Why doesn’t the Leaning Tower of Pisa fall over? - Alex Gendler

5,203,721 views ・ 2019-12-03

TED-Ed


请双击下面的英文字幕来播放视频。

翻译人员: 彬琳 张 校对人员: Tingting Zhao
00:08
In 1990, the Italian government enlisted top engineers
0
8041
4676
1990 年,意大利政府招募了 一批顶尖工程师
00:12
to stabilize Pisa’s famous Leaning Tower.
1
12717
4000
来维护著名的比萨斜塔。
00:16
There’d been many attempts to right the tower during its 800 year history,
2
16717
4072
在过去的八百年中 有过许多次修正斜塔的尝试,
00:20
but this team’s computer models revealed the urgency of their situation.
3
20789
5134
但计算机模型向这只团队 揭示了他们面临的严峻考验。
00:25
They projected the tower would topple if it reached an angle of 5.44 degrees—
4
25923
5669
他们预测这座塔将在 倾斜角度超过 5.44 度的时候倒塌——
00:31
and it was currently leaning at 5.5.
5
31592
3540
现在它的倾斜角度是 5.5。
00:35
No one knew how the tower was still standing, but the crisis was clear:
6
35132
4725
没有人知道为什么斜搭仍旧屹立, 但危机就摆在眼前:
00:39
they had to solve a problem that stumped centuries of engineers,
7
39857
4130
他们需要解决这个困扰了 无数代工程师的问题,
00:43
and they needed to do it fast.
8
43987
2475
并且是迅速解决。
00:46
To understand their situation,
9
46462
1640
为了更好的理解他们的处境,
00:48
it’s helpful to understand why the tower tilted in the first place.
10
48102
3730
让我们先来了解比萨塔倾斜的原因。
00:51
In the 12th century, the wealthy maritime republic of Pisa
11
51832
3974
在 12 世纪,富有的比萨海上共和国
00:55
set about turning its cathedral square into a magnificent landmark.
12
55806
4857
着手将主教座堂广场 变成它宏伟的地标建筑。
01:00
Workers embellished and enlarged the existing church,
13
60663
3480
工人们扩大并装饰了原有的教堂,
01:04
and added a massive domed baptistry to the plaza.
14
64143
3953
并在广场上加盖了带穹顶的洗礼堂。
01:08
In 1173, construction began on a free-standing campanile, or bell tower.
15
68096
7189
1173 年,独立式钟楼的修建也开始了。
01:15
The engineers and architects of the time were masters of their craft.
16
75285
3980
参与建造的工程师与建筑师 都是那个时代的大师,
01:19
But for all their engineering knowledge,
17
79265
2158
然而相对工程知识,
01:21
they knew far less about the ground they stood on.
18
81423
3914
他们对脚下的这片土地知之甚少。
01:25
Pisa’s name comes from a Greek word for “marshy land,"
19
85337
3890
“比萨”一词起源于 古希腊词汇“沼泽之地”,
01:29
which perfectly describes the clay, mud, and wet sand below the city’s surface.
20
89227
6109
恰好完美描述了藏在这座城市 地表之下的黏土、淤泥和湿砂岩。
01:35
Ancient Romans counteracted similar conditions with massive stone pillars
21
95336
4575
相似的条件下, 古罗马人将大理石柱立在地表岩床上
01:39
called piles which rest on Earth’s stable bedrock.
22
99911
4250
以增加建筑的稳定性。
01:44
However, the tower’s architects believed a three-meter foundation would suffice
23
104161
5324
然而,塔的建筑设计师认为三米的地基
足以支撑这个相对较矮的建筑。
01:49
for their relatively short structure.
24
109485
2520
01:52
Unfortunately for them, less than five years later,
25
112005
3446
不幸的是,不到五年,
01:55
the tower’s southern side was already underground.
26
115451
4003
塔的南侧已经陷入地下。
01:59
Such a shifting foundation would normally have been a fatal flaw.
27
119454
4218
通常情况下地基的倾移 将成为致命的缺陷。
02:03
If workers added more weight,
28
123672
1768
如果继续增加重量,
02:05
the pressure from upper stories would sink the structure
29
125440
3247
来自上层的压力将使建筑下沉,
02:08
and fatally increase the lean.
30
128687
2536
从而导致更严重的倾斜。
02:11
But construction halted at the fourth story for nearly a century
31
131223
4111
由于比萨陷入长久的战争时期,
02:15
as Pisa descended into prolonged warfare.
32
135334
3617
工程在第四层停滞了将近一个世纪。
02:18
This long pause allowed the soil to settle,
33
138951
3160
在这期间,土壤沉降
02:22
and when construction began again in 1272,
34
142111
3463
等到 1272 年工程再次开始时,
02:25
the foundation was on slightly more stable footing.
