several layers, filling, material, cavities and other possible singularities. [Pere Roca, 2010] Thus, measuring and testing different parts of the building [both the core and the faces] can achieve a proper evaluation of the current properties of a monument and proceed with a more accurate analysis of its structural performance.

PROPERTY

BOROSILICATE GLASS LIMESTONE SANDSTONE

DENSITY

2230

2550-2600

2240-2650 kg/m3

YOUNGâ&#x20AC;&#x2122;S MODULUS

35-55

14-25

GPa

TYPICAL COMPRESSIVE STRENGTH

200

30-200

50-155

MPa

TYPICAL TENSILE STRENGTH

8-22

4-22

MPa

POISSONâ&#x20AC;&#x2122;S RATIO

0.19 - 0.21

0.2 - 0.26

0.22 - 0.29 [ - ]

HARDNESS VICKERS

74 - 100

3 - 18

7 - 38

FRACTURE TOUGHNESS

0.6 - 0.7

3 - 18

0.6 - 1

MPa*m1/2

THERMAL EXPANSION COEFFICIENT

3.2 - 4

3.7 - 6.3

8 - 20

Table 17 . Typical properties of borosilicate glass, limestone and sandstone according to CES EduPack 2015. [Full properties tables are presented in Appendix 2]

Nevertheless, in the current case study, due to the limited knowledge on boundary conditions and exact mechanical properties of the masonry, it is difficult to accurately model and estimate the structural behaviour of the original structure. As the structural simulation of the monument is not in the scope of the research, the design of the new glass wall is a result of a simplified qualitative assessment of the main features of the existing structure. A comparison between the material and mechanical properties of the relevant materials shows basically that glass is a much stiffer material than limestone or sandstone, with relatively similar strength against compressive and tensile stresses, as well as similar density [see Table 17]. Due to the age and pathology of the monument we assume that these values tend to be in the lower margin of the values presented in Table 17, for limestone and sandstone, because of the strong impact of the sea salt and humidity on the material structure. Consequently, the strength of the masonry is of great importance in our case because of the decay of the materials. Historic structures carry their loads by massive and stiff forms to compensate for the relatively weak materials. However, modern structures rely on flexible forms using stiff materials and rigid connections. [Feilden, 1982] Moreover, it is not appropriate to burden the monument with extra weight than necessary. As glass has relatively similar density to limestone and sandstone, the new structure does not add any extra weight to the monument than

127

TRANSPARENT RESTORATION

it originally had; and as glass is stiffer, it means that it has higher strength and, thus, requires less volume, resulting in a lighter structure. For the aforementioned reasons, the new glass masonry wall can be of much less weight compared to the missing part of the original materials. That results in a glass structure with approximately 1/12th of the thickness, 1/4th of the volume and 1/4th of the weight of the original missing masonry, while the stiffness is four times increased [see Fig 05.4]. LIMESTONE & SANDSTONE

128

Fig 05.4 Comparison of the new glass masonry with the original masonry of the missing part in terms of thickness, volume, weight and stiffness.

Another important aspect, that affects the overall structural behaviour of the monument, is the connection of this thin glass masonry to the original massive stone masonry. A safe design must ensure than no high stresses occur in the connections. However, the significantly small thickness of the glass [12 cm] wall allows only a small area to receive and distribute the loads compared to the large thickness of the masonry wall [150 cm]. As stress can be described as the ration of the force and the area this force acts on [see Fig 05.5], we can easily ascertain that it is highly dependent on the cross-section of the structural element. Thus, in order to establish a more homogeneous and uniform loads transfer between the old and new structure, we introduce a variable masonry thickness, which increases the closer it gets to the existing masonry in order to create a larger cross-section of the contact areas [see Fig 246]. This transition is formed gradually at all the edges that are in contact to the original masonry [either horizontally or vertically, see Fig 05.7].

GLASS

t=150 cm

t= 12 cm

V=185 m3

V=52.5 m3

W=473 T

W=117 T

E=14 GPa

E=64 GPa

=F/A Fig 05.5 Idealized stress in a straight bar with uniform crosssection

05 FINAL DESIGN

Fig 05.6 Prototype with variable but symmetrical mass distribution, tested by Oikonomopoulou et al. [Oikonomopoulou et al, 2016]

Fig 05.7 Variable thickness of the masonry as it reaches the edges, along the height and the sides

A similar research of restoration with glass elements has been conducted by Oikonomopoulou et al. [Oikonomopoulou et al, 2016] where the performance of different glass configurations [float and cast glass] adhesively bonded to a brick masonry [using various types of adhesives] has been tested. The results have shown that the concept suggested in Fig 05.6 is the most promising for further development; the maximized connection surface between the two elements leads to a more uniform transfer of the loads, while by reducing the mass towards the centre, glass becomes lighter, yet stiff enough to ensure overall stability. The variations of the masonry in terms of the crosssection can be critical and need further investigation using more complex mathematical formulas or structural models. The most critical aspect is that when the thickness is not uniform, the self-weight of the element and consequently the support reaction are not aligned with the axis that transfers the loads. That introduces eccentric loading conditions and thus, a secondary bending moment, making the structure susceptible to buckling. For these reasons it is chosen to follow a symmetric [as possible] configuration of the glass units along the edges that connect to the existing masonry [see Fig 05.8].

d [a] the cross-section of the contact area is very small and this can result in high stresses

[b] the cross-section of the contact area is larger but eccentric loading conditions create a secondary bending moment M when the mass distribution is not symmetrical, which makes the structure prone to buckling

[c] a symmetric mass distribution allows for an alignment of the centre of gravity, the compressive load F and the support reaction R, which makes, in principle, the structure to be more resistant against buckling

Fig 05.8 Transfer of loads with different cross-sectional connection areas and different mass distribution of the glass masonry

129

TRANSPARENT RESTORATION

Glass, in most applications, appears as a slender material with small cross-section, which makes it prone to buckling, whether it is formed as a fin or a plate. Thus, when subjected to compressive load higher than the permitted, a sudden sideways failure occurs. In our case, cast glass, compared to float glass, has the advantage of a larger crosssection which can make it more resistant to buckling.

Fig 05.9 D e f o r m a tion of plate because of buckling with different boundary conditions. The first options with the two pinned edges seems to represent better the dry connections of the interlocking masonry.

Bryanâ&#x20AC;&#x2122;s formula [1891] gives the elastic critical stress for a long rectangular plate, supported along all edges and subjected to a uniform longitudinal compressive stress: critical

130

= k ( 2E) / 12(1-v2) (b/t)2 *

By implementing this formula in our case, assuming that the glass masonry is a monolithic plate, without any deviations in the thickness [see Fig 05.10], and given the compressive load F and selfweight W, we can derive that the minimum thickness required to prevent any critical stresses is 10 cm. A safety factor of 4 is taken into account. [see Appendix 3] It is evident that the buckling resistance of the plate is influenced by the restraint conditions, the dimensions and the elastic material properties of glass. Due to the assumptions made [a monolithic glass plate, with homogeneous thickness instead of a glass block masonry with variable thickness], the above result of 10 cm is a very optimistic scenario for our case, even with a safety factor of 4. Further investigation and structural simulations are necessary in order to get design values regarding the minimum allowable thickness. On the other hand, by increasing the cross-section of the contact areas, we create more favourable conditions against buckling. Taking the above into account, for the purpose of this research, the thickness suggested for the current design is 12.5 cm. This thickness refers to a single row of glass units; reaching the existing masonry the thickness of the glass consists of 5 rows, equal to 62.5 cm.

= elastic critical stress critical E=Youngâ&#x20AC;&#x2122;s modulus v=poissonâ&#x20AC;&#x2122;s ratio K=plate buckling coefficient [see Fig 05.6] b = width t = thickness

Fig 05.10 Monolithic glass plate 12.4 m high and 4.5 m wide assumed in the hand calculations. F stands for the compressive load of the above masonry and W stands for the self weight of the glass plate.

05 FINAL DESIGN

05.3 CAST GLASS UNITS

LEGO 2 is the glass block design chosen for the current system as it combines sufficient levels of transparency with adequate levels of complexity during manufacture and assembly according to Table 12 [see chapter 04.9]. A homogeneous mass distribution in the glass unit enables manufacture and ensures that all parts of the unit cool down at the same time, avoiding temperature differences and decreasing the risk of permanent stresses.

Symmetry in the design is vital for the construction of the masonry and enables the overlapping of the glass units.

V = 0.0027 m3 W = 6.021 kg 131

Fig 05.11 Basic cast glass unit

The round edges are necessary in order to have a better flow of the molten glass in our mold during the manufacture. Sharp corners and edges should be avoided as they are the most prominent parts to crack and be detached.

The dimensions is a combination of the rythme of the existing masonry and the permitted weight so as to be easily handled [max 10 kg]. In order to avoid a shape with the regular brick dimensions and consequently a facade, which would resemble to a brick masonry, a more elongated form is chosen for the units. The aesthetics of the glass masonry is further discussed in chapter 05.7.

TRANSPARENT RESTORATION

ASSEMBLY The main masonry consists of the aforementioned unit, however, as mentioned in the previous chapter, its thickness is not uniform in the entire length and height. In order to achieve an inseparable structure, more units are needed to create a transverse connections, as well as to form the corners. The necessary units are shown in the following diagrams: FULL UNIT The main unit that covers the largest part of the masony

TRANSVERSE UNIT Used to connect transversely 2 rows of full units

132

HALF UNIT Used to fill the voids at the edges

CAP UNIT Used as as cover wherever needed Fig 05.12 Assembly mode of the glass masonry corners

DOUBLE TRANSVERSE UNIT Used to connect vertically 2 rows of full units in their corner

CORNER UNIT Used to form the corners

05 FINAL DESIGN

A fragment of interest and high accuracy demands is the upper part of the lower glass masonry, where it reaches the existing structure. Special glass units are necessary in order for the new structure to be assembled. Given the constraints from the existing masonry, the units need to be assembled from the sides as shown in Fig 05.13 and extensively explained in the following chapter.

SLIDING CAP Used at the upper part of the masonry located right underneath the existing structure. These units are in contact with the stacked glass units and slide from the sides to fit in.

133

SLIDING UNIT Used at the upper part of the masonry located right underneath the existing structure. Due to the strict tolerances during the construction of that part these units introduce a sliding mode, as the normal ones could not fit. Fig 05.13 Assembly of the glass masonry at the parts underneath the existing monument

05.4 CONNECTIONS

As discussed in chapter 04.10, the connection between the existing and the cast glass masonry is established using stacked float glass prefabricated units. They are point fixed to the existing masonry every 1.5 m. The intermediate units are mechanically connected to each other using embedded connections in order to avoid harming the monument and ensure reversibility. As long as these components are stabilized in place the cast glass units are ready to be assembled, as shown in Fig 05.14.

TRANSPARENT RESTORATION

CAST GLASS UNITS The easy assembly mode of the units, their distinct orientation and lack of any adhesive interlayer enhance the overall construction process.

TRANSPARENT INTERLAYER

EMBEDDED CONNECTION

STACKED GLASS UNITS

134

Prefabricated units, of 10 mm float glass stacked and bonded together, are stabilized on top of the existing masonry and incorporate embedded connections to accomodate the cast glass units. Their dimensions are roughly 60 x 25 x 30 cm.

STEEL ROD 3 mm Connects the existing masonry to the stacked float glass components. The steel rods are placed every 1.5 m.

TRANSPARENT INTERMEDIARY

Fig 05.14 Connection between glass and stone masonry [glass is placed on top of the stone]

05 FINAL DESIGN

EMBEDDED CONNECTIONS

Titanium connections function as base for the assembly of the cast glass blocks.

Establish a dry connection between the stacked units.

FLOAT GLASS 10 MM Use of water-jet cutting to achieve the complex shape Fig 05.15 Prefabricated unit from stacked float glass panes 10 mm bonded adhesively together

The assembly of the masonry and connection to the existing structure when the latter is located above the former is the most challenging part of the design and construction. The following solution [see Fig 05.16] suggests the assembly of the glass masonry up to a certain level, while introducing special sliding cast glass units to be able to fit in place.

Fig 05.16 Connection between glass and stone masonry [glass is placed below of the stone]

135

TRANSPARENT RESTORATION

STEP 1 The glass masonry is built up to a certain level in order to leave space for the larger stacked units to fit 136

STEP 2 The stacked unit is stabilizad in place and connected to its adjacent one via embedded mechanical connection from the bottom

05 FINAL DESIGN

STEP 3 Customized units with sliding geometry in order to fit in are assembled from the sides first in the middle row 137

STEP 4 The rest upper 2 rows [just underneath the stacked unit] are also assembled with the sliding units

TRANSPARENT RESTORATION

CAST GLASS UNIT 250 x 125 x 50 [COVER]

CAST GLASS UNIT 500 X 125 X 50 [FULL UNIT]

3 4

TITANIUM CONNECTION EMBEDDED IN THE STACKED GLASS UNITS

CAST GLASS UNIT 250 X 250 X 50 [TRANSVERSE UNIT]

DELO-PHOTOBONDÂ® 4494 [UV-CURING ACRYLATE ADHESIVE, MEDIUM VISCOSITY]

STACKED FLOAT GLASS [25 LAYERS OF 10 MM ADHESIVELY BONDED IN A UNIT 250 X 625.5 X 200 MM]

TRANSPARENT RESIN

INTERLAYER 3 MM [PET,PETG,PMMA,PVC]

POLYCHLOROPRENE [NEOPRENE] TRANSLUCENT RUBBER INTERMEDIARY 5 MM

1 138

3 4 5

7 8 11 9 10 13

TRANSVERSE SECTION [CONNECTION OF GLASS - EXISTING MASONRY]

1:5

05 FINAL DESIGN

10 GROUT TO BOND AND STABILIZE THE STEEL ROD TO THE EXISTING MASONRY 11 STEEL ROD Ã&#x2DC; 20 MM 12 TITANIUM EMBEDDED CONNECTION BETWEEN THE STACKED FLOAT GLASS UNITS 13 EXISTING RUBBLE MASONRY [LIMESTONE AND SANDSTONE]

139

6 12

LONGITUDINAL SECTION [CONNECTION OF GLASS - EXISTING MASONRY]

1:5

TRANSPARENT RESTORATION

FLOOR STRUCTURE In the corner of the new glass facade, there is a recess at the existing ground resulting in a gap between the indoor space and the facade. This gap is bridged by adding once again glass; this time as a horizontal element, a floor. Float glass is used as a laminated component consisting of both fully tempered [upper layer] and heat-strengthened [middle and lower layers] glass. The laminated glass is placed on top of rubber strips to establish a soft connection to the cast blocks.

05.5 OTHER DETAILS

140

Fig 05.17 Exploded view of the floor structure

05 FINAL DESIGN

CAST GLASS UNIT 250 X 125 X 50 MM [COVER]

CAST GLASS UNIT 500 X 125 X 50 MM [FULL UNIT]

INTERLAYER 3 MM [PET,PETG,PMMA,PVC]

DELO-PHOTOBOND® 4494 [UV-CURING ACRYLATE ADHESIVE, MEDIUM VISCOSITY]

LAMINATED FULLY TEMPERED [TOP LAYER] AND HEATSTRENGTHENED FLOAT GLASS [4-10-10 MM] WITH SENTRYGLAS®PLUS 1 MM

TRANSLUCENT NEOPRENE RUBBER 5 MM

141

5 6

1 3

2 4

FLOOR DETAIL

1:2

TRANSPARENT RESTORATION

ROOF STRUCTURE The roof is designed as a monolithic element from soda-lime float glass. It has a curved shape on the one side, to follow the adjacent barrel dome of the existing structure, and ends up in a slightly inclined horizontal pane [slope of 10%] to wash out the rainwater. The connection to the glass masonry should allow for minimum movement [to take the displacements due to thermal expansion, loading], easy installation and be properly sealed. The system used in this connection derives from the fixing of the curtain walls. Cast-in channels [see Fig 246] are introduced to connect the two different types of elements coming from different directions [curved float glass with cast glass masonry]. The advantage in this case is that it allows for tolerance during construction, as the channel allows for multiple anchoring.

