Name: When Earthquake Damage is Invisible
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Even if a building appears to be undamaged after an earthquake, it could have used up some of its initial earthquake resisting capability.

Factors such as inadequate construction materials can make tall buildings vulnerable.

When Earthquake Damage is Invisible

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Even if a building appears to be undamaged after an earthquake, it could have used up some of its initial earthquake resisting capability.

Factors such as inadequate construction materials can make tall buildings vulnerable.

Tech & Engineering

How Earthquakes Affect Seemingly Undamaged BuildingsPublished: January 13, 2022Narrator: Although improved materials and welding techniques have made newer steel buildings far less susceptible to failures, older moment frames, including the famous Transamerica Pyramid and other buildings throughout California, remain unfixed and could even have become weakened by previous quakes.Ronald Hamburger: So if a building goes through an earthquake, even if it is apparently undamaged, it's used up some of its original earthquake-resistant capability.Swaminathan Krishnan: The problem is right now there are hundreds of tall buildings of that kind. They have not been opened up and they have not been retrofitted.Narrator: And if a big earthquake comes...Krishnan: We are going to see building collapses. That is what our modeling tells us.Narrator: A few moment frame buildings have been retrofitted. But a big deterrent is cost. To remove interior walls and ceilings to inspect connections, much less tear things apart and fix those connections, can be extremely expensive and may just be unnecessary. In 1985, a powerful earthquake struck Mexico City, where taller buildings saw relatively little damage, but many midsize, 10 to 20 story buildings, were tremendously damaged or totally destroyed. That's because their particular height resonated with the shock waves from this earthquake.Hamburger: Resonance is a phenomenon that occurs when the natural frequency of a structure closely matches the natural frequency of an exciting force.Narrator: Earthquakes send out vibrations of various wavelengths or frequencies. When they reach a cluster of buildings, those that suffer damage are often the ones whose height best matches those particular frequencies.Hamburger: When the ground shaking has in it high frequencies, meaning if the shaking is jarring, it's going to go do this, "Boom, boom, boom, boom, boom." That kind of shaking will selectively effect short buildings.Narrator: Whereas longer wavelengths can cause tall buildings to sway rhythmically. And in extreme cases, can collapse them. Other factors such as soil conditions or inadequate construction materials can also make tall buildings vulnerable.

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When Earthquake Damage is Invisible

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