The reuse of existing glass panes can reduce construction waste and the demand for new raw materials. However, uncertainty regarding the fracture strength of aged glass remains an important barrier to reuse, as failure is governed by surface flaws accumulated during service. This study investigated the effect of thermal treatment on the surface condition and fracture strength of naturally weathered glass and assessed whether fracture strength could be estimated using non-destructive surface measurements.

Specimens were obtained from approximately 42-year-old insulating glass units and tested in an untreated condition or after thermal treatment at 500°C, 540°C, or 600°C. Surface damage was characterized using optical microscopy, image analysis, and laser line scanning. Surface prestress was measured using a SCALP-05 device, while fracture strength was determined through coaxial double ring testing and evaluated using Weibull statistics. Finite element modeling was used to verify the stress distribution during testing, and Linear Elastic Fracture Mechanics was considered for predicting strength from measured flaw dimensions.

Microscopy and image analysis did not provide conclusive evidence of visible flaw healing after thermal treatment. Most scratches and defects remained detectable, while treatment at 600°C produced bubble-like features on some specimens. The mechanical results showed that the effect of thermal treatment depended on both temperature and the loaded glass surface. For the air side, thermal treatment did not consistently improve the lower-tail strength. For the tin side, treatment at 540°C produced the greatest improvement at low failure probabilities, increasing the failure strength by 33.2% at a failure probability of 0.8% and by 23.1% at 5%. Although treatment at 600°C resulted in a greater increase in median strength, it slightly reduced the strength at the lowest failure probability and introduced additional surface defects.

The laser line scanner was unsuitable for reliable characterization of strength-governing flaws because of transparency, reflectivity, scanning-spray effects, and insufficient spatial and vertical resolution. Consequently, fracture strength could not be reliably predicted from the measured flaw dimensions.

Overall, thermal treatment at approximately 540°C showed the most promising balance between improving the structural reliability of naturally weathered glass and avoiding additional material damage. However, the strength improvement could not be directly related to visible flaw healing, and the investigated non-destructive methods were insufficient for predicting the strength of individual panes. ... Read more

The construction sector is a significant contributor to the CO2 footprint in the Netherlands, emitting greenhouse gases that harm the global environment. To mitigate these emissions, all sectors must lower their CO2 emission. In construction, an effective strategy is reducing the use of primary materials through component reuse. However, flaws in glass components often result in the replacement of the entire panel. This research focuses on reusing glass panels to reduce waste and CO2 emissions. Through thermal treatment, aged glass could potentially be reused without compromising structural integrity. The glass used in this study is 15-year-old annealed soda-lime silica glass. The main research question is: To what extent can thermal treatment enhance the strength of naturally aged glass, affecting their potential for reuse?

Naturally aged glass, developing surface flaws over time from environmental exposure and human activity, was studied alongside artificially aged glass to assess differences in surface damage and thermal treatment effects. Microscopy and image analysis showed that naturally aged glass treated at 500°C and 600°C exhibited no clear healing trend. In contrast, artificially aged glass treated at 500°C caused minimal changes, while at 600°C, scratch width increased due to subcritical crack growth and a yellow discolouration occurred. Energy-dispersive X-ray spectroscopy revealed chemical changes on the air side of the glass, as the metal coating oxidizes during thermal treatment, altering the surface composition.

The strength of aged glass was evaluated using a coaxial double-ring test at 20 MPa/s, with results analysed via the 2-parameter Weibull distribution and weighted least squares regression. The tests revealed clear differences between naturally and artificially aged glass. Thermal treatment reduced the strength of naturally aged glass, with the 5% fractile decreasing by 28% after heating to 500°C and by 56% after heating to 600°C. In contrast, artificially aged glass improved, with the 5% fractile increasing by 13% after heating to 500°C and by 41% after heating to 600°C. SCALP-05 measurements assess surface stress in three groups: untreated glass, and glass treated at 500°C and 600°C. The average surface stresses measured were -6.49 MPa, -2.76 MPa, and -2.30 MPa. Although thermal treatment reduced surface stress, this effect was insufficient to influence overall strength conclusions.