Fig 05.18 Cast-in channel with T-shape bolt

142

Fig 05.19 Exploded view of the connection detail at the roof structure

CAST GLASS UNIT 500 x 125 x 50 MM [FULL UNIT]

CAST GLASS UNIT [250 x 125 x 100 MM]

INTERLAYER 3 MM [PET,PETG,PMMA,PVC]

DELO-PHOTOBOND® 4494 [UV-CURING ACRYLATE ADHESIVE, MEDIUM VISCOSITY]

TITANIUM UNIT [250 x 125 x 50 MM]

LAMINATED CHEMICALLY STRENGTHENED FLOAT GLASS [1010-10 MM] WITH SENTRYGLAS® PLUS 1 MM

STAINLESS STEEL EMBEDDED CONNECTION 20 MM

HALFEN© CAST-IN CHANNEL HTA-CE 40/22 [HOT ROLLED]

T-SHAPE BOLT M12 [FOR THE HORIZONTAL ALIGNMENT OF THE TITANIUM PLATE]

10 TRANSPARENT RESIN

05 FINAL DESIGN

5 8 7

ROOF DETAIL . ALTERNATIVE 1

1:2

143

9 6

8 10 2 7 3

ROOF DETAIL . ALTERNATIVE 2

1:2

TRANSPARENT RESTORATION

FOUNDATION In order for his restoration using structural glass elements to be feasible, we need to ensure a foundation which, at first, is stiffer than the existing decayed materials, in order to withstand the weight and loads of the new structure, and, secondly, allows for flatness of the cast glass masonry. The suggested foundation consists of a concrete beam [13 x 0.5 x 1 m], covering the entire width of the monument and attached to the natural rocks and remaining of the stone masonry wall. A titanium steel plate is fixed with bolts on top of it with protrusions shaped as a base for the glass blocks to be placed on top. The bolts are aligned in order to create a flat surface for the plate. The inbetween gap is filled with 0% shrinkage concrete. [Oikonomopoulou et al, 2016] The remaining limestones are carefully removed in phases, cleaned and used again, not as load-bearing components but as a cover of the concrete beam in order to achieve the appearance of the original monument having a 1 m high lower zone with three rows of limestones. 144

The lower part is also laterally fixed to the remaining masonry to account for horizontal loading due to earthquakes, for instance. On the one hand, these connections are rigid in order to work against buckling, and on the other hand, they allow for small displacement to prevent damaging the glass during horizontal loading. Stainless steel springs are introduced to allow for this flexibility. Titanium units [with the size of the glass units] are placed instead of glass units to fix the glass masonry to the remaining wall. These anchors are placed as shown below:

3 4 1 2

11 10

14 7 5

D1 . GLASS BLOCKS FOUNDATION

1:5

05 FINAL DESIGN

CAST GLASS UNIT 500 X 125 X 50 MM [FULL UNIT]

CAST GLASS UNIT 250 X 250 X 50 MM [TRANSVERSE UNIT]

INTERLAYER 3 MM [PET,PETG,PMMA,PVC]

DELO-PHOTOBOND® 4494 [UV-CURING ACRYLATE ADHESIVE, MEDIUM VISCOSITY]

CONCRETE BEAM 13 x 0.5 x 1 M

CONCRETE 0% SHRINKAGE

REINFORCEMENT Ø 20 MM

TITANIUM PLATE 3O MM HIGH

BOLT M12 [FOR THE HORIZONTAL ALIGNMENT OF THE TITANIUM PLATE]

10 DRAINAGE Ø 100 MM 11 GRAVEL 12 STEEL ROD Ø 20 MM 13 MORTAR 14 REMAINING HISTORIC MASONRY 15 STAINLESS STEEL ANCHOR FOR LATERAL SUPPORT 16 TITANIUM UNIT [250 x 125 x 50 MM]

17 MORTAR

145

10 8 5

D1 14

GLASS MASONRY FOUNDATION

1:20

TRANSPARENT RESTORATION

Fig 05.20 Exploded view of the lateral anchors in the lower part of the glass masonry

CAST GLASS UNIT 500 x 125 x 50 MM [FULL UNIT]

STAINLESS STEEL COMPRESSION SPRING

CAST GLASS UNIT 250 x 250 x 50 MM [TRANSVERSE UNIT]

STAINLESS STEEL CYLINDRICAL COVER 20 MM

INTERLAYER 3 MM [PET,PETG,PMMA,PVC]

10 STAINLESS STEEL PLATE 150 x 250 x 10 MM

DELO-PHOTOBOND® 4494 [UV-CURING ACRYLATE ADHESIVE, MEDIUM VISCOSITY]

11 STAINLESS STEEL PLATE 250 x 250 x 10 MM

TITANIUM UNIT [250 x 125 x 50 MM]

BOLT M10

13 GROUT TO BOND AND STABILIZE THE STEEL ROD TO THE EXISTING MASONRY

TRANSLUCENT NEOPRENE 5 MM

14 STEEL ROD Ø 20 MM

146

12 EXISTING RUBBLE MASONRY [LIMESTONE AND SANDSTONE]

3 5 6 8 10

7 11 2 4 1

D2 . LATERAL ANCHORING

1:5

05 FINAL DESIGN

05.6 CLIMATE PERFORMANCE

Fig 05.21 Sealed part of the new intervention

* Limestone and sandstone have very effective thermal mass, 2015]

Given the fact that the purpose of the current restoration is limited to structurally consolidate the existing monument, no new function is introduced. Thus the intervention merely suggests filling the form of the structure in the SE facade, leaving other parts, such as the half-collapsed roof and the openings in the NW facade intact. For these reasons a climate analysis in terms of thermal comfort is not necessary, as there is sufficient ventilated area. However, the treatment of the lower part in the restoration design should be further examined [seeFig 05.21]. According to the concept, this part is completely sealed by the glass masonry in order to protect the remaining material from the elements and particularly the sea salt, which is the main reason for decay of the historic materials. Thus, while the monument is safeguarded, there is the danger to create unwanted conditions that eventually harm both the existing and the new structure. These concerns may deal with aspects, such as overheat, trapped water, condensation and moisture. On the one hand, if no sufficient ventilation is introduced there is the possibility that the air behind the glass facade gets too hot, but also due to the proximity to the sea, humidity and condensation can also occur, especially, during night. On the other hand, the thermal mass of the remaining structure* [which is part of the fortress walls] as well as the ground substrate, can absorb heat or diffuse the moisture, respectively. Drainage provision [see foundation elaboration, chapter 05.5] is also crucial because, no matter how well a structure might be sealed, water always finds a way to penetrate. Trapped water, especially coming for the sea is dangerous for the historic materials. Natural ventilation of the lower part could be easily incorporated either by a grill at the glass floor or by some openings in the glass facade. The climate performance of the glass addition is out of the scope of this thesis, however, it is proposed that all the aforementioned conditions need to be further examined as a next step of the design. Thermal simulations could also give more accurate results of the behaviour of both the existing and the glass structure.

147

TRANSPARENT RESTORATION

The transparent restoration approach is based on the idea of transparency, as an inherent â&#x20AC;&#x153;quality of substanceâ&#x20AC;? [Rowe et al, 1963]. Glass is transparent, neutral and colourless, and, in extent, a competitive material for restoration purposes, causing minimum visual intrusion. The main concept for the examined case study is to introduce glass as an innovative restoration material, in a way that it respects the existing structure and creates an interrelation with it. This has been achieved in the design by adopting the existing construction technique and suggesting a glass masonry to fill the missing parts. However, in this case of transparent intervention, the total perception of the structure is in close relationship to both the levels of visibility and light transmission. Thus, an investigation of the micro-scale, in other words the surface quality of glass, is also part of this research, as a critical assessment of the aesthetics of this new restoration approach.

148

Fig 05.22 Various optical phenomena

05.7 AESTHETICS

05 FINAL DESIGN

When light strikes a body, radiation is reflected, absorbed and transmitted according to the properties of the material, the surface quality, the respective wavelength and the angle of incidence. The degree of light permeability, in other words light transmission, determines whether a material is transparent or opaque. However, the degree of transmission is a quantitative value and does not give information about the quality of the transmitted light or the perceived image. [Weller, 2009] Additional optical phenomena, such as diffusion, reflection and refraction can express these qualities [seeFig 05.22].

Fig 05.23 Transition of light in LEGO blocks through different media [air, glass, interlayer]

As discussed in chapter 02.4, the final glass surface can be treated in different ways [matte/ translucent], depending on its function; while a polished surface reflects light, a ground one diffuses it. Furthermore, the appearance of any structural defects in the glass [voids, cracks, internal stresses etc.] can change the refraction index of glass and result in distortion of the image. Similarly, the different media integrated in the structure [air,glass,adhesives/interlayers etc] can affect the refraction of light; the more these are, the more the distortion of the perceived image [see Fig 05.24]. Solid glass blocks can reach high levels of transparency and surface quality, as appears in the case of Crystal House, imitating a traditional brick masonry facade [see Fig 05.25]. However, what is the desirable appearance of a glass masonry, in conjunction with a rubble masonry monument?

Fig 05.24 Distorted image due to rain water

Fig 05.25 Crystal House glass wall

First, by examining the geometry of the bricks suggested in the design, it is clear that some distortion of light occurs, due to the different materials involved [glass, transparent interlayer]. Given the fact, that the glass bricks interlock to each other, several reflections occur, having as a result the image to be distorted [see Fig 05.23]. Thus, even if the surface of glass is completely polished, the result will be different than this of Crustal House. The manufacture of prototypes [see chapter 06.2] have been of great help in order to investigate the appearance of the glass surface. As the manufacture happens in a laboratory without any standardized procedures, the glass units differ a lot from

149

TRANSPARENT RESTORATION

an industrialized process. Roughness, bubbles, uneven surfaces and deviations in dimensions are some of the inevitable flaws that occur. Nevertheless, it appears that all these imperfections create a texturized effect, which makes glass resemble to stone. More specifically, two are the surface qualities achieved: either rough and translucent causing diffusion of light [Fig 05.26], or reflective and more transparent, allowing for a better perception of the image [see Fig 05.27]. In both cases there is a texture created on the glass, either due to the mold quality [translucent result] or the fusion level of molten glass [transparent result]. Following the initial concept of a new glass masonry that resembles the existing one, it occurs that a texturized final surface of the glass units fits better in our case, compared to the optical quality in the case of Crystal House. Maybe a slightly reflective, yet texturized surface [see Fig 05.27] could allow for a better perception of the surrounding landscape. An overall sense of translucency rather than transparency makes the glass blocks appear 150

Fig 05.26 Translucent and rough surface quality of the glass block prototype

Fig 05.27 Transparent, reflective surface quality of the glass block prototype

Fig 05.28 Stone in comparison to different glass surface qualities in detail; from left to right: clear glass block, stone, proposed texturized glass block

05 FINAL DESIGN

less shiny, more matte and â&#x20AC;&#x153;roughâ&#x20AC;? just as stone. More investigation should definitely be made in order to know how such can be achieved by a standardized manufacture process [maybe with the proper treatment of the mold or with fusion to give the desirable pattern].

Fig 05.29 Different edge treatments for float glass

In a similar way, the float glass in the stacked units, can be treated accordingly so that the edges have a translucent appearance [see Fig 05.29]. Additionally in order to achieve the most colourless glass quality and avoid any green tint, which is the most common case for widely available float glass, lowiron extra clear glass is preferred [see Fig 05.30].

Fig 05.30 Standard clear glass [bottom] and lowiron extra clear glass [top]

151

Fig 05.31 LEGO unit modulus

Fig 05.32 Existing masonry modulus

MODULUS Another aspect that affects the aesthetics of the restored monument, is the relation between the modulus of the existing and the glass masonry. Rubble masonry, usually, consists of primary stones and wedges, of various shapes and volumes. However, in the case of a glass masonry, a variety in shapes and sizes is not feasible as it would result in a very complex design, manufacture and assembly. Also, after the investigation of the glass units [see Table 12, chapter 04.9] it appears that the locking method introduced in the LEGO unit is more durable and feasible by only one type of unit. In order to avoid the glass masonry resembles to an ashlar masonry, it is decided to reject the standard brick/stone dimensions and follow the horizontal lines of the existing masonry in order to create a similar modulus [see Fig 05.32]. Thus, the final design of the glass blocks suggests an elongated shape [see Fig 05.31], which is high enough to allow for a certain level of perception of the surrounding landscape.

Fig 06.1 Detail of the cast glass unit before being released from the mold

06.

VALIDATION TEST

TRANSPARENT RESTORATION

Considering that the suggested interlocking cast glass masonry is an innovative structural system, experiments could provide some first indications of its structural performance. Due to the nature and design of glass units, the manufacture of the components covers the largest part of the preparation process; moreover, it is a valuable source of information and general knowledge concerning the specifications of the fabrication technique that can influence the design itself.

06.1 TEST SET-UP

The proposed glass wall is primary loaded in compression and glass is known for its high compressive strength exceeding 200 MPa. Thus, the structure is expected to perform well in compression. Therefore, a shear test is preferred over a compression test in order to give us an insight on the behaviour of the interlocking units and how they react to out-of-plane loading, such as the wind load. This test could give indications in two directions: first, on how the interlayer between the units works and, secondly, if the shape of the unit is efficient and creates a sufficient locking joint.

154

Five units [3 full and 2 half] are stacked in order to overlap and as the edge units are constrained [both from the sides and the bottom], force is applied on the middle unit until it fails [see Fig 06.2]. Because of strict time constraints and for the sake of the materials, a scale 1:2 is estimated suitable for the validation test.

GLASS UNITS The manufacture of the glass units is realized using the kiln casting technique [see Chapter 02.4], which suggests that the molds stay in the kiln for the entire time of heating-cooling-annealing. This method implements disposable molds, which are made from soft materials [in our case Crystal Cast investment powder] that can withstand high temperatures. To fabricate the disposable molds we also use a disposable model [made of wax], which can be later removed by steaming and â&#x20AC;&#x153;leaveâ&#x20AC;? the interior free for glass to take its place and be formed in the desired shape. The steps taken during the manufacture of the glass units is analyzed in the following steps. The time frame needed for the entire process and the manufacture of 8 glass blocks is 26 days.

06.2 PROTOTYPE MANUFACTURE

06 VALIDATION TESTS

155

Fig 06.2 Test set-up

TRANSPARENT RESTORATION

2 DAYS

MOLD DESIGN Rhinoceros 5 is used as the main software during the design process. After the full unit is defined, the mold can be defined as well. For practical reasons, in casting methods, two mold-parts are necessary in order to be able to release our unit. One of the faces is left open in order to have access and pour the material in our mold. The particular face is chosen so as to facilitate the casting process both during the intermediate steps, as well as, the final glass casting, but also in order to have

as much access to the interior of the mold as possible. This part is designed longer in order to ensure the desired width, as some shrinkage usually occurs at the casting material [wax]. An extra piece is designed to accommodate the half unit, which requires actually only one of the two molds. Additional holes are designed in order to ensure the aligning of the two parts penetrated and kept in place by wooden sticks [Ø 10 mm].

140 mm

FULL UNIT

156

248 23

WOODEN STICK Ø 10 mm

HALF UNIT

HOLE Ø 11 mm

MDF MOLDS

Fig 06.3 Illustration of the two molds [for full and half unit] digitally designed

06 VALIDATION TESTS

3 HOURS

22 HOURS

MDF MILLING

MOLD TREATMENT

The precision of the molds in terms of surface quality is related to the final glass surface. For this reason MDF is chosen as the most appropriate material, considering the given time frame. MDF milling can be very accurate and result in the desired shape and smoothness we need for our molds.

As soon as the MDF molds are ready they need firstly to be sanded [using sanding paper] to ensure the surface smoothness. For the following steps a set of tests is carried out in order to decide what combination of coatings can facilitate the release of the unit and at the same time keep the mold as intact as possible so as to reuse it. The best combination of coatings in terms of time and quality is to apply 2 layers of MDF primer, which “seals” wood’s porous surface and prevents wear, 2 layers of varnish to reduce the friction and 1 layer of release agent “Ease Release”. In between these steps sanding is also necessary. After every use, a layer of vaseline is also applied to ensure that no material is left on the mold.

