How do you include masonry partitions in beam design?

[RHause]

i have searched for this issue in other threads but have not found a helpful answer, so here goes the question: what is the best way to address masonry partition walls in a building where the uniform loading can be as high as 60 psf for a bay? I see in IBC that minimum partition loads of 15 psf can be ignored with live loads of 80 psf, but I do not want to under design on the dead load side... right now I am using 80 psf DL (55 psf - floor system, 10 psf beams, 5 psf misc mech, and 10 psf partition/misc DL) and the prescribed LL of 80 to 150 psf. For beams with a wall along hte entire lenght, I am ok designing for the wall, but tyring to design each beam/girder for individual wall loads seems silly and excessive... need advice...

 

[msquared48]

I would add in the weight of the wall locally to the affected beams, and definitely into any seismic calculations.

The 15 psf value is pertaining mainly to wood walls. CMU weight, a dead load, I would always add extra regardless of the live load.

Mike McCann
MMC Engineering

 

[asixth]

Agree with mike,

If you know the location of the blockwalls (i.e. starter bars will be provided when casting the slab) then calculate and include the weight of the cmu wall.

You will also need to look at the deflections that occur after the block partitions have been constructed (i.e. additional deflections due to creep and shrinkage).

I believe the methodology of designing for this in the US is to multiply your instantaneous deflection by 2 and this will be the additional deflection due to permanant loads (incremental deflection).

Keep your incremental deflections to span/500 and the total long-term deflections to span/250. Also, provide adequate control joints in the masonry mid-span where the beam curvatures are the greatest.

 

[haynewp]

What I did before on a composite deck floor was xref the cmu wall locations from architectural and locate and design the beams locally for the heavy line loads. I put a note to verify the final wall locations with the arch drawings and coordinate the support beams I had indicated, since the architect kept moving the cmu walls around.

 

[JLNJ]

CMU walls can be a killer when you have joists or other similar light framing systems. Where you can "ignore" them in the gravity desing of the beams and where you need to specifically take them into account is up to you.

Unless my live load is very high I find that I need to account for the CMU walls. It can be a pain in the neck chasing them around and keeping up with the layout since the architects will place them willy nilly throughout the building.

 

[RacingAZ]

I'm assuming you're talking about cmu partition walls in an elevated floor. I always discourage the architect to use this type of assembly on elevated floors due to the following reasons.

1. They get heavy pretty quickly (depends on height) and you'll find that you almost always have to provide a beam directly to support the wall line if you have steel floor framing (subject to L/600 criteria). On concrete floors, it may or may not be able to support the weight. Most of the time, you have to provide additional reinforcing as a minimum.

2. You're penalizing your floor system when other options are possible on the cheap. If the architect is after the look of the exposed cmu, you could easily get that with steel studs and masonry veneer. If it is the fire rating he is after, steel studs and gyp-board can give you at least 2 hour rating (or more with the masonry veneer). This assembly is way cheaper than CMU plus the associated cost of beefing up your floor framing.

3. The architect can easily rearrange the cmu locations and you'll be chasing the new locations, checking and reviewing the impact to your floor framing. That will not be the case for steel stud walls.

Mike is right. Also, try to calc out 2 or 3 locations and you'll find that you just can't make a blanket assumption that an increased design LL will take care of it. Increasing your design DL will take you back to my 2nd reason. You really need to look at each cmu location and review how it is affecting you floor framing. That's why I always go back to the architect first and "beg" to change the material by explaining the consequences.

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[RHause]

i agree Racing AZ but the CMU partitions are being driven by the client because they dont want students busting the gyp board....

 

[steellion]

Steel frame: Provide steel beams directly under CMU partitions. Limit deflection to L/600. You don't want the weight of the CMU to have to be supported by deck and a couple inches of concrete.

Agreed that CMU partitions on elevated floor slabs are not desireable, but sometimes there is no choice if it's client-driven. I just had the same situation where the partitions were CMU for security purposes.

 

[RHause]

what if the partitions are running perpendicular to the beams??? do you still meet l/500 or is l/240 ok?

 

[SteveGregory]

In some instances, I have used a 8" or 16" high CMU bond beam at the floor level to span between steel beams. The CMU wall continues on top of the bond beam.

This won't work if you have a door opening in the span.

 

[steellion]

It's actually easier if the partitions are perpendicular to the beams. Then the beam underneath is a really short span, so a W8x10 or W12x14 can be used and still easily meet the L/600 requirement. I'd also limit the perpendicular beams to a L/600 or 0.3" deflection at that point, but that's post-composite, not total deflection, since the concrete floor would have cured before masonry placement.