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masonry piers...filled?

J

just ducky

Registered User
Joined
Jan 12, 2018
Messages
7
Location
Michigan
I have an existing single story home, approximately 20 years old. The floor construction is wood engineered joists, supported by steel I beams, supported by hollow masonry blocks (4 tall) sitting on a concrete footing. I'm considering putting on a second story, and I've done the calculations on the beams and the spacing on the supports is more than adequate for two stories. My question is about the block piers. Should they not be filled with concrete and possible a rebar in each void?
 
Probably, but without an idea what of the materials and the total reactions, we'd all be guessing here. Need to know beam reaction and the size and compressive strength of the blocks. AHJ will most likely want the supporting calculations, perhaps from a licensed engineer, anyways.
 
Paul Sweet said:
I'd be more concerned about the size of the footings under the piers.
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Actually we investigated the footings, and they are actually more than sufficient. I plan to discuss with the building official the piers. They did inspect the building when it was built, and I'm curious what they can tell me about the former approvals. In any case, if this project moves forward, I'm planning to fill the cores, and install rerod in the voids.
 
just ducky said:
I'm planning to fill the cores, and install rerod in the voids.
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I’m curious how you plan to physically do that. You said the piers are 4 blocks high ... 32”. Then a steel beam, maybe 8”? Then engineered joists, maybe 12”? So you have maybe 20” above the top of the blocks ... how do you plan to get 32” rebar in place? And then I’m guessing the steel beam pretty much covers the top of the block ... how are you going to get concrete into the voids, and vibrate it to eliminate air pockets?
 
2015 IRC table 606.9 says hollow block is good for 70 PSI on the gross area. That would be 8960 lb. for 8" block, and 13,440 lb. for 12" block.
 
Maybe but what of the underlying soil bearing value, depth of water table, depth of frost?
So only mortar and weight are supporting the existing structure? Lucky not in a seismic zone.
 
Just Ducky is in Michigan, which is in seismic design category A. He said the house is about 20 years old, so it was probably built under the old CABO code, if there was a code. I don't remember the CABO code having much to say about seismic design for most of the country.

2015 IRC 606.7 allows unfilled hollow masonry piers to have a height 4 times their least dimension.
 
If the Piers are currently designed labor only be taking compressive load. Compressive load is where concrete is at its best. Rebar really doesn't help increase the compressive load significantly.
 
Paul Sweet said:
2015 IRC 606.7 allows unfilled hollow masonry piers to have a height 4 times their least dimension.
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I can't think of a reason to do that. There should be a connection to the footing as well. Even knowing that the likelihood of an earthquake is slight I still can't explain not grouting or anchoring four high CMU.
 
ICE said:
I still can't explain not grouting or anchoring four high CMU.
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Several excellent reasons.
1. Takes 30 min more per pier
2. Costs $50 more per pier
3. Not on the plans
4. Not in the code
5. We have always done it this way.
 
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