The influence of thermal treatment on surface flaws differs between naturally and artificially aged glass. Microscopy showed minimal changes in naturally aged glass despite reduced strength, while artificially aged glass appeared visually worse but showed strength improvements in strength testing. This is likely due to the primary failure mode: artificially aged glass is strengthened by healing of dominant scratches, whereas naturally aged glass is mainly affected by overall material weakening.

This research assessed whether thermal treatment could restore the strength of naturally aged glass for reuse. However, the results demonstrated that thermal treatment not only failed to enhance the strength of naturally aged glass but also caused a noticeable reduction in strength. Additionally, yellow discolouration occurred during thermal treatment. In conclusion, thermal treatment compromised both the strength and appearance of naturally aged glass, limiting its feasibility for reuse in construction.
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Inefficiencies in HVAC control and poorly designed glass façades can significantly impact energy demand and thermal comfort in buildings with extensive glass façades. Two potential solutions are the implementation of smart systems and retrofitting the glass façade. However, when considering these options in building design, it is often unclear which strategy is more effective. This thesis investigates the performance of smart systems using grey-box model predictive control (MPC) and the effectiveness of glass façade retrofitting strategies concerning energy savings and occupant thermal comfort. The case study for this research is an educational building with a vast glass façade. The study commenced with a review of relevant literature, followed by the development of the MPC system and an evaluation of its performance against various retrofitting strategies. The MPC system utilized a grey-box model for predictions and local optimization algorithms for control. The retrofitting strategies included the addition of films and curtains on the interior side of the glass façade. Results indicated a trade-off regarding the energy saving and thermal comfort between the two approaches. Compared to MPC, curtains did not reduce energy demand as significantly, but they provided better indoor thermal comfort. The study also found that the lumped model used in the MPC system had limitations for summer calculations and that some algorithms tended to be aggressive. In terms of retrofitting strategies, the application of curtains enhanced thermal comfort more effectively than adding films to the glass. ... Read more

The project addresses the mass demolition and reconstruction of post-war housing complexes in the Netherlands. It’s relevance is based on the negative ecological impact embedded within the production of building material, the waste production of demolition and the neglect of architectural heritage in common renewal practice.

It proposes an alternative method of solving the need for renewal in most post-war housing complexes through a radically circular transformation strategy. This strategy is based on three steps: preserve, reuse, reclaim. A porch flat ensemble in the area of Geuzenveld, Amsterdam Nieuw-West, is used as the design case.

A research was conducted in preparation of the design. It’s main research question: “how can renovation with reclaimed materials become a feasible alternative to reconstruction of the current housing stock?”. From this research, the application of reclaimed insulation and finishing material, was indicated to be highly effective strategies of mitigating the ecological impact of a renovation task. These findings have been incorporated into the design.