157

Fig 06.4 Milling of MDF into shape

Fig 06.5 MDF molds

Fig 06.6 Primer application to “seal” the porous MDF

TRANSPARENT RESTORATION

4-5 HOURS

WAX CASTING Wax is the material used to create our model as it can easily be removed later by steaming. After having our molds clamped together and placed on a flat surface, we can start with pouring hot wax [heated up to 70Â°C in a fryer for about one hour] inside the mold filling it completely. As soon as the wax starts to harden it shrinks due to the temperature difference. Ideally, because of the symmetry of the design and the even mass distribution, the shrinkage pattern should be symmetrical and even as well, however this is not happening in our case [see Fig 06.8]. One of the reasons for that phenomenon can be the design itself, with the protrusions and recesses, which indicate specific fluid paths. Also, it is observed that for the half units, where

the thickness of the open face is larger and there are no recesses, the shrinkage is more homogeneous. Another theory is that the bottom surface is not 100% flat and changes the centre of gravity of the fluid mass, resulting in different movement paths for the wax. After 4-5 hours our wax model is ready to be carefully removed. It is observed that if our wax model was left to cool down during the night the final result is worse than when removing it after some hours, when the wax was relatively warmer. In both cases, we can identify some inaccuracies in different parts of the surface, which can be attributed to shrinkage or bad reaction of wax to the mold.

158

Fig 06.7 The different states of wax in the MDF mold [up] just poured [down] hardened after a while

Fig 06.8 Different qualities of wax model depending on the curing time. It appears that the optimum time to let the wax cool down is 4-5 hours, in order to achieve a smooth surface [up]. Leaving the wax more than 5 hours or overnight to cool down [middle and bottom] results is an inferior quality and makes it more difficult to release it from the mold. Another observation is that the shrinkage occurs at the upper part of the units, possibly due to gravity.

06 VALIDATION TESTS

1.5 HOURS

1 HOUR

CRYSTAL CAST

STEAMING

When our wax model is ready, it is time to create our final mold that will be placed in the kiln. Crystal Cast M248 is a soft material, which withstands high temperatures [specidications recommend up

Once the disposable mold is ready we release it from the bounding box and remove any clay residues. Now we need to remove the wax model from the final mold to create space for the glass. We put the mold, having the wax facing down, on top of a bath of water in a boiler. We heat up the water and we cover the boiler with a plastic bag to trap the steam inside. In such way the wax melts slowly inside the water bath.

glass unit. We place the wax unit on a clean flat surface, having the side of pouring facing down, and we stabilize it there using clay. Clay can compensate for the shrinkage occurred at this side of the wax mold, so we need to ensure a straight upper edge of clay using a sharp knife. We add some soap water on the clay to have it easily detached from the Crystal Cast later. The next step is to create a bounding box using small wooden plates and clamping them together. We should calculate an offset of 1.5-2 cm from the sides so that the walls of the mold are not too thin [this could lead to the cracking of the mold]. The dimensions of our mold are 30 x 10 x 11 cm. Clay is used once again to seal the bounding box and prevent leakage. The mixture we use for our disposal mold is water combined with Crystal Cast powder in a ratio of 1:2.75 [1250 ml water and 3430 ml Crystal Cast]. After having mixed the two ingredients together to a homogeneous mixture, we pour it in our bounding box and let it dry for about 1 hour.

159

Fig 06.10 The mold covered with plastic foil on top of an improvised steaming bath

Fig 06.9 Crystal Cast investment powder application in a bounding box

Fig 06.11 The wax has been completely steamed out the Crystal Cast mold

TRANSPARENT RESTORATION

<< 1 HOUR

FINAL MOLD TREATMENT

VOLUME MEASUREMENT

When the steaming process is over and all the wax is removed from the crystal cast mold, we take it of the boiler using protective gloves, as it is still hot, and let it rest for a while. Once again we remove any residual materials [mainly clay]. As we can see the interior surface of the mold, it is easy to identify bumps, flaws and inaccuracies at the surfaces. Because of the shape of our unit, we can have access to the interior of our mold and very carefully start repairing them, scraping with a sharp knife any excess material. When this process is over we clean the interior with warm water.

As a next step, we need to measure the volume of the model in order to calculate the necessary amount of glass. We place the mold on a scale and add water to measure the water volume of our model. We multiply by 2.55 gr/cm3 [density of glass type B270, by SCHOTT] and we have the glass mass we need for our mold. As there is always some part of glass attached to the flowerpots during the firing process, we add 10% of this mass to our final glass quantity. Table 24 [see Appendix 4] shows an analytical overview of the exact glass quantity used for each mold. Finally, we engrave on the side of the mold its identification number and the amount of glass it should accommodate [see Fig 06.13]. The mold is now ready to be dried in the kiln overnight.

160

Fig 06.13 Labeling of each mold with a number and its weight

Fig 06.12 Removing the bumps in the Crystal Cast mold due to imperfections of the wax model

06 VALIDATION TESTS

<< 1 HOUR

FLOWERPOTS TREATMENT

GLASS TREATMENT

In order to put the glass in the kiln we use flowerpots, which we place on top of our molds. A pretreatment of these flowerpots is essential in order to ensure that no ceramic particles are mixed with the molten glass. Thus, first we sand the flowerpots, rinse them and let them dry in the kiln together with the molds over the night at approximately 75Â°C.

For the manufacturing process we are using soda-lime glass B270, by SCHOTT. We wash and dry them well in order to be clean and then we smash them in smaller pieces with a hammer to allow for adjustability in the mass. Finally, we measure the mass we need for each mold.

161

Fig 06.14 The flowerpots and Crystal Cast molds are put in the oven to get rid of the moisture Fig 06.15 Glass cleaning, smashing and measuring

TRANSPARENT RESTORATION

1 WEEK

FIRING We place the molds in the kiln and the flowerpots with the glass on top of them. In our case the flowerpots stand directly on top of our molds [with the exception of the mold No 8], which minimizes the chance of bubbles generation in our glass unit. For our molds we used either one medium flowerpot in the middle or two smaller ones symmetrically placed along the opening. The kiln must be programmed is such way so as to achieve a successful annealing process, which determines the quality of our glass units, as explained in Chapter 04.7. Due

to the Crystal Cast specifications [temperature up to 900°C] the temperature of the oven is programmed at 940°C [this corresponds to the oven environment; the temperature of the molds/glass is assumed to be lower, so a higher working temperature at 940°C is considered acceptable]. Three firings have taken place to manufacture all the units, having each one to last approximately one week. The annealing time is adjusted each time, according to the size of the blocks. [For an analytical kiln schedules, see Fig 10.6, Appendix 4].

162

Fig 06.17 During the first phase of the annealing process the speciments are rapidly cooled down by opening and closing the kiln door for almost an hour

Fig 06.16 The kiln set-up

Fig 06.18 By the end of the firing, glass has melted into the mold and shaped accordingly

06 VALIDATION TESTS

20 MINUTES

<< 1 HOUR

MOLD RELEASE

GLASS TREATMENT

When the kiln reaches room temperature we take the molds out and place them in a bucket of water for about 10-20 min in order for the Crystal Cast to dissolve and be easily removed. After being cleaned and all remaining particles are removed, our glass units are ready.

The manual fabrication results, unavoidably, in small imperfections on the glass surface [e.g. roughness, protrusions, depressions]. In order to avoid any stress concentrations due to these flaws, dental tools are used to remove any excess material.

Fig 06.21 Excess glass at the spot where the flowerpot was

Fig 06.19 The Crystal Cast mold dissolves in water and can be easily removed

Fig 06.20 The cast glass unit after being released from the mold

Fig 06.22 Scraping out the small bumps

163

TRANSPARENT RESTORATION

1 HOUR

MOLD TREATMENT The MDF molds are sawn from 3 sides [1 cm offset from the usable mold area] in order to fit to the thermoforming machine. In order to ensure the easy removal of the plastic sheet from the mold, we chamfer the corners.

164

INTERLAYER The interlayer we are using for the prototype is VivakÂŽ PETG, a transparent thermoplastic material widely used in purchase industry. Due to time and material constraints, it is chosen as it fulfills the main criterion of transparency and has adequate stiffness [2.02 MPa, according to www.bayer.com]. Moreover, another important advantage is the ability to be easily shaped. In our case, where the cast units show high shape complexity, this property facilitates greatly the manufacture process. For the forming of the plastic sheet we use the same MDF molds as we use in the fabrication of the glass units. The original thickness of the interlayer calculated in the digital model is 2mm. However, as the plastic sheets are directly available in 0.5 and 1.0 mm thicknesses we choose to use 2 layers of PETG. In order to achieve the highest accuracy, we use both of the MDF molds to have the exact imprint of both the top and the bottom faces of the unit. VivakÂŽ is very glossy so this may cause less friction between the interlayer and the glass than wanted. However, this is something that needs further investigation. Chapter 04.10 elaborates more on how friction works between the two materials.

Fig 06.24 Sawing of the MDF mold

Fig 06.23 The plastic sheet used as interlayer

Fig 06.25 Chamfering the corners

06 VALIDATION TESTS

<< 1 HOUR

THERMOFORMING

APPLICATION

We place our mold in the vacuum thermoforming machine and heat it at around 80Â°C. We place and clamp the PETG sheet in the rectangular hole, having the mold beneath it. When the desired temperature is reached and the sheet is flexible, the mold is lifted, while at the same time air is sucked from the bottom. The plastic is pushed against the mold and is shaped accordingly. We can now release the plastic from the mold with the help of pressured air.

The interlayer was originally calculated as 2 mm, so 2 layers of 1 mm sheet. However, there is a deviation in the dimensions of the final unit, due to the manual manufacture, surface quality and maybe natural shrinkage resulting in inaccuracies during the application of the interlayer. The interlayer is adjusted so as the interlocking areas of the glass units to be in contact to each other and do not allow for movement.

165 Fig 06.28 The application of 1 mm interlayer results in gaps between the glass units and especially the interlocking areas

Fig 06.26 Thermoforming of the interlayer

Fig 06.29 Adding more layers to make a thicker interlayer

Fig 06.27 The final shape of the interlayer

Fig 06.30 Final interlayer

TRANSPARENT RESTORATION

The experiment took place on the 2nd of June 2016 at the laboratory of Mechanical, Maritime and Materials Engineering Faculty under the supervision of Faidra Oikonomopoulou, Telesilla Bristogianni and Fred Veer.

06.3 SHEAR TEST

A Zwick Z100 displacement controlled universal testing machine of dimensions 400 x 400 mm, as shown in Fig 06.4. The main principle of this test is that the glass blocks are fixed on the bottom steel plate of the machine and a vertical steel element [cross-section 20 x 80 mm] is aligned with the block and pushes it down until failure. This setup ressembles an out-of-plane loading of our glass wall and tries to estimate the behaviour of the interlocking in shear.

Fig 06.31 Zwick Z100 displacement controlled universal testing machine

Five glass blocks are stacked vertically, overlapping

166

the steel L-shaped supports. In order to avoid direct contact with the steel elements and result in unwanted failure due to peak stresses occuring from the hard contact between the uneven glass surface and steel, an intermediary of neoprene is used in every surface of glass that is in contact to steel. Between the glass units the prefabricated Vivak sheets are used as interlayer. The two steel supports are also bolted together in six points to retain the distance between them during the experiment. For safety reasons, a sheet of plexiglass is placed in front of the set-up to prevent possible injuries due to unpredictable glass failure. Fig 06.33 shows the labeling of the glass blocks according to the manufacture process. Due to the manual fabrication, the surfaces of the blocks along its thickness can be either smooth, even and translucent [being in contact to the Crystal Cast mold] or uneven and more transparent [the side where the molten glass flows down from the flowerpot]. In order to achieve a good contact of all the blocks with the respective contact surfaces, it is chosen the side blocks [5, 6, 7, 8] to have the smooth, even surface at the bottom where they stand on top of the steel support. The middle block is treated in the opposite way: the smooth surface is placed on top to have a good contact with the steel head.

Fig 06.32 The steel â&#x20AC;&#x153;headâ&#x20AC;? pushing down the middle block over an intermediary of neoprene

1 5

6 Fig 06.33 Blocks labeling according to the manufacture sequence. The manufacture specifications and observations for each glass block are shown in Appendix .

06 VALIDATION TESTS

167

Fig 06.34 The set-up is placed on the machine and is ready to be tested

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EXPERIMENT RESULTS The glass block speciment reached an ultimate failure load of 17.3 kN [approximately 1,7 Tonnes] and a deformation of 2.23 mm [see Fig 06.35]. The failure occurred just in the middle glass block, leaving the rest intact. The initial crack occurred exactly in the middle of the bottom part of the unit and propagated upwards in its entire width resulting the unit to break in two pieces.

06.4 RESULTS & OBSERVATIONS 20000 18000

168

16000

Standard force [N]

As the speciment broke at its tensile zone, we cannot derive consistent numerical results concerning the shear strength of the interlocking unit, as it most probably failed due to bending [see Fig 06.37 a,b]. In order to attain a failure due to shear the speciments should have broken as shown in Fig 06.36. This means, that the crack initiated due to a flaw that might have occurred during manufacture. The failure pattern [see Fig 06.40] indicates that there is a relationship between the fusing lines, that appear in the inner glass structure in the polarized images, and the crack initiation. Also, according to the polarized images [see Table 25, Appendix 4], in almost all the speciments, it appears that the surface where the glass enters the mold is more colourful, meaning that some stresses still exist there due to the fusion of glass [a higher kiln temperature would result in a better mixture of glass, thus a more homogeneous mass].

14000 12000 10000 8000 6000 4000 2000 0 0

0.5

1.5

2.5

Deformation [mm] Fig 06.35 Force - Displacement diagram

Fig 06.36 Potential failure in shear

R S

[a] Loading conditions

[b] Compression zone at the top and tension zone at the bottom Fig 06.37 Estimation of acting forces and stress distribution during the test

[c] Shear forces around the interlocking zone

06 VALIDATION TESTS

Fig 06.38 Gap between the glass units, with [left] and without [right] the interlayer

Fig 06.39 The failure of glass at the upper area where it is in contact to the steel head of the machine

Another important aspect that affects the behaviour of the glass block in relation to its adjacents is the nature of the interlocking layer. Again due to the manual manufacture process, the block surfaces are not in perfect contact [see Fig 06.38]. The lack of standardized fabrication process and the intermediate materials used [MDF, coatings, wax, crystal cast] result in rough surfaces with large deviations in flatness and dimensions. Moreover, we can assume that the VivakÂŽ sheet, used as interlayer, has also not completely flat surfaces, due to the thermoforming process, which has resulted in a variable thickness. Thus, while two layers of 1 mm thickness were initially calculated, a final layer of 4 mm at the interlocking areas, and 2.5 mm at the rest flat area was achieved. Given the situation, the crucial thing is to create a good contact where the blocks interlock to each other, so that the distribution of forces is even and no movement occurs. This means that also during the experiment the flat surfaces of the adjacent blocks were not in contact resulting in no shear stresses or friction occurs at these areas. [see Fig 06.37c]. The aforementioned observations show that a great number of factors can affect an experiment. In our case these are: Manual manufacture process: a lot of materials are invoved diminishing in such way the accuracy of the final glass unit. Roughness and unwanted alteration of the shape, resulting mostly from the wax mold which shrinked in an unfavorable pattern, as well as bubbles were some of the flaws that could initiate a crack. The fabrication in controlled and standardized conditions would result in less tolerances and less flaws, such as bubbles etc. Soda-lime glass is used for the manufacture instead of the suggested borosilicate glass. The higher shrinkage rate of the former compared to the latter results in bigger tolerances.

Fig 06.40 The failure pattern of the middle block [top] in combination with the corresponding polarized image [bottom] show that there is a clear indication of the initial point of failure, right in the middle of the block, where the flowerpot was located during the firing. Also, the fusing lines seem to follow these of the crack propagation.

The interlayer does not behave as wanted as there is no actual contact between the glass blocks apart from the interlocking areas. Due to the strict timeframe of the current thesis the experimental data are not sufficient for statis-

169

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tical purposes and cannot be considered conclusive for determining the design values of the system in shear. Nevertheless, the following observations can be derived: The first impression is that the interlocking system behaves well, as the total deformation [2.23 mm] is less than the thickness of the interlayer [approximately 4 mm] at this point. This means that the interlayer protects against the hard contact of glass to glass when failure occurred. It also justifies the fact that the bricks did not crack at the interlocking areas. Flaws, attributed to the manufacture process, have prevailed over the interlocking connection, therefore it is expected that the interlocking system can withstand higher loads than the presented ones and the performance can also be improved of a stiffer interlayer is used.

