10-17-2006, 07:43 AM
Attaching a home foundation to bedrock is the preferred seismic connection. Softer soils can, and will, actually amplify the seismic effect. In some soils the movement is similar to Jello wiggling and liquefaction can result. Liquefaction is more likely if there is a lot of bound water or saturated soil conditions. Simply put it is better to take the jolt once than to have it amplify multiple times. One whack is better than ten whacks. Duration of the event matters a lot for this reason. A simple earthquake jolt is one thing. 30 seconds of jolts is another.
Kona may have benefited by the general lack of soil. Lots of raw stone.
Anchorage, in 1960, got, I believe, a 9.5 event that lasted seven minutes. Very bad.
The increase in requirement for "Simpson" steel fasteners is the result of engineering analysis of earthquake related building failures. Simpson does extensive testing and owns one of two earthquake simulators on the west coast. (The other is at U.C. Irvine). Simple nailed wood connections failed regularly. In addition the type of failure matters too. Most un-reinforced failures were of a "catastrophic" type. That means the structure resisted the seismic force to a point of complete failure. Collapse. A "gradual" type failure is preferred. Simpson ties can, alone, change the nature of a failure from catastrophic to gradual. Care to guess which one is more survivable?
I have seen test results of shear walled wood frame where the catastrophic failure occurred at 9 kps. (Think of kps as thousand/pound/second). Interestingly, reinforced concrete systems (ICF) tested to a gradual failure point of 89 kps.
My home is reinforced concrete. I built it myself for less than $100 psf.
I do try to remember though that nothing made by man cannot be defeated by nature. We do have the ability to do better. Simpson is cheap compared to a destroyed home.
One big thing affecting upcoming codes came from FEMA. Prior to the Northridge Earthquake the basic engineering standard was for people to survive earthquake events of “X” magnitude. That standard was very, very successful. Compare L.A. to Mexico City.
Following Northridge FEMA put the word out to the engineering community that from now on the buildings were expected to survive. Liability was the leverage applied. And now the safety factors in residential design are reaching the point in some locales (SoCal) where “affordable housing” is but a memory.
Just some facts. I did a lot of recovery work and building post mortums in L.A. after Northridge. I also noticed that for about one year after the event people were very earthquake aware. After that it was back to what's cheap and expedient.
Kona may have benefited by the general lack of soil. Lots of raw stone.
Anchorage, in 1960, got, I believe, a 9.5 event that lasted seven minutes. Very bad.
The increase in requirement for "Simpson" steel fasteners is the result of engineering analysis of earthquake related building failures. Simpson does extensive testing and owns one of two earthquake simulators on the west coast. (The other is at U.C. Irvine). Simple nailed wood connections failed regularly. In addition the type of failure matters too. Most un-reinforced failures were of a "catastrophic" type. That means the structure resisted the seismic force to a point of complete failure. Collapse. A "gradual" type failure is preferred. Simpson ties can, alone, change the nature of a failure from catastrophic to gradual. Care to guess which one is more survivable?
I have seen test results of shear walled wood frame where the catastrophic failure occurred at 9 kps. (Think of kps as thousand/pound/second). Interestingly, reinforced concrete systems (ICF) tested to a gradual failure point of 89 kps.
My home is reinforced concrete. I built it myself for less than $100 psf.
I do try to remember though that nothing made by man cannot be defeated by nature. We do have the ability to do better. Simpson is cheap compared to a destroyed home.
One big thing affecting upcoming codes came from FEMA. Prior to the Northridge Earthquake the basic engineering standard was for people to survive earthquake events of “X” magnitude. That standard was very, very successful. Compare L.A. to Mexico City.
Following Northridge FEMA put the word out to the engineering community that from now on the buildings were expected to survive. Liability was the leverage applied. And now the safety factors in residential design are reaching the point in some locales (SoCal) where “affordable housing” is but a memory.
Just some facts. I did a lot of recovery work and building post mortums in L.A. after Northridge. I also noticed that for about one year after the event people were very earthquake aware. After that it was back to what's cheap and expedient.
Assume the best and ask questions.
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Punaweb moderator