How much time do you have to leave a building before it collapses?

Question

Whenever you are experiencing an earthquake above 8 in the Richter scale.

Answer 1

This cannot be answered precisely. There are too many unspecified variables. Building collapse is highly complex and, even with all the scientific strength and materials breakthroughs we've had recently, buildings still collapse without warning. No one predicted the collapse of the World Trade Center Towers for example. And, this past winter, there was at least one cave in of a store under the weight of excessive snow buildup.

A Richter 8 is classified as a Great earthquake. Its energy is 31 times that of a 7, which is 31 times that of a 6; so an 8 has more than 900 times more destructive energy than a 6. And a 6 frequently results in some structural damage somewhere. The San Francisco quake of 1906 was a Richter 8 or thereabouts. [See source.]

Another analogy is that a Richter 6 has the energy about equal to the A-bomb dropped on Nagasaki. And a Richter 8 has the equivalent destructive energy of a 1 megton fusion weapon. As a former research associate at a national laboratory that designs 1 MT weapons, I can say without hesitation that any building will collapse if hit by the full force of a Richter 8 earthquake. And that collapse would happen within seconds.

But, and this is a BIG BUT, earthquakes are capricious critters. Often the full force of an earthquake does not hit even close by buildings. Because of something called destructive-constructive interference in sound waves (and earth motion is like the motion of sound waves) even buildings close in to the epicenter of a Richter 8 might survive because the earth motion cancelled out rather than built up.

On the other hand, constructive interference could build up the destructive energies and focus those energies some miles from the epicenter where the earthquake initiated. This was the case some years ago when Mexico City was devastated by a major earthquake that had its epicenter out in the Pacific Ocean off the western coast.

There are yet other variables to consider. Strutural damage is most likely to occur in buildings built on land fill rather than on bed rock. This happened in the 1989 Loma Prieta earthquake that skipped from the epitcenter below Sunnyvale in the south of the San Francisco Bay all the way north to San Francisco to ravage a land fill area known as the Marina. And, it also skipped way north to knock down the so-called Cypress freeway overpass. Dozens of people were killed when the slabs of freeway overpass collapsed some forty to sixty miles north of the epicenter.

Finally, the building structure itself has to be considered. Floating foundations are relatively new in the high-rise construction industry. Here, the buildings actually "float" on swiveling foundation so the energy of an earthquake is dissipated while the building sways like a pendulum...a pendulum that remains intact rather than collapsing.

So the answer to your question is: you have anywhere from a second or two, up to forever because the building might never collapse. Like so many physics questions, the answer is "it depends."

Answer 2

How would I know its collapsing? it would be too late...but if the building has spring in column foundation ,the building will swing before it collapse..will take 10 minutes depending on horizontal thurst and number of stories...the spring technology has been used since 1989 after the earth quack.That theory is described by myself in 1988 while doing my research in university.

Answer 3

not enough.