Foreword
Glass, a fundamental architectural material, has evolved significantly since the 1960s with innovations such as the float glass process. However, visual distortions remain due to thermal treatment, lamination and insulation processes. Eclat Digital and Buro Happold have collaborated on a white paper that examines the challenges of visual distortion in architectural glazing and presents digital prototyping as a transformative solution.
The collaboration between Eclat Digital and Buro Happold has been positive and fruitful, resulting in an innovative approach to the way optical distortions in architectural glazing are addressed and mitigated. This has captured the interest of our clients and key stakeholders, leading to its shortlisting for the CIBSE Society of Facade Engineering 'Product of the Year' award 2023.
Modern glass manufacturing processes and types of visual distortion:
Optical distortions are caused by geometric deformations in the glass itself, that can have a significant impact on its aesthetics and functionality. The main distortions – pillowing, lensing and rolling wave effects – are caused by variations in the thickness, density or surface properties of the glass.
Figure 1: 3 types of visual distortions
Visual distrotions:
Pillowing Effect:
Pillowing, characterized by the inward curvature of straight lines, is primarily caused by non-uniform glass thickness. This non-uniformity can result from improper annealing. If the annealing process is inadequate, residual stresses remain in the glass, causing it to warp under its own weight. In addition, external factors such as excessive heat or mechanical stress can cause pillowing.
Pillowing can significantly reduce the visual appeal of glass. In precision applications where optical accuracy is critical, pillowing can affect the functionality of the glass, distorting images and making measurements inaccurate.
Double-glazing glass is primarily susceptible to pillowing due to the weight of the two glass panes putting stress on the spacer that separates them. Over time, this stress can cause the spacer to deform, resulting in a non-uniform distribution of weight across the panes. Climatic loads also exert dynamic forces that cause the space between the panes to expand or contract.
Rollerwave Effect:
Rollerwave, characterized by a wavy or distorted appearance of objects, arises from irregularities in the glass surface. These imperfections, often caused by manufacturing defects or surface damage, scatter light rays in an unpredictable manner, creating the illusion of waves or distortions.
Rollerwave can significantly degrade the visual quality of glass, making objects appear blurred, distorted, or disjointed. This effect can be particularly problematic in applications where visual accuracy is critical, and diminish the aesthetic appeal of glass.
Tempered glass is less prone to distortion than untreated glass due to its increased resistance to stress and impact. The heat treatment process changes the internal structure of the glass, making it more resistant but also alters the flatness of the glass, introducing distortions such as roller waves. This disrupts surface parallelism, leading to noticeable visual distortions, particularly at acute viewing angles.
Lensing Effect:
Lensing, the magnification or shrinking of objects observed through glass, is primarily caused by curved glass surfaces. The curvature of the glass acts as a lens, bending light rays and altering the perceived size of objects.
Uncontrolled lensing can distort visual perception, causing discomfort and impairing accuracy. In architectural settings, lensing can create distorted views, while in tasks like driving or operating machinery, it can hinder precise perception.
Laminated glass, a composition of multiple layers of glass bonded together with a plastic interlayer, offers superior resistance to rollerwave effects. It mitigates rollerwave effects due to the interlayer’s shock-absorbing properties. However, laminating heat-treated glass can amplify lensing as the interlayer fills in non-flat areas. Combining two distorted pieces increases the effect, particularly in thinner or larger glasses.
Figure 2 : Animation illustrating rollerwave effect on building façade.
Digital prototyping for architectural simulation:
In response to the challenges posed by visual distortion in architectural glazing, Eclat Digital, in collaboration with Buro Happold, is introducing a ground-breaking approach – Digital Prototyping . Recognising that visual distortion often occurs after fabrication, causing contractual and cost issues, this approach aims to revolutionise the design and structural calculation tools for glass projects. This process seeks to converge design and structural calculation tools with a visual prototyping tool.
At the forefront of this initiative is OceanTM, which stands out for its accuracy and physically based rendering capabilities. OceanTM uses real data from optical characterisation and bases its calculations on well-established optical physical laws. Using a stochastic Monte Carlo approach to generating and sampling light paths, the algorithm simulates the trajectory of rays interacting with glass surfaces, providing a comprehensive understanding of potential visual distortions.
Visual distortion through digital prototyping:
The implementation of digital prototyping using OceanTM provides insightful simulations of various visual distortions commonly associated with architectural glazing. Through meticulous 3D modelling, the tool captures the impact of distortion and provides predictive and quantitative analysis.
Pillowing Effect:
OceanTM simulates the pillowing distortion in a double glazed unit, presenting a scenario where the aesthetics of a building are affected by distorted reflections. The curvilinear and distorted appearance of reflected curtain wall grids highlights the need for early detection and mitigation of pillowing.
Figure 3 : Illustration of pillowing effect on a tall building. Left: Tall building, all glass – inclined view from street level – NO distortions. Right: Tall building, all glass – inclined view from street level – Pillowing diagonal/1000.
Roller wave:
In a laboratory prototype scenario, the effect of roller wave distortion on a glass pane is vividly demonstrated. The ripple effect on reflected images emphasises the importance of controlling roller wave during the manufacturing process. The horizontal and vertical distortions are clearly visible in an “all glass tall building” scenario, highlighting the importance of aligning the roller wave lines during the glass panel assembly process.
Figure 4:: Illustration of rollerwave effect on a tall building. Left: Tall building, all glass – inclined view from street level – NO distortions. Right: Tall building, all glass – inclined view from street level – Roller wave ±0.15 mm.
Lensing effect:
Digital prototyping brings to life the visual distortions of the lensing effect in a double glazed unit. Magnification, blurriness and distortion become apparent, especially when objects are viewed through the glass at acute angles. The scenario within an ‘all glass tall building’ further emphasises the effect on reflected images and the need for careful alignment during the lamination process.
Figure 5: Illustration of lensing on a tall building. Left: Tall building, all glass – inclined view of another construction, from inside of the building – NO distortions. Right: Tall building, all glass – inclined view of another construction, from inside the building – Lensing out of phase ±0.15 mm
Advantages of Digital Prototyping in Architectural Glazing:
Integrating digital prototyping into the architectural glazing assessment process offers a wealth of benefits, transforming the traditional approach to design and reducing the risks associated with visual distortion.
This approach allows faster and earlier convergence of the design process, enabling architects and manufacturers to evaluate the best solutions before physical samples are produced. OceanTM physically based images empower design teams to make informed decisions, limiting the cost and time associated with producing multiple physical iterations.
By providing predictive and quantitative insights, digital prototyping reduces risks to the final aesthetic vision for facades, programme schedules and budget constraints. This proactive analysis ensures that the glazing specification meets expectations, setting a new standard for efficiency and accuracy in the architectural glazing industry. The use of digital prototyping represents a paradigm shift towards a more streamlined and effective approach to architectural glass design.
While inherent visual distortions cannot be completely eliminated, setting manufacturing tolerances within controlled limits is critical. Defining these limits is challenging, given the cost implications and complexity of combined distortions. Physical samples and mock-ups, which are often unrepresentative, require extended production time. Digital prototyping is proving to be an essential tool for early evaluation and risk reduction in achieving the desired glazing specification.
Conclusion
This collaborative white paper sheds light on the intricacies of visual distortion in architectural glazing and introduces digital prototyping as a ground-breaking solution. To delve deeper into this transformative approach and gain comprehensive insights, the full whitepaper can be downloaded here. Embrace the future of architectural glazing with Eclat Digital and Buro Happold’s innovative perspectives.
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