Mauro Overend

A transparent ultraviolet triggered amorphous selenium p-n junction

This paper will introduce a semitransparent amorphous selenium (a-Se) film exhibiting photovoltaic effects under ultraviolet light created through a simple and inexpensive method. We found that chlorine can be doped into a-Se through electrolysis of saturated salt water, and converts the weak p-type material into an n-type material. Furthermore, we found that a p-n diode fabricated through this process has shown an open circuit voltage of 0.35 V toward ultraviolet illumination. Our results suggest the possibility of doping control depending on the electric current during electrolysis and the possibility of developing a simple doping method for amorphous photoconductors.

Review of current status, requirements and opportunities for building performance simulation of adaptive facades†

Adaptive building envelope systems have the potential of reducing greenhouse gas emissions and improving the energy flexibility of buildings, while maintaining high levels of indoor environmental quality. The development of such innovative materials and technologies, as well as their real-world implementation, can be enhanced with the use of building performance simulation (BPS). Performance prediction of adaptive facades can, however, be a challenging task and the information on this topic is scarce and fragmented. The main contribution of this review article is to bring together and analyse the existing information in this field. In the first part, the unique requirements for successful modelling and simulation of adaptive facades are discussed. In the second part, the capabilities of five widely used BPS tools are reviewed, in terms of their ability to model energy and occupant comfort performance of adaptive facades. Finally, it discusses various ongoing trends and research needs in this field.

Structural Performance of Bolted Connections and Adhesively Bonded Joints in Glass Structures

AbstractHigh-strength adhesives provide an alternative, and potentially more efficient, load-bearing connection to conventional bolted connections in glass structures, but the relative structural performance of these connections has yet to be established, and the accuracy of existing predictive techniques is largely unknown. This paper describes the parametric and experimental investigations undertaken to compare the structural performance of nominally identical bolted and adhesive connections subjected to short duration loads. The paper also reports on the accuracy of existing empirical and numerical techniques for predicting the load-bearing capacity of these connections. The investigations show that the load-bearing capacities of the single-lap and double-lap adhesive connections can exceed that of the double-shear bolted connections, and that failure in the adhesive connections tends to be less catastrophic. The existing empirical methods provide good approximations of the load-bearing capacities of b...

Diagnostic Interpretation of Glass Failure

The prevalent use of large glass panels and the increasing use of glass in areas traditionally reserved for other materials, such as floors, roofs and staircases, is imposing unprecedented loads on glass. The fracture of glass caused by these onerous service loads and by the increasingly severe threats could result in human injury or death and often triggers claims and litigation. However, despite the widespread and documented cases of glass failure, there is a paucity of quantitative techniques for interpreting the causes of failure in glass. This paper attempts to redress the issue by providing a historical compilation of the existing knowledge on quantitative and qualitative techniques that explain glass failure. The static and dynamic fracture mechanics from this review form the basis of an empirical method, presented in this paper, that relates the fragment size to the fracture stress. This paper also describes a glass failure case study that illustrates some of the practical difficulties of carrying out a forensic analysis of glass failure.

A prototype whole-life value optimization tool for façade design

Façade design is a cross-disciplinary multi-objective optimization process. The major barrier to devising an optimal façade solution is the evaluation of the true values of alternative façade design options. A simple approach is to focus on a limited number of design criteria that can be evaluated through mono-disciplinary commercial software, while overlooking other cross-disciplinary design criteria. This paper describes a prototype whole-life value optimization tool for façade design, which accounts for the functional, financial, and environmental sustainability of alternative façade options. The tool adopts an integrated approach involving accurate simulation, systematic parametric analysis, and automatic design optimization. The tool is trialled on a real-world façade design project, and it successfully identified optimal façade solutions that outperform the original solutions obtained from the conventional façade design process.

Thermal Healing of Realistic Flaws in Glass

AbstractFor 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 attributable to crack healing. 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 attributable 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 fractil...

The mechanical performance of adhesively bonded steel-glass composite panels – Medium-scale tests and numerical models

