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Earthquake resistance: Linear, or not...? Kris Krieger 03-07-2008
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Posted by Kris Krieger on March 8, 2008, 1:01 am

>
>
> Kris Krieger wrote:
>
>>>>>
>>>>>
>>>>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?
>>>>
>>>>
>>>Can't be done, except in a computer model, cause there's too many
>>>variables. First, you have to define *failure* then design around that
>>>parameter. In SW FL for example the homes I design are supposed to
>>>sustain a 130 to 150 mph wind and usually they do.
>>>But that doesn't mean things won't fail.
>>>
>>>
>>
>>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?
>>
>>
>
> 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

Don's actually, he was trying to explain it with an analogy.

> below. One resource, partially paid for with your taxes:
> http://www.bssconline.org/

OK, that's *some* info, I'll just have to rummage around teh INternet
more more I think.


>
>>
>>
>>
>>>On my own house, it went through several hurricanes but some things
>>>did fail, though nothing structural.
>>>If any of those hurricanes would have stalled on my house there very
>>>well may have been structural failure.
>>>Some of the soffit tore loose, a design flaw (which was later
>>>corrected), that allowed wind to penetrate the envelope.
>>>If this wind would have sustained it may have lifted that portion of
>>>the roof and once that happens its all over.
>>>(I installed more, and longer, nails along the edge of the fascia that
>>>attaches the soffit and used 24 tubes of silicone caulk to secure the
>>>soffit to the stucco wall and fascia. This had the added benefit of
>>>thwarting the yellow jackets from nesting in the valleys of the
>>>soffit) Regarding the Golden Gate, what did they do, put it on pulleys
>>>so it'll sway like a pendelum?
>>>
>>>
>>
>>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.
>>
>>
>
> happy reading. in the links below:
>
> http://www.bssconline.org/links.html
>
> For your own hazards related calculations there are several FEMA tools
> and you can even get free training in them.
>

I don't know that houston has ever hd an earthquake, we're on gumbo/clay,
one giant delta I think. But the whole earthquake topic just interests
me, for no practical reason ;)


Posted by Troppo on March 8, 2008, 8:12 am

>
>>
>>>
>>>> Kris Krieger wrote:
>>>>> 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.
>>>>
>>>> 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
>>>>
>>>
>>> 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?
>>
>> Can't be done, except in a computer model, cause there's too many
>> variables. First, you have to define *failure* then design around that
>> parameter. In SW FL for example the homes I design are supposed to
>> sustain a 130 to 150 mph wind and usually they do.
>> But that doesn't mean things won't fail.
>
> 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?
>
>
>> On my own house, it went through several hurricanes but some things
>> did fail, though nothing structural.
>> If any of those hurricanes would have stalled on my house there very
>> well may have been structural failure.
>> Some of the soffit tore loose, a design flaw (which was later
>> corrected), that allowed wind to penetrate the envelope.
>> If this wind would have sustained it may have lifted that portion of
>> the roof and once that happens its all over.
>> (I installed more, and longer, nails along the edge of the fascia that
>> attaches the soffit and used 24 tubes of silicone caulk to secure the
>> soffit to the stucco wall and fascia. This had the added benefit of
>> thwarting the yellow jackets from nesting in the valleys of the
>> soffit) Regarding the Golden Gate, what did they do, put it on pulleys
>> so it'll sway like a pendelum?
>
> 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.

Earth tremours are usually cyclic, so anything like rubber plugs will
certainly help. I've experienced a Richter 7.8 in PNG, and seen what
happens to structures in similar shakes. In timber structures, multi-bolted
plates are preferable to single bolts, also trussed structures work well.
In PNG joints in traditional buildings are constructed out of a complex
weave of bush vine; acts as a torsion joint - moves, but tightens as it
moves.

Much depends on the land form and geotechnics. Gravelly, sandy soils absorb
the shock waves well, but there may be landslides. Soldered copper pipes
more likely to burst that threaded compression joints. A 7.8 in Mexico City
will cause far more destruction because its all clay in a bowl of rock -
wobbles like a jelly. I guess the problem in SF would be shear. The whole
west side is slowly on its way to Hawaii ...



Posted by Michael Bulatovich on March 8, 2008, 9:41 am
Troppo wrote:
>
>>
>>>
>>>>
>>>>> Kris Krieger wrote:
>>>>>> 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.
>>>>>
>>>>> 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
>>>>>
>>>>
>>>> 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?
>>>
>>> Can't be done, except in a computer model, cause there's too many
>>> variables. First, you have to define *failure* then design around
>>> that parameter. In SW FL for example the homes I design are
>>> supposed to sustain a 130 to 150 mph wind and usually they do.
>>> But that doesn't mean things won't fail.
>>
>> 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?
>>
>>
>>> On my own house, it went through several hurricanes but some things
>>> did fail, though nothing structural.
>>> If any of those hurricanes would have stalled on my house there very
>>> well may have been structural failure.
>>> Some of the soffit tore loose, a design flaw (which was later
>>> corrected), that allowed wind to penetrate the envelope.
>>> If this wind would have sustained it may have lifted that portion of
>>> the roof and once that happens its all over.
>>> (I installed more, and longer, nails along the edge of the fascia
>>> that attaches the soffit and used 24 tubes of silicone caulk to
>>> secure the soffit to the stucco wall and fascia. This had the added
>>> benefit of thwarting the yellow jackets from nesting in the valleys
>>> of the soffit) Regarding the Golden Gate, what did they do, put it
>>> on pulleys so it'll sway like a pendelum?
>>
>> 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.
>
> Earth tremours are usually cyclic, so anything like rubber plugs will
> certainly help. I've experienced a Richter 7.8 in PNG, and seen what
> happens to structures in similar shakes. In timber structures,
> multi-bolted plates are preferable to single bolts, also trussed
> structures work well. In PNG joints in traditional buildings are
> constructed out of a complex weave of bush vine; acts as a torsion
> joint - moves, but tightens as it moves.
>
> Much depends on the land form and geotechnics. Gravelly, sandy soils
> absorb the shock waves well, but there may be landslides. Soldered
> copper pipes more likely to burst that threaded compression joints. A
> 7.8 in Mexico City will cause far more destruction because its all
> clay in a bowl of rock - wobbles like a jelly. I guess the problem in
> SF would be shear. The whole west side is slowly on its way to Hawaii

I thought it was headed *under* the east side, and slightly south....



