CRAWL SPACE FLOOR and POSTS

[VBI]

I am looking to provide short concrete (or block) columns in a crawl space to support a wooden beam (supporting first floor above). There has been some settlement of the existing block columns which I assume is due to a poor underlying soil condition.

My thought is to construct a 12" reinforced mat slab ontop of the existing floor. This slab would then be the foundation for the short column foundations or even steel posts. Loads are relateively small at possibly 2000# at the column post and I thought this "empirecal" design would work where money is limited to do soil borings, geo-engineering, etc.

Thoughts?

 

[MiketheEngineer]

I would make it at least 18'' x 18'' and throw in some rebar to prevent cracking.

Is this not suseptible to freeze and thaw?? If so - you will need to go to frost line.

 

[concretemasonry]

Since the original settled, it can be assumed that the soil is a problem.

If you use a pier of 8x8x16 block (staggered joint and not just stacked). A pier with these dimensions (24x24) can have a 32x32 unreinfoeced footing is it is 4" thick. If it is 8" thick it can be 40x40 and still unreinforced.

With such a wide pier, the steel is unnecessary because there is no flexure and the thickness takes car of the shear. - Typical construction for residences in many parts of the country and you will have bearing pressures of less than 300 psf. - For 40x40, you be below 200 psf soil bearing.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[TDAA]

I thought this "empirecal" design would work where money is limited to do soil borings, geo-engineering, etc.

Since there seemed to be such good success with the soils the first time around, this is where I would cut back as well.

 

[oldestguy]

Assuming the settlement before resulted in some wall cracks, consider overloading the new foundation by jacking up on the floor support beams and raising that floor a little above what is level. Leave it there for a day or two and then lower things and fill in as necessary for permanent support. The idea here is with an overload, chances are the new footing will have settled all that it might "decide to do" in the future.

Now you can patch the cracks.