Masonry Insulation 1

[SteelPE]

I am in the process of designing a large industrial building. The overall building height is 26'-0" with 8'-0" tall masonry walls around the perimeter (to help with the durability of the building). The building falls under IBC 2015 requirements. The CMU that is proposed is the CMU with foam inserts in the cells of the CMU (I believe they are called Korfil)

The entire building is designed and detailed. I received a call from the architect today regarding the perimeter masonry. As we talked about the masonry requirements he mentioned that he is having issues with the energy requirements of the building. He intends to leave the foam inserts in the grouted cells. This is in conflict with what I have been taught and what is on our general notes which requires the GC to remove the insulation in grouted cells. As we have done this for 20 years, I believe the method we have implemented, of having the gc remove the foam inserts, is correct. I also remember my boss arguing with contractors over the removal of the foam.

The issue I have with leaving the insulation in place is that the grout is no longer bonded to the masonry block (with the proposed block it is bonded on only 1 side of the cell). How do you handle insulated block in this instance? Can you still design the block as if it was a solid unit (using working stress or LRFD methods found in ACI 530)?

Two things I recognize that work to our advantage:

1)the wall isn't very tall.
2)the wall isn't load bearing.

It seems the architect didn't pick this up at the beginning and we are now dealing with the issue after the drawings have been completed.

 

[jayrod12]

Does the wall work as an unreinforced wall? Is there a girt providing a horizontal support at the top of the 8ft? If so, it likely does work as an unreinforced wall and therefore would be comfortable letting it slide in this case.

 

[KootK]

I would think that any grouted cores would no longer be capable of transmitting longitudinal shear between the faces of the blocks. As such, the grouted cores, and any rebar in them, wouldn't be good for much other than direct bearing perhaps.

 

[GC_Hopi]

Have you checked with the block manufacturer to see what test data/values they have.

 

[SteelPE]

I don't know why I'm apparently the only one with these issues:

https://www.eng-tips.com/viewthread.cfm?qid=226562

I don't know if others run into similar problems.

I don't even remember having this issue 12 year ago or what project it was related to.

 

[SteelPE]

FYI, upon finding that old thread I found this data on their website:

http://www.cbisinc.com/library.html

It seems like all of the reports they have are 30+ years old. As I stated above, the walls are not overly critical for this project. I did look at the drawings and most of the walls are 8'-0" high with a support at the top. We do have one small area with drive in doors where the masonry is 15'-4" tall.

Going to need to twist myself into a pretzel to justify this.

The sad part is, this is need for energy compliance in the Northeast part of the US. This particular project is a large bakery where they have issues getting the heat out of the building, not keeping it in.

 

[EngineeringEric]

at the ratio of wall you are talking about, the architect could us the current building code to look at the average U-value for the 5-exposed sides of the building and you may not even need Korfil. I think your teammate is being lazy on their end and wants you to make something work that can't or shouldn't.

If you increase your wall thickness you may be able to span vertically as plain unreinforced non-load bearing block? then no grout.


Enter a Rant:
Letting the R-value of a building increase for 5, for 8ft of wall at the cost of significantly compromising the structural integrity of a building always pisses me off. If it really matters, add 2 more inches of rigid foam to the ceiling. Or make it a cavity wall... all of those are preposterous because of the cost, so you just make that CMU wall bend and crack and break and let in water and fail in 5 years; but hey! it had a marginally acceptable R-value for a year
:Exit Rant

 

[SteelPE]

Eric,

I think I have oversimplified the issue as I am sure the architect has looked at that already. There are property line issues which require large amounts of these walls (600-700') to have a fire rating of 3 hours. We also have 3 hr rated panels on top of these walls (that are 8" thick mineral wool panels).

This isn't the first time I have had this type of building with odd requirements from the architect. Just disappointed that it's coming up at the end of the design phase when it should have come up at the beginning. Now we have foundation pockets, outside face of foundation to center of steel, girts, bracing, eave details etc all completed based upon the requirements at the start of the project. To go back and change that would be a Herculean effort that we would most likely fail at (as we would undoubtedly miss some details).

 

[GC_Hopi]

That link to the manufacturer also had some info from 2006 regarding flexural design. Link

 

[KootK]

Well color me wrong... their structural report spoke right to the longitudinal shear issue that I was worried about and it turns out that's not an issue.

I'd love to know:

1) If shear transfer is soley via the one side where the grout is in direct contact with the block and;

2) If the system exhibits much sensitivity to construction quality. I imagine that you'd need everything in there snug for it to perform.

 

[JLNJ]

I feel your frustration.

Many architects don’t believe these inserts work as claimed as insulating elements and structural engineers are skeptical of the bond mechanism.

KootK’s graphic looks like a 12” wall where the grouted portion around the rebar probably works pretty well on its own without the face shells contributing at all. There just isn’t much meat left in an 8” CMU insulated core.

No through-wall flashing? No bond beams? No linteled openings? Keep the verticals spaces as far as possible? 3 hr rated walls have even MORE solid area and are even worse for transmission (check that Korfil works with those beefy 3 hr ungrouted 8” walls). I’m with Eric. We might be kidding ourselves here.

 

[XR250]

That seems pretty sketchy to assume a one-sided bond for composite or just simple shear transfer. I suppose the foam could transfer the out-of-plane loads effectively to the concrete column in the center.

 

[masonrygeek]

To diverge from the main topic of structural engineering and into energy analysis for a minute - using the prescriptive tables for insulation in the energy codes is often limiting for concrete masonry, especially single wythe walls. Instead of the prescriptive tables, it is better to use the U-factor method or COMcheck to verify energy compliance. COMCheck allows some tradeoffs and using more roof insulation as Eric mentions is possible instead of more wall insulation. If the architect isn't using those methods they may struggle to get the walls to meet code. NCMA's TEK 6-2 (

https://ncma.org/resource/rvalues-ufactors-of-single-wythe-concrete-masonry-walls/)

covers this topic pretty well.

Although NCMA makes a comment about grouting an insulated core being OK, I think that removing the insulation inserts for a partially grouted wall is appropriate and might still meet the energy code requirements.