170

The interlocking system, as tested, has sufficient strength [17.3 kN] against windload [1 kN/m2]. Additional tests against dynamic loads [earthquakes] which are also important due to the location of the case study, or the performance of different interlayers are necessary in order to derive design values. GLASS UNIT EVALUATION The manual manufacturing process of the units results in a different quality of the glass compared to standardized methods. However, several observations are made in order to have a better insight of how glass casting works, and what could possibly be improved. Apart from the visual inspection, where the quality of the glass surface, any bubbles or inaccuracies due to the mold fabrication can be identified, polarized films are used in an attempt to explore the interior structure of the glass units. Transparent objects, like glass, have one index of refraction, however when there are residual stresses inside the glass, the index of refraction changes. When we put a glass unit between two polarized films, with a 90Â° rotation angle between them, possible stresses are revealed through colors, giving a qualitative assessment of the internal stresses [see Fig 06.42]. It is not possible to estimate the amount of stress, neither if it is compressive or tensile. The observations concerning the manufacture process are presented as follows:

06 VALIDATION TESTS

The first batch of bricks [numbers 1,2,3] show zero or minimum colours, meaning that the annealing time in the kiln was appropriate in order to avoid internal stresses. However, despite the fact that for the following firings a longer annealing time is used, the colours are more visible, especially in the half blocks, which have more mass [see Fig 06.41].

Fig 06.41 Different levels of internal stresses between a full [up] and a half [bottom] block. The latter, having more mass, requires more time for annealing.

Colours are mainly observed around the interlocking areas [see Fig 06.42] and the short side which is in contact to the air and the molten glass enters the mold. This could be caused by the geometry of the blocks, which compels the molten glass to follow specific flows, but also, because of the relatively low temperature in have resulted the glass pieces to have not completely fused.

Fig 06.42 Colours appear behind the polarized films may indicate the existence of internal stresses

Fig 06.43 Black and white areas appear when looking at the large surface of the unit as it is placed in the kiln

Fig 06.44 Bubbles at the one side of sample 8

White and black areas are identified behind the polarized films [see Fig 06.43], which, once again, could be an indication of the flows that glass follows when entering the mold. The distance between the flowerpot and the mold contributes significantly to the formation of bubbles inside the glass. In sample 8, where the flowerpot is placed 3 cm higher, bubbles are observed at this area [see Fig 06.44]. This is justified, as the larger the distance between the flowerpot and the mold, the more the air inserted. A general observation is that the different materials used [MDF, coatings, wax, Crystal Cast] can alter the final dimensions of the glass block. Wax pouring is the most important step of the process as this is the shape imprinted by the Crystal cast investment powder and consequently the final shape. However, the behaviour of wax is very unpredictable as it shrinks significantly resulting in recesses on its surface. A further development of the manual fabrication process in order to avoid so many materials would result in faster fabrication, a more accurate shape and quality, as well as more coclusive results for the experimental process.

171

Fig 07.1 iv . Detail 1:2 scale of the prototype Ice Fallsfabricated at Hearst tower in the .context Foster + ofPartners this research . New York . 2006

07.

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An innovative restoration approach as the one discussed in the current research has specific demands in every step of the process regarding the data acquisition, the fabrication and construction. These steps can be described as follows: treatment of the historic material, 3D scanning, glass manufacture, construction and maintenance.

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As resulted from Chapter 01, glass can be used to consolidate a structure by reinforcing but it does not intervene in the actual materials. The historic materials should be treated with the conventional strengthening methods that each one requires. Moreover, like in our case, the new glass structure can act as a barrier for the protection of the monument against the elements. In any case, the existing materials should be pretreated in order to accommodate the new â&#x20AC;&#x153;transparentâ&#x20AC;? intervention.

Glass is a material, which demands a high degree of accuracy and given the boundary conditions of the rough, uneven surfaces of the remaining structure, a high design precision is necessary to achieve a successful result. For this reason, 3D scanning tools are suggested in order to imprint the existing structure and provide a solid, reliable background as a design base. The areas of interest are primarily the faces connected to the glass structure, however, the overall scanning of the monument is feasible and in some cases preferable, in order to ensure the validation of the design.

07.1 METHODOLOGY

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After having proceeded with the final design and detailing of the suggested concept, comes the fabrication of the required glass elements and their related components [interlayers, embedded connections etc].

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The construction phase requires, at first, the appropriate organization of the place according to the construction plan. Some aspects, we should take into account are the need for a temporary supporting installation [e.g. scaffolding], any special environmental conditions suggested for the materials used [e.g. levels of humidity], the need for equipment to carry heavy components, as well as the transportation routes for both the materials and the workers. In a secondary level, a careful design of the construction process is necessary in terms of the assembly order.

Last but not least, we need to ensure the longevity of both the new and the old structure; thus, strict maintenance guidelines should be followed in order to preserve the aesthetics and the integrity of the restored part.

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While masonry is assumed one of the most durable historic building materials, it is the most susceptible to damage by improper maintenance or repair techniques. After the identification of the damages and the extent of decay, careful measures should be taken always in collaboration with a specialist in preservation technology. MEASURING THE DAMAGE EXTENT Laboratory and in-situ field methods of measuring the extent of damage are necessary in order to decide what kind of treatment is needed [Doehne & Price, 2010] DRAINAGE Water, and especially salt water, is the main enemy of our historic masonry as the salt results in crystallization inside the stone, decreasing its strength. Before the new intervention takes place, we need to ensure that the lower part of the masonry, which is mostly damaged and has recessed due to material detachment, is water and moisture free. For this reason, proper drainage should be provided. [www.cityofrevelstoke.com] 176

REPAIRING TECHNIQUES Repointing is used to repair deteriorated mortar joints. Damaged mortar should be carefully removed by hand-raking the joints to avoid damaging the materials [see Fig 07.5]. New mortar should be compatible with existing one, so not too dense or stiff. Lime-mortars are more preferable, while Portland cement, though stronger, can harm the historic materials [www.gsa.gov]. Injections [see Fig 07.2] are used to consolidate the materials in micro scale. Lime, grout, barium hydroxide, organic polymers, alkoxysilanes and cycloaliphatic epoxy resins are some of the possible intermediary materials that can be used to bond and strengthen

07.2 MATERIAL TREATMENT In-situ field methods [minimally destructive]: Optical/laser profilometry Monitor surface roughness Close-range photogrammetry Laser-interferometry Infrared thermograpgy Laser holography Ultrasonic waves transmission etc. Laboratory-based methods [samples extraction required]: Polarized light microscopy Scanning electron microscopy Biaxial flexural strength measurements Hygroscopic moisture content X-ray tomography etc.

Fig 07.2 Dispersed lime injection grout for stabilization

WIDELY APPLIED TREATMENTS

UNDER-DEVELOPMENT TREATMENTS

NANO-LIME PARTICLES SUSPENDED IN ALCOHOL WATER-BASED HYDROPHOBIC COATINGS SPRAY-ON LATEX FOR CLEANING ARCHITECTURAL INTERIORS PORTABLE, LARGE-SCALE LASER SYSTEMS FOR CLEANING BIOREMEDIATION

COUPLING AGENTS FOR LIMESTONE CONSOLIDATION IMPROVED POULTICING METHODS TREATMENTS FOR CLAY SWELLING OF STONE NANO-PARTICLE-MODIFIED SILANE CONSOLIDANTS; CALCIUM ALKOXIDES; CALCIUM OHOSPHATE OR OXILATE TREATMENTS NANOTECHNOLOGY CLEANING AGENTS

Table 18 . Stone Conservatorâ&#x20AC;&#x2122;s tool kit according to Doehne and Price [Doehne & Price, 2010]

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the inner masonry structure [Doehne & Price, 2010]. Rebuilding of collapsed parts is also a common case. The new materials should be carefully chosen in order to be compatible. The quarry used for the construction of the current tower is located in the surrounding area and could still be a source of raw materials. Additionally, detached stones found in the chambers of the tower, the outdoor area or even the bottom of the sea adjacent to the SE façade could be cleaned and reused for the consolidation of some parts of the masonry. Fig 07.3 Cleaning of limestone during [Colosseum restoration, 2014]

Fig 07.4 Soft-bristled brushes and toothbrushes appropriate for the cleaning of limestone [Colosseum restoration, 2014]

Fig 07.5 Removal of previous poorly-done repairs using hammer and chisel [Colosseum restoration, 2014]

CLEANING Masonry should only be cleaned in order to remove heavy soiling [e.g. pollution, dirt, moss] or prevent further deterioration. If properly done, it enhances the aesthetics and the structural ability of a historic building. The gentlest methods to apply are water-washing [see Fig 07.3], use of detergents and natural bristle brushes [see Fig 07.4]. Abrasives, chemical agents or sandblasting techniques should be avoided, as they can permanently damage the historic materials [www.cityofrevelstoke. com]. High-pressure water cleaning methods may also damage the historic masonry and the mortar joints. Surface cleaning tests are necessary to avoid unwanted short or long-term effects [www. gsa.gov]. PROTECTIVE COATINGS Protective coatings against water and microorganism growth [mould, moss, algae] should be applied in the existing masonry. Water-repellent coatings appear to be a better option than waterproof coatings as they allow the masonry to “breath”, while preventing liquid water from penetrating into the wall. Typically such coatings are colorless in order not to alter the appearance of the masonry. (Elizabeth A. Campbell 2014)

PREVENTIVE CONSERVATION

DOCUMENTATION TOOLS

MICROCLIMATE STABILIZATION AND SHELTERS MITIGATION OF RAPID ENVIRONMENTAL CONTROL FOR SALTLADEN STRUCTURES BASED ON COMPUTER MODELS AND OBSERVATIONS WIND FENCES, TREES, REBURIAL ETC.

3D LASER SCANNING TO QUANTIFY SURFACES QUANTITATIVE CALIBRATION OF DIGITAL COLOR IMAGES SOLVING THE LIGHTING PROBLEM - REPEAT PHOTOGRAPHY [PTM IMAGES, COLOR MATCHING]

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The detailed recording of ruined monuments has been one of the greatest challenges for geodesists, archaeologists, architects and engineers who aim at a precise representation of our cultural heritage. The development of 3D laser scanning technology has achieved today significant innovations regarding 3D data collection, representation, rendering, reconstruction and surveying, enabling the digital generation of historical buildings, sites and ruins. Factors such as inaccessibility, large volumes, dangerous conditions and complexity of the structure can make the documentation very difficult if not impossible. [A.Gulec Korumaz et al, 2010]

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According to Fig 07.7 there are various methods to acquire 3D data, depending on the size of the objects, the degree of accessibility and the desired resolution. The techniques are divided between active, where the measured object must be actively illuminated, and passive, which work with ambient light. [Pezzati & Fontana, 2008] Except for photogrammetry, which combines 2D records to obtain the volumetric information of an object, the rest passive techniques are not widely used due to the reproduction of data in a plane or flat surface. Thus, the most common methods that are applied today in the conservation science are the triangulationbased and the time-to-flight laser scanning. Table 18 shows an overview of the main characteristics of these systems. [Margarida Pires & Borg, 2008]

07.3 3D SCANNING TECHNOLOGY

Fig 07.6 3D laser scanning of an artwork using laser trinagulation

FRINGE PROJECTION MULTIPLE LINE PROJECTION

MOIRÃ&#x2030; COLOUR-CODED PHASE-SHIFTING

TRIANGULATION

SINGLE LINE PROJECTION

SINGLE POINT PROJECTION PULSED ACTIVE

TIME-OF-FLIGHT MODULATED HOLOGRAPHY MICRO-PROFILOMETRY

3D MEASURING OPTICAL METHODS

MULTI-WAVELENGTH WHITE-LIGHT

PHOTOGRAMMETRY SHAPE FROM SILHOUETTES PASSIVE

SHAPE FROM SHADING BINOCULAR VISION CONFOCAL MICROSCOPY

Fig 07.7 Classification of optical 3D measuring main techniques

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SITE PLANNING SCANNER POSITION REFERENCE POINTS SETTING [USED WHEN MORE THAN 1 SCAN ARE REQUIRED]

DEFINITION OF SCANNED AREA SCANNING RESOLUTION TOTAL NUMBER OF SCANS SCANNER CALIBRATION

3D DATA ACQUISITION POINTS CLOUD

POLYGON MESHES

POST PROCESSES MERGING ALIGNING

IMAGE ANALYSIS DETECTION OF DEFECTS

STORAGE & BACKUP

3D MODELING EDITING TEXTURE MAPPING COLOUR Fig 07.8 Workflows related to 3D scanning process

3D laser scanning methods take profit of the coherence properties of laser light, in the form of a highly directional light beam of pure color, in order to acquire, store and process the information of the related object, using sensitive sensors to detect the light reflected from the object. [Margarida Pires & Borg, 2008] Such technologies can provide sufficient documentation with exact geometry and texture. One of the most important drawbacks of laser scanning is the huge amount of data it handles, which can lead to extremely time-consuming post-processing of the point-clouds, especially when high-resolution is needed. On the other hand, processing in low-resolution results in less accurate models. [A.Gulec Korumaz et al, 2010] We should mention here that the evaluation of resolution [minimum distance between two scan points] refers to the correspondence between the scanned data and the original surface; thus, close-range scanners provide better results than long-range scanners. The lenses, the sensors, the scanned area and the software algorithms used in the data processing are some of the variables that influence the degree of accuracy. [FACTUMarte, 2016] The exact process of 3D scanning and various workflows are shown in Fig 07.8. [Margarida Pires & Borg, 2008] It is evident that a great range of possibilities exists nowadays and makes feasible the digital design of a historic complex. A great advantage is that such a technique is completely safe for the historic fabric, non-invasive and harmless, as there is no interference with the measured object.

Fig 07.9 archaeological site of the forum in Pompeii (Italy) performed integrating terrestrial images, long-range TOF scanning and aerial images

The overview of all the possible methods to acquire 3D images shows that the most appropriate techniques for our case is a combination of both long and close range scanners. The former provides the 3D image of the entire faรงade in order to know what are the boundary conditions of the new intervention and further estimate the appropriate form and thickness. The latter could be used in order to acquire the detailed imprint of the areas of the monument connected to the glass structure; a higher resolution and degree of detail is necessary, in this case, in order to accurately design the stacked float glass components and achieve a connection of high precision, so that the two parts can fit to each other.

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TIME-OF-FLIGHT

3D SCANNING PRINCIPLE

Fig 07.10

TRIANGULATION

Mathematical relations between the direction of the emitted laser beam and the direction of the detected reflection allow for information on the position of the object surface points. Fig 07.11

MICRO-PROFILOMETRY

180

A short laser pulse is sent to the object surface, reflected back and detected on a photosensor. Using the known speed of light in the air and the laser pulse travel time since emitted by the laser source till the detection on the sensor, the distance to the illuminated surface point may be easily computed.

Fig 07.12

Table 19 . Overview of the main characteristics of laser scanners

Uses the interference phenomena of laser light and the analysis of the optical fringes produced, to detect and image an object surface texture and profile.

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RECORDING DISTANCE

EQUIPMENT

RESOLUTION

LONG - MEDIUM RANGE [1 - 1000 m]

5 mm

CLOSE RANGE [up to 1 m]

100 µm

APPLICATION

Fig 07.13 FARO Focus3DX 330 laser scanner

181

1 cm - 1 m Fig 07.14 Lucida 3D Scanner

VERY CLOSE RANGE [up to 4 cm]

< 1 µm a < 1 cm2

Fig 07.15 FRT MicroProf

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The glass components used in the current design include laminated float glass, laminated curved glass, stacked float glass and glass blocks. The special demands and limitations concerning the manufacture of each of these components are discussed in this chapter. The two production techniques used are these of float and cast glass.

