Placeholder Image

字幕列表 影片播放

  • Earthquakes have always been a terrifying phenomenon,

    地震一直是令人懼怕的自然現象

  • and they've become more deadly as our cities have grown,

    且隨著都市的發展而越來越致命

  • with collapsing buildings posing one of the largest risks.

    建築物的倒塌是最大的危機

  • Why do buildings collapse in an earthquake,

    為什麼建築物在經歷地震時會倒塌?

  • and how can it be prevented?

    我們又該如何預防?

  • If you've watched a lot of disaster films,

    如果你曾看過災難片

  • you might have the idea

    也許會認為

  • that building collapse is caused directly by the ground beneath them

    建築物倒塌是因為直接接受地表

  • shaking violently, or even splitting apart.

    劇烈的晃動,甚至是地裂

  • But that's not really how it works.

    但實際上並不是那樣的

  • For one thing, most buildings are not located right on a fault line,

    首先,大部分的建築物都沒有蓋在斷層上

  • and the shifting tectonic plates go much deeper than building foundations.

    況且,板塊運動是在比建築物地基還要深很多的地底發生的

  • So what's actually going on?

    所以到底發生了什麼事呢?

  • In fact, the reality of earthquakes and their effect on buildings

    事實上,地震對於建築物的影響

  • is a bit more complicated.

    要比想像中複雜的多

  • To make sense of it, architects and engineers use models,

    為了搞懂這些,建築師和工程師利用模型

  • like a two-dimensional array of lines representing columns and beams,

    像是二維的線狀陣列來表示柱子和橫樑

  • or a single line lollipop with circles representing the building's mass.

    或是一根根棒棒糖狀的東西來表示建築的質量

  • Even when simplified to this degree, these models can be quite useful,

    雖然是非常簡化的模型,但還是很有幫助的

  • as predicting a building's response to an earthquake

    因為建築物對於地震的反應

  • is primarily a matter of physics.

    可以用物理來解釋

  • Most collapses that occur during earthquakes

    大部分在地震中倒塌的建築

  • aren't actually caused by the earthquake itself.

    並不是地震本身造成的

  • Instead, when the ground moves beneath a building,

    而是當建築物下方的土地搖晃時

  • it displaces the foundation and lower levels,

    讓地基和低樓層的部分跟著移動

  • sending shock waves through the rest of the structure

    接著往上傳導震盪波

  • and causing it to vibrate back and forth.

    讓建築物開始前後搖晃

  • The strength of this oscillation depends on two main factors:

    這種震盪的大小跟兩種主因有關:

  • the building's mass, which is concentrated at the bottom,

    第一個是建築物的質量,主要集中在建築物下方

  • and its stiffness,

    第二個是剛性

  • which is the force required to cause a certain amount of displacement.

    也就是需要多少力量才能造成相當的位移

  • Along with the building's material type and the shape of its columns,

    伴隨著使用的建材和柱子的形狀

  • stiffness is largely a matter of height.

    剛性跟建築物的高度也有很大的關聯

  • Shorter buildings tend to be stiffer and shift less,

    較矮的建築通常剛性較大且不容易位移

  • while taller buildings are more flexible.

    較高的建築物則比較容易搖晃

  • You might think that the solution is to build shorter buildlings

    你也許會認為解決辦法就是盡量蓋比較矮的建築

  • so that they shift as little as possible.

    讓它們盡可能不要位移

  • But the 1985 Mexico City earthquake is a good example of why that's not the case.

    但1985年的墨西哥城大地震已經證明了那是錯的

  • During the quake,

    在搖晃期間

  • many buildings between six and fifteen stories tall collapsed.

    很多介於六到十五層樓間的大樓倒塌了

  • What's strange is that while shorter buildings nearby did keep standing,

    奇怪的是,除了那些比它們矮的房子沒有倒之外

  • buildings taller than fifteen stories were also less damaged,

    那些超過十五層樓高的大樓也沒有倒

  • and the midsized buildings that collapsed

    事後發現那些倒塌的中等高度建築物

  • were observed shaking far more violently than the earthquake itself.

    在地震時晃得比地震本身還大

  • How is that possible?