The project resulted in a transformation design of the porch flat ensemble that saves 1.808.751 kg CO2-eq and 26.122.919 MJ of energy in terms of material use, relative to a conventional reconstruction design.
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The research dives into Amsterdam Nieuw-West, exploring the principles of Western Garden Cities and the use of adaptability in the construction process. The Western Garden Cities are an elaboration of Cornelis van Eesteren's Algemeen Uitbreidingsplan (General Expansion Plan) from 1935. This city district is part of the Western Garden Cities and has recently been listed by the National Cultural Heritage Agency of the Netherlands to have national importance. This area is listed because of the meaningful urban plan and the execution of it after World War II. However, in the 1980s, the Western Garden Cities even became synonymous with squalor, crime and social problems. The current housing stock is considered obsolete, both architecturally and physically. The area faces many problems and threats, making it an ideal location for transformation and renewal. Recognizing the pressing housing crisis and the urgent need to transform existing buildings in a circular way, the research looks into innovative approaches of building with adaptability, to efficiently revitalize this city district. The research proposes design guidelines for the transformation of porch flats, the most common building typology, in Amsterdam Nieuw-West. It is the repetition and the recognisability of these residential buildings that allows for improvements. The guidelines are a list of intervention strategies that can be implemented in the transformation of the post-war porch flats in Nieuw-West, they respect the heritage status of the neighbourhood and are complemented by a set of adaptability strategies. These guidelines are a helpful tool for transforming porch flats in the area with a diverse range of small interventions. However, the guidelines don't form definitive answers, but are rather a flexible framework which is useful as a starting point in the design process.
The design case is located at the Johan Jongkindstraat, close to Lelylaan station.The plot has 6 porch flats with a residential function and 5 smaller buildings with both a residential and public function. The design project forms the location in order to implement the design guidelines provided by the research and forms an example of how to transform in Amsterdam Nieuw-West. The design carefully looked at the design guidelines and implemented them. It also looked at site-specific interventions that were needed to increase living comfort. With the right design interventions, connections were made, repetition was broken, heritage was preserved with new improvements related to current wishes and the entire plan was future-proofed. This project goes beyond monotony and shows that with these interventions, the satisfactory scores in the Western Garden Cities can improve.
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To reach the European Union climate targets of 2020 the rate of refurbishment must increase. The problem is that there are many barriers to refurbishment, which causes a low rate and low quality. The objective is to overcome these barriers and stimulate facade refurbishment. This thesis looks at the improvement, that can be made when replacing an existing skin by a new facade focusing on improving the structural efficiency and touch upon building physics.
The main driving forces of this thesis are parametric design and optimisation. A parametric design is crucial for this thesis to perform a variation study. Different shapes of the facade are simulated with a custom made genetic algorithm to optimise the shape of the facade. First of all, the cost can be influenced by minimising the amount of material by altering: cross-sections, beam distances, etc. Secondly, by changing the shape of the facade a more aerodynamic building can be created. When the curvature increases, the wind load can be reduced which can make the structure more efficient. The wind load on the facade is determined with the computational fluid dynamics (CFD). The part about building physics focusses on ventilation. A ventilation system is designed which emphasises the importance of integrating the ventilation system with the second skin. The design builds upon the results of the CFD simulation and the structural model. The performance of the system is quantified by determining the usage of natural resources. ... Read more

Currently, tons of high-quality borosilicate glass are discarded to landfills each year, taking up space on valuable land. Within the existing soda-lime glass recycling industry it is not possible to use recycled borosilicate glass due to its higher melting temperatures and a difference in chemical composition. In fact, borosilicate glass disturbs the recycling process of soda-lime glass, resulting in more unused waste. Borosilicate glass is a type of glass that has favourable properties for application in the built environment, such as high optical qualities and a low thermal expansion coefficient. However, due to its high melting temperature and high energy consumption it is much more expensive to produce compared to the more common soda-lime glass. Nevertheless, in general it is possible to recycle glass waste almost 1:1, therefore, it is a waste to dump such high-quality glass on landfills. Cost and energy consumption issues related to the fabrication of borosilicate glass can be decreased by using recycled crushed glass (cullet) to the melt. Cullet reduces the required melting temperature, resulting in a lower energy consumption and a cheaper production process. However, a fully closed borosilicate glass recycling loop is not possible. The current borosilicate glass product industry has very strict quality control. Recycling glass introduces contaminations in the glass melt, which could generate flaws and cracks in the end product. This means it is not feasible to use recycled glass in these industries. This research proposes a promising approach to tackle the borosilicate glass waste problem and the recycling issues related to contamination: using the collected borosilicate glass waste to produce cast glass components. The bulkiness of such a component allows for a higher amount of impurities without risk of failure and a decrease in quality. In addition, cast glass allows for self-supporting facade systems in many configurations due to their increased cross-section and high-compressive strength capability. To allow disassembly of such a cast glass facade system a dry-interlocking system is proposed. Such a system can ‘close’ the recycling loop of borosilicate glass by feeding in waste glass from traditional borosilicate products into a new cast glass recycling loop. The challenges and opportunities regarding recycling borosilicate glass were researched by conducting experiments. Several mixtures of borosilicate glass with different chemical compositions were cast into small specimens to assess the mixability and corresponding mechanical properties of recycled borosilicate glass. In terms of mixability, good results were observed when the cullet is ground to powder, although there is a risk of contamination during grinding and thus degrading quality. Using fine cullet is also promising, but there is an increased risk of internal stresses. Specimens with a homogeneous chemical composition showed that it is possible to create borosilicate glass components with a lower firing temperature. In addition, these homogeneous specimens illustrated through a three-point bending test that recycled borosilicate glass has comparable mechanical properties to non-recycled borosilicate glass. This indicates that recycled borosilicate glass is suitable for application in cast glass components for use in the built environment. Due to time constraints and the preliminary nature of this research the number of specimens was relatively small. This thesis presents a dry-interlocking cast glass component system applied in a case study. The case study concerning the existing Casa da Música is meant to illustrate the possibilities of applying high-quality glass in an aesthetically pleasing facade system and to showcase the possibilities of recycling borosilicate glass. At the end-of-life of this design the facade can be disassembled. The components can either be directly reused in another building or recycled again. The proposed solution can reduce the growing amount of glass waste. ... Read more

