Architects design buildings.
Civil engineers build bridges.
Structural engineers keep it all from twisting, crumpling and shaking apart.
It's a tricky business. As one much-bandied quote puts it, "Structural engineering is the art of molding materials we do not wholly understand into shapes we cannot precisely analyze, so as to withstand forces we cannot really assess, in such a way that the public does not suspect the extent of our ignorance" [sources: AGCAS; Merriam-Webster; Schmidt].
Such know-how is vital to mastering green construction's novel materials and envelope-pushing practices, whether used in a high-rise, a home or a structure built to harness the wind, yoke the waves or orbit high overhead and monitor the climate.
Whether traditional or out there, green structures excite us by emphasizing particular goals -- like zero emissions -- and accomplishing them via potentially beautiful, arresting forms. As the selections in this list demonstrate, green structural engineering poses new architectural questions and new criteria for evaluating the answers.
Eastgate Building (Harare, Zimbabwe)
Termites need not number among a building's worst enemies -- they can also inspire a remarkable rethinking of heating, refrigeration and air conditioning. Take the Eastgate Building, which trades traditional AC in favor of a buggier blower: a ventilation system incorporating the heat-regulating tricks found in towering termite mounds throughout southern Africa. These conical mounds, which can grow to several meters high, maintain a nearly constant internal temperature while exterior conditions swing from 108 to 37 F (42 to 3 C) [sources: Biomimicry Institute; Griggs; Tuhus-Dubrow; Turner].
Architect Mick Pearce and engineers at Arup Associates dreamed up the design, which imitates a termite mound's constantly changing arrangement of breeze-catching holes through a system of fans, vents and funnels. The office complex, which uses 10 percent as much energy as other similarly sized buildings, represents but one brainchild of the small but growing subindustry known as biomimetic architecture [sources: Biomimicry Institute; Tuhus-Dubrow].
Millennium Dome (London, U.K.)
Once regarded as a political embarrassment and economic disaster, the Millennium Dome (later rechristened the O2) has since bounced back as a concert and sports venue. Puffing up from East London's dodgy Docklands area like an enormous, glowing sea urchin, it encompasses a sprawling and virtually uninterrupted internal space using remarkably little material: roughly 1-2 pounds per square foot (4.9-9.8 kilograms per square meter), compared to the 30-40 pounds (146.5-195.3 kilograms) typical of most roofs [sources: Gross; Lyall; RSH+P; Solomon].
The mutant urchin's spines are actually 12 steel masts (one for each month), each towering 328 feet (100 meters) and together supporting a Teflon-coated, glass-fiber roof above more than 1,076,000 square feet (100,000 square meters) of enclosure. The building measures roughly 1,200 feet (a symbolic 365 meters, one for each day of the year) across and 0.62 miles (a full kilometer) around, and reaches a maximum height of 164 feet (50 meters) [source: RSH+P].
Whether the dome represents an environmental triumph or tragedy remains controversial. Its construction drove a massive toxic waste cleanup and area reclamation project, and used remarkably few materials. Unfortunately, its polytetrafluoroethylene roofing material (PTFE, better known as Teflon) generates ozone-harming chlorofluorocarbons (CFCs) and hydrogenated CFCs when produced. Still, it beats the original plan to use dioxin-linked PVC-coated polyester [sources: Higgs; Melchett; Williams].
Jarrold Bridge (Norwich, U.K.)
Designed to link a newly constructed development with the historic Norwich city center, Jarrold Bridge defies the limitations of both old and new while appearing to defy gravity.
As a crossing for bikers and pedestrians alike, the structure improves the environment in more ways than one: first, by employing a cantilevered design that minimizes environmental disruption with grace and flair, and second by reducing the need for vehicle bridges. Vehicle bridges tend to occupy substantial footprints, both metaphorically, in terms of building materials used and runoff pollution created, and literally, with respect to the substantial space taken up by their land-based entrances and exits and their water-anchored supports [sources: ISE; Ramboll].
A cantilever is a simply a beam anchored at only one end. With no further supports needed, Jarrold Bridge practically levitates above the water below, leaving River Wensum traffic and local views unhindered. Weathering steel, sustainably sourced hardwood and stainless steel with no applied finishes together create a long-lasting bridge that sheds no toxic runoff and requires little maintenance. Bridge lights dimly illuminate the walkway, not the water, protecting the local fish and wildlife from intrusive glare [sources: R G Carter; ISE; Ramboll].