Posted by Troppo on March 8, 2008, 6:01 pm

> Troppo wrote:
>>
>>>
>>>>
>>>>>
>>>>>> Kris Krieger wrote:
>>>>>>> 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.
>>>>>>
>>>>>> 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
>>>>>>
>>>>>
>>>>> 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?
>>>>
>>>> Can't be done, except in a computer model, cause there's too many
>>>> variables. First, you have to define *failure* then design around
>>>> that parameter. In SW FL for example the homes I design are
>>>> supposed to sustain a 130 to 150 mph wind and usually they do.
>>>> But that doesn't mean things won't fail.
>>>
>>> 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?
>>>
>>>
>>>> On my own house, it went through several hurricanes but some things
>>>> did fail, though nothing structural.
>>>> If any of those hurricanes would have stalled on my house there very
>>>> well may have been structural failure.
>>>> Some of the soffit tore loose, a design flaw (which was later
>>>> corrected), that allowed wind to penetrate the envelope.
>>>> If this wind would have sustained it may have lifted that portion of
>>>> the roof and once that happens its all over.
>>>> (I installed more, and longer, nails along the edge of the fascia
>>>> that attaches the soffit and used 24 tubes of silicone caulk to
>>>> secure the soffit to the stucco wall and fascia. This had the added
>>>> benefit of thwarting the yellow jackets from nesting in the valleys
>>>> of the soffit) Regarding the Golden Gate, what did they do, put it
>>>> on pulleys so it'll sway like a pendelum?
>>>
>>> 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.
>>
>> Earth tremours are usually cyclic, so anything like rubber plugs will
>> certainly help. I've experienced a Richter 7.8 in PNG, and seen what
>> happens to structures in similar shakes. In timber structures,
>> multi-bolted plates are preferable to single bolts, also trussed
>> structures work well. In PNG joints in traditional buildings are
>> constructed out of a complex weave of bush vine; acts as a torsion
>> joint - moves, but tightens as it moves.
>>
>> Much depends on the land form and geotechnics. Gravelly, sandy soils
>> absorb the shock waves well, but there may be landslides. Soldered
>> copper pipes more likely to burst that threaded compression joints. A
>> 7.8 in Mexico City will cause far more destruction because its all
>> clay in a bowl of rock - wobbles like a jelly. I guess the problem in
>> SF would be shear. The whole west side is slowly on its way to Hawaii
>
> I thought it was headed *under* the east side, and slightly south....
>

You might be right - can't find my plate tectonics stuff. I thought the
Baja was a case of 'tear along the dotted line ...'

Posted by Kris Krieger on March 8, 2008, 6:24 pm

>
[snip]
>>
>>> On my own house, it went through several hurricanes but some things
>>> did fail, though nothing structural.
>>> If any of those hurricanes would have stalled on my house there very
>>> well may have been structural failure.
>>> Some of the soffit tore loose, a design flaw (which was later
>>> corrected), that allowed wind to penetrate the envelope.
>>> If this wind would have sustained it may have lifted that portion of
>>> the roof and once that happens its all over.
>>> (I installed more, and longer, nails along the edge of the fascia
>>> that attaches the soffit and used 24 tubes of silicone caulk to
>>> secure the soffit to the stucco wall and fascia. This had the added
>>> benefit of thwarting the yellow jackets from nesting in the valleys
>>> of the soffit) Regarding the Golden Gate, what did they do, put it
>>> on pulleys so it'll sway like a pendelum?
>>
>> I couldn't really tell 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.
>
> Earth tremours are usually cyclic, so anything like rubber plugs will
> certainly help. I've experienced a Richter 7.8 in PNG, and seen what
> happens to structures in similar shakes. In timber structures,
> multi-bolted plates are preferable to single bolts, also trussed
> structures work well. In PNG joints in traditional buildings are
> constructed out of a complex weave of bush vine; acts as a torsion
> joint - moves, but tightens as it moves.

Is PNG Papua New Guinea...? Maybe I can fond some pic online. I relaly
like that idea, intertwined materials to create a cabling system.
SHeathe it the way scales sheathe a lizard's body or a bird's foot. SO,
rather than flat rigid bsum-board walls, have a system of membranes (to
hold in insulation) and overlapping planes... Problem is, I don't
knowwhether that's an interesting idea, or just a nutty idea =:-o

If it's actualyl an *interesting* idea, maybe I should try to model
something in 3D, now that my system is finally fully-working again ;)


>
> Much depends on the land form and geotechnics. Gravelly, sandy soils
> absorb the shock waves well, but there may be landslides. Soldered
> copper pipes more likely to burst that threaded compression joints. A
> 7.8 in Mexico City will cause far more destruction because its all
> clay in a bowl of rock - wobbles like a jelly. I guess the problem in
> SF would be shear.

That sounds logical. Also, much of SF Iincludingalmost all of downtown)
is, it turns out, built on soils that are guaranteed t undergo
liqufaction <?sp?>

> The whole west side is slowly on its way to Hawaii
> ...

C'mon and take a free riiiide...! (Heh, Old song)

Page 5 of 9       < 1 2 3 > last >>
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