pouring piers into forms

[Haaheo okole puka]

Unit bonds with epoxy typically average 125psi. How many square inches is a 6" depth set anchor? Absolutely nothing relative to a seismic event load.

[Haaheo okole puka]

1/2" rebar has 1.57 square inches per inch of length surface area. By 6" = 9.42" square surface bond at 125psi is 1178 lbs. resistance force to extraction. Here's the rub, a vertical shock force of a structure resisting downward motion of the earth with a mere 1178lbs resistance force applied to a .625" diameter hole in lava, will result in one of two things, snapping lava rock upward or instant extraction of the anchor from the rock. Failure.

[Haaheo okole puka]

The things to consider are:
1) The Big Island is categorized as a Seismic Zone 4 just like the greater California Coast. Our design standard is based on .4g ground force acceleration (GFA). Simplified as .4g GFA.
2)The possible direction of your loads applied to the subject point and the structural characteristics of said point.

[DanielP]

quote:

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Originally posted by Haaheo okole puka

The things to consider are:
1) The Big Island is categorized as a Seismic Zone 4 just like the greater California Coast. Our design standard is based on .4g ground force acceleration (GFA). Simplified as .4g GFA.
2)The possible direction of your loads applied to the subject point and the structural characteristics of said point.

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All those specs are well and good, but remember, here it is acceptable and common practice to set post and pier on a pile of gravel with no vertical tie down.

[Haaheo okole puka]

Let's apply this to a model. A basic square single story structure with a combined rough design 70psf load at 24'X24' with enormous beams and 4 supporting post at the corners atop footing. 24' square is 576sf times 70psf design load which totals 40320lb divided by the 4 support points is 10,080lb load force per post footing. Using the seismic .4g acceleration load we take 10,080 x .4 = 4032lb applied GFA. Using the average 125psi epoxy bond applied to a 1/2" rebar anchor we take the 4032lb subject GFA divide it by the epoxy bond of 125psi which requires a 32.256si bonding surface. Now we divide the 32.256si by the 1/2" rebar si per inch of 1.57si per inch length = 20.55 anchor depth for one rebar anchor. If we apply 4 rebar anchor we derive 5" depth each and apply the customary 1.25-1.5 CYA factor and we conclude 7.5" depth each of 4ea 1/2" rebar. Now - assume the worst for your rock and be your own judge and jury after mother nature calls up THE bitchin' Earthquake of the century.

[Haaheo okole puka]

Now if you want to minimize the gamble you would need a cross section of your rock via core sample near each footing location.
This will tell you the depth of the flow over the previous flow. Let's use a hypothetical result. 6" is the upper flow depth.
How would you begin to comprehend what that would mean for your anchor depths if only 7"?

[Haaheo okole puka]

When I expressed a 16" roto-hammer bit, it is to ensure a reasonable guarantee of safety with regard to GFA situations and actual flow depths.
Does it make sense now?

[Haaheo okole puka]

quote:

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Originally posted by DanielP

quote:

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Originally posted by Haaheo okole puka

The things to consider are:
1) The Big Island is categorized as a Seismic Zone 4 just like the greater California Coast. Our design standard is based on .4g ground force acceleration (GFA). Simplified as .4g GFA.
2)The possible direction of your loads applied to the subject point and the structural characteristics of said point.

---

All those specs are well and good, but remember, here it is acceptable and common practice to set post and pier on a pile of gravel with no vertical tie down.

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Such building techniques proved fatal in the last century of this islands history. So... do you have a true foundation wall anywhere on this structure? Code currently requires it with post and footing applications.

[Haaheo okole puka]

Unfortunately, I cannot supply you with the structural characteristics of your rock. All flows differ with regard to structural integrity. That's based on the density of the rock and several other content factors, there is no one single answer for that.

[Haaheo okole puka]

What's this all boil down to? If you're truly serious about anchoring your house you will spend the money for a site evaluation or you will sink the appropriate bar deep 16"-24"-36" and you can rest easy it most likely will not fail.