07.4 GLASS MANUFACTURE

FLOAT GLASS Annealed float glass is widely available and produced in a standard line developed by Pilkington Company in 1952 [see chapter 02.4]. The standard manufacturing size is 3.2 x 6 m, but nowadays oversized panels are also feasible. What limits the size of glass is usually the size of the post processing machines: the cranes used to move the panes from the cutting table to the storage [panels 4.2 x 25 m have been produced in China], the tempering and lamination autoclaves [the largest autoclave can laminate up to 3.20 x 15 m and belongs to Sedak company] as well as the transportation requirements [maximum standard shipping container of 2.33 x 13.71 x 2.65 m]. Customized products are available upon request but can significantly increase the overall costs. 182

Fig 07.16 13m tall curved, toughened and laminated glass panels are fabricated as one piece, Apple IFC by Eckersley â&#x20AC;&#x2DC;O Challaghan, Shanghai

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While, borosilicate is the main glass type used for the current design [see chapter 04.8], soda-lime silicate glass is chosen for the roof and floor elements made of curved and float glass respectively. The main reason is that these elements are not an integral part of the glass masonry and can behave differently in terms of thermal expansion. Float soda-lime glass is preferred, as the most common glass is float production and the most cost-efficient solution. Fig 07.17 Principle of splice-lamination at Apple Store, Sydney

180

Fig 07.18 The glass roof is fabricated as one monolithic element consisting of three laminated panes

135 164

Fig 07.19 Floor glass element [3 laminated layers]

The roof structure consists of flat and curved parts, which can be easily formed into shape with a bending process. In order to achieve maximum transparency and avoid visual obstacles due to mechanical connections at the edges, the roof is manufactured as a monolithic element [see Fig 07.18]. The overall length is 7.60 m and the maximum width is 2.30 m. An oversized element like this could be possibly fabricated as one piece, as in the case of Apple IFC in Shanghai [see Fig 07.16]. This glass element could actually be laminated in Sedak, Germany; they produce and laminate up to 3.2 x 16 m glass panels [www.sedak.com] Yet, if this is not feasible, splice lamination could be an option as well. This technique has been developed for the Apple Cube 1.0, where the 10 m long glass fins have been constructed by laminating layers of 6 m long panels and also applied at the Apple Store atrium in Sydney [see Fig 07.17] reaching the height of 13.5 m [Oâ&#x20AC;&#x2122;Callaghan & Marchewka, 2009]. To form curved glass panels two options are available: hot and cold bending [see chapter 02.4]. In our case, a radii of 2.20 m is required so we choose the first option of hot bending, which meets these requirements. Moreover, according to Sedak comfeasible [www.sedak.com].

Both the roof and the floor structure [see Fig 07.19] consist of three layers of float glass; 10 mm each layer would be enough. Fully tempered and heat-strengthened glass preferred compared to annealed glass due to their higher yield strength. The safety of these elements is achieved by redundancy, owing to the lamination of multiple layers, thus, is one breaks the other two still hold it into position and are able to carry the loads.

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The process is as follows: float glass panels are cut according to the design and stacked on top of each other using an adhesive tape, having the embedded steel connections inserted and glued in between the layers. The fabrication is completed in the factory and the units are transferred then to the construction site.

FILM

COST AESTHETICS LOAD-BEARING CAPACITY ADHESIVE APPLICATION SAFETY DISASSEMBLY more efficient less efficient

› ›

›

The bonding between the layers should be strong enough as these components are transferring the forces between the old and the new masonry. The embedded connections, should be further investigated to see how they could affect the composite stacked glass units, as they are made from a different material and therefore, expand in a different rate. For this reason, titanium connections are chosen due to the lower thermal expansion coefficient [aex=8.6 * 10-6 K-1] than steel [aex=14 * 10-6 K-1], as well as, ensure a thicker interlayer between glass and titanium to account for the thermal expansion.

LIQUID

›

184

STACKED FLOAT GLASS The connection between the glass blocks and the existing building is realized by glass components consisting of stacked float glass. Borosilicate glass is used in this case, as we want this part to behave as one structure together with the interlocking system. Thus, a similar thermal expansion coefficient is of great importance to ensure a similar movement due to temperature differences. The ability of cutting the layers of float glass into any shape can achieve the desirable imprint of the uneven masonry surface. The typical dimensions of a stacked unit are 600 x 300 mm, when the maximum dimensions fro borosilicate glass could be up to 1150 x 850 mm [BOROFLOAT 33, SCHOTT, see Appendix 2].The bonding of these layers can be realized either using a liquid adhesive [Laminata House, Leerdam] or an adhesive film [Glass Angel, Zwolle]. According to Roy van Heugten (Heugten 2013) liquid and film adhesives can be compared as shown in Fig 07.20. For the current design, given the large number of glass layers [25] an adhesive film [tape] is chosen to ensure a fast manufacture. The mechanical behaviour should be further examined though, to ensure that there is an adequate adhesive film for the stacked units. Moreover, as the aesthetic result does not demand a total transparency, any small imperfections or bubbles, due to the film application, are negligible.

Fig 07.20 Qualitative comparison of liquid and film adhesives according to Roy van Heugten. There is no comparison between the qualities, but only between the adhesive types. Costs can vary among the different types for both liquid and film adhesives, but in general the production process of liquids is more difficult, time-consuming and expensive. Films are never perfectly transparent and bubbles are more probable to occur in contrast to liquids. However the application of liquids is more demanding as it needs time for curing, spacers to keep an even thickness and higher degree of caution, which makes the entire process slower. The load-bearing capacity between the two types can also vary among the different products but in general, liquids adapt better to the micro-profile of the glass panels. In terms of safety and disassembly, the two adhesives behave in a similar way [Heugten, 2013]. Of course, the design and orientation of the stacked panels determines which of these qualities should be taken into account when choosing the type of adhesion. EMBEDDED STEEL CONNECTION

EMBEDDED STEEL CONNECTION

ADHESIVE INTERLAYER BOROSILICATE FLOAT GLASS Fig 07.21 Stacked glass unit in detail

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Fig 07.22 The steel molds filled with molten glass

Fig 07.23 Moving of the glass bricks to the annealing kiln

Fig 07.24 The different parts of the steel mold

CAST GLASS There are two ways to produce cast glass components: hot pour and kiln casting [see chapter 02.4]. For the manufacture of the glass units used for the experiment, the latter technique is chosen as the most affordable in terms of cost and facilities [see chapter 06.2]. However, for the real fabrication of glass units, the hot pour casting method would be more appropriate. The advantage of this process is that it makes use of permanent molds [usually made of steel or graphite], which are expensive compared to the disposable ones, but reusable. Additionally, these molds ensure high accuracy at the surfaces of the glass unit that are in contact to the mold, as well as, smooth finishing if the mold is properly preheated: if the mold is cold, the hot glass freezes instantly and results in a rough, wavy surface. On the other hand, if the mold is too warm, then the glass tends to stick on it [Oikonomopoulou et al, 2016] The glass bricks manufacture process for the Crystal House in Amsterdam by Poesia® provides an insight of the industrialized production line of cast glass components. A total of 7500 solid glass blocks have been fabricated according to the following process: a “scoop” of molten glass is poured into the preheated steel open mold manually. The glass [around 1250°C] is left in the high precision

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mold to rapidly cool down to 700Â°C for a few minutes. Then, the upper part of the mould is removed and the glass brick can be easily transferred to the annealing kiln to gradually cool down to room temperature [see Fig 07.22, Fig 07.23, Fig 07.24]. The main disadvantage of this process is that during the cooling and annealing process, natural, inevitable shrinkage occurs to the glass volume [see Fig 07.24]. Thus, post processes, such as CNC cutting and polishing are necessary to achieve a flat surface and minimize any local projections [Oikonomopoulou et al, 2016]. However, as explained in chapter 04.7, post processing can significantly increase the overall cost of the manufacturing process.

186

Fig 07.25 Due to the temperature differences between the core and the surfaces of the glass unit, natural shrinkage occurs in all the surfaces. However, in an open mold and with the contribution of gravity, larger shrinkage is observed.

Given the special shape of the units, having protrusions and depressions in each side respectively, two-component high precision molds that work under pressure are the most adequate. They are currently used for the production of high precision optical components, such as lenses, or decorative objects, and suggest that the hot glass is pressed to take the shape of the mould [see Fig 07.26]; in this way no grinding or polishing is needed. In our design, we have 8 types of glass units and by extension 8 different molds. While high precision molds could be expensive, the total amount of glass blocks needed is more than 17.000, so this compensates for the total cost. In any case, more than 8 mold will be needed, as they tend to wear out after a certain number of uses, but also to achieve a faster production line. Borosilicate glass is preferred instead of sodalime-silicate glass, due to its low thermal expansion coefficient [around 3.2 - 4 K-1]. Thus, the glass masonry is not subjected to temperature changes and is less prone to thermal shock [the warm climate of Greece in combination to the close proximity of the monument to the sea may result in high temperature differences, especially at the lower part of the masonry]. Borosilicate glass is also subjected to less shrinkage during annealing, and higher dimensional accuracy. Moreover, the combination with a pressurized precision mold, could even eliminate any post-processing of the final product. This method has been used for the fab-

Fig 07.26 Pressed glass manufacture

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rication of the borosilicate glass bricks of the Atocha Memorial, where a ± 1 mm dimentional tolerance was attained [Christoph & Knut, 2008). This is sufficient for the current design, as the interlayer between the glass blocks [3 mm] can account for such a tolerance. Another important aspect is the annealing time; taken into account the cases of Crystal House and Atocha Memorial, where sodalime and borosilicate glass are used respectively, it is evident that the latter can result in a faster annealing and manufacturing process [see Table 20]. Moreover, borosilicate glass is lighter than sodalime. These advantages can generally compensate for the high cost of such type of glass including the raw material and the energy demands during the manufacture [borosolicate demands higher working temperatures than soda-lime, around 1500°C].

Fig 07.27 Steel mold surface quality

upper part

possible holes Ø 1 mm to allow air escape

handles

Steel can provide an excellent surface quality [see Fig 07.27], whether graphite could be more easily treated according to the surface result we want to achieve [rough, texturized etc.]. Release coatings [e.g. nickel coating] are also important in the case of steel. The mold consists of three parts in order to facilitate the glass unit release. Like in the case of Crystal House, no hinges are incorporated, so as to avoid any unwanted seam or damage of the glass units during the release. The three parts are aligned with the use of special sockets. Small holes of minimum diameter are introduced in the mold design so as to help air escape and avoid any air bubbles, while preventing the melt to escape [see Fig 07.28].

middle part

alignment sockets lower part

Fig 07.28 Suggested precision mold

CRYSTAL HOUSE . SODA-LIME GLASS

ATOCHA MEMORIAL . BOROSILICATE GLASS

h = 65 mm 200 mm

210 mm

DIMENSIONS

h = 70 mm

105 mm

157.5 mm

210 mm

300 mm

VOLUME [mm3]

1433250

2149875

2866500

4200000

MASS [kg]

3.5

5.37

7.165

8.4

ANNEALING TIME [h]

20-24

Table 20 . Comparison of annealing time between soda-lime and borosilicate glass products. While borosilicate block has bigger volume, it requires less annealing time than the larger blocks of soda-lime. Moreover, we observe that annealing time is multiplied exponentially depending on the volume.

187

TRANSPARENT RESTORATION

The fabrication process suggested for the current case study is illustrated below:

STEP 1 Middle and lower parts of the mold are preheated and stacked

STEP 2 Pouring of molten glass into the mold in a standard-known portion

STEP 4 The glass unit remains inside the mold for a few minutes to retain its shape during the process of fast cooling

STEP 5 The upper part is removed and the molten glass is shaped accordingly

STEP 7 The new assembly is rotated

STEP 8 Carefully the middle and lower part are also removed. The interlocking protrusions face up.

STEP 3 The upper part is hydraulically pressed down to fit in the other two parts of the mold, while giving shape to the molten glass

188

at the bottom and the protrusions face up Fig 07.29 Manufacture process step by step

STEP 6 A steel plate is placed on top to create a flat surface for the glass block to rest

STEP 9 The glass unit is transferred to the annealing kiln where it cools down at a very slow rate in order to release the internal stresses

[mm ]

[kg]

NUMBER OF UNITS*

2767622

6.17

12000

<< 15

CORNER UNIT

2811046

6.27

230

<< 15

TRANSVERSE UNIT

07 FEASIBILITY

2792111

6.22

2000

<< 15

VOLUME 3

MASS

ANNEALING TIME* [h]

2792111

6.22

400

<< 15

HALF UNIT

1370993

3.05

2000

<< 5

CAP UNIT

1162309

2.6

200

<< 5

SLIDING UNIT

189

1251269

2.8

500

<< 5

SLIDING CAP UNIT

DOUBLE TRANSVERSE UNIT

BASIC UNIT

UNIT TYPOLOGY

1042585

2.32

500

<< 5

* approximate estimation

Table 21 . Overall of the glass units introduced in the interlocking system and the estimation of the manufacture specifications

TRANSPARENT RESTORATION

The use of an interlayer in between the glass elements to form dry connections is discussed in chapter 04.10 and it occurs that a plastic foil is the most adequate for this purpose. There are multiple processes to achieve the desirable shape taking into account the quantity and the production rate, tolerances and surface finish, detailing and form, plastic type and size of the product. The phases that each process includes are: heating [to soften or melt the plastic], shaping [under constraint] and cooling [so that the shape can be retained]. PET, PETG, PMMA and PVC belong in the family of thermoplastics and are the most promising materials to use for the dry connections. The raw materials for thermoplastics are pellets or granules, while already fabricated sheets can be also formed.

190

Given the desired shape, the processes that can be applied in our case are injection molding and thermoforming. Table 22 shows an overview of the main characteristics of these forming methods in respect to the pre-selected materials. It appears that there are not distinct differences between the two forming processes. Injection molding seems to have better results in terms of tolerances and surface quality, requires no further treatment and is applicable to all materials. Both methods are suitable for a large volume of products and have a high production rate. The batch of interlayers required in the current design reaches the 17500 units, resulting in a good ration of batch size and cost per unit. The price range for thermoforming is 8-50 â&#x201A;Ź [CES EDUPack 2015, see Table 22], while for injection molding 10-22 â&#x201A;Ź per unit. The former uses sheets as raw materials, which are more expensive, but has low tooling and capital costs, while the latter uses very cheap molds and raw materials [pellets/ granules], but has high capital and tooling costs. Injection molding appears to perform better as a forming technique, as a uniform thickness can be achieved and the interlayer itself should be less stressed, compared to thermoforming. The relevant costs are also in favour of this method, so it is preferred for the current design.

07.5 INTERLAYER MANUFACTURE

07 FEASIBILITY

INJECTION MOLDING

DRAPE FORMING

PLUG-ASSESTED FORMING

VACUUM FORMING

PRESSURE FORMING

RAW MATERIAL

PET PETG

PVC PMMA

FORMING PRINCIPLE

THERMOFORMING

SHEETS

PELLETS / GRANULES

[THINNING CAN OCCUR TO CORNERS]

0.5 - 1 mm

0.1 - 1 mm

SHEET TRIMMING

[-]

COST/UNIT

POST PROCESS

TOLERANCE

QUALITY

191

[RETRIEVED FROM CES EDUPACK 2015]

› Table 22 . Comparative table of interlayer forming processes

*less feasible/low quality

› more feasible/high quality

TRANSPARENT RESTORATION

The construction of the glass masonry is preferable to take place during May â&#x20AC;&#x201C; June in order to reduce the probability of rainfalls [see Appendix 1]. As it is an interlocking dry system two months should be enough for the construction. Special environmental conditions are required according to the specifications of the UV-curing sealant and to have a better control of the construction. The tower is accessible by car/truck/small crane by the main entrance [see Fig 07.30] and there is plenty of space around the monument for the storage of the materials. In order for the construction to run smoothly, the following steps should be followed:

07.6 CONSTRUCTION

Fig 07.30 The main entrance at the north part of the castle Areas for material storage and accomodation of small crane trucks that enable the transfer of materials to the lower platform at the sea level

Ramp for transfering the materials to the level of the monument

192

Platform at the level of the sea, which is the base for construction

Scaffolding

Transportation route ot the sea level

STEP 1 Organize the construction site; transportation routes for materials and people; storage of materials; working platforms

07 FEASIBILITY

STEP 2 Site inspections

STEP 3 3D scaning of the contact areas

STEP 4 Scaffolding and protective tent on top of the sea in SE faรงade

193

STEP 5 Installation of the foundation

STEP 6 Building of the lower part of the glass masonry

STEP 7 Building of the middle part of the glass masonry [Special treatment of the components underneath the existing building]

STEP 8 Building of the upper part of the glass masonry assisted by an indoor scaffolding

STEP 9 Installation of the roof

STEP 10 The restored monument as a new attraction point for the historic castle and the entire city of Methoni

TRANSPARENT RESTORATION

A crucial parameter that has influenced the concept development and the design strategies is the idea of reversibility. The Venice Charter [see chapter 01.4] suggests that a restoration should be reversible in order to allow for future alterations, without harming the historical structure. These alterations could be the development of new consolidating techniques, in terms of technological advancements, or the option for another treatment. Reversibility is achieved with the proper design of connections. Mechanical connections [Optical House], which are easily disassembled, are proved to be durable and ensure stability but also pose visual obstacles, which is an important aspect in the concept of transparent restoration with glass. On the other hand, transparent adhesives is a common practice for cast glass masonries [Atocha Memorial & Crystal House], allowing maximum transparency but in a permanent and irreversible way.

