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RE: Earthquake-Proof Design

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So much depends on what you want to do with it, and what earthquake-proof means.  You could build a concrete shearwall blockhouse or a highly ductile steel moment frame—either could be earthquake-proof, or anything in-between depending on how you define the earthquake.  The devil is in the detailing for any weirdness (irregularity) in the building, and what kind of behavior you want out of the structure. The structure itself is irrelevant if the foundations cant transfer the loads.  

 

You could argue that meeting the code will make it earthquake-proof within the statistically defined limits of the things covered by the code.  What is the owner willing to accept?  I’ve never designed anything that I didn’t think was earthquake-proof—within the limits of the design lateral forces.

 

We do the best we can with the tools we have but the statistical sample of the information that seismic loadings are based on is so very small that there are no guarantees.  It’s the difference between frequency and probability.  We know what’s happened in the past to the degree that our observations are accurate (frequency). From that we try to predict what will happen in the future (probability), but we are continually being surprised because we have so few observations.  The structural design is a function of the loading, and the loading is a function of what the geotech and the code tell us it is.  I think it’s pretty cool that we do as well as we do given the very limited information we are working with.

 

Bottom line, IMHO is that there’s no golden ticket out there.  It really depends on what you want to do with the structure, the maximum risk allowable by law for life-safety performance (the codes), and the amount of risk individual owners are willing to take.  If they don’t want to take any risk and they don’t want any cracks in the plaster, a concrete bunker is a good way to go but make sure they glue everything down and have tiedowns on the appliances and cabinets. The building might come through fine but all the load will be transferred to whatever’s in the way since there will be no ductility to absorb energy.

 

 

Shaun Dustin, MS, PE

Doctoral Candidate

USTAR Biofuels Initiative

Utah State University
4130 Old Main Hill
Logan, UT 84322

sdustin(--nospam--at)cc.usu.edu

435-770-7816

 


From: Donald Bruckman [mailto:bruckmandesign(--nospam--at)verizon.net]
Sent: Friday, November 02, 2007 9:53 AM
To: seaint(--nospam--at)seaint.org
Subject: Earthquake-Proof Design

 

Listen, you clowns…I leave town for one day and come back to 93 messages about just about everything BUT engineering.  So, either I start a thread lambasting Prof. Astenah’s cheesy, stinkin’ football team and how we Trojans will be up there soon to kick Bear, OR I will start a new thread about EQ design.

 

I’ll start with that and see if it morphs into a football board.

 

I have a client that bought a piece of land in North LA County.  I’ve been to the site and it’s a really pretty, sort of bucolic little area full of chaparral and butterflies.  Unfortunately, it also has, about a 3 wood away, the grinding fury of two continental tectonic plates sliding by each other. I think they call it The San Andreas Fault.

 

So, after the preliminary discussion wherein I say, “There is no such thing as an earthquake-proof building…blah blah blah…”, we got serious and he and I agreed that I would try to get as close as I could by affecting the design in such a way that the threat could be minimized.

 

So, with that in mind, I told him, for instance:  Tall building?   Not so much….Irregular building with re-entrant corners….not so much….Now, more broadly, the question for the board:

 

What are the other various strategies that would minimize the risk?

 

--DB