# Earthquake resistance: Linear, or not...?

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• posted on March 7, 2008, 6:54 pm
I was watching something about earthquakes and building (or retrofitting) for earthquake resistance. I'm assuming it's a "curved graph", but maybe not? So I was wondering, if something is made to survive an earquake of X.Y , would it fail catstrophically at X.Y+1, or would damage increased in a way that'd be mroe of a cruved line of a graph...? I'd assuem teh latter, but what seems logical, isn't always how things work.
Also, if a cinderblock house can be made earthquake-resistant by running rebar through the spaces and backfilling with concrete or whatever, would that also work for brick (since at least some bricks now are cellular rather than solid)?
And, is there special morter? IOW, would ti be an acrylic-based moreter or some other type of elastic base material?
TIA!

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• posted on March 7, 2008, 7:00 pm
Kris Krieger wrote:

It doesn't work like that. The interactions involved are more complicated that the question assumes. FYI, the Richter scale is exponential:
http://en.wikipedia.org/wiki/Richter_scale

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• posted on March 7, 2008, 9:18 pm

I know the Richter scale is exponential, but I'm still wondering whether a structure builkt to withstand X.Y fails at X.Y+1. So, they aer currently retrofitting the Golden Gate Bridge to withstand soemthng like 8.3, but does that mean it will fail (i.e. disintegrate) at 8.4, or what?
I'd Google it but don't know how to frame the inquiry properly.

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<%-name%>
• posted on March 7, 2008, 9:34 pm
Kris Krieger wrote:

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• posted on March 8, 2008, 3:46 am

SO, if it's designed to withstand 150mph, and a 160mph wind occurs, the whole thing simply disintegrates instantly...?
What I'm trying to figure is, if people are in a bldg (house, highrise, whatever) rates to withstand X.Y, but a quake of X.y+1 occurs, does the bldg just completely disintegrate/implode into shards at that point and kill everyone inside?

I couldn't really teel from the program - in many areas, it looks like they're reinforcing it, but I don't knw whether other areas might be put onto rubber "floats" - I couldn't tell. But San Francisco (IIRC) has been literally lifted and placed onto rubber plugs that are supposed to absorb the shaking. THey also described the swaying that some wooden houses can withstand.
So that's what all got me wondering about building for earthquake resistance, and what the limits of that are.
I'm not sure I asked the question properly, either.

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• posted on March 8, 2008, 4:16 am

You're asking a question that can't be answered simply. You'd design a building for 150 mph winds, but there are factors of safety involved. The probability that a failure will occur with a wind higher than the design load increases but it's not linear, it's not simple and it's often times not calculable. The only way to test it would be to overload it to destruction.
There are localized conditions and unforeseeable benefits and disadvantages that help or hinder the chances of a buildings survival. The surrounding terrain could help or hurt, for instance. The design might have been based solely on nailed sheathing and the cowboy with the nailgun might have missed the studs with a bunch of nails. These things are not included in design calculations. A building might withstand a wind load 50 percent higher than the design load, or it might fail at or below the design load due to unaccounted for variables, faulty calculations and assumptions, or poor construction.
So, I guess what I'm saying is make sure your insurance is paid up! ;)
R

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• posted on March 8, 2008, 5:57 am

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So then how can anyone actually say at all that a bldg can withstand this or that strength earthquake, if any/all would pancake unpredictably? I think I'm more confused now than I was before...

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• posted on March 8, 2008, 11:15 pm
wrote:

Felxibility, yup, that does seem to be a main, or poss. *the* main, point. I saw one thing (let's face it, if thre is somehting on about earthquakes, i watch it...) which showed buildings in Turkey - new houses that were monolithing construction (cinderblock) fell apart, btu traditional houses, which started with timber frames taht included diagonal supports (not so differnt from old ENglish half-timber methods), which then were filled in with bricks, remained standing, with only a rew exceptions.
Your point re: the trusses is also a good one. So, yup, it seems that a building has to be a *system* to survive unusual conditions, as opposed to merely being a collection of disparate parts...
Let's hear it for cells (as in the biological/living things) ;)
Actually, only half a joke - are you catching any of the new series about the Body? Last week, they discussed bones, and the high degree to which bones are cellular is structure (as opposed tosolid) and *flexible* - it was maazing to see how far a bone could bend before failing (breaking). Biology has had millions of years to "experiment" and offers intersting examples. Makes me wonder whether,a t some point, we'll be able to *grow* buildings - although that's an entirely different topic.
Meanwhile, the interactions between materials, and structures, and the resulting resistance to stresses, is an interesting thing. I'm thinking that the "weaklink" in wooden structures, as far as earthquake resistance goes, might be the nails, since wood itself seems far superior. SO I'm wondering whether it'd be "sturdier" (to use the term a bit inaccurately but hopefully the meaning is clear) to use fitted joints, as were used in the "pre-nails" days...?