194

The innovation of the current design is that it introduces a new way of assembling cast glass units, which combines a transparent interlayer and the advantages of interlocking geometries. The interlayer does not require any bodning to keep the structure stable, as the glass blocks fit to each other and are restrained due to their geometry. Additionally, mechanical embedded connections are used wherever is needed to create a firm connection between the members, which once again create minimum visual impact. Such a system enhances both the assembly and the disassembly. The former contributes to a fast construction, with no time wasted for curing of the materials and less labor, decreasing the overall costs. The latter serves the guidelines suggested for restoration practices. Another important extension of such a demountable design strategy is the ability of recycling by reusing the glass units. As no permannet bonding occurs, the blocks can be easily disassembled, transferred and reassembled again if needed at another location or for another purpose, without any further process. Thus, by reusing, we avoid all thsi energy needed for the manufacturing process, which turns glass into a rather unsustainable material.

07.7 ASSEMBLY & DISASSEMBLY

07 FEASIBILITY

07.8 MAINTENANCE STEP 1 Removal of the damaged glass block, by carefully smashing the remaining pieces

STEP 2 Cleaning of the inner surfaces

STEP 3 Adhesive application and fitting of the new units

STEP 4 The aesthetics and structural integrity of the glass masonry are restored

Fig 07.31 Repairing steps for damaged glass unit

Fig 07.32 Fungus growth between unsealed glass blocks [masonry sample exhibited in BK entrance, TU Delft, June 2016]

Glass is a durable material and practically maintenance-free, as it is not subjected to weathering, thus the maintenance of the structure relates to basic cleaning requirements, repointing and replacement of damaged blocks. CLEANING NanoShell® provides a large variety of protective coatings, among others for glass and stone [both limestone & sandstone]. These hydrophobic coatings are colorless, contain nanoparticles, which ensure self-cleaning result, are resistant against dust and seawater, while reducing the growth of microorganisms and bacteria. NanoShell Glass® and NanoShell Stone® are applied every 5 and 25 years respectively. [www.nanoshell.co.uk] REPAIRING | REPLACING Minor scratches or cracks, as well as, slight fogging may occur to the glass blocks but are not assumed to affect their structural performance. On the other hand, large cracks, due to thermal shock or impact loads, should be encountered with the replacement of the glass blocks. The damaged block must be broken out without damaging the adjacent blocks. The dry connections enable the replacement process. Due to the interlocking geometry of the unit, it is impossible to fit in a new full unit, unless if it is located on the top layer. Two smaller units should be put instead covering the two sides of the wall, leaving a void in the middle. Before the application of the new units, the inner surfaces should be cleaned and the interlayer should be carefully removed at the areas where the new units are placed. As the locking method does not exist anymore the new units should be adhesively bonded to the adjacent blocks, in order to stay in position and ensure the uniform transfer of the loads [see Fig 07.31]. Repointing [replacing of the damaged joints] is necessary when the sealants between the glass blocks are damaged or missing. Fungus and algae can easily grow between the glass blocks, are undermine the overall aesthetics of the restoration treatment [see Fig 07.32].

195

Fig 08.1 Polarized image of the glass block, as an evaluation tool regarding the internal stresses

08.

CONCLUSIONS

TRANSPARENT RESTORATION

The current research suggests an innovative way to restore monuments, using glass elements. According to the objectives set in the beginning of the research, the final proposal introduces a combination of cast, float and stacked glass elements in an attempt to address aspects such as reversibility, structural consolidation and transparency [see chapter 00.3].

198

Reversibility is achieved by minimizing the bonding between the glass and the original structure. So far in similar glass structures [see chapter 04.6], the solutions introduced have been either transparent and permanent [adhesive connections] or reversible but visually intrusive [mechanical connections]. In the current design an innovative dry connection has been developed, which makes use of a transparent interlayer between the glass elements, simply by stacking one on top of the other. Additional mechanical embedded connections are used wherever is necessary. Finally, no adhesion takes place resulting in a 100% demountable structure.

However, in order for such a system to work, the structural integrity of the glass units should be ensured, given the large volume of the structure and the constant loads it receives [e.g. wind]. An interlocking system has been developed in order to provide motion constraints due to the self-geometry of the glass units. Regarding the structural consolidation of the monument, a uniform distribution of loads has been ensured with the use of an intermediary between the glass and the original masonry, across the entire contact areas. Another aspect of consolidation of a monument is the protection of its materials. As the lower part of the tower has long suffered from humidity and the sea water, in the new intervention, it is entirely sealed so as to protect it against the elements and halt the deterioration of the materials [limestone and sandstone], which are extremely vulnerable to internal crystallization caused by sea salt.

08.1 DESIGN EVALUATION

08 CONCLUSIONS

Transparency, in our case, does not speak for the fine optical quality of glass; it is a means to highlight the monument, by providing a simultaneous perception of both its original and current state, while at the same time being discrete. The option for cast glass has great advantages in terms of visibility, compared for example to horizontally stacked float glass [as both have a similar construction technique that resembles to the one of traditional masonry], as it introduces less visible lines. Moreover, the surface treatment of the glass blocks results in a translucent appearance, with less reflections and textured effect, resembling in such way to the existing masonry grain. The transparent foil used an as interlayer, causes again minimum to zero visual intrusion. Fianlly, where mechanical connections cannot be avoided, there are designed as embedded connection in the glass components.

199

08.2 COMPATIBILITY ASSESSMENT

The compatibility of the new intervention with the existing building is an important recommendation in restoration practices suggested by the Venice Charter [see chapter 01.4]. Compatibility is a property that can refer to aesthetic or technical aspects related to the form, the structure, the materials and the safety mechanisms. Glass and limestone/sandstone are assumed to be incompatible materials in terms of material properties. This can be particularly challenging when they need to be bonded together regarding their different chemical composition, density and thermal behaviour [Karron, 2015]. Glass being stiffer requires less volume in order to reach the stiffness levels of the existing masonry, reaching approximately 1/4 of the original volume and weight. This proves, that despite the different properties, materials can be compatible with the proper configurations. The construction technique and workmanship are closely related to the architectural value that is embedded in a historic monument [see chapters

TRANSPARENT RESTORATION

01.5 and 03.8]; they are part of its authentic image. Respecting these values, a glass masonry is chosen for the largest part of the current restoration. Cast glass units are built in a similar way with ordinary stone masonries with some small adjustments due to the specifications of glass. Nevertheless, the idea remains the same: glass units are stacked one on top of the other in an overlapping pattern while an interlayer is placed in between to take the tolerances just like mortar does with stone. This approach resembles to the original structure and provides an honest perception of the aesthetics of the original image. The form and the outline of the rectangular-shaped monument are kept as they were, according to previous photographs and references, in order not to cause any false conjecture. Additionally, the aesthetics of the monument is not altered due to the quality and texture of the glass units, which are treated in order to resemble to stone [see chapter 05.7].

200

Moving on to the compatibility of the glass structure regarding the structural consolidation of the monument, the most important aspect is that the intervention should not harm the historic fabric. This feature draws our attention to the design of connections between the glass and the original structure. They should be designed as the weakest link, so in case of overloading the connection is what fails first and not the historic matter, functioning as a warning mechanism. In the suggested design, the connections are dry introducing a soft interlayer, which is stabilized by few mechanical point anchors, is flexible and of sufficient thickness in order to account for displacements due to loading or thermal expansion. Also the interlocking glass masonry has a variable thickness, increasing at the contact areas to the existing structure [up to approximately 60 cm] in order to allow for a more uniform transfer of the loads between the different elements [glass-stone masonry].

The research presented in the current thesis shows how structural glass elements can be used instead of conventional materials for the restoration and structural consolidation of historic monuments. Materiality is an important aspect in such cases as it can either highlight or undermine the aesthetics of a structure. Glass is neutral due to its

AESTHETICS CONSTRUCTION TECHNIQUES

COMPATIBILITY

MATERIAL PROPERTIES

CONNECTIONS

POSTBREAKAGE BEHAVIOUR FORCE TRANSFER MECHANISM

Fig 08.2 Aspects related to compatibility

08.3 CONCLUSIONS & RECOMMENDATIONS

08 CONCLUSIONS

transparency and bears the contemporary stamp, which makes it remarkable for restoration applications. It could be the answer to the ongoing debate between restoring and preserving. The transparent properties of glass can allow for minimal visual intrusion, while at the same time its mechanical properties can sufficiently consolidate a damaged structure with the proper design. The most innovative part of the proposal lies in the design of the connections. Dry connections lead the way to reversible solutions, as the absence of any adhesives that permanently bond the glass elements, allow for disassembly. While the Venice charter suggests that any intervention should be reversible to allow for future alterations and do not harm the monument, most restoration projects do not apply such design strategies. This is also easily identified in the restoration treatment applied in our case study. On the one hand, compatible materials are chosen to not alter the image of the monument, but on the other hand the treatment is irreversible and do not allow for alterations without intervening in the historic fabric [see Fig 08.3]. Fig 08.3 Current restoration treatment of the tower using compatible materials [local limestone/sandstone] but irreversible construction methods

Fig 08.4 The coat of arms found after excavation on the site could be reconstructed as a monolithic cast glass unit

However, dry connections could not be feasible if it was not for the development of an interlocking system for the cast glass units to ensure stability. LEGO unit fulfils the constraint requirements in our case, however, the general idea of interlocking geometries can significantly contribute to other applications according to the special characteristics of the restored part. Arches, vaults, domes behave differently than walls or columns and require different configurations or locking methods of the glass components. Additionally, factors such as the texture and the rhythm of the existing building affect the design of the glass modulus. Masonries are the primary structures found in historic monuments and their aesthetics and grain can be interpreted in a contemporary way by using cast glass elements. Table 07 [see chapter 02.7] gives an overview of the possible applications of cast glass in historic structures, not only as structural but also as complex ornamental elements [see Fig 08.4]. We should outline here, that the feasibility of an interlocking dry glass masonry lies to the use of an interlayer in order to prevent the hard contact between the glass elements and ensure a uniform load distribution.

201

TRANSPARENT RESTORATION

Interlocking units have additional advantages such as a fast assembly and disassembly, decreasing the time and cost of construction, but more importantly it allows for the reuse of the glass units. Demanding high working temperatures during the fabrication, glass is assumed a rather unsustainable material. However, the suggested demountable dry system can ensure that the glass remains clean of other substances so that it can either be re-used or easily recycled. We can conclude that such dry connections turn glass â&#x20AC;&#x153;greenerâ&#x20AC;? as, through the design, they make a more sustainable use of it.

202

A general recommendation that emerged from the research is that glass is not suitable for every restoration project. Factors such as the historic background, the embedded values [social, aesthetic,technical etc], the age and the rarity of a monument contribute significantly in the decision towards the suitability of such an innovative approach. For this reason, a meticulous assessment of the existing conditions of the monument is a prerequisite before any concept generation. Moreover the purpose of restoration is also critical when using glass elements. In our case, the purpose is merely the structural consolidation against the danger of total collapse; however, when the historic building is meant for re-use the indoor comfort is an important aspect of the design. Thus, further investigation of the climate performance, for instance, of a glass structure should be studied as it sets additional design parameters. Another field that requires further development is the climate performance of the lower sealed part of the monument. Glass protects the historic materials from further deterioration, but the exact performance of this part of the structure could be better investigated by thermal simulations in order to identify the special requirements and measures to be taken. One of the most challenging aspects of the design is the treatment of the rough surfaces that occur due to partial collapse of materials. For the current design, a different glass configuration of stacked glass units is chosen as an intermediate zone between the existing and the glass masonry. The small thickness of float glass can easily adjust to

08 CONCLUSIONS

the rough and uneven surfaces by the proper cutting, which turns stacked float glass into a considerable configuration in this part of the monument. Nevertheless, chapter 04.10 [see Table 14] shows that 3d-printing technology has potential for such connections, as it allows for custom-made components according to the imprint of the existing surface. Depending on the designerâ&#x20AC;&#x2122;s preference this technology could introduce a large variety of materials, either conventional, such as concrete, or innovative, such as plastics, which imitate glass but are lightweight, more easily treatable and shaped. This field seems promising and is worthy of further investigation as a next step of the research. In the current proposal, a qualitative assessment is made to estimate the structural behaviour of the proposed system. The lack of information on the mechanical properties of the existing materials does not allow for further and detailed analysis of the structural performance. Test measurements of samples taken from the site, as well as structural simulations could provide more accurate results for other interrelated aspects, such as the appropriate interlayer to be applied or the efficiency of the interlocking dry connections. The manufacture of 1:2 glass units at the laboratory as part of the current thesis has revealed several aspects that should be discussed. Parameters such as the annealing, the mold accuracy, the working temperatures, but primarily the shape of the unit can affect the final quality. The introduction of multiple materials [MDF, coatings, wax, Crystal Cast] influence the levels of accuracy and facilitate flaws generation. However, the most important conclusion of the process is that the actual shape of the unit can affect the fluxes of the molten glass inside the mold and consequently any internal stresses. A computational fluid dynamics analysis could predict such behaviour of molten glass and facilitate the optimization of the desired shape or the prediction of the glass shrinkage. Moreover, using a standardized manufacture process, we could proceed with experiments that will conclude to more realistic and accurate results concerning the strength of the interlocking masonry.

203

TRANSPARENT RESTORATION

A versatile methodology has been followed from the beginning of this research in order to get an insight on critical aspects, both in the fields of restoration and glass technology, and further investigate their common areas. The restoration methodology emerged from the literature review has proved very useful as it sets the basis for the elaboration of my design. Additionally, the restoration principles and guidelines [see chapter 01.4] have been a constant reference point throughout the research, elaboration and generation of the design strategies. From the awareness of our built heritage back in the Renaissance, to the massive arbitrary interventions supported by Viollet-le-Duc, restoration, today, respects the stratification of the monument so that any treatment does not detract from the authentic image of the monument. In this spirit, initiated by William Morris in the late 19th century, Franco Minissi does an attempt to reinterpret the image of the monument and introduces Plexiglas as a transparent solution, in order to â&#x20AC;&#x153;completeâ&#x20AC;? the missing parts, while allowing for an open dialogue to the current setting. 204

Through the review of this evolution, it appears that the spirit of each era contributes significantly

Fig 08.5 Perception of the glass restoration treatment during the day

08.4 REFLECTION

08 CONCLUSIONS

to the respective restoration theories. Maybe what our era has to contribute is the technological advancements, so that what Minissi did not manage to achieve 50 years ago, due to lack of appropriate technologies, can be implemented today with glass, given its improved structural performance and durability against the elements. The most valuable contribution of this research is the development of an interlocking glass masonry based on dry connections to consolidate the new hybrid structure, which sets new ground in the fields of both restoration and glass technology. With further and extensive investigation, this system could be the answer to reversible restoration treatments, as originally suggested by the Venice Charter, which, however, are not evident yet; maybe because, the use of traditional materials and construction techniques have not allowed a development towards design for disassembly. Innovation does not only deal with generating new ideas, but also providing the means for past solutions with innovative intentions to be implemented today. In this context, the current research proves that restoration with glass can be feasible and Minissiâ&#x20AC;&#x2122;s vision can finally take shape.

Fig 08.6 Night view of the tower. Adequate lighting highlights the missing part of the monument.

205

Fig 09.1 The 8 glass units manufactured in the context of the research

09.

