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Earthquake resistance: Linear, or not...?

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Earthquake resistance: Linear, or not...? Kris Krieger 03-07-2008
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Posted by RicodJour on March 7, 2008, 11:16 pm
>
> 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.

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

Posted by Kris Krieger on March 8, 2008, 12:57 am
a84b-30b5855e56dd@f47g2000hsd.googlegroups.com:

>>
>> 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.
>
> 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.

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...

>
> 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
>


Posted by Kris Krieger on March 8, 2008, 6:15 pm

>
>> news:b1a6236b-9840-4683-
>> a84b-30b5855e56dd@f47g2000hsd.googlegroups.com:
>>
>>>>
>>>> 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.
>>>
>>> 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.
>>
>> 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...
>
> Good question, and I don't know the answer.
> Frankly, it never occurred to me til you brought it up.
> A Simpson HETA20 truss anchor will *withstand* 1875 lbs of uplift but
> what does that mean?
> It DOESN'T mean the 10d's holding the roof sheathing won't lift.
> What good is a truss anchored to the wall if the sheathing is gone and
> the interior of the house destroyed?
> You might google Aubuchon Homes who I believe have been in the
> forefront of setting the design standards for the state of Florida in
> years past. As far as earthquake stuff goes, my knowledge is limited
> to general science stuff I've seen on the toob but I believe
> flexibility is the key.

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...?


Posted by Kris Krieger on March 11, 2008, 5:42 pm

>
>>
[Edited]

>> As far as earthquake stuff goes, my knowledge is
>>> limited to general science stuff I've seen on the toob but I believe
>>> flexibility is the key.
>>
>> 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?
>
> No, but I'm going to.
> (short story: My wife and I have gotten into the habit of watching
> that show, 'How It's Made' on Discovery while eating supper and
> invariably they'll show a commercial about 'The Body' and eveytime
> they do I say, 'One of these days I'm gonna watch that show'. Its sort
> of a joke. So far I haven't watched it. We don't watch much.)

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'.

>> 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.
>
> According to Per Corel that exactly how its going to happen, sort of.
> He envisions his 3DH buildings constructed at the molecular level by
> microscopic robots and after a building is completed the robots will
> be reprogrammed to perform constant maintenance.

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.


>> 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...?
>
> Here's a prediction, which I originally predicted some 10 years ago.
> Under the right conditions the wood trusses will fail because the
> number of nails required will effect the stability of it.

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.

> Right now, something like 18 nails are *required* at each
> truss/hurricane anchor and to me that many holes in the wood isn't a
> good thing. Ever seen a piece of wood with 18 nails in close
> proximity? It ain't pretty - the wood is horribly splintered.

Yes, and true.

> I'd rather see 12 guage angle steel reheaded into the top/side of the
> concrete tiebeam and through bolted through the truss heels - the
> angle steel would go up and over the top chord and be bolted from both
> sides. This would be less strain on the wood in the truss. The plywood
> roof sheathing, not OSB, 3/4" plywood, would be installed with #12 x
> 3" screws @ 8" o/c along the perimeters of the sheets and all plywood
> seams would receive 2x4 deadwood. These things would add about 15-20%
> to the cost of the roof but would add considerably to the overall
> integrity of it. **No inspector is ever going to count all the nails
> in every hurricane anchor on every house.

Hmm. Interesting idea. I'm saving that one.

((Isn't the largest cost of most houses actually the land, rather than
the structure...?))



Posted by Kris Krieger on March 11, 2008, 6:30 pm

>
>>
>>>
>>>>
>> [Edited]
>>
>>>> As far as earthquake stuff goes, my knowledge is
>>>>> limited to general science stuff I've seen on the toob but I
>>>>> believe flexibility is the key.
>>>>
>>>> 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?
>>>
>>> No, but I'm going to.
>>> (short story: My wife and I have gotten into the habit of watching
>>> that show, 'How It's Made' on Discovery while eating supper and
>>> invariably they'll show a commercial about 'The Body' and eveytime
>>> they do I say, 'One of these days I'm gonna watch that show'. Its
>>> sort of a joke. So far I haven't watched it. We don't watch much.)
>>
>> 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'.
>>
>>>> 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.
>>>
>>> According to Per Corel that exactly how its going to happen, sort
>>> of. He envisions his 3DH buildings constructed at the molecular
>>> level by microscopic robots and after a building is completed the
>>> robots will be reprogrammed to perform constant maintenance.
>>
>> 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.
>>
>>
>>>> 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...?
>>>
>>> Here's a prediction, which I originally predicted some 10 years ago.
>>> Under the right conditions the wood trusses will fail because the
>>> number of nails required will effect the stability of it.
>>
>> 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.
>>
>>> Right now, something like 18 nails are *required* at each
>>> truss/hurricane anchor and to me that many holes in the wood isn't a
>>> good thing. Ever seen a piece of wood with 18 nails in close
>>> proximity? It ain't pretty - the wood is horribly splintered.
>>
>> Yes, and true.
>>
>>> I'd rather see 12 guage angle steel reheaded into the top/side of
>>> the concrete tiebeam and through bolted through the truss heels -
>>> the angle steel would go up and over the top chord and be bolted
>>> from both sides. This would be less strain on the wood in the truss.
>>> The plywood roof sheathing, not OSB, 3/4" plywood, would be
>>> installed with #12 x 3" screws @ 8" o/c along the perimeters of the
>>> sheets and all plywood seams would receive 2x4 deadwood. These
>>> things would add about 15-20% to the cost of the roof but would add
>>> considerably to the overall integrity of it. **No inspector is ever
>>> going to count all the nails in every hurricane anchor on every
>>> house.
>>
>> Hmm. Interesting idea. I'm saving that one.
>>
>> ((Isn't the largest cost of most houses actually the land, rather
>> than the structure...?))
>
> Probably the most expensive single piece of land I've been involved
> with was $850k for less than 1/4 acre on Useppa Island and the house
> that was built on it was valued at over $2 mil.

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...)

> Most of the stuff I've done was a far less ratio.
> My own property in the Cape cost $3500 in 2001 for 1/4 acre and in
> 2006 I sold it with a house on it for $300k and the original cost of
> the house was $155k + add-ons.

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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