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• posted on March 11, 2008, 9:42 pm

[Edited]
Both are intresting, although sometimes the "how it's made" topics are less interesting to me than teh biology-related things - such as, I wasn't fascinated with how pencil erasers are made ;) Mechanical topics are interesting, tho'.

THe problem is that I never could get a handle on what "3DH" actually *means*. I also never caught the bit about the mini-robots, either, so thanks for pointing that out... I had a hard time understanding the explanations. I looked at the pics of models, but i guess I didn't get out of them what was intended...
Anyway, re: "grow buildings", I mean, biologically, not using robots. More along the lines of breeding a tree, for example, that stays under a certan height, and grows in a way that creates hollow chambers. Not even my own idea, really, but somehting I came across in a "scifi" novel.

Not surprising - the strength and flexibility of wood, like that of bone, is not a funciton merely of the existence of verious types of cells and "biological glue" so to speak, it's a funciton of the *interconnectedness* of the cells and any other materials. THink abotu the qualities of cartelege, and then think what would happen if it were punched full of holes. People think of wood as "hard", more than they think of it as "flexible", and same is true of bone. But part of the strength *is* the flexibility, and that flexibility is comprimised once the material is made discontiguous so to speak.

Yes, and true.

Hmm. Interesting idea. I'm saving that one.
((Isn't the largest cost of most houses actually the land, rather than the structure...?))

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• posted on March 11, 2008, 10:30 pm

I don't mean "valued" (evaluation), I mean, straight cost to build. OTOH I admittedly have no contact with the work of \$2-mill-+ properties (or even \$1+ mil, for that matter...)

That's it, what you can get for \$X thousand (of house - i.e. not including property) is, from what I have been able to find, rather superior in quality to what you could get for the same money in a developer-built place, mostly becasue developers tend to go for size rather than quality - but that's just my impression, because I've never been able to dig up the hard numbers.

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• posted on March 12, 2008, 7:07 am

The word that you are looking for is Ductility not flexibility. Such as a ductile moment frame. Hope this answers the question.
CID...

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<%-name%>
• posted on March 12, 2008, 12:37 pm

Sorry, Chuck but this thread is on earthquakes - the AC duct relocation question is a couple threads over. ;)
Don is always looking for a word - and he's going to use every word he knows until he finds it. =:O
R

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• posted on March 13, 2008, 8:09 am
wrote:

Ductility is a term for the behavior of the structure by letting it yield during a eartquake and go back when the quake is over. Look up the defination in a dictionary for the word ductility. It is not reference to AC ducts in this case. Oh well, I will do it for you.
1. capable of being hammered out thin, as certain metals; malleable. 2. able to undergo change of form without breaking.
Now Don knows it also.
CID...

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<%-name%>
• posted on March 13, 2008, 8:58 am

Did you hear a whooshing sound when you read my post? Just curious...
R

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• posted on March 13, 2008, 8:19 pm
wrote:

Yup, I did. Bones are felxible. Wood is flexible.
Flexible = able to bend without incurring damage
Ductible = capable of being drawn out
A spring is flexible. The metal that is drawn out to create the wire used to make the spring is ductible.

Or, living near all tat wter in Miami, maybe "ducktability" ;)

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• posted on March 14, 2008, 3:44 am
Kris Krieger wrote:

Or may plasticity, since you live in America

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• posted on March 16, 2008, 5:28 pm
wrote:

THat'd be Plasti City =:-o

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• posted on March 16, 2008, 5:27 pm
wrote:

See, "stream", "duck"... I see a pattern emerging here...
;)

Our house in Massachusetts has floor registers; I don't think it's all that uncommon "up north", since it's harder to force heat downwards to the floor, and not as critical to force air-conditioning upwards.
OTOH, they also collect stuff that way, and air-flow can be problematic so I ended up making duct-covers so as to direct airflow better, and reduce the amount of stuff that'd get into them.

I can imagine what a PITA it could be, after watching the original ducting being installed in our place.
(OK, let's be honest, I just dislike forced-air gas heat...)

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• posted on March 13, 2008, 8:13 pm

I though "ductile" meant "can be drawn out/extruded"?

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• posted on March 8, 2008, 5:13 am
Kris Krieger wrote:

The answer is that the failure is not necessarily so. Building do not normally implode without controlled explosions. the design itself can mitigate against specific failures as you suggest with your wind example below. One resource, partially paid for with your taxes: http://www.bssconline.org /

For your own hazards related calculations there are several FEMA tools and you can even get free training in them.