ELi5: why are there glass skyscrapers in earthquake territory?

32 views

Why are there glass skyscrapers in earthquake territory?

In San Francisco, the Salesforces building has many glass windows. Won’t the glass break during an earthquake and fall on pedestrians on the street. Do engineers expect the glass not to break during an earthquake?

In: 5

Not all glass is made equal.

Glass in skyscrapers built in the 1980s will likely all fly off buildings in a large earthquake, killing pedestrians below. But modern skyscraper glass is engineered with flex and impact resistance, more like windshield glass. But unlike windshields, it isn’t mounted in a way that it will pop out: instead, it will stay seated and flex with the building.

Also, buildings are designed to sway with a quake, so it would take a very particular kind of quake to unseat or shatter the glass in a modern skyscraper.

Im not familiar with this type of stuff but if i had to assume there is most likely a glass made to resist the force of the earthquake. They definitely wouldnt create a skyscraper like that there without thinking of such precautions.

Easy answer: because it’s safe. Earthquake-prone cities have anti-earthquake building standards; the skyscrapers you see are built the way they are because they’re known to be safe in the event of an earthquake.*

*or, at least, they’re safe enough relative to cost, in the opinion of the people making the safett stabdards.

The mounting systems almost always have a sufficient amount of flex to them; expansion joints between panes, flexible seals and such. They aren’t rigidly held in place like a normal house window. Keep in mind that skyscrapers everywhere will flex and expand/contract under windy conditions or hot/cold weather; earthquakes aren’t that much different as far as windows are concerned. On top of that, the panes are laminated like bullet-proof glass such that when panels do break (usually from something hitting them), they’re still held in place to prevent them from falling. So they’re designed to not break from building movement, and even if they do break, they’re designed to do so safely.

It’s much better than having stone/concrete exteriors. NYC has the permanent scaffolds in front of so many buildings to protect pedestrians for when pieces of a facade of a building does drop off. Instead, newer buildings tend to be completely covered in windows that fail in a safe manner. Not to mention that glass is more weather resistant over time than the stone/concrete facades.

The real answer to the question you asked (*why*, not *how*) is:

Because the person paying for the building wanted a glass one, and the architect was confident that it could be done safely.