Slab Homes

[sputnut]

so, what should we look for in terms of a big one? (6.7 and up)

comin' your way soon!

[MarkP]

If I were to design a house to be isolated from earthquake movement I might very well put it on columns but they would be very high tech columns. Any resemblance to the typical 4" x 4" balanced on a rock would be purely coincidental. The tofu block plantation style is mostly about building cheaply.

I have often thought that the best foundation for around here would be a nice thick well reinforced slab with a foot of gravel underneath as a bond breaker.

[Carey]

The main structures here that failed in the Kiholo Bay earthquake were some of the older post & pier, the lava rock churches (Kapa`a) & the Summer Palace) & some slabs separating from walks..

The lava rock were probably the most expensive & at least on the of post & pier was the most damaging, as the structure "walked" off the piers & crushed the work vehicles stored under the owners house....one of the problems with using the space available under the post & pier if you are counting on the structure "walking"

Course there were some things that building inspections SHOULD have caught, like missing jack studs & load beams....but that is not a design problem, just the lack of execution....(& yes...that double entendre HAS crossed my mind a time or 2...)

[Keala]

Guadua bamboo is used as building material for earthquake resistance in Asia and South America.

/Keala/

[gogould]

Reinforced concrete post on pier would not be doing much walking tied into the reinforced slab on grade, even with the 1st floor up 8- 10ft. Reinforced concrete is amazingly flexible when engineered right. I like all the ways it can be formed with arches and window trims and so on. Those arches make sense when you look at how much strength they add. It easily gives infinite variations of curves and open areas and is By God fireproof and termiteproof for the residential structure.
I actually feel a rush of excitement just thinking about it.

[hotinhawaii]

I think the post and pier homes that failed were the old kind where the posts sat on the piers with no straps to hold them there. the "tofu" block was a 6x6 block set on a larger block with the post just setting on top. I am not sure who ever thought that was a good plan! The new pier blocks are strapped to the posts.

[Rob Tucker]

Precast piers on a house are basically the structural equivalent of a mobile home. They work fine on a nice day.

[Carey]

I've always had one question in the "walking" post & pier, aside from the fact you should not store anything underneathtath you would not want the house "walking" on...What happens to the 'hard' connections that the structure has, little things like water lines, drainpipes, even electric & tele would seem to get a little ...ummm... 'stressed' hooked up to a structure that is "walking"

Rob - I think I would vote for the mobile home (if it still had rubber on the ground) over the precast piers...
Would love to see in there is any data on your 'Rumber' product as sill plates in earthquake construction...seems like that would be a good shock system...

[jackson]

The older homes that failed were also single wall. Double wall construction also adds stability. An 8.5 or a 9 and none of it matters much. I'm contemplating earthquake insurance but it is about 1K minimum. Anyone else have this?

[Rob Tucker]

quote:

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Originally posted by Carey

Rob - I think I would vote for the mobile home (if it still had rubber on the ground) over the precast piers...
Would love to see in there is any data on your 'Rumber' product as sill plates in earthquake construction...seems like that would be a good shock system...

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The Rumber material does have a good purpose in earthquake design as a mud sill material, especially over time. It will not rot or deteriorate, so it's properties remain constant over the life of the structure.

Most mud sill material is made of Douglas Fir for it's compressive strength. The mud sills carry the full weight (load) of the structure. Those loads increase in an earthquake. A lot of primary damage to wood sills has been documented in earthquake analysis.

Douglas Fir has a compressive strength of approx. 1,000 psi. Rumber has a compressive strength of approx. 20,000 psi.

So Rumber has a number of attributes which make it desirable for some load points of a wood frame structure. Rumber is also excellent as a decking surface. What Rumber lacks is good tensile strenth which makes it unsuitable for studs, joists or rafters.

If a framing system is desired my preference is light gauge galvanized steel. It far out performs wood, is cost competitive, is termite and root proof and, properly ordered, produces almost zero waste.

Why people are so committed to building with wood is something I don't understand. Wood framing has become so distrusted in engineering circles that substantial steel connectors (Simpson) are now required. So many steel connectors that, in fact, wood is becoming an infill material between steel connections. An infill material that is expensive, rots, burns, is eaten by insects, warps and has a short useful lifespan.

My opinion.