REFERENCES

TRANSPARENT RESTORATION

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208

Bourtchouladze, R. (2003). Memories Are Made of This: How Memory Works in Humans and Animals: Columbia University Press Campbell Elizabeth A. , C. M. D. (2014). Historic Stone Masonry Restoration. Journal of Facade Design and Engineering, 31(2). Carvalho, P. L. L. d. (2014). (De)materializing Detail: Technology, Structure, Design Development of a reinforced glass connection technique. (Doctoral Thesis), Universidade do Minho. Dyskin Arcady V. , Y. E., Alexei J. Kanel-Belov, Elena Pasternak. (2001). Toughening by Fragmentation - How Topology Helps. ADVANCED ENGINEERING MATERIALS, 3(11). Dyskin A. V. , E. P., Y. Estrin. (2012). Mortarless structures based on topological interlocking. Frontiers of Structural and Civil Engineering, 6(2), 188-197. doi:10.1007/s11709-012-0156-8 Dyskin A. V. , E. P., Y. Estrin (2012). “Mortarless structures based on topological interlocking.” Frontiers of Structural and Civil Engineering 6(2): 188-197. Estrin Y., A. V. D., E. Pasternak. (2011). Topological interlocking as a material design concept. Materials Science and Engineering C, 31(6), 1189-1194. doi:10.1016/j.msec.2010.11.011 Feilden, B. M. (1982). Conservation of historic buildings. London ;, Butterworth Scientific.

09.1 BIBLIOGRAPHY

09 LITERATURE

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Lefaki, S. (2013, 18-19 April 2013). Revaluating architecture with glass. Paper presented at the COST Action TU0905 Mid-term Conference on Structural Glass proceedings of COST Action TU0905 Mid-term Conference on Structural Glass, Leiden, Netherlands

Heugten, R. v. (2013). Load-bearing glass columns: The stacked column Part 2. (Master of Science), Eindhoven University of Technology.

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Haldimann, M., A. Luible and M. Overend Structural Use of Glass (SED 10), IABSE Heugten, R. v. (2013). Load-bearing glass columns: The stacked column Part 2. Master of Science, Eindhoven University of Technology.

Oikonomopoulou Faidra, T. B., Fred Veer, Rob Nijsse. (2016). Challenges in the Construction of the Crystal House Façade. Paper presented at the Challenging Glass 5. Conference on Architectural and Structural Applications of Glass, Ghent University.

Hubert, M. (2015). Lecture 9: Annealing and Tempering. CelSian Glass & Solar Retrieved 17.04.2016 Hung-Ming Cheng (2012). The Workflows of 3D Digitizing Heritage Monuments, Laser Scanner Technology, Dr. J. Apolinar Munoz Rodriguez (Ed.), ISBN: 978-953-51-0280-9, InTech, Available from: http://www.intechopen.com/books/laser-scanner-technology/the-workflows-of-3d-digitizing-heritage- monuments Jokilehto, J. (2002). History of Architectural Conservation Conservation & Museology S., Retrieved from Ebook Library http:// public.eblib.com/choice/publicfullrecord.aspx?p=298354 Karron, K. (2015). Restoration of Architectural Monuments with Load Bearing Solid Glass Blocks. Sample Design Proposal For Glass-Stone Connection. (Master), Tallinn University of Technology.

Faidra Oikonomopoulou, T. B., Rob Nijsse, Fred Veer. (2015). Innovative structural applications of adhesively bonded solid glass blocks. Paper presented at the Glass Performance Days 2015, Tampere, Finland. Oikonomopoulou F., F. V., R. Nijsse, K. Baardolf (2014). “A completely transparent, adhesively bonded soda-lime glass block masonry system.” Journal of Facade Design and Engineering 2: 201-221. Orbasli, A. (2008). Architectural conservation : principles and practice. Oxford :, Blackwell Science. Pave Rogério, H. U. (2010). Structural Behaviour of Dry Stack Masonry Construction. Portugal SB10: Sustainable Building Affordable to All, Vilamoura, Portugal.

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Peng Song, C.-W. F., Daniel Cohen-Or. (2012). Recursive interlocking puzzles. ACM Transactions on Graphics, 31(6), 10. doi:10.1145/2366145.2366147 Pere Roca, M. C., Giuseppe Gariup, Luca Pela. (2010). Structural Analysis of Masonry Historical Constructions. Classical and Advanced Approaches. Archives of Computational Methods in Engineering, 17(3), 299-325. doi:10.1007/s11831-010-9046-1 Pezzati, L. and R. Fontana (2008). 3D Scanning of Artworks. Handbook on the use of lasers in conservation and conservation science. M. S. M Schreiner, Renzo Salimbeni, European Cooperation in the Field of Scientific and Technical Research (Organization), COST G7 (Project). Brussels, Belgium, COST Office. Pfaender, H. G. (1996). Schott Guide to Glass. London, Chapman & Hall Pires Margarida, C. B. (2008). 3D Laser Scanning of Architectural Sites. Handbook on the use of lasers in conservation and conservation science. M. S. M. Schreiner, R. Salimbeni. Brussels, Belgium, COST Office. Quincoces, A. (2007). Glass Sets the Stage for Sorrow. SCHOTTsolutions, 1, 4. Rice, P., & Dutton, H. (1995). Structural glass (2nd ed. ed.). London :: Spon. 210

Rowe, Colin, and Robert Slutzky. 1963. “Transparency: Literal and Phenomenal” eds. Todd Gannon and Jeffrey Kipnis. Perspecta 8: 44–54, from Carvalho, P. L. L. d. (2014). (De)materializing Detail: Technology, Structure, Design Development of a reinforced glass connection technique. Doctoral Thesis, Universidade do Minho. Schreiner, M., Strlic, M., Salimbeni, R., European Cooperation in the Field of, S., Technical, R., & Cost, G. (2008). Handbook on the use of lasers in conservation and conservation science. Brussels, Belgium: COST Office Stanley-Price, N. (2009). The Reconstruction of Ruins: Principles and Practice. In A. R. a. A. Bracker (Ed.), Conservation: Principles, Dilemmas and Uncomfortable Truths: Elsevier. Schittich, C., G. Staib, D. Balkow, M. Schuler and W. Sobek (2007). Glass Construction Manual, Birkhäuser Vivio, B. A. (2014). Transparent Restorations: How Franco Minissi Has Visually Connected Multiple Scales of Heritage. Future Anterior, 11. doi:10.1353/fta.2014.0014 Vivio, B. A. (2015). The “narrative sincerity” in museums, architectural and archaeological restoration of Franco Minissi. Frontiers of Architectural Research, 4(3), 202-211. doi:http://dx.doi. org/10.1016/j.foar.2015.06.002

Weizmann Michael, O. A., Yasha Jacob Grobman. (2015). Topological Interlocking in Architectural Design. Paper presented at the Emerging Experience in Past, Present and Future of Digital Architecture, Hong-Kong. Weller, B. (2009). Glass in building : principles, applications, examples. Wurm, J. (2007). Glass structures design and construction of self-supporting skins Retrieved from ebrary http://site.ebrary. com/id/10222839

09 LITERATURE

09.2 FIGURES

The figures that do not have a reference are created by the author.

Fig 00.1

http://www.manfredonianews.it/wp-content/uploads/2016/03/Basilica-di-Siponto-A.D.2016.1.jpg

Fig 01.27

https://www.youtube.com/watch?v=7_diXmKZp_8

Fig 01.28 Fig 00.4

http://blogs.sch.gr/nipmeth/%CE%BC%CE%B1%CF %82/#prettyPhoto

https://www.behance.net/gallery/35565455/ BASILICA-di-SIPONTO

Fig 01.29 Fig 01.1

https://gogobrowniemission.files.wordpress. com/2015/05/dscf6731.jpg

https://commons.wikimedia.org/wiki/KaiserWilhelm-Ged%C3%A4chtniskirche#/media/ File:Ged%C3%A4chtniskirche1.JPG

Fig 01.3

http://www.ilondra.it/covent-garden-market/

Fig 01.30

http://www.artsetter.com/artwork/gina-verster/ maison-de-verre

Fig 01.4

http://reproarte.com/en/choice-of-topics/style/ renaissance/design-for-the-dome-of-the-milancathedral-detail

Fig 01.31

Vivio, 1015: 204

Fig 01.32

Vivio, 1015: 207

Fig 01.33

Vivio, 2014: 10

Fig 01.34

Vivio, 1015: 210

Fig 01.35

Vivio, 2014: 10

Fig 01.36

Vivio, 2014: 14

Fig 01.37

Vivio, 1015: 205

Fig 01.5

https://en.wikipedia.org/wiki/Notre_Dame_de_ Paris

Fig 01.6

http://coeur2courpiere.lamotrice.com/blog/lartde-batir-les-villes-les-eglises

Fig 01.7

https://pl.wikipedia.org/wiki/Historia_Warszawy

Fig 01.11

http://www.thehindu.com/news/cities/Tiruchirapalli/two-temples-in-a-state-of-neglect/article7807930.ece

211

Fig 01.38

Vivio, 2014: 3

http://fe-mail.gr/pages/posts/greece_europe_ world/greece_europe_world3757.php

Fig 01.39

Vivio, 2014: 6

Fig 01.13

http://www.oxrbl.com/dphil-research-projects/

Fig 01.40

Vivio, 2014: 13

Fig 01.14

https://travelbyterry.wordpress.com/category/ golden-circle-2013/

Fig 01.41

Vivio, 2014: 15

Fig 01.42

http://shells.princeton.edu/Ham.html

Fig 01.15

http://www.wikiwand.com/en/Lead Fig 01.43

Fig 01.16

http://www.nevworldwonders.com/2014/05/64wonder-parthenon.html

http://ameliesblog.global2.vic.edu.au/2011/10/09/ coops-shot-tower-melbourne-central/

Fig 01.44

https://en.wikipedia.org/wiki/Reichstag_building

Fig 01.17

courtesy of Telesilla Bristogianni Fig 01.45

Fig 01.18

https://alocato.com/go/pittsburgh-pa/

Fig 01.21

http://www.ysma.gr/en/restoration-principlesand-methods

http://www.lastampa.it/2015/04/02/societa/ montagna/gite-e-percorsi/val-venosta-tra-lesacre-montagne-del-mondo-dWiV1DLhedOzpB05OV7WyJ/pagina.html

Fig 01.46 Fig 01.22

http://giampolinicourtney.com/brick-restorationand-reconstruction/1mqbb6scxjzf1v1ildta39xoglk ng2

https://www.flickr.com/photos/iprinke/18871061306

Fig 01.47

https://en.wikipedia.org/wiki/Esma_Sultan_Mansion

Fig 01.48

http://www.costasvarotsos.gr/inst42-en.html

Fig 01.49

http://inhabitat.com/glassy-renovation-bringsnatural-light-into-canadian-museum-of-nature/

Fig 01.50

http://www.archdaily.com/624930/kou-an-glasstea-house-tokujin-yoshioka

Fig 01.12

Fig 01.23

https://de.wikipedia.org/wiki/Broletto

Fig 01.24

http://architizer.com/projects/huge-skylightchurch/

Fig 01.25

https://www.youtube.com/watch?v=zvEtZexIk9Q

Fig 01.26

https://www.nps.gov/tps/how-to-preserve/ briefs/16-substitute-materials.htm

TRANSPARENT RESTORATION

Fig 01.51

http://www.dezeen.com/2012/07/26/convent-desant-francesc-by-david-closes/

Fig 02.3

http://www.gardenenvy.net/2012_12_01_archive. html

Fig 01.52

http://www.hexapolis.com/2014/12/08/menokin18th-century-house-set-to-be-restored-withglass/

Fig 02.4

http://museumtoeren.be/museum/antwerpen/ mas-museum-aan-de-stroom/

Fig 02.5 Fig 01.53

http://architizer.com/projects/huge-skylightchurch/

http://www.archdaily.com/29755/ civic-center-in-st-germain-philippeharden/5010701728ba0d4222001f22-civic-centerin-st-germain-philippe-harden-image

Fig 01.55

Schittich, Staib et al. 2007 Fig 02.7

Fig 01.56

Schittich, Staib et al. 2007

http://fresno.pntic.mec.es/msap0005/2eso/ Tema_08/Category.html

Fig 01.57

Schittich, Staib et al. 2007

Fig 02.8

http://diamondglass.com.sg/product/low-ironglass/

Fig 01.58

http://www.gmp-architekten.de/projekte/ museum-fuer-hamburgische-geschichte-innenhofglasueberdachung.html

Fig 02.9

Oikonomopoulou et al, 2014: 202

Fig 02.10

Weller, 2009

Fig 02.11

http://www.doitpoms.ac.uk/tlplib/BD5/printall. php

Fig 02.12

Balkow,1999

Fig 02.13

Schittich et al, 2007

Fig 02.14

Overend, M., (2010) Recent Developments in Design Methods for Glass Structures. The Structural Engineer Journal, Vol.88 (14) 20 July 2010, p.18-26

Fig 02.15

Wurm, 2007

Fig 01.59

https://en.wikipedia.org/wiki/Coop%27s_Shot_ Tower

Fig 01.60

https://en.wikipedia.org/wiki/Reichstag_dome

Fig 01.61

Schittich, Staib et al. 2007

Fig 01.62

www.badruine-badenweiler.de/en/home/

Fig 01.63

www.gadarchitecture.com/en/esma-sultan-

Fig 01.64

www.gadarchitecture.com/en/esma-sultan-

Fig 01.65

http://www.costasvarotsos.gr/inst42-en.html Fig 02.16

Schittich et al, 2007

Fig 01.66

http://inhabitat.com/glassy-renovation-bringsnatural-light-into-canadian-museum-of-nature/

Fig 02.17

http://www.google.com.gt/patents/ US20120214004

http://www.archdaily.com/624930/kou-an-glasstea-house-tokujin-yoshioka

Fig 02.18

Wurm, 2007

Fig 02.19

Wurm, 2007

212 Fig 01.67

Fig 01.68

http://www.dezeen.com/2012/07/26/convent-desant-francesc-by-david-closes/

Fig 02.20

Wurm, 2007

Fig 01.69

http://architizer.com/projects/huge-skylightchurch/

Fig 02.21

http://www.simtech.be/en/our-brands/flexlamlaminating-solutions/

http://architizer.com/projects/huge-skylightchurch/

Fig 02.22

https://www.sedak.com/de/browse/1/article/ publikumsmagnet-sedak-laminat-mit-14m-aufder-glasstec/

Fig 01.70

Fig 01.71

http://architizer.com/projects/huge-skylightchurch/ Fig 02.23

Louter C, 2007

Fig 01.72

http://architizer.com/projects/huge-skylightchurch/

Fig 02.24

Louter C, 2007

Fig 01.73

http://www.menokin.org/mission/

Fig 02.25

http://www.waagner-biro.com/en/divisions/steelglass-structures/references

Fig 01.74

http://www.menokin.org/mission/ Fig 02.26

Fig 01.75

http://www.menokin.org/mission/

https://zbindendesign.wordpress.com/category/ education-3/

Fig 01.76

http://www.menokin.org/mission/

Fig 02.27

Weller, 2009: 12

Fig 01.77

http://whatawonderfulhome.tumblr.com/ post/85109796746/the-warehouse-17c-madrid-byarturo-franco-office

Fig 02.28

http://fusing-ru.livejournal.com/19314.html

Fig 02.29

Courtesy of Ronald Jorissen

Fig 02.1

http://www.cmog.org/article/reflections-glasstelescope-mirrors

Fig 02.30

Courtesy of Telesilla Bristogianni

Fig 02.31 Fig 02.2

http://www.oddee.com/item_98475.aspx

http://www.dezeen.com/2016/04/20/crystalhouses-amsterdam-chanel-store-mvrdv-glassfacade-technology/

09 LITERATURE

Fig 02.32

http://www.domusweb.it/it/arte/2014/04/16/ you_imagine_what_you_desire_.html

Fig 02.61

https://www.teachengineering.org/activities/ view/cub_tower_activity1

Fig 02.33

http://www.ferret.com.au/c/SCHOTT-Australia/ SCHOTT-Tubing-glass-tubes-rods-and-profilesp2518718

Fig 02.62

Weller, 2009

Fig 02.63

Weller, 2009

Fig 02.34

http://www.ferret.com.au/c/SCHOTT-Australia/ SCHOTT-Tubing-glass-tubes-rods-and-profilesp2518718

