[00:00.00]Listen to part of a lecture in an engineering class.
[00:04.28]Professor: We've been looking at some engineering challenges of the past few decades, how engineers have to consider special demands like a budget and time constraints when they're designing buildings and other structures. [00:17.86]Today, we're gonna focus on environmental challenges, problems engineers face from the great outdoors. uh, what comes to mind? Alice?
[00:25.63]Male student: well, if you're designing building, you'd have to see what kind of soil or rocks you're dealing with.
[00:31.50]Professor: Good. um. What else? Mike?
[00:33.99]Male student: Well, weather conditions.
[00:35.37]Professor: Ok, uh, go on.
[00:37.09]Male student: Like in a desert, the heat, the dry climate would probably affect the materials for the structure, even the design.
[00:44.50]Professor: Okay. now, a really good example of this, a Challenge it took until the 1990s to figure out how to deal with is a bridge up in Canada called the confederation bridge. [00:57.92]This is a long winding bridge, standing a width of, but here you can see it on this slide. [01:04.64]The confederation bridge connects Prince Edward island, which is off the eastern coast of Canada to the mainland, and it has to cross a body of water 8 miles wide. [01:16.59]The Northumberland strait now this straight has some of the harshest weather conditions in Canada. [01:24.50]Talk about challenges for an engineer. Ice wind, incredible cold. [01:29.78]I grew up on Prince Edward island. I should know every time we take that ferry, it was the only way to cross back then. [01:37.51]There were long lines, is just to get on and the ride was long, the schedule unreliable. [01:44.02]Because of ice and winds. Uh, Mike, you a puzzle?
[01:47.96]Male student: Yeah, I don't get it. Why'd it take so long for them to build this bridge? [01:52.12]I mean, sure, it's called up in Canada and all but well, I remember some pictures in our book of bridges up in northern Europe where it's probably even colder than Canada. [02:00.90]And they were built much earlier than the 1990s.
[02:03.76]Professor: Well, well remember, temperature is just part of the picture. [02:07.80]You've got cold, icy winds over a lot of water along long stretch of freezing water. [02:15.61]Uh, it's not the longest bridge in the world. Well, its longest in Canada, but it is the longest bridge anywhere over water that freezes. [02:24.96]So this means you've got ice, huge masses of ice, and this ice goes floating down the straight and it has to get through. [02:34.17]So why is this a problem? Well, we've got a look at how most bridges like those European bridges you mentioned probably are supported. [02:43.79]Remember when we look at basic bridged design earlier in the year. What was the basic shape of the piers? [02:49.99]The supports for these bridges with long spans?
[02:53.35]Female student: Well, they're like these columns, a row of cylinder shapes like columns supporting the span of the bridge.
[03:00.88]Professor: Okay, now think about it with these basic columns, remember, we called them peers. [03:08.52]Uh, you've got a real problem when sheets of ice start crashing up against them. Here. Let me show you what I mean.
[03:14.45]Now imagine these sheets of ice floating down the strait. [03:19.74]They're gonna run right into those peers and compress into these ice chunks and get stuck there. [03:26.19]So what did the engineers do? well, they know that once those chunks of ice form, that's it. [03:33.81]They can block the passage here where the boats would have to pass between the piers. [03:39.16]Very dangerous, and there's nothing you can do to break up those chunks of ice once they start piling up like that. [03:45.94]Now, that's where the engineers' abilities to analyze the problem and come up with a design solution. that's where it all comes into play.
[03:56.13]And the ones who built the confederation bridge, wow, they really showed what they were made of. [04:02.90]They designed this special type of supporting piers, which were basically like the column shaped ones we've been looking at. [04:10.40]But for the bottom of each pier, they designed what they called shields, a protective base that turned the overall shape from a cylinder into a kind of inverted cone. [04:23.25]This was critical because the base, the cone part is where the pier comes in contact with the water and ice [04:31.50]Here take a look at a close up of the base. So you can see what I mean. [04:35.68]So now when that sheet of ice approaches, instead of immediately getting crushed into those ice chunks, it starts to slide up this sloping part of the base, which changes the direction of the ice sheet from horizontal to upwards at a diagonal. [04:54.19]And this causes the ice to crack and break up into smaller pieces. [04:59.69]And this means that those ice pieces can keep on moving past the peers down the strait, and it doesn't all build up there at the bridge.
[05:10.03]Now, this wasn't the only problem the engineers had to deal with. [05:14.40]As I said earlier, the Northumberland straits, a big unobstructed area that acts like a natural wind tunnel.
托福14天冲刺微信战团