《那些古怪又讓人憂心的問題》第102期:樂高大橋(2)

Extreme forces

極大的力

The North Atlantic is a stormy place. While our bridge would manage to avoid the fastest-moving parts of the Gulf Stream current, it would still be subjected to powerful wind and wave forces.

北大西洋風暴頻發，也許我們的樂高大橋能夠避開墨西哥灣流中快速移動的那部分，但它仍然會受到強風和大浪的衝擊。

How strong could we make our bridge?

我們的大橋能造得多結實？

Thanks to a researcher at the University of Southern Queensland named Tristan Lostroh, we have some data on the tensile strength of certain Lego joints. Their conclusion, like the BBC's, is that Lego bricks are surprisingly tough.

好在有南昆士蘭大學的研究人員特里斯坦•洛斯塔奇，我們能夠獲取某些種類樂高連接件的抗拉強度。和英國廣播公司得出的結果相似，他們得出的結論也是樂高積木非常結實。

The optimal design would use long, thin plates overlapped with each other:

最佳的設計是把又長又薄的盤片互相重疊放在一起：

This design would be pretty strong-the tensile strength would be comparable to concrete-but not nearly strong enough. The wind, waves, and current would push the center of the bridge sideways, creating tremendous tension in the bridge.

這樣的設計結構強度非常高——抗拉強度和混凝土有得一比——但還是遠遠不夠用。大風、海浪和洋流會把大橋的中部往一個方向推，在橋身中產生出極大的拉力。

The traditional way to deal with this situation would be to anchor the bridge to the ground so it can't drift too far to one side. If we allow ourselves to use cables in addition to the Lego bricks,10 we could conceivably tether this massive contraption to the sea floor.11

解決這個問題的傳統方法是把橋身錨定在地面上，這樣橋體就不會往一個方向漂出太遠的距離。如果我們還允許用繩索來建造樂高大橋，10我們就可以用繩索把巨大的橋身錨定在海牀上。11

But the problems don't end there. A 5-meter bridge might be able to support a vehicle on a placid pond, but our bridge needs to be large enough to stay above water when waves are breaking over it. Typical wave heights on the open ocean could be several meters, so we need the deck of our bridge to be floating at least, say, 4 meters above the water.

但問題還沒解決呢。一座5米寬的橋或許可以在平靜的小池塘裏浮起一輛汽車，但我們的樂高大橋需要在大風大浪的情況下仍然保持位於大浪上方。開闊海面上普通的浪高可達數米，因而我們需要讓橋面浮在離水面至少4米的地方。

We can make our structure more buoyant by adding air sacs and hollows, but we also need to make it wider-otherwise it will tip over. This means we have to add more anchors, with floats on those anchors to keep them from sinking. The floats create more drag, which puts more stress on the cables and pushes our structure downward, requiring more floats on the structure . . .

我們可以通過增加氣囊和空心腔體來增加整體的浮力，但這樣一來我們需要加寬橋面，否則它就會翻轉傾覆。這意味着我們需要動用更多的錨，錨上還要綁上浮筒以防止沉下去。增加的浮筒會增大阻力，會在繩索中產生更大的應力，把整個橋體往下拉，這樣一來我們又需要更多的浮筒……

Sea floor

海牀

If we want to build our bridge down to the sea floor, we'll have a few problems. We wouldn't be able to keep the air sacs open under the pressure, so the structure would have to support its own weight. To handle the pressure from the ocean currents, we'd have to make it wider. In the end, we'd effectively be building a causeway.

如果我們打算把大橋建造在海牀上，那麼會面臨許多問題。在巨大的壓強下，氣囊完全無法張開，因而整個結構必須要承載自身的重量。要解決洋流衝擊帶來的問題，我們需要把橋造得更寬。於是最後我們相當於造了一條鋪道出來。

As a side effect, our bridge would halt the North Atlantic Ocean circulation. According to climate scientists, this is “probably bad.”12

這樣的一個副作用是北大西洋洋流將會被阻斷，氣候科學家表示由此引起的後果“很有可能是很糟糕的”。12

Furthermore, the bridge would cross the mid-Atlantic ridge. The Atlantic sea floor is spreading outward from a seam down the middle, at a rate-in Lego units-of one stud every 112 days. We would have to build in expansion joints, or drive out to the middle every so often and add a bunch of bricks.

此外，我們的大橋還會穿過大西洋中脊上方。大西洋海牀正在從中間的一條裂縫向兩邊延伸，速度大約是每112天移動1塊樂高積木的距離。因而我們需要在橋身上設置伸縮縫，或者頻繁地去大洋中間添加幾塊積木。