35
145574
3582
地基的基脚变得相对稳定。
02:29
Under the direction of architect Giovanni di Simone,
36
149156
3552
在建筑师乔瓦尼 · 迪 · 西蒙尼 (Giovanni di Simone)的指导下,
02:32
workers compensated for the tower’s minor tilt
37
152708
2986
接下来几层的建造中
02:35
by making the next few floors taller on the southern side.
38
155694
4519
钟楼南侧略高于北侧, 以此来修正塔的微小倾斜。
02:40
But the weight of the extra masonry made that side sink even deeper.
39
160213
4585
然而额外的砖石结构加速了塔楼南侧的下沉。
02:44
By the time they completed the seventh floor and bell chamber,
40
164798
3340
等到第七层及钟室竣工时,
02:48
the angle of the tilt was 1.6 degrees.
41
168138
4125
塔已经倾斜了 1.6 度。
02:52
For centuries, engineers tried numerous strategies to address the lean.
42
172263
4513
数个世纪以来,工程师们 无数次尝试修正它。
02:56
In 1838, they dug a walkway around the base to examine the sunken foundation.
43
176776
5211
1838 年,为了探究下沉的地基, 他们围绕地基挖掘出一条走道,
03:01
But removing the supporting sand only worsened the tilt.
44
181987
4060
然而挖走支撑的沙土 导致了更严重的倾斜。
03:06
In 1935, the Italian Corps of Engineers injected mortar to strengthen the base.
45
186047
6473
1935 年,为了加固塔基, 意大利工程军向基底灌注砂浆,
03:12
However, the mortar wasn’t evenly distributed throughout the foundation,
46
192520
3980
然而砂浆灌注不均匀
03:16
resulting in another sudden drop.
47
196500
3112
引发了又一次下沉。
03:19
All these failed attempts, along with the ever-sinking foundation,
48
199612
3995
所有失败的尝试, 伴随沉降的地基
03:23
moved the tower closer to its tipping point.
49
203607
3088
使得倒塌一触即发。
03:26
And without definitive knowledge of the soil composition,
50
206695
3158
由于缺乏对土壤构成的认知,
03:29
engineers couldn’t pinpoint the tower’s fatal angle
51
209853
3503
人们无法计算出塔何时会倒
03:33
or devise a way to stop its fall.
52
213356
3177
也无法阻止它发生。
03:36
In the years following WWII,
53
216533
2262
第二次世界大战结束后,
03:38
researchers developed tests to identify those missing variables.
54
218795
4107
学者们尝试确定这些缺失的变量。
03:42
And in the 1970’s, engineers calculated the curved tower’s center of gravity.
55
222902
6023
20 世纪 80 年代, 工程师们计算出塔的重心曲线,
03:48
With this data and new computing technology,
56
228925
2790
再加上新的计算机技术,
03:51
engineers could model how stiff the soil was, the tower’s trajectory,
57
231715
4702
土质硬度,塔的轨迹
03:56
and the exact amount of excavation needed for the tower to remain standing.
58
236417
5139
以及精确的挖掘量才得以确定。
04:01
In 1992, the team drilled diagonal tunnels
59
241556
3680
1992 年,施工队挖出倾斜的隧道,
04:05
to remove 38 cubic meters of soil from under the tower’s north end.
60
245236
5329
从北端的塔基挖走 38 立方米的土壤。
04:10
Then, they temporarily counterbalanced the structure with 600 tons of lead ingots
61
250565
5986
随后,他们用 600 吨铅锭 来过渡性的平衡塔身,
04:16
before anchoring the base with steel cables.
62
256551
3260
最后用钢索来固定地基。
04:19
More than six centuries after its construction,
63
259811
2794
在竣工的六个世纪之后,
04:22
the tower was finally straightened… to a tilt of about four degrees.
64
262605
5247
塔的倾斜角终于被修正到 4 度左右。
04:27
No one wanted the tower to fall,
65
267852
2020
没有人希望它倒塌,
04:29
but they also didn’t want to lose the landmark’s most famous feature.
66
269872
4116
但他们也不想失去 这个地标建筑最出名的特征。
04:33
Today the tower stands at 55– or 56– meters tall,
67
273988
4851
如今,塔高约 55 到 56 米,
04:38
and it should remain stable for at least 300 years
68
278839
3470
作为缺陷之美的里程碑,
04:42
as a monument to the beauty of imperfection.
69
282309
3484
它将至少屹立 300 年。
关于本网站

这个网站将向你介绍对学习英语有用的YouTube视频。你将看到来自世界各地的一流教师教授的英语课程。双击每个视频页面上显示的英文字幕,即可从那里播放视频。字幕会随着视频的播放而同步滚动。如果你有任何意见或要求,请使用此联系表与我们联系。

https://forms.gle/WvT1wiN1qDtmnspy7