Japan Pavilion for Expo 2000 (Hannover, Germany)
A cardboard-supported structure might sound like a truly lousy place to own a house cat (break out those extra scratching posts), but architect Shigeru Ban favors the material as cheap, easy to work with and readily available -- a source of endless new architectural and structural engineering opportunities. These qualities mesh well with Ban's humanitarian efforts, including the cheap temporary housing he designed for Rwandan refugee camps [sources: Corkill; Etherington].
To Ban, whatever green qualities his structures possess is accidental; he regards the green movement as another passing fashion. But when Hannover Expo 2000 (a world's fair) asked him to keep with its environmental theme, he rose to the occasion. Seeking to minimize industrial waste, he designed the Japan Pavilion to reuse or recycle the most material possible. Its undulating tunnel arch -- a grid of gently swooping paper tubes covered by a paper membrane and supported by pulling cables -- measured 242 feet long, 82 feet wide and 52 feet high (73.8 x 25 x 15.9 meters) and featured a wooden arch for strength at each end [source: Shigeru Ban].
Wind has been picking up quite a bit over the past half-decade. In fact, as of 2013, wind energy has blown past the competition to become the world fastest-growing renewable energy resource [source: LaGesse]. But let's not blow things out of proportion: For wind to really reach its energy potential, turbines must become better at catching the wind from any direction and converting it into power. More than that, devices must be developed to store that power efficiently and deliver it evenly, so that electricity is available under any wind conditions.
A few examples of progress reveal that this burgeoning industry has caught its second wind. Inspired by humpback whale fins, the company WhalePower added air-catching scalloped edges to its turbine blades, and both Quiet Revolution and Windspire Energy developed turbines that can capture winds from any direction without needing to swivel. Honeywell and WePOWER continue to plug away at ever-more efficient turbines, even as environmentally conscious builders begin mounting them on roof edges to catch updrafts [source: Merolla].
Meanwhile, a group at the Massachusetts Institute of Technology has developed a novel turbine energy storage system using a hollow, submerged concrete ball: While its blades turn, part of the electricity generated powers a pump that drives seawater out of the container; when winds die off, water flows back in, spinning a turbine and generating electricity [source: Harbison].
Charles David Keeling Apartments (San Diego, Calif.)
The University of California's San Diego campus is no stranger to eye-catching architecture. Beyond its famously fanciful Geisel Library, cradled atop its concrete tree, the 50-year-old campus hosts a what's what of modernist styles.
The Charles David Keeling Apartments, with their shuffled, rectilinear shapes, sparse ornamentation and concrete-and-glass construction, certainly fit in with their modern neighbors. But they also build on the greener aspects of modern aesthetics -- wide use of glass to maximize natural light, emphasis on sun and shade to enhance comfort, employment of materials in unadorned states -- and take them to their logical, green conclusions.
The building shapes and window arrangements maximize natural ventilation, which lowers energy consumption by 38 percent, while a system of panels, walkways and low-E (low thermal emissivity) glass reduce incoming solar radiation. The buildings also include solar cells and a conservation-and-reuse water system that extends from landscaping to low-flow toilets and on-site wastewater recycling. Vegetation on the rooftops cools the apartments while also directing water to retention basins, reducing pollutant levels in stormwater runoff [source: Goodman].
Appropriately, the building is named for an American scientist who numbered among the first to warn the world of the greenhouse effect.
R128 House (Stuttgart, Germany)
Werner Sobek is an old hand at designing the future. He's also a bit of a green-structure luminary, too. Let's look to his R128 House for proof.
The problem of constructing a house suited to Stuttgart's steep valley walls without sacrificing one iota of the gorgeous view is enough to challenge any architect, but Sobek also opted to make his R128 house a study in sustainability [sources: Dwell; Werner Sobek].
The 100 percent recyclable, mortise-and-tenon house is fully modular, and assembles and breaks down more easily than most Ikea furniture. R128 produces no emissions and provides all the energy it needs via its solar cells. It features glass walls on all sides, consisting of high-quality, insulating triple-glazed panels [sources: Dwell; Hart; Werner Sobek].
It's not the home for the modest soul but, then again, that's kind of the idea. Just be sure to bring a lot of Windex.