Glass is a fascinating material which has been used for load bearing structures in the past decades. The development of structural glass has been moving towards more transparent structures.
The thermal properties of glass can be used to create heat bonds. Heat bonds can be produced in two ways: welding and fusing. With welding, the regions that are to be connected are locally heated. With kiln formed fusing, the elements to be bonded will be globally heated in an oven. This results in the research question: What is the best method, among glass welding and kiln formed glass fusing, to produce heat bonded systems for applications in glass structures?
In theory, safety measures consist of three basic strategies: creating secondary load transfer mechanisms, protectioning and overdimensioning.
These strategies can be used on the scale of the system and the structure. The heat bonded system could theoretically be laminated, reinforced and tempered. On a structural level, safety can be ensured by a combination of the strategies.
To produce glass welds, the glass is preheated in an oven. A small opening in the oven is made and a line burner is used to heat the to be welded area from both sides. One element is pressed down on the other to make the connection. The oven is closed and the specimen is annealed.
Finite element models have been used to analyze thermal shock failure during the weld production process. The recommendations for production were to use an additional flame on the bottom of the specimen or to maintain the surroundings at elevated temperature. The latter option is applied in the experiments.
The results were three transparent, all-glass, soda lime T-shaped objects. Little residual stress remained in the products.
The fused objects were globally heated in an oven. The glass was fused in moulds, made of a gypsum plaster. The products were translucent, all-glass, soda lime, T-shaped objects. The objects deformed significantly during production. Little residual stress remained in the products.
Throughout the experiments, factors have changed. An aspect with no direct influence on the product was quenching after maximum temperature. Adapting the mould and polishing the glass edges prior to fusing had an influence on the objects' shape or texture. None of the factors influenced the order of magnitude of the deformation or the seam between the elements.
A structural test has been performed to compare the specimens with a glass T-shape bonded with transparent UV-curing adhesive. The connections were loaded in shear. The results of the failure loads and stress at failure are of the same order of magnitude. The largest spread was among the fused specimens, the smallest among the welded.
The cause of failure is most probably a combination of elevated stress due to the stiffness and support of the test set-up and peak stress due to irregularities on the glass surface. Other causes could have contributed to failure.
The welded glass product requires most time, energy, skill and money. The adhesive product requires least time and energy. The welded and fused objects had neither acceptable dimensional accuracy, nor a smooth fillet in the joint.
In the current state of development, glass fusion results in less residual stress, requires less skill and is cheaper to produce. Glass welding results in a transparent glass to glass connection and its structural performance is promising. Further research is encouraged into the heat bonded and adhesive connections to create fully transparent connections for structural glass. ... Read more

Glass has been used for centuries. Originally to create weapons, jewellery and decorative ceramics. Nowadays as windows, reagent bottles and electronic devices. It’s only in the last two centuries that there has been substantial development of float glass. The resulting products provide comfort, protection, energy reduction, security and transparency. It is for this reason that glass in modern architecture grew very rapidly in the past decade. Glass panels increased in size and with that growth, the thickness of glass panels has increased from a modest 8 mm to a currently more regular thickness of 32 mm. On top of this, the required insulation values of glass constructions also increased. Future glass panels can include triple or more layers to provide for the required insulation, creating even heavier panels. At a time where we strive to make ever larger and heavier glass panels, shouldn’t we investigate new ways of pushing technological boundaries in order to save material rather than using more of it?

