Reinforcement of CMU Wall (after the fact)

[dengebre]

We have a renovation project where we need to reinforce an excisting 8" CMU wall in order to bring it up to Code. The existing wall has minimal vertical reinforcement (if any) and a 1-2 course bond beam across the top. This will be an obvious constructability issue. Has anyone run into this before? If so, we are curious how the contractor was able to do it. Thanks!

 

[JedClampett]

Never done it, but it seems like it's going to be a nightmare (fouled cells, misaligned cells, conduits in the cells, etc.) to place bars and grout.
Is there an option to add vertical steel members and anchor them to the CMU wall, floor and roof framing?

 

[rrmiv]

When you say "in order to bring it up to Code" do you mean for strength or for seismic detailing requirements? If the former, we have added interior steel girts (CMU spanning vertically) or pilasters (CMU walls spanning horizontally between pilasters). If the latter, we have heard of post-tensioning existing walls into the wall footing, but never done it.

 

[concretemasonry]

You will need to find out more about the wall you are dealing with - The amount of reinforcement and very importantly, the block configuration and core alignment (some site investigation will be required).

Common 2 core blocks (smooth ends or open ends) can be a problem. If the wall was built using the proper units (8" o.c. cores and vertically aligned webs) it can be much easier to install rebar and grout without the common excessive grout leakage to other semi-connected adjacent cores.

I was involved in constructing a facility with about 100,000 sf of 8'-8" high CMU walls(8" o.c. vertical rebar with a bond beam) that were installed between recently built post tensioned slabs. Because the correct units were used and it was planned to be done that way, it was easy.

Your situation will require determination of what is currently in place.

Dick

 

[dengebre]

The existing wall varies from 8'-10' in height and is constructed using regular block in running block. The cores appear to be in reasonable alignment. It is a regular CMU wall, albeit very lightly reinforced. It was originally a residential structure built to a pre-1980's code.

 

[concretemasonry]

The terms "regular" block and"reasonable alignment" are really quite general and do not describe what you need to consider in a reinforcement unless you do an exterior job. Lightly reinforced is meaningless for a structural situation if you do not know what is there.

I have seen many pre-1980 loadbearing structures using 6" block and light reinforcement, but they used the proper units and constructed the walls to the code and standards (basically the forerunner of ACI 530).

Dick

 

[MiketheEngineer]

DOT's across the country and some basement repair companies use a carbon fiber type cloth epoxied to the existing wall. Not sure if this will work - but you might look into it....

 

[concretemasonry]

The surface applied carbon fibers are usually applied to restrain/stabilize a wall that has already failed.

It may be a viable option if the wall has not experienced any excessive loads that have caused excessive movement or cracks. Good for flexure, but difficult to justify for vertical or compressive loads.

Dick

 

[DaveAtkins]

I have heard you can break a hole near the top of the wall, thread a rebar into the vertical cells, and grout solid.

DaveAtkins

 

[Zambo]

I would go for the old fashioned method of cutting, breaking out and casting a beam or column where required, if the wall will be sound in the temporary state.

 

[hokie66]

You can saw out part of the face shell on one side in each core to be reinforced, place bars in pairs so they can lap, form the face and grout. Getting continuity at the bottom and top is the tricky part.