The strength of aged glass

Glass is known for its excellent durability, but the strength of glass is very sensitive to the characteristics of its surface, which is known to accumulate damage during its service life. There is however, a lack of strength data on weathered or aged glass, particularly on thermally or chemically treated glass. In this study a carefully calibrated sand trickling test is used to produce surface damage equivalent to erosive action of 20 years of natural weathering on different types of glass: soda-lime-silica annealed, soda-lime-silica fully toughened and aluminosilicate chemically toughened. The soda-lime-silica glass specimens are tested destructively in their as-received and artificially aged form in a conventional coaxial double ring set-up, while the alumino-silicate chemically toughened specimens are tested in an improved coaxial double ring set-up. Fractography is subsequently used to identify and measure the critical flaw size on each specimen. The strength data are analysed statistically and the design strengths for each glass type are obtained. It is found that all glasses suffer a loss in strength after artificial ageing, with fully toughened glass providing the best post-aged performance. It was also found that the degree of toughening in the glass affects the erosion resistance, with chemically toughened glass outperforming the other glasses in this respect.EPSRC, Eckersley o' Callaghan, Onassis Foundatio

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

AbstractLaminated 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.</jats:p

High strain-rate effects from blast loads on laminated glass: An experimental investigation of the post-fracture bending moment capacity based on time–temperature mapping of interlayer yield stress

To enhance the resilience of buildings, laminated glass panels are increasingly used in glazed façades. These ductile panels provide a superior blast resistance to that provided by monolithic glass panels, due to the improved residual capacity offered by the polymer interlayer following the fracture of the glass layers. The complex interaction between the attached glass fragments and the interlayer is still only partially understood. To help address this, this paper investigates experimentally the post-fracture bending moment capacity of laminated glass. Three-point bending tests are performed at low temperature on specimens pre-fractured before testing, to ensure controlled and repeatable fracture patterns. The low temperature simulates the effects of the high strain-rates that result from short-duration blast loads by taking advantage of the time-temperature dependency of the viscoelastic interlayer. In these experiments, polyvinyl butyral is considered as the interlayer, this being the most common interlayer for laminated glass used in building facades. A new time-temperature mapping equation is derived from experimental results available in the literature, to relate the temperatures and strain-rates that result in the same interlayer yield stress. The results of the low-temperature tests demonstrate an enhancement of the ultimate load capacity of the fractured glass by two orders of magnitude, compared to that at room temperature. This suggests an improved post-fracture bending moment capacity associated with the now stiffer interlayer working in tension and the glass fragments working in compression. Due to the time-temperature dependency of the interlayer, a similar enhancement is therefore anticipated at the high strain-rates associated with typical blast loading. Finally, the assumed composite bending action is further supported by the results from additional specimens with thicker PVB and glass layers, which result in enhanced capacity consistent with the bending theory of existing analytical models.EPSRC Grant Reference No. EP/L016095/1 and ICE Research and Development Enabling Fun

Adhesively-bonded GFRP-glass sandwich components for structurally efficient glazing applications

Composite sandwich structures made of thick glass face sheets adhesively-bonded to glass fibre-reinforced polymer (GFRP) core profiles have the potential to outperform existing non-composite glazing configurations but their feasibility has yet to be investigated and there are no analytical models that describe their structural response. This paper presents the new analytical models for predicting deflections and strains in adhesively-bonded GFRP-glass sandwich beams. The new analytical models successfully account for: the shear deformations of the core and adhesive layers; the local bending of the constituent parts about their centroidal axes; and the global bending of the sandwich component as a whole. The deflections and strains predicted by analytical models are validated by finite element simulations and compared with the results of destructive tests performed on adhesively-bonded GFRP-glass beams in a four-point bending configuration. The analytical models were also evaluated for alternative GFRP-glass configurations tested by others. The GFRP-glass beams specially assembled in this study confirm the physical feasibility of constructing these proposed components.The authors would like to thank the Engineering and Physical Sciences Research Council – United Kingdom for the financial support of the project

Knowledge-rich optimisation of prefabricated façades to support conceptual design

One of the principal challenges in façade design is to support the architectural intent by devising technically viable (i.e. standard-compliant and manufacturable) solutions from as early as possible in the design stage. This is increasingly relevant as prefabricated façades increase in complexity and bespokedness in response to current societal, financial and environmental challenges. In this paper a process that addresses this challenge is presented. The process consists of two sub-processes 1) to build product-oriented knowledge bases and digital tools for supporting design on a project-by-project basis and 2) to help designers identify a set of optimal solutions that consider the façade-specific trade-off between architectural intent and performance requirements, while meeting the largest number of production-related constraints. This process was applied to a case study and the results were compared with those obtained from a recently-developed façade. It was found that, although the proposed process produces optimal solutions that are approximated, designers can benefit from more control over the product’s manufacturability, performance and architectural intent in less time.Laing O'Rourke pl