Where regular float glass is a rather thick, hard and brittle substance that can break easily when subjected to large stresses, thin glass can be found on the other side of the spectrum with its flexibility, clarity and higher strength. Thin glass has rarely been used for architectural applications, mainly because technologies for manufacturing thin glass in construction element sizes were not available or were often too expensive. This product however shows large potential provided sufficient interest is shown from different sectors to lower the price and stimulate innovation. This research will therefore focus on how to implement thin glass on a larger architectural scale and embrace its features to create thinner and stronger load-bearing glazing elements in areas where regular float glass doesn’t work. Several design configuration are proposed, of which the thin glass as cold bent laminated panels is the chosen principle to further explore. The main goal of this research is then to gain insight in the structural and post-breakage behaviour of cold bent laminated thin glass panels. Two layers of Leoflex glass from AGC are to be cold bent into a sinusoidal shape with Saflex DG41 provided by Qdel and SentryGlas provided by Trosifol as the interlayers. From the moment the panels are released from their mould, a certain spring back can be observed. Afterwards, the relaxation phase is initiated. Additionally, experiments are performed on a smaller scale panel for a point load applied in the middle of the upper bent surface. ... Read more

The search for a transparent, reversible, and reusable consolidation system for monuments led to the ambition to test possible cast glass interlocking brick designs using numerical calculations. The focus of this research is hence the design, simulation and evaluation of a possible cast glass interlocking geometry using Finite Element Analysis (FEA). For this purpose, design criteria are formulated from literature; considering glass, polyurethane (used as interlayer) and interlocking systems. As interlocking systems are determined by their boundary conditions, a case study of a monument is chosen to provide additional design criteria. The goal of the case study is to provide a reversible and reusable restoration and consolidation alternative for the current invalid restorations.
The design criteria obtained then are combined into an initial geometry, whose parameters are varied to test their sensitivity to its shear capacity, using FEA. Christensen’s failure criterion is used to locate prone areas in the geometry, and to evaluate the theoretical moment of failure. This output value combines the three principal stresses into a failure envelope, hence can generate contour plots to envision peak-stress-prone areas. This is important especially for glass structures, as they are prone to peak tensile stresses.
From the results design diagrams are created and applied on a conceptual cast glass interlocking consolidation design for the monument chosen as case study: The Lichtenberg Castle ruin.
The initial design is moreover prototyped to check its interlocking capabilities, residual stresses and deviations introduced by shrinkage.

Being able to evaluate possible geometries using FEA can decrease costs and time when searching for a new interlocking geometry. Prone areas are easily highlighted using the Christensen’s failure criterion output. Hence peak stress sensitive or invalid geometries can be discarded before reaching the prototyping stage, which is time consuming and costly.
The creation of a methodology to predict this behaviour is hence valuable for further research on other cast glass geometries and can moreover be applied in any other field when analysing solid complex geometries.
Another goal is to find a cast glass brick design which not only can consolidate the monument of the case study, but is moreover applicable in other projects or configurations. The brick then is not a one-solution design, but can be reused in other projects.

The geometry hence is varied using Grasshopper plug-in for Rhinoceros. By exporting the geometry using a STEP-file, a solid can be loaded into DIANA FEA, where it can be analysed using their newly implemented output value of the Christensen’s failure criterion.
The geometry of the monument is gained through a 3D laser scan, resulting in a point cloud. The point cloud is adapted using Autodesk Recap, then further processed in Rhinoceros.

The Christensen’s failure criterion output is a proper and fast way to evaluate possible cast glass brick designs. Any compressive stresses on the interlocking brick geometry are beneficial for its shear capacity, as is an increase in interlocking amplitude or brick height. Increasing the amplitude however affects the allowable tolerance negatively, which is also the case for a decrease in brick height. Decreasing the brick height hence results in both negative effects.
The conceptual design for consolidation of the Lichtenberg Castle tower can replace the current interventions with equal or higher capacity, even for all conservative assumptions and simplifications. The design can still be altered less conservative after more experimental results and simulations come available.

The methodology applied can now be further developed and performed on other complex geometry designs. The presented multifunctional cast glass interlocking brick design, and its variations can be further investigated and applied in other projects. ... Read more