Thermal Healing of Realistic Flaws in Glass

For any given environmental conditions the tensile strength of glass is a function of the geometry of the critical flaw and the residual stresses in the vicinity of the flaw. The strength of heat treated glass is conventionally considered to be equal to the sum total of the residual stress and the extrinsic strength of annealed glass. Recent experiments Suggest that there is an additional contribution to strength due to crack healing. In order to quantify it, uniaxial and equibiaxial strength tests on both as-received and carefully annealed glass specimens were performed for different edge geometries and edge finishes. The results show that strength recovery due to healing is significant and this strength gain appears to correlate with the quality of the edge finish. Possible explanations of this phenomenon are provided. Independently of healing effects, it was also found that the edge quality has a marginal effect on the mean strength, but has a significant positive effect at low fractile values often used in design applications.The contribution of Chris Cavanagh to part of the experimental testing, Trend Marine Ltd and Engineering and Physical Sciences Research Council (EPSRC) is gratefully acknowledge

Increasing the design strength of glass - fractography and stress testing

p. 867-880Brittleness is the unintended, but inevitable consequence of producing a transparent ceramic for architectural applications such as the soda-lime glass. Its tensile strength is particularly sensitive to surface imperfections, such as that from natural weathering and malicious damage. Although a significant amount of testing of new glass has been carried out, there has been surprisingly little testing on weathered glass. Due to the variable nature of the causes of surface damage, the lack of data on weathered glass leads to a considerable degree of uncertainty in the long-term strength of exposed glass. This paper presents the results of recent tests on weathered annealed glass which has been exposed to natural weathering for more than 20 years. The tests include experimental investigations using the co-axial ring setup as well as optical and atomic force microscopy of the glass surfaces. The experimental data from these tests is subsequently used to extend existing fracture mechanics-based models to predict the strength of weathered glass. It is shown that using an automated approach based directly on finite element analysis results can give an increase in effective design strength in the order of 70 to 100% when compared to maximum stress methods. It is also shown that by combining microscopy and strength test results, it is possible to quantitatively characterise the damage on glass surfaces.Zammit, K.; Overend, M. (2010). Increasing the design strength of glass - fractography and stress testing. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/695

Towards a New Way of Capturing Occupant Well-being

Occupant well-being is undergoing a surge of interest in both the research community and industry, as the potential benefits of increased levels of well-being become better quantified and understood. Well-being science itself is also constantly evolving, moving from the traditional negative view of depression and mental disorders as markers of well-being, towards the more positive notion of flourishing, which is feeling good and functioning well. This paper first sets out the key elements of well-being, as found in psychology literature. Surveys and interviews are the main methods used to capture the well-being of individuals and populations, yet completion rates can be low, occupants distracted or irritated by requests to complete surveys and the data infrequent or irregular. Instead, cameras emerge as a potential economic way to gain information about occupants. Their comfort, health and well-being can be monitored with a high frequency, low intrusion and low cost through the use of facial emotions and movements. To this end, a small pilot study is carried out to examine the effectiveness and practicality of data capture by cameras. Data from a new naturally ventilated office building in Cambridge, United Kingdom, is inspected alongside more traditional well-being assessment techniques. It finds that occupants quickly forget that they are being monitored by the cameras and are very engaged with the research, keen to see if it can help improve their workspace. The results and experience from this pilot study form the basis of a more extensive programme of investigations that are described at the end of this paper. The aspiration is to develop this method so that it can be deployed as part of a wider toolkit to holistically capture high quality information about the comfort, health, and well-being levels of building occupants

The mechanical response of cold bent monolithic glass plates during the bending process

Cold bending of glass involves the straining of relatively thin glass components, (typically plates), at ambient temperatures, and is a low energy and cost effective manner of creating curvilinear forms required in modern glass applications. Cold bending is also popular because it is thought to eliminate the optical imperfections in curved glass plates that arise during alternative and more conventional thermal bending techniques. Experimental and numerical investigations on the cold bending of monolithic glass plates into anticlastic shapes are undertaken and described in this paper. The aim is to characterise the cold bending behaviour during the bending process and to evaluate the surface/optical quality of the curved plates. Two distinct phenomena of interest are observed: (i) a change in the deformation mode that under particular boundary and loading conditions lead to snapthrough buckling and; (ii) a local instability termed “cold bending distortion” that appears on curved plates when certain applied displacement limits are exceeded. This cold bending distortion is found to occur at stresses significantly below the fracture strength of the glass plate, but the distortions can be sufficiently large to breach optical serviceability requirements. An optical quality evaluation procedure for predicting the cold bending response and the resulting optical quality of monolithic glass plates are provided at the end of this paper.The authors gratefully acknowledge financial and technical support from Eckersley O'Callaghan, and financial support from the Research Fund for Coal and Steel of the European Community and the Engineering and Physical Sciences Research Council UK (EPSRC).This is the final version of the article. It first appeared from Elsevier via https://doi.org/ 10.1016/j.engstruct.2016.03.01