    怎麼會這樣呢?

  • The answer has to do with something known as natural frequency.

    答案跟自然頻率有很大的關聯

  • In an oscillating system,

    在一場震盪中

  • the frequency is how many back and forth movement cycles occur within a second.

    頻率代表著一秒鐘前後移動循環的次數

  • This is the inverse of the period,

    跟週期正好相反

  • which is how many seconds it takes to complete one cycle.

    週期是一次循環需要花幾秒的時間

  • And a building's natural frequency, determined by its mass and stiffness,

    而一棟建築物的自然頻率(由質量與剛性決定)

  • is the frequency that its vibrations will tend to cluster around.

    就是會讓震動累積的頻率

  • Increasing a building's mass slows down the rate at which it naturally vibrates,

    增加一棟建築的質量會讓自然震動的速率變慢

  • while increasing stiffness makes it vibrate faster.

    如果增加剛性,則會讓震動變快

  • So in the equation representing their relationship,

    所以在表示它們之間關聯性的等式中可以看到

  • stiffness and natural frequency are proportional to one another,

    剛性和自然頻率成正比

  • while mass and natural frequency are inversely proportional.

    質量和自然頻率則是成反比

  • What happened in Mexico City was an effect called resonance,

    在那次墨西哥城大地震中,發生了所謂的共振

  • where the frequency of the earthquake's seismic waves

    也就是地震的震波頻率

  • happen to match the natural frequency of the midsized buildings.

    剛好與中等建築物的自然頻率吻合

  • Like a well-timed push on a swingset,

    就像是盪鞦韆時有人在最佳的時機推你一把讓你盪更高

  • each additional seismic wave amplified the building's vibration

    每一次的震波都會讓建築物在當時搖晃的方向下

  • in its current direction,

    晃得更厲害

  • causing it to swing even further back, and so on,

    讓它擺動越來越劇烈

  • eventually reaching a far greater extent than the initial displacement.

    最後終於支撐不住而倒塌

  • Today, engineers work with geologists and seismologists

    現今,工程師跟地質學家與地震學家合作

  • to predict the frequency of earthquake motions at building sites

    想要預測地震在建築工地上搖晃的頻率

  • in order to prevent resonance-induced collapses,

    以預防共振所造成的倒塌

  • taking into account factors such as soil type and fault type,

    他們運用土質、斷層種類,

  • as well as data from previous quakes.

    還有過去發生的地震資料來計算

  • Low frequencies of motion will cause more damage to taller

    低運動頻率會對較高和剛性低的建築

  • and more flexible buildings,

    造成較大的損害

  • while high frequencies of motion pose more threat

    相反的,高運動頻率則會對較矮且剛性高的建築

  • to structures that are shorter and stiffer.

    造成較大的威脅

  • Engineers have also devised ways to abosrb shocks

    工程師們也運用最新科技發展出吸收震盪

  • and limit deformation using innovative systems.

    和減少變形的方法

  • Base isolation uses flexible layers

    「基礎隔震」利用有彈性的樓層

  • to isolate the foundation's displacement from the rest of the building,

    來阻隔地基的位移造成整動建築物的搖晃

  • while tuned mass damper systems cancel out resonance

    「調諧質塊阻尼器」則是減緩建築本身的擺動

  • by oscillating out of phase with the natural frequency

    以避免共振的發生

  • to reduce vibrations.

    進而減少震動

  • In the end, it's not the sturdiest buildings that will remain standing

    結論是,最堅固的建築並不會撐最久

  • but the smartest ones.

    智慧建築才是我們需要的

Earthquakes have always been a terrifying phenomenon,

地震一直是令人懼怕的自然現象

字幕與單字

影片操作 你可以在這邊進行「影片」的調整,以及「字幕」的顯示

B2 中高級 中文 美國腔 TED-Ed 建築物 地震 頻率 質量 自然

【地震知識】什麼樣的房子比較容易在地震中倒塌? (Why do buildings fall in earthquakes? - Vicki V. May)

  • 2346 199
    Coco Hsu 發佈於 2016 年 05 月 12 日
影片單字