Glass is often used in conjunction with steel framing but the two materials rarely act in a fully composite manner; the in-plane and out-of-plane loads on the framed glass structures are often resisted by the steel frame with the glass being used as infill panels. Steel-glass composite façade panels would increase structural and material efficiency as well as the aesthetical appeal. This paper investigates the mechanical performance of single-glazed and double-glazed medium-scale steel-glass composite panels subjected to flexural loads. The glass panels are linearly bonded to the reinforcing steel frames by Araldite 2047 adhesive, a two-part high strength acrylate. The paper also assesses the validity of two non-linear numerical models of the composite panels developed with different finite element analysis software. This research was undertaken at the University of Cambridge during a short-term scientific mission (STSM) supported by the COST Action TU0905. To achieve composite action in a steel-glass façade element the transfer of high longitudinal shear forces between the components is necessary. Studies on adhesives performed at different research institutions Overend et al. (2010 and Belis et al. (2011) show which adhesive types are suitable for linear bonding. The over-arching conclusion from this work is that, while silicones are often used for structural sealant glazing systems to achieve flexible structural connections, stiffer adhesives like epoxies and acrylates are necessary for composite steel-glass elements. Nhamoinesu and Overend (2012) performed small-scale investigations to select a suitable adhesive for composite steel-glass elements based on criteria like cohesive or adherend failure preceded by substantial plastic strain in the adhesive, relatively high joint flexibility, adhesive shear strength of at least 7.5MPa and a minimum loss of strength after exposure to temperature of up to 80°C. The acrylate Araldite 2047 showed the best mechanical characteristics under short-duration testing and was therefore also used for the investigations presented in this paper. 2 FLEXURAL TESTS ON MEDIUM SCALE STEEL-GLASS COMPOSITE PANELS 2.1 Specimen preparation & test procedure Three different specimen types (Figure 1) were assembled using 700mm by 300mm by 10mm thick fully toughened glass panels manufactured to BS EN12150-2, these were adhesively bonded to 700mm by 30mm by 10mm mild steel rectangular hollow sections (RHS) with a wall thickness of 1.5mm. The bonding surface of the steel was sanded using 220 grit sandpaper; all surfaces were thoroughly cleaned with acetone before adhesive application. 3mm thick PTFEcoated aluminium strips were placed on the ends of the steel profiles to act as spaces for the required 3mm adhesive thickness. A specially machined aluminium jig lined with a PTFE release film surrounded the perimeter of the glass panels to prevent the adhesive from flowing out of the joint during application as well as to align the steel hollow sections with the glass panels. Araldite 2047, a two-part high strength acrylate with a working time of approximately 11 minutes was applied to the edges of the glass using a manual dispensing gun. The assembled specimens were left to cure at ambient temperature and approximately 40% relative humidity for at least 7 days before testing. The following specimen types were tested: Type A – double glazed with one-way spanning steel RHS reinforcement linearly bonded to the long edges of the glass by 3mm thick Araldite 2047 acrylate (Figure 1 left) Type A* – similar to Type A except that the steel RHS were not adhesively bonded but simply layered between two glass panels Type B – double glazed with two-way spanning steel RHS reinforcement linearly bonded around the full perimeter of the glass by 3mm thick Araldite 2047 acrylate (Figure 1 middle) Type C – single glazed with one-way spanning steel RHS reinforcement linearly bonded to long edges of the glass by 3mm thick Araldite 2047 acrylate (Figure 1 right) Figure 1. Different tested composite panels: Type A (left), Type B (middle) and Type C (right). The specimens were subjected to four-point bending tests (Figure 2) on an Instron 5500R testing machine with a 150kN load cell. Displacement transducers where placed to measure displacement of the glass at mid-span and the displacement of the loading bars. Four unidirectional strain-gauges were placed 3.5mm, 50mm, 100mm and 150mm from the long edge of the glass respectively as shown in Figure 2. The gauges were used to measure the distribution of longitudinal normal stresses across the glass flange. Significant differences in the longitudinal normal stress in the glass would indicate shear lag, a phenomenon that is particularly pronounced in wide flanges. Another strain gauge was placed at the centre of the glass panel in order to measure the maximum normal stress in the glass at failure. The tests were displacement controlled with a displacement rate of 0.75mm/min. Three specimens of each type were tested to destruction and all tests were performed at ambient temperature and approximately 40% relative humidity. Figure 2. Dimensions of the composite panel (Type A) and position of supporting bars, loading bars, displacement transducers and strain gauges.

Knowledge-Based Engineering in the design for manufacture of prefabricated façades: current gaps and future trends

ABSTRACT The use of prefabricated façades provides a timely means to increase efficiency in the delivery of buildings, while maximising the expected environmental service performance. In order to achieve high performance and low cost, these products require manufacturability and supply chain knowledge to be integrated earlier than usual in the design process. Knowledge-Based Engineering (KBE) applications can potentially fulfil this need by providing a digital Product Model that informs designers about manufacturability aspects and expected performance. This paper explores the currently available digital tools, as well as KBE and its applicability in façade design. It is first demonstrated that there is a fundamental gap in state-of-the-art digital tools: rather than integrating design principles and manufacturing constraints, existing and emerging tools continue to focus on single disciplines with no consideration for the actual manufacturing stage. The applicability of KBE is then evaluated by reviewing the current use of this approach in the building and other industries, namely, aerospace and shipbuilding. It is found that, although KBE is rarely used in façade design, there are significant opportunities for it to be applied in this sector, due to the similarity in terms of design tasks and priorities with the two other industries reviewed in this paper.

A comparative study on high-performance glazing for office buildings

ABSTRACT High-performance glazing is commonly used in facades of contemporary commercial buildings. Compared to conventional glazing, high-performance glazing has the potential of achieving a better balance between occupants’ requirements and the energy demand of the building. Since each technology has its own strengths, it is necessary to understand their performances under different design scenarios in order to put them to the best use. In this article, we conduct a comparative study on 13 glazing scenarios on the facade of a typical cellular office room model. The simulations provide the energy demand/generation and indoor environmental quality of the scenarios in three geographic locations (London, Helsinki, and Rome), four orientations, and four window-to-wall ratios (WWRs) (30%, 50%, 70%, and 90%). It was found that photovoltaic integrated glazing with large WWRs and solar control glazing are generally superior to conventional insulating glazing in minimizing total energy demand. Electrochromic glazing provides a superior and stable indoor environment. More generally, the results provide a grouping of the technologies on the basis of their performance characteristics and a ranking of the different glazing options for different design scenarios, which could guide selection in real-world applications.

Thermal performance of novel frame-integrated unitised curtain wall

Framing of unitized curtain walls is dimensioned to carry wind load without taking advantage of potential composite contribution of glass. Subsequently, it is unnecessarily deep, occupying valuable space, and protrudes to the inside, causing visual disruption. Moreover, it is generally made of high thermal conductivity metal alloys, contributing to substantial thermal transmission at joints. An innovative frame-integrated unitised curtain wall has been developed that, compared to conventional systems, reduces structural depth significantly, allows an inside flush finish and reduces thermal transmission at joints. The idea is to adhesively bond a Glass Fibre Reinforced Polymer (GFRP) frame to the edge of the Insulated Glass Unit (IGU), thereby achieving low thermal transmittance and composite structural behaviour. The frame is to fit within the glazing cavity depth. This paper provides a description of the proposed system and assesses its thermal transmittance and risk of condensation through comparative analytical and numerical thermal analysis with a conventional system taken as reference.