Towards human-centred intelligent envelopes: A framework for capturing the holistic effect of smart façades on occupant comfort and satisfaction

Intelligent buildings have the potential to simultaneously revolutionise the way humans live and reduce energy demand in buildings. In particular, the so-called, smart / dynamic / adaptive building envelope can selectively modulate the energy transfer between the building and its environment in response to transient outdoor conditions and indoor requirements, thereby providing a low-carbon means of achieving occupant satisfaction and well-being. However, the effect of smart facades on holistic occupant comfort and satisfaction with the environment is yet to be fully captured and quantified. This information is essential for evidence-based design and control of smart building envelopes. In this paper, the smart façade characteristics that underpin satisfactory environmental conditions are identified and metrics for their transient and holistic assessment are discussed. A methodology to capture the effect of smart façades on the holistic occupant comfort and satisfaction is then proposed together with its implementation into an early stage design tool. Finally, a ranking system is suggested to assess and compare alternative smart façade technologies according to their overall effect on user satisfaction and productivity for a UK climat

Occupant-Facade interaction: a review and classification scheme

The interest in occupant interaction with building controls and automation systems is growing due to the wider availability of embedded sensing devices and automated or intelligent building components that can integrate building control strategies with occupant-centred data and lead to greater occupant satisfaction and reduction in energy consumption. An area of particular interest is the interaction strategies between occupants and the so called automated facades, such as dynamic shading devices and switchable glazing. Occupant-Facade interactions are often disruptive and source of dissatisfaction because of conflicts between competing requirements, e.g. energy-efficiency and indoor environmental quality. To solve these conflicts, expertise from several disciplines is required, including Behavioural Science and Building Physics, but the absence of common research frameworks impedes knowledge transfer between different fields of expertise. This paper reviews existing multi-disciplinary research on occupant interaction with facades, buildings and automation systems and provides a new classification scheme of Occupant-Facade interaction. The scheme is based on an extensive review of interactive scenarios between occupants and facades that are summarised in this paper. The classification scheme was found to be successful in: 1) capturing the multidisciplinary nature of interactive scenarios by clarifying relationships between components; 2) identifying similarities and characteristics among interactive scenarios; 3) understanding research gaps. The classification scheme proposed in this paper has the potential to be a useful tool for the multi-disciplinary research community in this field. The review also showed that more research is needed to characterise the holistic and multi-disciplinary effect of occupant interaction with intelligent building components.EPSRC Doctoral Training Accoun

The optimal thermo-optical properties and energy saving potential of adaptive glazing technologies

The development of dynamic building envelope technologies, which adapt to changing outdoor and indoor environments, is considered a crucial step towards the achievement of the nearly Zero Energy Building target. It is currently not possible to evaluate the energy saving potential of innovative adaptive transparent building envelopes in an accurate manner. This creates difficulties in selecting between competing technologies and is a barrier to systematic development of these innovative technologies. The main aim of this work is to develop a method for devising optimal adaptive glazing properties and to evaluate the energy saving potential resulting from the adoption of such a technology. The method makes use of an inverse performance-oriented approach, to minimize the total primary energy use of a building. It is applied to multiple case studies (office reference room with 4 different cardinal orientations and in three different temperate climates) in order to evaluate and optimise the performance of adaptive glazing as it responds to changing boundary conditions on a monthly and daily basis. A frequency analysis on the set of optimised adaptive properties is subsequently performed to identify salient features of ideal adaptive glazing. The results show that high energy savings are achievable by adapting the transparent part of the building envelope alone, the largest component being the cooling energy demand. As expected, the energy savings are highly sensitive to: the time scale of the adaptive mechanisms; the capability of the façade to adapt to the outdoor climatic condition; the difference between outdoor climatic condition and the comfort range. Moreover important features of the optimal thermo-optical properties are identified. Of these, one of the most important findings is that a unique optimised technology, varying its thermo-optical properties between a limited number of states could be effective in different climates and orientations.The present work has been developed in the framework of a PhD research project. The authors are grateful to EPSRC and Wintech Ltd. for funding the PhD. The authors are also grateful to the National Natural Science Foundation of China (No. 51408427) for their support.This is the final published version of the article. It was originally published in Applied Energy (Favoino F, Overend M, Jin Q, Applied Energy, 2015, 156, 1-15, doi:10.1016/j.apenergy.2015.05.065). The final version is available at http://dx.doi.org/10.1016/j.apenergy.2015.05.06

The Potential of Smart Glazing for Occupant Well-Being and Reduced Energy Load in a Central-Mediterranean Climate

