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Imagine the future. What does it hold? What factors will be most influential in shaping the world around us and the built environment we serve to engineer? If we correctly envision the challenges and opportunities ahead of us, we can most effectively deliver leadership that paves the way to the future.
Globalization to tomorrow
Globalization is a permanent transformation. Emerging nations following the footsteps of capitalism are illustrating a cost-effectiveness that facilitates a widening diversification of worldwide wealth. Contemporary architecture reflects this empowerment with works that double as tokens of technological attainment on the world stage.
Recently-built projects both domestic and abroad display complex shapes achieved through extensive analysis. Transparency serves as a prominent architectural cloak and conveys elegance through advanced engineering. These beautiful buildings command attention, and increasingly stunning feats of engineering innovation can be expected in the future.
At the same time, the global community is mobilizing in response to the unparalleled challenge of irreversible climate change. From international diplomacy to consumer decision-making, this issue permeates modern life — and will continue to do so far into the future.
Buildings in the United States are responsible for approximately 40 percent of domestic energy use and 70 percent of domestic electricity consumption (according to the U.S. Green Building Council), and they are to blame for 40 percent of domestic carbon dioxide emissions (according to the U.S. Department of Energy). Enclosure systems are critical to the energy performance of buildings. Consequently, the design of modern enclosures involves not only pressures toward complex transparency, but strategies responsive to the energy impacts of eliminating insulation.
Modern computing capabilities also enable new performance expectations to integrate into the design of building enclosures. In particular, terrorist events of recent years are prompting security concerns and broadening the emergence of blast resistance as a design requirement.
The challenge of transparency
How should building enclosures address transparency, energy efficiency, and blast resistance? Transparency promotes elegance and the minimal use of materials. Energy efficiency is supported with insulation and well-sealed interiors. Blast resistance is accommodated through strength, ductility, and redundancy.
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No material presently attains the pinnacle of all three attributes. Of the criteria, transparency is the easiest to eliminate in order to achieve the other two. It is also arguably the least important. Does this mean that opaque building enclosures are the wave of the future?
Increasingly opaque systems are a real possibility. Yet architectural trends do not change overnight, and transparency performs a critical function in promoting the quality of life of the building occupants.
What avenues are available in responding to these issues? What systems, approaches, and technologies support the enhanced performance of transparency features for building enclosures of the future?
Avenues of advancement
Several modern processes and techniques enable designers to achieve various project goals.
Layering — Glazing composed of multiple layers facilitates various strategies to improve performance.
Laminated glass consists of multiple thicknesses, or lites, of glass joined with strong interlayer materials. Among other functions, the interlayers help to retain shards of broken glass and prevent them from injuring building occupants during explosive events. Insulating glass (IG) units are composed of two glass skins separated by a sealed gaseous volume to improve thermal resistance and to attenuate sound. These technologies have been widely implemented for years. Yet they also transition to future solutions.
Advanced interlayer materials in laminated glass hold the potential of delivering improved rigidity and post-breakage retention under blast loading. SentryGlas by DuPont offers strength and stiffness capabilities significantly beyond traditional polyvinyl butyral (PVB) interlayer material. Glass-clad polycarbonate, a concept implemented in security settings, provides an impact-resistant composition capable of transitioning into the larger architectural marketplace. As material technology advances, solutions in the form of high-strength laminates can be expected to play an increasingly prominent role in enhancing the performance of glass under extreme loading.
Metallic coatings and ceramic frit patterns presently support the thermal resistance of IG units. Argon, a better insulator than air, is available as a separator gas. The option of triple glazing involves dual gaseous layers that impede convection. Continuing advancements in coating technologies and ongoing options for gaseous barriers hold the potential of progressively improving the thermal resistance capabilities of IG units.
An intricate approach to layering a glass enclosure is to implement a multiple wall system. A dual wall can take advantage of an interstitial airspace measured in feet rather than in fractions of an inch. Yet precise and accurate cost estimating and thermal analyses are required to ensure that the anticipated economic and performance benefits are realized. As software continues to support the complexity of engineering studies, the implications of innovative systems will be increasingly well projected.
Operable systems — Sensing and responding to changing environmental circumstances, operable systems take a situational approach to negotiating performance objectives. Though this strategy may not directly contribute to the matter of blast resistance, it offers a close relationship to environmental studies.