Repair of Soda-Lime-Silica Glass

Glass strength is very sensitive to damage accumulation during its service life. Repair methods for glass have been proposed over the last decades to volumetrically fill or remove existing flaws from the surface of glass. However, the lack of information on the strength recovery attributable to glass repair methods restrict their use to low consequence class applications in buildings thereby making replacement of damaged installed glass the only safe and practical solution when dealing with damaged glass. Repair methods involving volumetric filling of visible flaws with resins, removal of visible flaws with polishing and chemical repair with acid treatment of visible flaws are undertaken in this study to investigate the strength recovery in 60 artificially aged annealed glass specimens. It is found that the polishing provides the most promising strength recovery results showing a 132% and a 40% increase in design and mean strength whilst the acid treatment provides the worst performance. Polishing repairs are further investigated in this study to determine their efficacy in strength recovery after environmental ageing (exposure to UV, humidity and freeze-thaw cycles)

The impact of using Closed Cavity Façades (CCF) on buildings’ thermal and visual performance

Abstract Glazing is a critical buildings element as it is the most vulnerable envelope part to heat gain and heat loss accounting for around 50% of a building’s energy consumption. However, conventional glazing technologies have relatively low-performance characteristics which cause significant heat losses during winter and undesired heat gain in summer. In this regard, this study investigates the thermal and visual performance of various design configurations of a novel glazing technology, named Closed Cavity Façade (CCF), in comparison with traditional glazing technologies. Several CCF configurations were examined using Energy Plus and IDA ICE and compared to the baseline Double Glazing Unit (DGU) (traditional or thermochromic). MATELab, an office-like test facility at the University of Cambridge was used as the model for the simulations, which was beforehand experimentally validated. The results showed extensive benefits of CCFs compared to DGU systems, in terms of thermal performance and comfort. A 22-41% or 21-37% decrease in annual total energy consumption, compared to traditional DGU or thermochromic respectively, are identified along with a positive effect on thermal comfort with a significant reduction in radiant discomfort. Further investigation showed that glass coatings and solar shading device’s characteristics play an important role in achieving further performance improvements.</jats:p

Artificial ageing of glass with sand abrasion

The strength of glass is governed by the condition of its surface which deteriorates progressively as surface flaws accumulate on exposure to weathering action during its service life. Therefore, knowledge of the strength of naturally aged glass is crucial in order to ensure its safe use in load-bearing applications. Artificial ageing tests can be very useful in this regard, but they have traditionally focused on degradation in light transmittance properties rather than the strength of glass. Experimental testing has been undertaken in this study to investigate the effectiveness of a falling abrasive method for the artificial ageing of glass. Abrasive medium is allowed to fall freely on monolithic glass and induce a random surface flaw population. 390 annealed glass specimens grouped in 26 series were artificially aged using different combinations of ageing parameters. The specimens were subsequently subjected to destructive and non-destructive testing to determine the influence of each ageing parameter and to establish a combination that produces strength characteristics similar to those of naturally aged glass. Existing artificial ageing recommendations were found to significantly overestimate design strengths by up to 253% at low probabilities of failure, Pf = 0.008 and are therefore, deemed unsafe. However, it was found that the falling abrasive method using a different combination of ageing parameters provides good correlation to the strength of naturally aged glass.The authors gratefully acknowledge financial and technical support from Eckersley O’Callaghan, and financial support from the Engineering and Physical Sciences Research CouncilUK (EPSRC) and Onassis Foundation

Design and control optimisation of adaptive insulation systems for office buildings. Part 1: Adaptive technologies and simulation framework

The increasing insulation levels imposed by building regulations have the effect of reducing heating energy use, while increasing cooling energy use and/or reducing thermal comfort especially in summer. Adaptive insulation technologies could provide an opportunity to reduce building energy use while simultaneously improving indoor environmental quality, but there is a lack of information about the performance of these novel technologies. This paper is the first of a two part study, which aims to evaluate the performance of adaptive insulation. Part 1 proposes a simulation framework for optimising adaptive insulation design and control parameters and explains its implementation. The customised simulation strategy optimises design and control aspects of adaptive building envelopes by minimising the total primary energy use and thermal discomfort within a building. Moreover the simulation model for adaptive insulation is validated qualitatively. Part 2 applies this framework in a parametric study to explore the potential of adaptive insulation.The British authors would like to acknowledge support from EPSRC Doctoral Training Grant (EP/K503009/1) and project RG70518, funded by Wintech ltd. The Chinese author would like to acknowledge the financial supports from the National Natural Science Foundation of China (Grant No. 51408427)