The ever-increasing aesthetically driven demand for fully glazed façades poses a design challenge; not least in controlling the cooling demand and occupant well-being of such buildings, especially in a central Mediterranean climate. This paper outlines the ever-important need to design for occupants and for designers to keep in mind, first and foremost, occupant well-being rather than aim solely to create energy-efficient buildings. The original objective of buildings was to provide shelter. Today however, the need for occupant comfort and its direct effect on productivity cannot be ignored. This need, therefore, ought to feature a central role in any building design. Studies show that occupant well-being is directly related to a range of environmental factors, particularly daylight distribution, glare and indoor air temperature. The use of external shading devices and more commonly, indoor blinds are often the adopted approaches to attempt to achieve indoor occupant comfort, often to the detriment of views. Adaptive facades seek to address the need to somehow strike a balance between occupant comfort and energy efficiency. These facades range from exterior and interior shading devices with varying control strategies, to the different forms of adaptive/switchable glazing technologies intended to control the visual light transmittance and solar radiation transmitted into a building’s interior. In the opinion of the authors, electrochromic glazing has a great potential in a cooling-dominated central Mediterranean climate, to achieve a compromise between occupant visual and thermal comfort whilst retaining unobstructed outdoor views at all times. Research shows that the potential benefits of electrochromic glazing have not yet been studied enough in real-life scenarios,and this paper further introduces the objectives for field study within two identical offices, having a South-South-East orientation, located in a central Mediterranean climate

The effects of high strain-rate and in-plane restraint on quasi-statically loaded laminated glass: a theoretical study with applications to blast enhancement

Abstract: Laminated glass panels are increasingly used to improve the blast resilience of glazed facades, as part of efforts to mitigate the threat posed to buildings and their occupants by terrorist attacks. The blast response of these ductile panels is still only partially understood, with an evident knowledge gap between fundamental behaviour at the material level and observations from full-scale blast tests. To enhance our understanding, and help bridge this gap, this paper adopts a ‘first principles’ approach to investigate the effects of high strain-rate, associated with blast loading, and the in-plane restraint offered by blast-resistant frames. These are studied by developing simplified analytical beam models, for all stages of deformation, that account for the enhanced properties of both the glass and the interlayer at high strain-rates. The increased shear modulus of the interlayer results in a composite bending response of the un-fractured laminated glass. This also enhances the residual post-fracture bending moment capacity, arising from the combined action of the glass fragments in compression and the interlayer in tension, which is considered negligible under low strain-rates. The post-fracture resistance is significantly improved by the introduction of in-plane restraint, due to the membrane action associated with panel stretching under large deflections. This is demonstrated by developing a yield condition that accounts for the relative contributions of bending and membrane action, and applying the upper bound theorem of plasticity, assuming a tearing failure of the interlayer. Future work aims to complete the theoretical framework by including the assessment of plate-action and inertia effects

Optimal control and performance of photovoltachromic switchable glazing for building integration in temperate climates

The development of adaptive building envelope technologies, and particularly of switchable glazing, can make significant contributions to decarbonisation targets. It is therefore essential to quantify their effect on building energy use and indoor environmental quality when integrated into buildings. The evaluation of their performance presents new challenges when compared to conventional “static” building envelope systems, as they require design and control aspects to be evaluated together, which are also mutually interrelated across thermal and visual physical domains. This paper addresses these challenges by presenting a novel simulation framework for the performance evaluation of responsive building envelope technologies and, particularly, of switchable glazing. This is achieved by integrating a building energy simulation tool and a lighting simulation one, in a control optimisation framework to simulate advanced control of adaptive building envelopes. The performance of a photovoltachromic glazing is evaluated according to building energy use, Useful Daylight Illuminance, glare risk and load profile matching indicators for a sun oriented office building in different temperate climates. The original architecture of photovoltachromic cell provides an automatic control of its transparency as a function of incoming solar irradiance. However, to fully explore the building integration potential of photovoltachromic technology, different control strategies are evaluated, from passive and simple rule based controls, to optimised rule based and predictive controls. The results show that the control strategy has a significant impact on the performance of the photovoltachromic switchable glazing, and of switchable glazing technologies in general. More specifically, simpler control strategies are generally unable to optimise contrasting requirements, while more advanced ones can increase energy saving potential without compromising visual comfort. In cooling dominated scenarios reactive control can be as effective as predictive for a switchable glazing, differently than heating dominated scenarios where predictive control strategies yield higher energy saving potential. Introducing glare as a control parameter can significantly decrease the energy efficiency of some control strategies, especially in heating dominated climates.This work was conducted as part of a PhD research sponsored by UK EPSRC and Wintech Ltd. The authors acknowledge the support of the COST Action TU1403 – Adaptive Facades Network (www.adaptivefacade.eu) and the University of Sydney (IPDF fund). The experimental data used as an input in this work were partially supported by Regione PUGLIA (APQ Reti di Laboratorio, project “PHOEBUS” cod. 31) and by Italian Minister for Education and Research which funded the R&D program “MAAT” (PON02_00563_3316357 − CUP B31C12001230005). The devices were fabricated at the Center for Biomolecular Nanotechnologies of Istituto Italiano di Tecnologia and characterized in the laboratories of CNR-Nano in Lecce. The contribution of the fourth author to the work reported in this paper was supported by the Australian Research Council through its Future Fellowship scheme (FT140100130).This is the final version of the article. It first appeared from Elsevier at http://dx.doi.org/10.1016/j.apenergy.2016.06.107