Exterior sunshades, interior blinds, insulating shutters, and an endless assortment of gadgetry may be connected to networks of sensors to develop operable systems capable of assessing environmental conditions, processing performance implications, and assuming configurations consistent with preprogrammed priorities.
At the extreme, transparency and thermal resistance can be separately maximized.
However, operable systems involve special costs in designing, fabricating, installing, and maintaining potentially extensive systems with a myriad of moving parts. As with the design of multiple wall systems, reliable cost-benefit information is necessary to ensure that the planned advantages of operable systems are, in fact, accomplished.
The intricacy of operable systems is likely to evolve slowly amidst careful examination of the long-term performance of earlier approaches. Yet the information basis of operable systems, environmental and occupancy information, integrates with an existing need.
Climate sensors introduced onto the facades of new and existing buildings of varying size and construction in a variety of environments, in combination with records of occupancy patterns and energy consumption, offer the keys to an invaluable volume of information helpful to optimizing the present designs of building enclosures of all types. Resolution of the maintenance and durability issues associated with exterior sensors also establishes groundwork for the development of increasingly complex operable systems.
Optical illusions — At the expense of delivering expansive transparency to building occupants, optical illusions can bridge modern architectural styling with powerful improvements to thermal and structural performance.
Spandrel glass has long provided a solution to hiding structural members and mechanical systems from view on high transparency envelopes. As demands for energy efficiency and blast resistance increase, spandrel glass may also shield opaque walls that maximize these performance characteristics. Vision units may be strategically mapped to facilitate occupancy requirements while the overall enclosures are configured toward specific performance objectives.
Currently in development, photovoltaic paint introduces a broad long-range opportunity to capture solar energy striking opaque regions of building enclosures. Photovoltaic paint mimics photosynthesis through nanotechnology and captures energy across the full spectrum of visible light.
Yet architectural pressure toward aesthetic innovation can be expected to demand more than mere shielding of opacity. Organic light emitting diodes (OLEDs) offer lightweight, energy-efficient solutions to provide backlighting or visual displays. Because the diodes are capable of near transparency when off, exciting possibilities emerge even in regard to vision glass. Technology presently exists to transmit 3-D images without special glasses being worn by the observers. As this capability makes its way to the architectural marketplace, the visual complexity of building enclosures accelerates toward a revolutionary arena.
Designers of advanced display enclosures must provide for the durability and serviceability aspects of these systems while accommodating the entire balance of architectural performance expectations.
Material possibilities — The issues of balancing transparency, energy efficiency, and blast resistance would ultimately dissolve with the commercial availability of materials exhibiting simultaneously exceptional characteristics in all of these respects.
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Acrylics and polycarbonates are lightweight alternatives to glass with lower thermal conductivities and greater impact resistances. Both materials can also be molded. Among the drawbacks, though, are vulnerabilities to scratch damage and potential material incompatibilities. Protective coatings, however, are available.
Aerogels are extremely lightweight, highly porous solids formed by carefully drying gels to eliminate the liquid content while retaining the internal particle structures. The resulting insulators can consist of up to nearly 100 percent air by volume, with overall densities measured in relationship to air. Some formulations of aerogel approach transparency. NASA has applied aerogel to provide thermal protection to Mars spacecraft, and aerogel insulation products are beginning to transition into construction.
As material science and nanotechnology proceed to emerge offerings, building enclosure systems stand to benefit from this innovation.
Conclusion
Globalization is changing our world, and with it, the intricacies of our practice and the complexities of our responsibilities.
Transparency is a visually and technologically attractive encasement of contemporary construction. Yet elevating environmental considerations require innovation to improve energy performance in the absence of conventional insulation. In addition, blast resistance is gaining prominence as a design criterion.
Thickened systems and operable features offer opportunities to improve the energy performance of transparent facades. Optical illusions with spandrel units facilitate exterior displays with advanced technological wonders. Material science holds the potential for products with new performance capabilities.
How will these challenges and opportunities configure to form our future? The answers are up to us.
Steve Thomas, P.E., is a senior staff I engineer in Simpson Gumpertz & Heger’s Building Technology group. He can be reached at sjthomas@sgh.com. Russell H. Davies, P.E., is a senior project manager also with Simpson Gumpertz & Heger. He can be reached at rhdavies@sgh.com.
