Towers Of Woods, Not Steel
木造環保高樓 不用鋼材
By Henry Fountain

The movement to construct tall buildings largely with wood as an environmentally friendlier alternative to steel and concrete has received a boost from an unusual source – a leading architectural firm known for its towers of steel and concrete.
不以鋼筋和混凝土，主要是以對環境更為友善的木材來打造高樓的運動，獲得了一大鼓勵，而且這個鼓勵頗不尋常，是來自以建造鋼筋混凝土摩天大樓著稱的一家一線建築公司。

Skidmore, Owings & Merrill, the Chicago-based firm that has designed a long list of skyscrapers, including the new One World Trade Center in Lower Manhattan, has developed a structural system that uses so-called mass timber – columns and thick slabs that are laminated from smaller pieces of wood. In a report this year, the firm showed how the system could be used to build a 42-story residential tower that would have a lower carbon footprint than a conventional structure.
總部設在芝加哥的「史基摩爾、歐文斯與美林」公司設計過許多摩天大樓，包括曼哈坦下城新的世貿中心一號大樓。這家公司研發出一種結構系統，使用的是所謂的質量木材，亦即以小塊木頭壓製而成的木柱和厚板。該公司今年發表了一份報告，說明如何運用這套系統打造一棟高達42層的住宅大樓，這種建築的碳足跡低於傳統結構。

“We wanted to see what we can do to help on the sustainability side,” said William F. Baker, a partner in the firm. With its system, about 70 percent of the structural material is wood; most of the rest, including the foundation, is concrete.
「史基摩爾、歐文斯與美林」公司合夥人貝克說：「在環境永續這件事上，我們想知道我們能做些什麼。」這套系統的建材七成是木材；其他部分多為混凝土，包括地基。

Benton Johnson, an engineer who worked on the report, said wooden high-rises could help solve the problem of providing adequate housing to the billions of people living in cities – while also addressing climate change. “We know that we need to build a lot more buildings,” Mr. Johnson said. “And we know that we need to lower CO₂.”
參與報告製作的工程師強森說，木造高樓有助於解決一個問題，可為城市中的數十億人口提供足夠的住處，同時兼顧氣候變遷問題。強森說：「我們知道我們需要建造許多樓房，我們也知道，我們需要減少二氧化碳的量。」

Until now, tall wooden buildings had been championed by architects and engineers mostly from smaller firms outside the United States. They welcomed the Skidmore, Owings & Merrill report.
直到現在，倡導木建築高樓的建築師和工程師，多數屬於美國以外的一些規模比較小的公司。他們對「史基摩爾、歐文斯與梅林」公司的報告表示歡迎。

Michael Green, an architect in Vancouver, British Columbia, who helped devise a different structural system for wooden towers that was detailed in a report last year, said: “This is the first new way to build in a hundred years.”
加拿大卑詩省溫哥華市的建築師葛林去年協助設計了另一套木造高樓結構系統，並且發表了詳細的報告，他說：「這是百年來第一種嶄新的建築方式。」

Few modern tall wooden buildings have been built around the world, and only one, an apartment building in Melbourne, Australia, has reached 10 stories. Mr. Green’s design of a 27-meter mixed-use building in Prince George, British Columbia, will make it the tallest wooden building in North America when it is completed next year.
目前世界上高大的現代木造建築仍屈指可數，而且只有一棟位於澳洲墨爾本的公寓高度達到10層樓。葛林設計的27公尺高混合使用大樓位於卑詩省喬治王子城，明年竣工後將是北美最高的木造大樓。

Constructing more and taller towers will require changes in building codes – most of which limit wood structures to four stories or fewer – and construction methods. Architects, engineers, contractors and developers will have to be convinced that wooden buildings can be safe and profitable. Production of steel and concrete produces significant amounts of the greenhouse gas carbon dioxide, while wood holds the carbon from CO₂ removed from the atmosphere through photosynthesis. So using wood in the structural elements can help offset the carbon emissions from the construction process and from the operation of the finished building. This is not conventional frame construction, in which thin elements are nailed together, but more akin to building with concrete slabs. Mr. Baker said as long as forests were managed, sustainable wooden buildings should not have much of an impact. There are also millions of fir trees in North America that were killed by a beetle infestation and that could be used to produce the timber panels.
建造更多更高的木造大樓有賴建築法規和工法的改變。多數法規限制木建築不得高於四層樓。此外還須說服建築師、工程師、承包商和開發商，木建築是安全的建築而且有利可圖。生產鋼筋和混凝土會製造大量溫室氣體二氧化碳，而木材在行光合作用時則會封存大氣中二氧化碳裡的碳。因此，以木頭為建材有助於抵消施工過程與完工後建築運作過程中的碳排放。它與將數個薄元件釘在一起的傳統框架結構不同，與以混凝土板打造建築較相似。貝克說，只要做好森林管理，永續性的木建築不會對環境造成明顯衝擊。此外，北美有數百萬株杉木因為被一種甲蟲感染而死亡，這些樹木可以用來製造板件。

The Skidmore, Owings & Merrill system uses a type of engineered wood called glued laminated timber, or glulam, for the building columns, and cross-laminated timber slabs for the central core, floors and shear walls, which provide stiffness against wind loads. But the concept calls for concrete beams along the perimeter of each floor and elsewhere to allow for longer spans and more flexibility in layouts.
史基摩爾、歐文斯與美林系統使用的是一種稱為夾層木，又稱膠合木的工程木材製造建築的立柱，又以交叉夾層木建造中柱、樓板和結構牆，提供對抗風荷載所需的硬度。這種工法需在每層樓的周邊和另一些地方設置混凝土梁，以提供更長的跨度和設計上的靈活性。

Mr. Green, in his report, presents a system that could be used to build towers in seismically active areas like Vancouver. Rather than concrete, he uses some steel beams to allow the building to better respond to earthquake forces.
葛林於報告中提出可在溫哥華等地震活躍區建造高樓的一套系統，這種系統使用鋼梁而不是混凝土梁，能讓建物更耐震。

Andrew Waugh, a British architect whose nine-story building in London has become a showpiece of the wooden-tower movement, said both reports would help build momentum for taller buildings.
英國建築師伍沃在倫敦興建的九層大樓已經成為木造大樓運動的樣板建物，他認為這兩份報告將為建造更高的木樓增添動力。

“It’s such an exciting time,” Mr. Waugh said. “It feels like the birth of flight – it’s one of those kinds of moments in engineering.”
伍沃說：「這是如此令人興奮的時刻，宛如飛行的誕生，它是工程界的那種時刻之一。」

原文參照：
http://www.nytimes.com/2013/09/24/science/appeal-of-timber-high-rises-widens.html

Graphic：Making a Case for a Timber Tower
http://www.nytimes.com/interactive/2013/09/24/science/0924-sci-timber.html

2013-10-22聯合報/G5版/UNITEDDAILYNEWS 王麗娟譯 原文參見紐時週報八版上