Cinder Block House

[jjeng2]

I have a residence that was constructed with cinder block and is about 40 years old. The foundation is 12" block and the bearing walls are 8" block. The masonry was poorly constructed with some mortar joints overflowing and some not completely filled. Currently it has a full basement and a framed first level. There is an unoccupied attic space and roof bearing on the walls. The Architect wants to remove the attic and roof and put a new second floor at the attic level, bearing on the walls and a new roof.

Where can I find references for the strength of these blocks? Would anyone recommend testing their compression strength and the mortar? I told him he cannot bear on the walls with additional load unless I can find a way to justify it.

 

[UcfSE]

Can you grout the walls solid?

 

[jjeng2]

UcfSe,
That is one of the possibilites I am considering if we can get access to the tops of all the cells. I have several ideas on "upgrading" the walls but I am looking for references on the strength of the block so I can make sure its required and justify reinforcing.

 

[JAE]

ACI 530 is the design document that is probably most applicable - especially if it is referenced through your applicable building code. The first place to start would be the correct, applicable code (talk to your building dept.) and then see what is in the code or referenced by the code for the applicable masonry provisions.

Once you have that, then you need to determine whether any of the cells are grouted, reinforced, and at what spacing.

Then, a determination of masonry strength can be made by either actually removing a section of the block and having it tested in a lab (a prism test), or by assuming a strength based on "typical" values that were common 40 years ago - where you'd go for that I'm not sure - perhaps checking with your local block suppliers...they could tell you what unit strength of block was typical back then and then you'd have to inspect the mortar (although mortar doesn't have a huge effect on f'm, it should be considered).

Having said all that, you could probably assume 1000 psi and be fairly safe. Most "typical" f'm values in the US are 1500 psi.

 

[jjeng2]

For everyones reference the NCMA told me that they have a minimum of 1000psi unit strength on the gross area which equates to about 1350psi F'm and I could use those numbers with modern codes equations.