Geostationary Operational Environmental Satellites
The Geostationary Operational Environmental Satellite (GOES) series of orbital spacecraft have played a vital role in monitoring Earth's weather and climate since NASA launched the first of the family on Oct. 16, 1975 [sources: NOAA OSO].
The system kicked into high gear with the launch of its second generation, the GOES I-M series, which took observation times of the Earth from 10 to 100 percent. Launched from 1994 to 2001 and since decommissioned, GOES 9-12 unraveled the mysteries of clouds and fog, ocean currents, storms and winds, and even snow melt. It did so by fusing sensor data from the visual and infrared bands with information from a global array of data collection stations, balloons and buoys. The current system, GOES N-P, packs improved versions of similar instruments and some new ones as well [sources: NOAA OSD; NOAA OSO].
Traditionally, at least two GOES satellites operate at a time, one over each coast of North America. Currently, GOES-13 is designated GOES-East and GOES-15 is labeled GOES-West. In addition, GOES 12 monitors South America. The next generation of craft, expected to launch in 2015, will add new gadgets, including a lightning mapper and two solar instruments to better monitor the sun's output of X-rays and extreme ultraviolet radiation [sources: GOES-R Program Office; NOAA OSO; NOAA OSO].
Educated guesses of recoverable oceanic wave energy can reach into the tens to hundreds of terawatts (trillions of watts) per year, but figuring out an environmentally friendly way to tap those tasty waves has historically left engineers feeling sunk. Lately, however, the field has experienced a sea change, thanks to folks like Ocean Power Technologies.
The Autonomous PowerBuoy's appeal derives from both its small footprint and its straightforward principle: A 5-foot (1.50-meter) tall buoy bobs on the waves, pulling on an anchoring spar linked to a rotary motor on the seafloor. The up-and-down wave motion cranks the motor, which generates electricity. If that sounds simple, it's not: To handle variances in pulling power caused by different-sized waves, the float needs an onboard computer to adjust the spar's resistance 10 times per second [sources: Fecht; OPT].
A number of PowerBuoys currently operate in the waters around Hawaii, each generating 0.04 megawatts of power, but buoys planned for Scottish waters might bump that number to as much as 0.15 megawatts. According to manufacturer Ocean Power Technologies, once set up in grids, the bobbing contraptions might scale up to hundreds of megawatts [sources: Fecht; OPT].
Federal Center South (Seattle, Wash.)
There's an old joke that the Army Corps of Engineers' solution to any problem is simply to pour more concrete. Well, you wouldn't know it to view the agency's Northwest District headquarters, which not only places in the top 1 percent of energy-efficient office buildings nationwide, but is also light, airy and abundant with wood, glass and flowing spaces -- all on a reclaimed and remediated Superfund site [sources: Gendall; Goodman].
Designed by ZGF Architects and built by Sellen Construction, the building channels light from a central atrium and exterior windows into various meeting spaces, while low-slung cubical walls allow light to penetrate the cubicle bullpen as well. Window shading outside and inside controls heat load, as does the use of clerestory windows. Wooden sections were built in part using materials reclaimed from a nearby decommissioned warehouse. To keep the inside cool, exterior air passes through MERV 15-level filtration to flow through the floors, chilled sails cool the indoors via radiant cooling principles and a thermal storage tank employs a phase-change material (PCM) to pack away cooling energy against future need [sources: Gendall; Goodman].
By the way, minimum efficiency reporting value, or MERV, is an air filter effectiveness rating, and it's based on worst-case-scenario performance. So a MERV 15 filter like the one described here is 85-95 percent efficient at removing particles measuring 0.3-10 microns -- the scale of sneeze particles and individual bacteria [sources: EPA; Wilkinson].
Despite what the nursery rhyme says, London Bridge is not falling down and never has. But the bridge spanning the Thames has been rebuilt over and over.
Author's Note: 10 Green Structural Engineering Marvels
We've come a long way from what modernist architect Le Corbusier called "machines for living in." Or should I say full circle? Human dwellings such as igloos, teepees and thatch-roofed bamboo huts have long used local materials and patterns suited to local environments -- the essence of sustainability.
Of course, it's possible that in a few decades the pendulum will swing back toward a more cookie-cutter approach, at which time these structures might strike our children as ludicrous, but I doubt it. After all, we still appreciate midcentury modern's attempts to soar while reviling the squat brutalism that followed. Besides, we'll probably be too busy building levees and sweating the electric bill to notice.
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