Foundation Question: Pier, post and bond beam

[SpyingOnMyKeystrokes]

I've been considering cabin designs that minimize concrete needed in the foundation.

I've been trying designs that use 12" diameter piers (as deep as 48") rebarred / tied together by a fairly hefty bond beam (12" depth x 24-36" width at perimeters) and column bases set into the bond beam for posts above (post and beam structural support).

I'm wondering if the bond beam, that would sit at about grade elevation, is going to be susceptible to frost expansion and liable to crack? Can this be done in a cold northern climate?

Anyone with experience using this method have questions?

[SpyingOnMyKeystrokes]

LOL. That should say, "answers," not "questions." It is I who has the question, and you who hopefully has the answers, or perhaps, the question replies.

[akwoodchuck]

Not only will that not work in a cold climate, it's WAYYY more concrete than you need even to build a code-compliant, conventional foundation...

[Don_P]

First question would be, what is your frost depth? Typically a grade beam foundation is rectangular in the opposite plane of what you describe, it is designed as a structural spanning reinforced beam between points of support. It is engineered and typically a good bit more expensive than a conventional spread footing. A frost protected shallow foundation might be an alternative, or permanent wood foundation, or precast foundation on a gravel trench.

Those in turn support braced walls, real structural support, vs post and beam by which I suspect in the way you are thinking is not structural support.

[ChugiakTinkerer]

And what's the application?  For a house you'll want a perimeter foundation or else something engineered for the ground conditions.  For a remote camp it may not be that critical.

Also, if you update your profile to show your location we'll have a better idea of what's appropriate.

[MountainDon]

Have you selected a location for this project already?

What building code is used there?  Full-time residence or part-time?

Some locations may be lax in code enforcement while others go "by-the-book" to the extent that they may stop the project and could require demolition or changes be made to bring the structure into compliance.

Frost depths and snow loads need to be known before foundation design.  Snow load here where I am can vary by 20 PSF or more depending on what side of a mountain ridge one is located. Soil type can also vary a lot by moving a few miles one way.

[SpyingOnMyKeystrokes]

Thanks for all the replies!

First, I realize I interchanged, "bond beam," with, "grade beam." I understand grade beam to be simply poured at ground level with reinforcement laid throughout. Reinforcing rebar would be bent from the top of pier and tie into the grade beam.

This idea came from reading about some pier and post foundation requirements where tides, high winds and flooding are possible, and an actual bond beam is required at the top of posts/columns to prevent twisting of piers. I'm wondering if it would work in any northern climate where code requires 36-48" frost depth.

Part of the hope is reducing the digging/excavation for foundation to an Auger attachment for bobcat.

The amount of concrete is far less than a 36-48" depth perimeter footing and stem wall, as far as I've calculated.

I've seen pier and post barns built in the South this way, without the grade beam.

As far as I understand, a post and beam structure on piers should transfer various force and load to the posts and down to the concrete piers. I may not be understanding correctly.

The grade beam I was thinking of would keep walls up and away from ground moisture. I am thinking of using straw bales atop a pony wall framed between posts that are situated directly above piers that exceed frost depth. I'm hoping to direct the weight and loads primarily through a post and beam frame and down to the piers.

Is it totally unrealistic to hope the grade beam would not heave from frost? Would it act somewhat like a bond beam in this case?

I attached a link to a sketch.

Thanks for any responses.

https://drive.google.com/open?id=1Yi9nluVw1CLea66zVHu5ifiTiMCBImhi

[Don_P]

It would appear this entire design is going to need to be engineered, not just the foundation.
Just some thoughts from looking at the sketch. The grade beam is eccentric on the pier so it is going to want to rotate counterclockwise in the sketch view if the pony wall takes load. Upsizing the pier to span entirely under it would be one possible solution. If the cantilevered floor is taking the load and the pony wall is non load bearing that is perhaps another matter. There are crushable forms for grade beams on expansive soil. Frost heave is a type of expansive soil I suppose.

I cannot answer these questions and that is when I call the engineer.

[SpyingOnMyKeystrokes]

Well at least you're not pretending to be an engineer! LOL.

Not sure about the counterclockwise rotation, because the weight is primarily being transferred to the floor beam that supports the cantilevered floor, thus transferring the weight to the post above the pier. The pony wall is supposed to be a helper for potential settling of piers. Pony wall could be framed in-between the posts if some type of rotation were an issue, although I've never heard that description before.

The majority of the post and beam frame weight should transfer to the piers, and they would be fairly close together, perhaps 10' o/c.

The main question is, will the piers act as contact points below frost depth, and will the grade beam act in enough unison to cause freezing water to expand downward below it, into the aggregate, instead of heaving the beam upwards? If it tries to heave, and acts in unison, I'd think it would transfer force upward to the areas where the posts are carrying the load, and provided it doesn't crack, just cancel out around the entire frame structure.

Will probably need engineering. Thankfully I know some who won't try to spend me out!!!!!