CMU Wall Opening Reinforcement

[cgstrucg]

Hello,

I have a project in NYC in which there is a CMU wall which has #6 bars as reinforcement, is almost 40 ft high and the contractors are trying to create an opening in it for some duct work (4 ft wide and 8 ft high). The CMU wall is not designed for that huge opening and I am wondering if anyone has come across this kind of situations before.

I am not sure how to reinforce this CMU. I just have an idea which is not what I am going to do but just putting it here to get things started - putting an HSS right next to it to support the duct work but that would be like a very tall HSS.

Any ideas will be really appreciated.

Thanks

 

[charliealphabravo]

How does the opening align with the horizontal and vertical reinforcement?

Typically the procedure is to retrofit reinforced and grouted cells around the proposed opening and to replace any encountered steel. This may require cutting or removal of face shells to install rebar and then forming and grouting them in place. The rebar might also be doweled into the foundation depending on the situation. Ideally you want to minimize the volume of cast-in-place since it can double the dead load.

Unfortunately there is not much guidance from ACI on the repair and retrofitting of concrete masonry. Basically it comes down to a skilled mason reproducing the effect of new construction.

Edit: Sometimes you will see masonry openings reinforced with plate steel, angle, etc. I wouldn't have a high degree of confidence with this method in a large wall for strain compatibility reasons.

 

[EZBuilding]

A few questions need to be answered before we can start responding adequately.

Is this an exterior wall exposed to components and cladding wind pressures?
What is the thickness of the wall?
What is the spacing of the reinforcement.

40 feet tall is very tall...

 

[cgstrucg]

It's an interior wall, 8" thick with 16" O.C. horizontal reinforcements. Still, have to look at vertical detailing but should be standard. That's the point with 40ft fall, that big an opening is cause of concern in case of seismic loads. Please let me know if you need more information.

 

[cgstrucg]

Any idea on this? Thanks GBP

 

[KootK]

Please let me know if you need more information.

- How much non-jointed wall will remain to the left of the opening?
- Now much non-jointed wall will remain to the right of the opening?
- How much wall will remain below the opening?
- How much wall will remain above the opening?
- Is the wall a bearing wall?
- Is the wall a shear wall?
- Are you in a high seismic environment?
- Is the wall vertically spanning?

Frankly, I can envision many permutations of these answers where such an opening would be of very little concern. As you've no doubt gathered, posting an elevation sketch of your wall would be prudent.

 

[hokie66]

So the horizontal bars are #6 at 16"? I take it the wall spans horizontally, so the height would be somewhat inconsequential. Your idea of a vertical support at the jambs of the opening should work. I take it the wall is fully grouted, which would mean the wall can span over the 4' wide opening easily for gravity loading.