Fig 02.64

http://dir.indiamart.com/impcat/spider-glazing. html

Fig 02.65

Wurm, 2007

Fig 02.35

http://imagensubliminal.com/caja-de-arquitectosde-bilbao/?lang=es

Fig 02.67

Weller, 2009

Fig 02.36

http://www.slideshare.net/klivsie/ch03-9297580

Fig 02.69

http://www.detail360.de/architekt/maedebachredeleit-partner-architekten-pfid_141108.htm

Fig 02.37

John Klein, 2015 Fig 02.72

Fig 02.38

John Klein, 2015

http://www.huftonandcrow.com/projects/gallery/ the-walbrook/

Fig 02.39

http://www.tradekorea.com/product/detail/ P252766/cnc-automatic-glass-cutting-table-glass-cutting-machine-glass-processing-machine. html

Fig 02.73

http://www.cbcurtis.net/benedict/Humanities%20 Site/roman_republic.html

Fig 02.74

http://www.free-ed.net/free-ed/Resources/ Trades/carpentry/Building01/default. asp?iNum=0704

Fig 02.75

http://theredlist.com/wiki-2-351-382-1160-1122view-usa-profile-horn-roni.html

Fig 02.76

http://www.subtilitas.site/post/91172017214/ kruunenberg-en-van-der-erve-laminata-

Fig 02.40

http://www.indiamart.com/dowengifabllp/

Fig 02.41

Wurm, 2007

Fig 02.42

Wurm, 2007

Fig 02.43

Wurm, 2007

Fig 02.44

http://www.trendhunter.com/trends/recycledwine-glasses-umbra-frosine

Fig 02.77

http://www.geograph.org.uk/article/GlasgowUnderground-System

Fig 02.45

Fig 02.78

http://afasiaarchzine.com/2013/10/oma_26-4/

Fig 02.46

http://www.enclos.com/site-info/news/bendingglass-in-the-parametric-age Wurm, 2007

Fig 02.79

Fig 02.47

http://glennyglassdeco.com/products

http://www.gettyimages.nl/detail/illustratie/ washington-d-c-1850-to-1899-birds-eye-view-ofstock-afbeelding/154325010

Fig 02.48

http://lookingforgold.blogspot.nl/2014/05/sunglass.html

Fig 02.80

http://www.archdaily.com/628411/torre-del-borgo-gianluca-gelmini/554ad4bce58ece423b00010atorre-del-borgo-gianluca-gelmini-image

Fig 02.49

http://ltaqbl.en.made-in-china.com/product/ KXNxpqsOieVC/China-Double-Glazing-Glass-forCurtain-Wall.html

Fig 02.81

http://wallpapercave.com/mt-fuji-wallpaper

Fig 02.82

http://www.jqjacobs.net/southwest/cajon.html

Fig 02.83

http://imgur.com/gallery/JzmHw

Fig 02.84

http://www.allposters.com/-sp/Tile-Roof-Karitena-Peloponnese-Central-Arcadia-Greece-Posters_ i4064263_.htm

Fig 02.86

http://romeartlover.tripod.com/Palmyra3.html

Fig 02.88

http://ifarchitecturewasntthere.blogspot. nl/2013/10/charette-02-hare-coursing.html

Fig 02.89

http://www.ligonier.org/learn/series/tearing_ down_strongholds/

Fig 02.50

http://www.glastory.net/curved-glass-an-obstacle-or-an-opportunity-in-glass-architechture/

Fig 02.51

http://www.glastory.net/curved-glass-an-obstacle-or-an-opportunity-in-glass-architechture/

Fig 02.52

http://bermanglass.com/

Fig 02.53

http://www.glazette.com/Glass-KnowledgeBank-24/processing-glass.html

Fig 02.54

Wurm, 2007

Fig 02.55

Wurm, 2007

Fig 02.56

Weller, 2009

Fig 02.90

https://ca.wikipedia.org/wiki/Terra_Alta

Fig 02.57

Weller, 2009

Fig 02.92

http://clipart.me/premium-buildings-landmarks/ classic-style-column-vector-set-11757

Fig 02.58

https://www.s3i.co.uk/ Fig 02.93

Fig 02.59

Weller, 2009

https://commons.wikimedia.org/wiki/File:Kos,_ Greece_ancient_column_capital.jpg

Fig 02.60

Weller, 2009

Fig 02.94

http://www.panoramio.com/photo/62914764

213

TRANSPARENT RESTORATION

Fig 02.95

http://www.conceptmat.com/en/roof-trusses.php

Fig 04.20

http://www.celsian.nl/

Fig 02.96

http://www.ajhw.co.uk/books/book350/book350v/ book350v.html

Fig 04.21

http://www.celsian.nl/

Fig 04.22 Fig 03.1

http://www.wow.com/wiki/Methoni,_Messenia

http://ww.daliulian.net/cat105/ node763253/22935#22935

Fig 03.2

Aggelopoulou et al, 2015

Fig 04.23

Oikonomopoulou et al, 2014

Fig 03.3

Aggelopoulou et al, 2015

Fig 04.25

http://davidpratt.info/andes1.htm

Fig 03.4

Aggelopoulou et al, 2015

Fig 04.26

http://openbuildings.com/buildings/the-katanaresidences-profile-3575/media/232001/show

Fig 03.5

Aggelopoulou et al, 2015 Fig 04.27

Fig 03.6

Aggelopoulou et al, 2015

http://brickandpress.com/hydraform-sistemalego-kirpich-bl

Fig 03.10

http://messiniaka.blogspot.nl/2013/05/blog-post. html

Fig 04.29

Estrin Y., A. V. D., E. Pasternak, 2011

Fig 04.30

Peng Song, C.-W. F., Daniel Cohen-Or, 2012)

Fig 03.11

Aggelopoulou et al, 2015 Fig 04.33

http://www.fao.org/docrep/s1250e/S1250E5K.GIF

Fig 03.12

http://sp.lyellcollection.org/content/291/1/201/ F5.large.jpg

Fig 04.36

http://www.thingsiliketoday.com/un-lampadariodi-lego-trasparenti/

Fig 05.5

https://en.wikipedia.org/wiki/Stress_(mechanics)#/media/File:Axial_stress_noavg.svg

Fig 03.14

Courtesy of Ioanna Aggelopoulou

Fig 03.15

Aggelopoulou et al, 2015

Fig 03.16

Aggelopoulou et al, 2015

Fig 05.6

Oikonomopoulou et al, 2016

Fig 03.19

Aggelopoulou et al, 2015

Fig 05.18

http://www.salamenterprisesllc.com/HALFEN%20 Cast-in%20Channel%20System.php

Fig 03.20

http://castillosdelmundo.es/?page_id=3456 Fig 05.22

http://www.zenzoa.com/urban-wonder/

Fig 04.4

http://tectonicablog. com/?s=Gramazio+%26+Kohler

Fig 05.24

http://www.pentaxforums.com/forums/129-weekly-photo-challenges/176938-weekly-challengechallenge-196-through-glass.html

214 Fig 04.5

http://www.grasshopper3d.com/forum/topics/ brick-pattern-thru-image-help Fig 05.25

Oikonomopoulou et al, 2015

Fig 04.6

https://gr.pinterest.com/ pin/383650461980326142/

Fig 05.29

http://www.popularwoodworking.com/projects/ aw-extra-111512-glass-for-woodworking

http://www.us.schott.com/architecture/english/ references/memorial-madrid.html

Fig 05.30

http://www.studiolglassworks.com/options/flatglass/

Fig 07.2

http://www.marionrestoration.com/us-courthouse/

Fig 07.3

http://www.wsj.com/articles/SB100014240527023 04518704579521583112244014

Fig 04.8

Fig 04.9

Knut et al, 2007

Fig 04.10

http://openbuildings.com/buildings/11-marchmemorial-profile-3383/media

Fig 04.11

Knut et al, 2007

Fig 04.12

http://www.designboom.com/architecture/hiroshi-nakamura-nap-optical-glass-house/

Fig 074

http://www.wsj.com/articles/SB100014240527023 04518704579521583112244014

Fig 04.13

Oikonomopoulou et al, 2014

Fig 07.5

http://www.wsj.com/articles/SB100014240527023 04518704579521583112244014

Fig 04.14

http://www.magazindomov.ru/2013/03/24/domso-steklyannym-ekranom-v-yaponii/

Fig 07.6

http://www.science4heritage.org/COSTG7/booklet/chapters/3D.htm

https://karmatrendz.wordpress.com/2013/04/03/ optical-glass-house-by-nap-architects/

Fig 07.9

http://www.mdpi.com/2072-4292/3/6/1104/htm

Fig 04.16

Courtesy of Faidra Oikonomopoulou

Fig 07.10

http://www.photonics.com/Article. aspx?AID=56085

Fig 04.17

Oikonomopoulou et al, 2014 Fig 07.11

Fig 04.18

Courtesy of Ronald Jorissen

http://marketing.lmi3d.com/laser-displacementsensors-from-analog-to-digital

Fig 04.19

Oikonomopoulou et al, 2014

Fig 07.12

http://www.photonics.com/Article. aspx?AID=49296

Fig 04.15

09 LITERATURE

Fig 07.13

http://www.directindustry.com/prod/faro-europegmbh-co-kg/product-21421-1322485.html

Fig 07.14

http://www.factum-arte.com/pag/682/Lucida

Fig 07.15

http://www.umformtechnikmagazin.de/umformtechnik-produkte/einstieg-in-die-optischeoberflaechenmesstechnik_360_de/

Fig 07.16

http://www.wired.com/2015/12/these-are-thetech-giants-that-won-2015/

Fig 07.17

James Oâ&#x20AC;&#x2122;Callaghan & Marchewka, 2009

Fig 07.22

Courtesy of Ronald Jorissen

Fig 07.23

Courtesy of Ronald Jorissen

Fig 07.24

Courtesy of Ronald Jorissen

Fig 07.27

Courtesy of Ronald Jorissen

Fig 10.2

https://commons.wikimedia.org/wiki/ Category:Maps_of_weather_and_climate_of_ Greece#/media/File:SolarGIS-Solar-map-Greeceen.png

Fig 10.3

www.weather-and-climate.com

Fig 10.4

www.weather-and-climate.com

Fig 10.5

http://en.climate-data.org/location/214974/

215

Fig 10.1 Flowerpots filled with glass B270, by SCHOTT, are used in the kiln casting

10. 1

APPENDICES

TRANSPARENT RESTORATION

According historical testimonies and records the most destroying earthquakes in Messinia County and the entire southwest Peloponnese are [Aggelopoulou et al, 2015]:

218

399 BC. Ileia 387 BC . Ileia 551 . west Peloponnese August 1303 . Methoni & Coroni 28th Novermber 1838 . Kalamata 28th March 1885 . Messinia 27th August 1886 . west Messinia . 7.5 R 29th December 1896 . north of Kalamata 22nd January 1899 . Kyparissia . 6.6 R 6th October 1947 . west Messinia . 7.5 R 24th August 1951 . west coast of Messinian Gulf . 5.5 R 16th August 1959 . Messinia . 5.5 R 2nd October 1961 . Messinian Gulf . 5.7 R 26th March 1979 . Ileia . 6.0 R 13th September 1986 . Kalamata . 6.0 R 18th November 1997 . Strofades . 6.1 R 10th October 2001 . sea south of Kalamata . 5.1 R 1st March 2004 . NE of Kalamata . 5.4 R 14th February 2008 . sea south of Methoni . 6.7 R 21st June 2008 . sea south of Methoni . 6.0 R

10.1 APPENDIX 1 CLIMATIC DATA

Fig 10.3 The wind direction distribution per year [%] in the city of Methoni

Fig 10.4 Average precipitation [rain/snow]

Fig 10.2 Solar irradiation map of Greece and area of interest

Fig 10.5 Temperature fluctuations in the city of Methoni

10 APPENDICES

SCHOTT BOROFLOATÂ® 33 [www.schott.com]:

1150 x 850

0.70 1.10 1.75 2.00 2.25 2.75 3.30 3.80 5.00 5.50 6.50 7.50 8.00 9.00 11.00 13.00 15.00 16.00 18.00 19.00 20.00 21.00 25.40

DIMENSIONS [MM]

3000 x 2300

THICKNESS [MM]

1700 x 1300

10.2 APPENDIX 2 MATERIAL SPECIFICATIONS

Table 23 . BOROFLOAT 33 dimensions and thicknesses

219

TRANSPARENT RESTORATION

The glass masonry is assumed as a flat plate of uniform thickness. The loads are as follows: Compressive load F [weight of existing masonry] mmasonry = dmasonry * V = 2500 * 19.4 * t = 48500*t kg F = 475.6t kN

10.3 APPENDIX 3 BUCKLING CHECK

The axial stress occuring from this compressive load is: = F/A = 475.6t/4.5t = 105.7 kN/m2 critical F

The overall axial load is F + W = 475.6t + 1271.6t = 1747.2 kN As the glass masonry is a combination of glass and a transparent interlayer, the Youngâ&#x20AC;&#x2122;s modulus of this composite structure can be calculated with the following formula: E = (Lglass + Linterlayer)/[(Lglass/Eglass) + (Linterlayer/Einterlayer)]

220

where Lglass = glass block thickness = 0.05 m Linterlayer = interlayer thickness = 0.003 m Eglass = 64 GPa Einterlayer = 2 GPa E = (0.05 + 0.003)/[(0.05/64) + (0.003/2)] = 23.23 GPa = 23230000 kN/m2 As the design is about an innovative dry glass masonry, never tested before and implemented in unusual conditions [existing monument], we choose a saftery factor of 4. The critical compressive stress is given as follows: 4 * 105.7 = 422.8 kN Therefore we can apply Bryanâ&#x20AC;&#x2122;s formula: critical

= k ( 2 E) / 12(1-v2)(b/t)2

where: = 6988.8t kN critical E = 23230000 kN/m2 v = 0.2 k=4 b = 4.5 m t=?

critical

= k ( 2 E) / 12(1-v2)(b/t)2

422.8 = 4 (3.142*23230000) / 12(1-0.22) (4.5/t)2 422.8 = 916154032 / (233.28/t2) 422.8 * 233.28 = 916154032 * t2 98630.784 = 916154032 t2 t = 0.01 m = 10 cm

10 APPENDICES

10.4 APPENDIX 4 LAB DATA WEIGHTS OF GLASS UNITS x 2.55

GLASS MASS [gr]

+ 10%

UNIT

WATER MASS [gr]

UNIT WEIGHT [gr]

FULL

370

944

1029

FULL

387

987

1120

FULL

392

999.6

1088

HALF

481.5

1227.8

1343

HALF

522.6

1332.6

1466.5

FULL

387.3

987.6

1080.4

FULL

356.4

908.8

998.3

HALF

521

1328.5

1459 221

Table 24 . Overview of the weight of glass used for each of the 8 blocks manufactured

FIRING SCHEDULES

FIRING SCHEDULE 1 FIRING SCHEDULE 2 FIRING SCHEDULE 3

Fig 10.6 Firing schedules used for the manufacture of the glass blocks at the lab

TRANSPARENT RESTORATION

222

GLASS BLOCK

POLARIZED IMAGE

10 APPENDICES

# FIRING

KILN ARRANGEMENT

OBSERVATIONS very smooth surface inaccuracies/imperfections

big flowerpot

medium flowerpot

rough surface uneven width probably due to overflow of glass in one flowerpot

223

rough surface obvious flows of molten glass

rough surface obvious flows of molten glass some mixture of Crystal Cast with glass 2

TRANSPARENT RESTORATION

GLASS BLOCK

POLARIZED IMAGE

224

Table 25 . Data and observations for the cast glass blocks manufactured in the context of this research

10 APPENDICES

# FIRING

KILN ARRANGEMENT

OBSERVATIONS rough back surface imperfections obvious flows of molten glass bubbles

rough surface low quality inside the locking areas obvious flows of molten glass

225

medium flowerpot

smooth up surface rough bottom surface obvious flows of molten glass

small flowerpot elevated 3 cm

3 heatresistant block

rough bottom surface bubbles

TRANSPARENT RESTORATION

10.5 APPENDIX 5 PHYSICAL MODEL SC 1:100

226

10 APPENDICES

227

TRANSPARENT RESTORATION

228

10 APPENDICES

229

TU DELFT 2016