New Concrete "Pier" in Existing CMU

[JoshH726]

I've created this cartoon to try to solve an issue with a 10k +/- load coming from a new 5-1/2" sqr header post (I didn't provide the post, just evaluating the wall). Post supports a new bearing wall in a 3 story cottage. Post lands on an existing 8" block (empty, no grout) exterior wall. The new addition turns this exterior wall into an interior wall though with new framing landing on the wall 16" oc. Running the numbers with 2011 masonry code assuming f'm=1000 psi, bearing in the block doesn't work. Sandy soil, so I'm going with 2000 psf for soil bearing.

So attached is my first past. I don't have much experience in residential remodel, mainly focus is heavy industry. But I'm interested in this type of work, and more importantly, you're input. So please go easy and keep the condescension to a minimum

I'm sure there are several ways to skin this, but I'm looking for a practical and workable solution. My main concerns are the best way to lag the existing wall to the new concrete. Are there better ways then doweling with rebar?

 

[manstrom]

Makes sense. Could you grout a few more cells and delete the rebar? I don't like masonry, but 10k isn't that much.

If bearing is an issue, can you make the baseplate wider? Add gussets if needed?

Also, your f'm might be closer to 1500 psi

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[JoshH726]

Manstrom, I was told the house was originally constructed in the early 1900s, but the block (see photo) looks newer. So I was trying to be conservative, maybe overally so? My thought was to dowel them together. Do you think the new concrete will bond enough without the dowels? I don't see how grouting my of the block cells would help, but I'm still developing my comfort with masonry. For reference, the load is landing above the word "wall"

 

[manstrom]

I think you can make a strong pier by grouting more than 1 cell, the load will distribute. The rebar would tie cells together as long as they are filled, but I think you can keep it as just grouted masonry.

Check out

http://www.eng-tips.com/viewthread.cfm?qid=281714

for load distribution in a cmu wall.

The CMU doesn't look that old. But there is nothing wrong with being conservative in values.

Bearing from the baseplate to the masonry may control. Like I said, try a wider baseplate.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[KootK]

1) Using the existing CMU to hold up the post is probably the way to go as Manstrom has suggested. Grouting the whole height of the wall could be difficult. Who knows what manner of crap is in there. Is there a bond beam at the top that could distribute the load for you? Usually there is.

2) If you go with your original plan, I wouldn't bother with the dowels. When you demo the wall to build your concrete pier, make the block look like a zipper on either side. Grout the zipper space along with the pier and everything should be well keyed together. Besides, do you even need the CMU to be joined to the new pier?

3) Depending on your aesthetic needs and foundation detail, you could just run your post right down to the footing and not bother with the new grouted pier.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.