I live in Winnipeg, Manitoba, Canada. It's -40 Fahrenheit and Celsius this morning with the windchill. When I was a kid I was led to believe we'd live in domed cities in the future (in addition to being served by robots and driving flying cars). Would domes over cold-weather cities be worthwhile? Are there materials available today that could hold up to the stress? —Michael Stephensen
I live in Chicago, Illinois, U.S.A. Right now it's 80 degrees Fahrenheit. Odd time to reply? The hell. It'll be plenty brisk here in six months (eh, probably six weeks), and writing about bitter cold while simultaneously experiencing it is more than I can bear.
The short answer is no, we don't have materials up to the challenge of doming a city the size of Winnipeg. But we're getting closer—carbon nanotubes have an incredible strength-to-weight ratio, and may someday yield dome-building materials that would let northern city dwellers go naked (well, coatless) in January. Nonetheless, formidable challenges remain. Let's examine a few.
As you rightly surmise, a dome's diameter is limited by the stresses on the supporting structure. You can minimize these by making the bottom of the dome thick and the top paper-thin, making the dome inflatable (i.e., held up by air pressure), or hanging the roof on cables from steel towers passing through it. (Google "Millennium Dome" to see what this looks like.)
Next, you have to consider the elements—wind, rain, and snow. Let's start with a small-scale example: doming your neighborhood with a hemisphere 1,000 feet in diameter. Domes are resistant to wind loading, but a 30-mile-per-hour wind on a 500-foot-tall hemispherical dome still exerts a total lateral force of 96 tons. Since this thing will enclose people's homes, businesses, and Starbucks, it has to be able to handle a lot more wind than that—in the opinion of my assistant and engineering consultant Una, at least a 100-mile-per-hour gust, for a lateral force of over 1,000 tons. A simple inflatable dome would be ripped to shreds.
Rain isn't a big issue, but since we're talking about Canada we have to consider snow loading. Some snow will slide off the dome but not all. If a quarter of our 500-foot dome is covered with an inch of accumulation, the roof load is going to be more than 250 tons. Maybe you could install de-icers and snow-clearing machines, but they'll add cost and weight. And we haven't even mentioned hail.
Other dome downsides: a nonporous dome will trap the heat and pollution generated by the people living under it, and if it's transparent you've basically got a giant, stinky greenhouse. Either you're going to have to riddle the base with passages and fans for ventilation, or cut vents in the dome itself—weakening it and reducing some of the benefit in the winter.
Then there's wildlife—you want some, right? Migratory birds will be unable to migrate, unless you somehow manage to safely catch and release them outside your dome each year. With year-round mild-to-hot temperatures, you could find yourself looking at a serious insect problem. And if humidity builds up under the dome, say hello to mold.
So: impossible, right? Not if you manage expectations. Last year the Singapore Sports Hub opened for business featuring the world's largest free-standing dome, with a roof that can be opened or closed depending on the weather. While not hemispherical, with a diameter of 310 meters—1,017 feet—it can certainly cover your 1,000-foot neighborhood. Using a steel structure and translucent plastic panels, the dome is designed to withstand anything Singapore's climate can throw at it.
More covered exterior spaces are in the offing. The planned Skidome Denmark, featuring six indoor and two outdoor ski slopes, consists of three huge, hollow arches intersecting over a river; the largest spans a half mile and rises to 360 feet at the center. Mind you, the low ceilings inside might feel claustrophobic, but hey—sacrifices must be made.
If you had something more visionary in mind, we'll need to go pretty far back. Around 1960 Buckminster Fuller (his name was bound to turn up here eventually) and Shoji Sadao designed a climate-controlled dome two miles across to cover midtown Manhattan. In 1971 a German-funded study floated the idea of building a utopian city under a 1.2-mile-wide inflatable dome at 58 degrees latitude in the Arctic, providing a warm environment for up to 40,000 people.
In 1979 plans were drawn up to dome Winooski, Vermont, a town of 7,000 people beleaguered by 20-below winters and crushing snowfall. Covering roughly 800 acres, spanning 6,600 feet, and rising 250 feet in the center, the Winooski dome would have been held up by air pressure, requiring all entering or leaving to pass through an airlock. The pollution problem was to be handled by electric cars and monorails. When federal funding didn't pan out (no shock), the idea fizzled.
That's likely why you don't hear much about domed cities anymore, apart from the occasional dubious scheme kicking around the Internet. Super plastics might make it physically possible to raise a city-scale dome someday. But how would you raise the cash?
Send questions to Cecil via StraightDope.com or write him c/o Chicago Reader, 350 N. Orleans, Chicago 60654.